Back in the old days (around 1997), I didn't hear much talking about things like "x" a/r, garret, hybrid, mitsu, ball bearings, etc. It use to be people just upgarding to 14b's, 16g's, 20g's, etc. Now there so much talk about this and that that I've had a hard time following. Mainly because I've only had one type of turbo for so long. And lately, I've just searched threads to see what people go with as far as a turbo for "x" setup and try to see what works best for them (as I'm sure many others do). But screw all that. I wanna be educated and know for myself.

Can you guys with the turbo knowledge please break down some of the terms and help me (and others) decipher some of what I need to know?

Things such as the difference between a mitsu, garret, etc.
Meanings of .63, . 70 a/r, etc.
Reason you'd want or NOT want to port the turbine inlet or outlet? Or both?
Can someone tell me what a 67 mm inducer is? Or any other size?
What's the difference between a 50, 60 trim, etc.?
What's a 360 degree center thrust bearing?
And so much more I'm not even listing.

When looking at a website such as Slowboy, some of the turbo's have different options and I have no clue why I'd wanna get this or that, and maybe not something else.

There's so much out there I don't know where to begin? And when discussing turbo's, I see so many people bickering that it makes it hard for me to be able to decide for myself. Hoping many of you turbo wisemen can help out and post your knowledge. Thank you!

Scott

Not a bad idea.

I'm going to sticky this in hopes of getting some useful information in here.

Hoping maybe some or at least one vendor would chime in as well. Heck, they know about their turbo's that they're selling. Would think they'd be the best one's to ask. Also would help if they didn't have to explain to every customer who calls (which takes time out of doing other things at work that probably needs to get done) if people could just educate themselves and just have to place an order.

If anyone can get access to the Talon Digest, there is a great, multi-page, explanation of turbos that I printed off a couple of years ago. Unfortunately, I can not seem to find access to the Talon Digest anymore to provide a link to the information.

ISUJakey said:

If anyone can get access to the Talon Digest,

Click to expand...

Anyone can.
http://www.me.mtu.edu/~edan/talon/

Come on people, step up to the plate here. I'm always seeing people trying to argue their knowledge and all. Yet no one's trying to help out in this thread for everyone else's sake in tuner land? Just answer whatcha know if nothing else. Don't have to answer every single question.

Defiant, by chance know which one of those in there is about the turbo's? That's a heck of a lotta links to go reading thru to have to find.

Appreciate anyone who will take the time to help out in this thread.

I'll step up to the plate, but this is going to take a couple of days to write in order to cover this proper. Might take two or three pages and several illustrations, problem is most people have a 3-5 line attention span on message boards. In addition, 2 or 3 of those questions have been covered in depth in various places on the internet.

sleestack said:

I'll step up to the plate, but this is going to take a couple of days to write in order to cover this proper. Might take two or three pages and several illustrations, problem is most people have a 3-5 line attention span on message boards. In addition, 2 or 3 of those questions have been covered in depth in various places on the internet.

Click to expand...

For those willing to learn, the attention span would endure 2-3 pages. And for those not all that interested, still better to have the info posted than not. I know I've searched for some info but always find the threads where people start griping that they're right. Back and forth. Or just the threads saying, this turbo is better...this wheel is great on it. And then return reply, that turbo is ancient technology. That's pretty much what I see when searching. Any info I see is hard to tell if it's fact or opinion. Any of the various places you're speaking of, I'm not aware of but I'd appreciate ya pointing me in the right direction Thanks!

Guess i'll add more questions that I'm wondering about...

What's the difference between a T3 and a T4 or a T3/T4?
What's a 270 and a 360 standard thrust?

Um, that's all I've got for now.

Hey guys hows it going. I'm going to step up to the plate. My spelling is not the best but here goes.


The whole garret turbo explanations. First the different in the bearings as you stated was, what is a 270 or 360 race bearing or ball bearings?


Well inside of the center section of a turbo there are bronze bushings that the turbo shaft spins extremely fast with oil. In older and more common the bearings are 270 degrees they are not a full round bearing which can make shaft play more commom in turbos. In some of the newer turbos like say the precision 60-1 you can get a with 260 bearing which are completely a full circle allowing for longer lasting and faster spooling turbos. Next we have dual ball bearings which are found in turbos like the gt35r and gt30r as examples. Theses turbos have real ball bearing where the tolerances and perfect and deliever great spool time. I mean good. So there is the major differences in the turbo center section bearing types.


next question is what is a trim as many guys talk about around here.

Many garret turbos are sized in trim. Trim is nothing special expect a big math calculation of the inducer/exducer times and divided by more numbers that the average person will not have to worry about in there life time. As you read about these turbos usually a 60 trim is bigger than a 50 trim. A 50 trim TO4B will get you to that 400 hp mark or can you handle the 60 trim which pushes enough air to support the big number on the dyno. But can you handle or do you want bigger?

Next you ask why to port a turbo inlet out let both?

well here goes a shot at what I think. well on the exhaust housing of a turbo you need a certain amount of exhaust gas pressure to make your turbo spin fast enough to create boost which we all love so much. So us power driven peopletake our turbos apart and start to port them to get more exhaust gas in the inlet of that turbo to make it spin sooner because you are putting more gas in that area of that turbo. Then people port the outlet of the turbo to get that extra gas back out and into your big 3.0 inch exhaust I HOPE U Have. well next many people port the wastgate outlet to get the bypassed air out to your exhaust and not to spin that exhaust wheel any faster at high rpms and that right there explains the 16g boost creep, but why would you put a big bolt on, on or a garret on with out a nice shiny tail 38 or 44? now that makes sense in my would and I now money is the problem with many people. I now we dont have any.

Next you state what is a T3 turbo or t3/t4 or a straight monster t4?

Well a t3 garret turbo has been around for many many years. it can be found on a 84-86 Nissan 300zx with a .63a/r or even older saab turbos. A t/3 means the compressor size of the turbo.Most I say most t3 are too small for our cars. That is why you see many people running t3/t4 hybrids which combine a t3 exhaust housing which a big t4 compressor housing to flow some serious air to feed our monster motors we are trying build. a straight t4 usually a monster exhaust housing in lam-mans terms which are used on Supras and some DSM but they require more exhaust gas pressure to spin and 90 percent of us dont have this much gas to blow out on these things.

Next maybe one of the most important things is choosing a turbo which I'm only going to touch briefly on because my hands are getting very tried by now and no I'm not the best typer in the world, and I sit here looking at my DSM in the drive way and want to go get on that 60-1 that lurks under the hood of that beast.

This is where the whole A/R comes in to play and the amount of air a turbo can make, the surge limit of the turbo, make boost, flow charts and all of the other good things that us DSM fans need to now about. So hear goes my best shot at this and I wont get to complicated. Where first we look at the 14b stock for most an upgrade for other. Yes it does 20pounds of amazing boost, and the exhaust housing cracks due to the heat that is trapped due to the internal waste gate design. It has a 06 exhaust housing which means the exhaust size, while the more common upgrade is the 16g which flows alot more air will push over 20psi of oh so loving boost. But you have to remember that the for the most apart that the exhaust housing and the intake side of the turbo are in haromy. By which I mean is the the turbo pushes a certain amount of air into the motor and the exhaust housing is the right size to flow the exhaust gas back out. That is way a b16g have a 7cm exhaust housing, just porting a 6cm exhausting wont flow as much as a 6cm. Think of it as funnel. put more and more water in it but you only get so much out. Increase that bottom hole size and now the funnel breathes which means your motor can breath now.
Part 1 is over I need to go get food I will continue with this in a minute or so.
so just be patient it coming

class is back in session and I grabbed a soda and downed a few tacos, looked under the hood my car and checked out that precision turbo down under that tubular manifold. Back on the topic now.



where we yes I had something to say, hey V8's are slow man, not all v8's are slow just remember that. My buddy has a TT chelleve that both of us build. it a v8 and it scares the pants off me. When the car hooks shut up and hold on. But anyways that has turbos that we love so back to the 16g and The garret turbo discussion that we want to read about. Now that we made 300 whp on a 16g with a few mods, some people make more dont get me wrong, some people try the 20g, bigger badder TD06 compressor housing bigger exhaust housing flows some serious air pretty close to the common bolt on 50trim. with that 20g some good and bad power can be made. But people like to say why? why by a 20g why buy a 50 trim. People say why. Well I have been through these turbos and watch them all dyno numbers of times and I can tell you what they make for power. If your at the 20g mark and want to upgrade You might want to start to consider a new


Turbo 20g plus
External waste gate setup 38 or bigger
2g manifold ported is nice
nice o2 housing
and a intake we problay a 3 inch inlet
and new feed and return lines, stainless

now not all the parts above are needed but I suggest them and you ask why. I say this because I have been there done that and it broke so I spent the money and did it right the second time, not the first like I want everyone to read this to due. Do it right the first time and have fun with your new turbo and not have to fix it every day. Now that the Mitshu turbo is out of your mind and you want a big bolt of series turbo you see .63 a/r or .83 a/r Dont get scared. never be scared this is just another way of sizing the exhaust housing in garret term think for a second


Mitshi Terms
Small B I G
6cm 13cm

Garret terms
small BIG
.43a/r 1.15 a/r (What the TT chevelle has) Ha Ha

now for the most of us we fall in the middle or this category
like the .63 a/r class. For example my precison has a .63 a/r and it is a 60trim. It has alright spool time and the turbo huffs some good air. Now you think I want to flow alot of air, but wait you also want a good spool up time. you always need to give a little to get a little in life we cant have the best of all the worlds. But wait they invented dual ball bearing garret turbos. Yes there big, yes they flow alot and the spool is good. That is why you can take a GT35R with a .83 a/r exhaust housing and have it spool pretty good even the the a/r is so high. But most of us dont have the money for a 35r, at least I dont so I deal with the lag. It is okay.
there is so much more I want to write about like clipping the turbo wheels and ceramic blades and how the turbos work in newer FORD yes I said FORD turcks. Didn't you hear hear. The ford truck turbos are amazing Oh u dont know. Well on your way to work do me a favor one favor I ask of all you people of read this article that took me hours to write and I promise there is more to come.

Just do this when you see a new FORD diesel truck roll down your window and listen, then due the same to a Cummins diesel and listen. And write back to me. and tell me what you hear.
Thanks for reading, and if people want more write in and say you want to hear from me.

Mark

Sure everyone appreciates the info. But now for another question....

Let's take a turbo from here. I'll just pick one. Take a look at this one.

http://www.extremepsi.com/store/customer/product.php?productid=17273&cat=508&page=1

Okay now how would you go about selecting the right compressor housing, exhaust housing, and the trim you want to use to get a balanced setup? Is this an educated guess, flip a coin, or maybe just ask them for the flow rates that maybe they've already tried out with different setups applied? I know people have different goals and different engines. Many things can make the spool time and power vary. Things such as the engine you have (2.0, 2.1 destroked, 2.3 stroker, 2.4 stroker, etc.), the compression ratio, whether you have an aftermarket sheetmetal intake, the cams you have, size of the i/c pipes, size of the intercooler, etc. etc. etc.

But how would one go about trying to get the perfect match for a "x" setup? And in means other than just asking for opinions here on the forums being that everyone seems to have a different opinion as to which turbo is best. Myself for example, I'm having to read TONS of threads on lots of different turbos, ask spool times, what people are making for power, 1/4 mile times, etc. and trying to make the best decision off that. Not sure if it's the best way but that's where I'm at at the moment as far as how I'm making my decision for what I want...at the moment anyway. Can't speak for others.

Hope this thread keeps going and more useful info coming

Yikes! It's hard to answer these questions when answers take so long to write all the while more questions are getting shot out so fast and so general. So please be patient with the questions while I hammer these out, I will try to answer one per night for the next week.

Simply put, Mitsu is to Garrett as Ford is to Chevy, at least in the DSM market anyway. Mitsubishi is an extremely diverse company that manufactures everything from commercial power plants to televisions. In order to simplify supply concerns and control costs they make several of the components that make up the products they sell. So they manufacture specifically sized turbochargers for their automotive sister company. For example, Mitsubishi Engine manufactures the TDO5 14Bs for the 90-94 Mitsubishi Eclipse.

Garrett, on the other hand, makes a universal line of turbochargers designed for a generic operating range of horsepower. They don’t exclusively make a single turbo for any specific engine on a large scale. If contracted to supply a turbocharger for an OEM, they’re solution is usually a selection from there diverse portfolio of turbos. Garrett offers a greater range of compressor wheel offerings that far surpass the flow capacities of the largest Mitsu compressor wheels.

There are exceptions to this of course , but to keep this primer concentrated and to the point as possible I won’t go into details on every manufactures entire product line. But for a quick example, Greddy (Trust) contracts Mitsubishi to make generic (T78, T88) turbochargers for it’s own line of proprietary turbochargers for the aftermarket.

In the beginning of DSM performance modding, Garrett turbos with their square flanged turbine inlets didn’t easily bolt on to DSM engines with round flanged manifolds without complex adaptor plates or custom-made, expensive, hand-built headers. Efforts in performance gains started in modifying the stock turbos within Mitsu’s offerings.

Mitsubishi makes hundreds of combinations of turbos for hundreds of applications so it has always been possible to interchange individual components in these turbos, between platforms, to increase the performance of a turbocharger. For example, taking the stock 14b compressor out of the stock 1st gen turbo and replacing it with the factory upgrade 20g compressor wheel and housing from a Cyclone/Typhoon turbo, then clipping the turbine wheel and throwing in the larger 7cm turbine housing from a JDM Galant VR-4 makes a Buschur Racing spec 20g (the tried and true “ole school” bench mark in DSM performance). Larger turbine wheels were soon discovered in the Fuso delivery truck power plant program. These larger turbine wheels made it possible to upgrade the compressor past the size of a 20g compressor wheel and actually see benefits. This is where the “hybrid” turbo entered the spotlight.

Mitsu compressor wheels cap in size after the 20g wheel, with the exception of the hard to find and costly 25g. It was necessary to think outside the box for the greater good . That is where Robert Young (then a turbo rebuilder for Turbochargers.com, now owner of Forced Performance) came up with the idea to put the more diverse Garrett line of TO4E compressor wheels in the Mitsu housings with minor modifications. When used in conjunction with the larger TDO6 and 6h turbine wheels found in the FUSO truck apps, these Garrett compressor wheels opened new doors for DSM aftermarket performance. This new line of turbos was deemed the “Frank” series of turbos. Several combinations of turbos where standardized as Frank 1, 2, 3, 4, 5 and later 6. Each Frank turbo combination had it’s pros and cons (some more than others). It was then thought to simplify the series into one smaller more responsive turbo for mostly street use (Green) and one larger street/strip turbo that could really dish out the horsepower (Red). There have since been other variants on the hybrid idea by several different companies. Now some of the more popular ideas on the hybrid idea involve casting a new turbine housing that bolts a complete Garrett CHRA (cartridge) into a housing that bolts right up to the DSM 60mm round flange manifold. For example, the FP30 series of turbos have a custom-cast 304SS racing volute housing that plugs the latest generation of Garrett Ballistics Concepts GT Ball-Bearing turbos that bolt right to a ported EVO or 2nd gen manifold.

It has become more and more popular in recent years to have a custom tubular manifold made that can bolt a straight Garrett turbo to the DSM cylinder head. When properly made with equal-length runners and correct phasing these headers allow an increase in performance with the versatility of being able to use a straight Garrett turbo. The only downfall is the additional costs involved in the custom fabrication of the header and the O2 housing since these have flanges specific to the Garrett T3 and T4 turbine housings.

So in conclusion, the main, most important differences between the Garrett and Mitsu turbos are the turbine inlet and outlet flanges and the greater compressor wheel variety and capacity in the Garrett turbos. Stay tuned...

HOLY ZOMBIE! That's the kind of information that should be required reading for anyone who seeks information about any turbo past, present, or future. I'm surely not the most educated man on turbochargers but I also feel like I have gained enough information over the years to say i'm not a newbie. After reading that post (sleestack) I've come to the realization that I'm not even close to knowing all there is to know regarding the subject. Sometimes it feels good to be stupid . Anxiously awaiting part II. Excellent information.

Thanks again,

Brew

Here is a big one, I am going to let a big secret (for some) out of the bag here for you guys so bear with me through this.

First of all, know that there are compressor housing A/R’s and turbine housing A/R’s. Since turbine housing A/R is likely the context of your question I will address that here.

A/R ratio is a term we use in the industry to differentiate flow capacities between like housings with similar exterior dimensions with different size volutes. What is a volute? A volute is the spiral shaped cone on the inside diameter of the turbine housing that begins right about the point in the housing where you can no longer see into it, after the inside diameter changes from the shape of the flange opening to the shape of the volute (usually a teardrop shape). The volutes job is to harness the energy (heat, pressure, velocity and sound) from your motor and concentrate it onto the turbine wheel to generate power to turn the compressor wheel. The number designation given is a ratio derived by taking the cross-section area of the beginning of the volute over the distance from the middle of the cross-section to the center of the turbine wheel (axis).



So what does this number tell you about flow? By itself, …nothing. This number is used to compare housings of similar castings with the only difference being the volute. Here is where I am going with this. Say you have a housing whose area is 1.45 in2 over a radius of 1.69 inches, that makes the A/R= .85. Well, say you have another housing whose area is 1.8 in2 over a 2.1 inches radius. Well, the A/R is still .85 so that means they flow the same …right? WRONG! So what does that tell us? You cannot compare turbine housings between families just by the A/R. Reason I go into this is that I have people ask me all the time what the A/R of a FP30 housing is. Why? There is only one FP30 volute, so how is knowing what it’s A/R is relevant? You can however compare the A/R between all T31 housings, or all T4 housing, etc.

The shape of the volute can affect the way the potential energy is harnessed. The closer to the shape of a teardrop the volute takes, the easier energy is transferred around the housing and into the turbine wheel. Most OEM castings like the 7cm Mitsu housings have a compromised volute (teardrop cut in half) for water line clearance to the bearing housing and ease of casting. On the other hand, most aftermarket housings like the FP30 and Garrett T31 housings have a better shaped volute patterned after Garrett Motorsports housings for maximum efficiency.



Here is where A/R comes in to play. Say you are buying a straight Garrett 50 trim with a Stage III turbine wheel. When it comes to the turbine housing you have 3 popular choices. You have a .49, .63, and .82. They all have very similar exterior dimensions and look exactly alike but on the inside they are very different.

NOTE: The following scenarios include hypothetical spool times and performance numbers used to illustrate the difference between turbine housing sizes and may not necessarily reflect the performance characteristics of this specific combination on your car exactly.

The .49 has the smallest volute so it will make our turbo respond fast, with the least amount of lag of the 3 choices. This small volute makes it spool fast but once the turbo is spooled and the wastegate is open, this small volute now becomes a restriction to the flow of exhaust gas speeding out of the manifold looking for freedom to the atmosphere. Backpressure (pressure that builds in the manifold before the turbos turbine) builds to 63psi before the turbine and less and less exhausted air/fuel mixture is allowed to exit the combustion chamber which limits your horsepower. You reach 20psi of boost by 3400rpm but because of your diluted A/F mixture in the cylinders you reach 345 hp by 5700rpm at 20psi. This makes a great autocross turbo because you make plenty of power down low with enough torque at the bottom of third gear in turn 4 to pick up half a second lap time.

Say you decide to go with the .63 turbine housing. Instead of 63psi of backpressure you only get 33psi. This allows a cleaner charge in the combustion chamber. A lot less backpressure builds in the manifold and as a result you make much more power on top, as much as 360hp by 5700rpm. The penalty is that instead of reaching 20psi of boost by 3400rpm, you don’t see 20psi till 3700. This can be a much better compromise for a car driven on the street that sees occasional duty at the local drag strip.

All out setups that demand every ounce of performance from their turbocharger require the largest A/R they can tolerate within reason. The .82 housing offers the least restriction to flow of the three. You may not see 20psi till 4000, but you’ll be able to hit 380hp on pump at that boost. Backpressure is kept in the high 20’s.

Restriction varies with mod level. Guys with fewer mods that affect VE are less affected by the restriction a smaller housing. So, for a guy with a stock motor with basic upgrades a .49 housing might be nice. By the time you add heavy cams, port the head, install a sheet metal intake many, etc. even a .63 A/R housing might be out of the question. Conversely, a guy with a stock motor might not see any better backpressure readings with a .82 than with a .63, now all he has is a lazy car. For help on where you should start, share your data with friends that have similar setup’s that have backpressure data, or get the advice of an experienced turbo professional.

Most people never know what their back pressure is. I mean how many of us really have a pressure transducer tapped in their manifold? I’ll tell you, I see it without fail. All these guys have that ridiculous EGT gauge tapped religiously in their #1 runner. I honestly think only the Autometer blinky light A/F meter for a narrow band OEM O2 sensor a more worthless piece of shit gauge to occupy gauge space, but I digress. You don’t have to have a gauge permanently mounted in sight for backpressure. Only need to make this measurement after you make a change that affects your engine VE. VE is volumetric efficiency. VE is a measure of your engines ability to move air through it. Head porting, camshafts, intake manifolds, air filters, intercoolers, turbos and exhaust systems all affect your engines VE. Examples of modifications that don’t affect your VE are fuel injectors, piggyback ECU controllers, blow-off valves, fuel pressure regulators, fuel pumps, and MSD ignitions. You also don’t have to have a fancy stand-alone ECU with an expensive 5 bar MAP to take backpressure measurements. Next time you are in AutoZone, take a look in the hillbilly section. Next to the chrome naked girl silhouette mud flaps you’ll find cheap oil pressure gauges. Pull that stupid EGT probe out temporarily and run some copper tubing to the hole with a 1/8 NPT compression fitting. Run enough tubing to protect the gauge from the heat of the exhaust manifold. Then run rubber tubing to a generic fuel filter assembly, then run more tubing to the cockpit to that bitchin oil pressure gauge. The fuel filter acts as a dampener to reduce the pressure oscillations from the exhaust “putts” and allow you to make a cleaner measurement. Get a friend to ride with you to watch the gauge. The gauge may not even flinch till you hit boost, but then should rise quickly with boost and continue climbing with RPM till you reach your engines max VE point then taper off (usually around 5700 with a stock intake manifold).

So now that you have your backpressure reading how much is too much? Generally speaking, you don’t want more than a 1:1.5 ratio of boost to backpressure. So if you’re at 20psi of boost you should not see more than 30-35psi of backpressure. If you do then you should upgrade the turbine side, you’ll make more horsepower for every pound of boost you run.

Turbine wheels and exhaust system diameters can also affect your backpressure reading, but to stay on topic I will address turbine wheels and pipes later on. For the most part, turbine wheels being part of the CHRA, are not easily changed by the average do-it-yourself tuner. For now, just know that if you upgrade your housing and your backpressure reading doesn’t come down where it should, your problem might be your turbine wheel. If this is the case or if larger turbine housings are not available you might consider a complete turbo change.

Stay tuned…

Thanks for the information.

This makes a LOT more sence now.

Here is a bunch of information off of the Garrett website (www.turbobygarrett.com):

This is Turbo Tech 102 on their site (sorry the pictures did not copy over, they can be seen on the Garrett site):

1. Wheel trim topic coverage

Trim is a common term used when talking about or describing turbochargers. For example, you may hear someone say "I have a GT2871R ' 56 Trim ' turbocharger. What is 'Trim?' Trim is a term to express the relationship between the inducer* and exducer* of both turbine and compressor wheels. More accurately, it is an area ratio.

* The inducer diameter is defined as the diameter where the air enters the wheel, whereas the exducer diameter is defined as the diameter where the air exits the wheel.

Based on aerodynamics and air entry paths, the inducer for a compressor wheel is the smaller diameter. For turbine wheels, the inducer it is the larger diameter (see Figure 1.)


Figure 1. Illustration of the inducer and exducer diameter of compressor and turbine wheels




Example #1: GT2871R turbocharger (Garrett part number 743347-2) has a compressor wheel with the below dimensions. What is the trim of the compressor wheel?

Inducer diameter = 53.1mm
Exducer diameter = 71.0mm






Example #2: GT2871R turbocharger (part # 743347-1) has a compressor wheel with an exducer diameter of 71.0mm and a trim of 48. What is the inducer diameter of the compressor wheel?
Exducer diameter = 71.0mm
Trim = 48




The trim of a wheel, whether compressor or turbine, affects performance by shifting the airflow capacity. All other factors held constant, a higher trim wheel will flow more than a smaller trim wheel.
However, it is important to note that very often all other factors are not held constant. So just because a wheel is a larger trim does not necessarily mean that it will flow more.


2. Understanding housing sizing: A/R

A/R (Area/Radius) describes a geometric characteristic of all compressor and turbine housings. Technically, it is defined as:

the inlet (or, for compressor housings, the discharge) cross-sectional area divided by the radius from the turbo centerline to the centroid of that area (see Figure 2.).


Figure 2. Illustration of compressor housing showing A/R characteristic



The A/R parameter has different effects on the compressor and turbine performance, as outlined below.

Compressor A/R - Compressor performance is comparatively insensitive to changes in A/R. Larger A/R housings are sometimes used to optimize performance of low boost applications, and smaller A/R are used for high boost applications. However, as this influence of A/R on compressor performance is minor, there are not A/R options available for compressor housings.

Turbine A/R - Turbine performance is greatly affected by changing the A/R of the housing, as it is used to adjust the flow capacity of the turbine. Using a smaller A/R will increase the exhaust gas velocity into the turbine wheel. This provides increased turbine power at lower engine speeds, resulting in a quicker boost rise. However, a small A/R also causes the flow to enter the wheel more tangentially, which reduces the ultimate flow capacity of the turbine wheel. This will tend to increase exhaust backpressure and hence reduce the engine's ability to "breathe" effectively at high RPM, adversely affecting peak engine power.

Conversely, using a larger A/R will lower exhaust gas velocity, and delay boost rise. The flow in a larger A/R housing enters the wheel in a more radial fashion, increasing the wheel's effective flow capacity, resulting in lower backpressure and better power at higher engine speeds.

When deciding between A/R options, be realistic with the intended vehicle use and use the A/R to bias the performance toward the desired powerband characteristic.

Here's a simplistic look at comparing turbine housing geometry with different applications. By comparing different turbine housing A/R, it is often possible to determine the intended use of the system.

Imagine two 3.5L engines both using GT30R turbochargers. The only difference between the two engines is a different turbine housing A/R; otherwise the two engines are identical:
1. Engine #1 has turbine housing with an A/R of 0.63
2. Engine #2 has a turbine housing with an A/R of 1.06.

What can we infer about the intended use and the turbocharger matching for each engine?

Engine#1: This engine is using a smaller A/R turbine housing (0.63) thus biased more towards low-end torque and optimal boost response. Many would describe this as being more "fun" to drive on the street, as normal daily driving habits tend to favor transient response. However, at higher engine speeds, this smaller A/R housing will result in high backpressure, which can result in a loss of top end power. This type of engine performance is desirable for street applications where the low speed boost response and transient conditions are more important than top end power.

Engine #2: This engine is using a larger A/R turbine housing (1.06) and is biased towards peak horsepower, while sacrificing transient response and torque at very low engine speeds. The larger A/R turbine housing will continue to minimize backpressure at high rpm, to the benefit of engine peak power. On the other hand, this will also raise the engine speed at which the turbo can provide boost, increasing time to boost. The performance of Engine #2 is more desirable for racing applications than Engine #1 where the engine will be operating at high engine speeds most of the time.


3. Different types of manifolds (advantages/disadvantages log style vs. equal length)

There are two different types of turbocharger manifolds; cast log style (see Figure 3.) and welded tubular style (see Figure 4.).


Figure 3. Cast log style turbocharger manifold




Figure 4. Welded tubular turbocharger manifold



Manifold design on turbocharged applications is deceptively complex as there many factors to take into account and trade off

General design tips for best overall performance are to:
Maximize the radius of the bends that make up the exhaust primaries to maintain pulse energy
Make the exhaust primaries equal length to balance exhaust reversion across all cylinders
Avoid rapid area changes to maintain pulse energy to the turbine
At the collector, introduce flow from all runners at a narrow angle to minimize "turning" of the flow in the collector
For better boost response, minimize the exhaust volume between the exhaust ports and the turbine inlet
For best power, tuned primary lengths can be used
Cast manifolds are commonly found on OEM applications, whereas welded tubular manifolds are found almost exclusively on aftermarket and race applications. Both manifold types have their advantages and disadvantages. Cast manifolds are generally very durable and are usually dedicated to one application. They require special tooling for the casting and machining of specific features on the manifold. This tooling can be expensive.

On the other hand, welded tubular manifolds can be custom-made for a specific application without special tooling requirements. The manufacturer typically cuts pre-bent steel U-bends into the desired geometry and then welds all of the components together. Welded tubular manifolds are a very effective solution. One item of note is durability of this design. Because of the welded joints, thinner wall sections, and reduced stiffness, these types of manifolds are often susceptible to cracking due to thermal expansion/contraction and vibration. Properly constructed tubular manifolds can last a long time, however. In addition, tubular manifolds can offer a substantial performance advantage over a log-type manifold.

A design feature that can be common to both manifold types is a " DIVIDED MANIFOLD" , typically employed with " DIVIDED " or "twin-scroll" turbine housings. Divided exhaust manifolds can be incorporated into either a cast or welded tubular manifolds (see Figure 5. and Figure 6.).


Figure 5. Cast manifold with a divided turbine inlet design feature






Figure 6. Welded tubular manifold with a divided turbine inlet design feature



The concept is to DIVIDE or separate the cylinders whose cycles interfere with one another to best utilize the engine's exhaust pulse energy.

For example, on a four-cylinder engine with firing order 1-3-4-2, cylinder #1 is ending its expansion stroke and opening its exhaust valve while cylinder #2 still has its exhaust valve open (cylinder #2 is in its overlap period). In an undivided exhaust manifold, this pressure pulse from cylinder #1's exhaust blowdown event is much more likely to contaminate cylinder #2 with high pressure exhaust gas. Not only does this hurt cylinder #2's ability to breathe properly, but this pulse energy would have been better utilized in the turbine.

The proper grouping for this engine is to keep complementary cylinders grouped together-- #1 and #4 are complementary; as are cylinders #2 and #3.


Figure 7. Illustration of divided turbine housing




Because of the better utilization of the exhaust pulse energy, the turbine's performance is improved and boost increases more quickly.

4. Compression ratio with boost

Before discussing compression ratio and boost, it is important to understand engine knock, also known as detonation. Knock is a dangerous condition caused by uncontrolled combustion of the air/fuel mixture. This abnormal combustion causes rapid spikes in cylinder pressure which can result in engine damage.

Three primary factors that influence engine knock are:

Knock resistance characteristics (knock limit) of the engine: Since every engine is vastly different when it comes to knock resistance, there is no single answer to "how much." Design features such as combustion chamber geometry, spark plug location, bore size and compression ratio all affect the knock characteristics of an engine.
Ambient air conditions: For the turbocharger application, both ambient air conditions and engine inlet conditions affect maximum boost. Hot air and high cylinder pressure increases the tendency of an engine to knock. When an engine is boosted, the intake air temperature increases, thus increasing the tendency to knock. Charge air cooling (e.g. an intercooler) addresses this concern by cooling the compressed air produced by the turbocharger
Octane rating of the fuel being used: octane is a measure of a fuel's ability to resist knock. The octane rating for pump gas ranges from 85 to 94, while racing fuel would be well above 100. The higher the octane rating of the fuel, the more resistant to knock. Since knock can be damaging to an engine, it is important to use fuel of sufficient octane for the application. Generally speaking, the more boost run, the higher the octane requirement.
This cannot be overstated: engine calibration of fuel and spark plays an enormous role in dictating knock behavior of an engine. See Section 5 below for more details.

Now that we have introduced knock/detonation, contributing factors and ways to decrease the likelihood of detonation, let's talk about compression ratio. Compression ratio is defined as:


or




where
CR = compression ratio
Vd = displacement volume
Vcv = clearance volume




The compression ratio from the factory will be different for naturally aspirated engines and boosted engines. For example, a stock Honda S2000 has a compression ratio of 11.1:1, whereas a turbocharged Subaru Impreza WRX has a compression ratio of 8.0:1.

There are numerous factors that affect the maximum allowable compression ratio. There is no single correct answer for every application. Generally, compression ratio should be set as high as feasible without encountering detonation at the maximum load condition. Compression ratio that is too low will result in an engine that is a bit sluggish in off-boost operation. However, if it is too high this can lead to serious knock-related engine problems.

Factors that influence the compression ratio include: fuel anti-knock properties (octane rating), boost pressure, intake air temperature, combustion chamber design, ignition timing, valve events, and exhaust backpressure. Many modern normally-aspirated engines have well-designed combustion chambers that, with appropriate tuning, will allow modest boost levels with no change to compression ratio. For higher power targets with more boost , compression ratio should be adjusted to compensate.

There are a handful of ways to reduce compression ratio, some better than others. Least desirable is adding a spacer between the block and the head. These spacers reduce the amount a "quench" designed into an engine's combustion chambers, and can alter cam timing as well. Spacers are, however, relatively simple and inexpensive.

A better option, if more expensive and time-consuming to install, is to use lower-compression pistons. These will have no adverse effects on cam timing or the head's ability to seal, and allow proper quench regions in the combustion chambers.

5. Air/Fuel Ratio tuning: Rich v. Lean, why lean makes more power but is more dangerous

When discussing engine tuning the 'Air/Fuel Ratio' (AFR) is one of the main topics. Proper AFR calibration is critical to performance and durability of the engine and it's components. The AFR defines the ratio of the amount of air consumed by the engine compared to the amount of fuel.

A 'Stoichiometric' AFR has the correct amount of air and fuel to produce a chemically complete combustion event. For gasoline engines, the stoichiometric , A/F ratio is 14.7:1, which means 14.7 parts of air to one part of fuel. The stoichiometric AFR depends on fuel type-- for alcohol it is 6.4:1 and 14.5:1 for diesel.

So what is meant by a rich or lean AFR? A lower AFR number contains less air than the 14.7:1 stoichiometric AFR, therefore it is a richer mixture. Conversely, a higher AFR number contains more air and therefore it is a leaner mixture.

For Example:
15.0:1 = Lean
14.7:1 = Stoichiometric
13.0:1 = Rich

Leaner AFR results in higher temperatures as the mixture is combusted. Generally, normally-aspirated spark-ignition (SI) gasoline engines produce maximum power just slightly rich of stoichiometric. However, in practice it is kept between 12:1 and 13:1 in order to keep exhaust gas temperatures in check and to account for variances in fuel quality. This is a realistic full-load AFR on a normally-aspirated engine but can be dangerously lean with a highly-boosted engine.

Let's take a closer look. As the air-fuel mixture is ignited by the spark plug, a flame front propagates from the spark plug. The now-burning mixture raises the cylinder pressure and temperature, peaking at some point in the combustion process.

The turbocharger increases the density of the air resulting in a denser mixture. The denser mixture raises the peak cylinder pressure, therefore increasing the probability of knock. As the AFR is leaned out, the temperature of the burning gases increases, which also increases the probability of knock. This is why it is imperative to run richer AFR on a boosted engine at full load. Doing so will reduce the likelihood of knock, and will also keep temperatures under control.

There are actually three ways to reduce the probability of knock at full load on a turbocharged engine: reduce boost, adjust the AFR to richer mixture, and retard ignition timing. These three parameters need to be optimized together to yield the highest reliable power.

For further in-depth calculations of pressure ratio, mass flow, and turbocharger selection, please read Turbo Systems 103 Expert tutorial.

Now I know a properly sized turbine housing is always the best way to do things. But I've seen some pretty big power #'s out of some small turbine housings. Which would make me thing that the turbine wheel has more to do with the power a turbo can make than the turbine housing. I know 1.8-2.0L Honda's have been making 600-700whp on .63 a/r t3 hotside for some time now. From the car's I've seen a turbine bigger than the T3 .63 a/r 4 bolt housing isn't need for even up to 600whp on a 2.4L. AMS got 587whp on 30psi with a built srt-4 with a .63 a/r GT35R.

Nicely done Brian. There is a lot of good information in your post that will help out plenty of members.

93AWDTalon1 said:

Now I know a properly sized turbine housing is always the best way to do things. But I've seen some pretty big power #'s out of some small turbine housings. Which would make me thing that the turbine wheel has more to do with the power a turbo can make than the turbine housing. I know 1.8-2.0L Honda's have been making 600-700whp on .63 a/r t3 hotside for some time now. From the car's I've seen a turbine bigger than the T3 .63 a/r 4 bolt housing isn't need for even up to 600whp on a 2.4L. AMS got 587whp on 30psi with a built srt-4 with a .63 a/r GT35R.

Click to expand...

You are correct on the turbine housing. It is a huge part of the equation and one that people don't really consider much. For the most part, people just stick witht eh .63 t3 on our cars. You bring up the AMS SRT and I will also remind you that all of the AMS evos you see that are laying down big numbers are also using .63 GT35r. I surely haven't seen any 700whp cars running the .63 housing though. However, that doesn't mean any of the cars wouldn't have any gains by moving to a larger hotside. The reason you don't see it much on the 62/65 lb/min wheels is that they can be maxed out flow wise on the small housing. That means by switching to a larger housing would only allow you to make the same power at a lower PSI. While this is great, it adds more lag. For the most part I think people who are buying a turbo kit would rather turn the knob a little more than have a laggier turbo on the street.

I forgot to ad that ams evo the highest I've seen it make was 668whp on a 2.3L w/ a .63 gt35r.
Slowboyracing got 640whp at 40psi on their bolton .48 a/r gt35r on a 2.3L.
Now I'm not saying that bigger housing won't make more power but why go with one unless you really plan to go insanely high on power or just like the extra lag.

First off I would like to dispell the common misconception that a bigger compressor wheel will move more air at a given PSI. Boost is basically back pressure in the intake. Therefor, 19 psi from a 50 trim is gong to be the same as 19 psi from a 56 trim gt 40 wheel. Often though, bigger compresor wheels can come with bigger turbine wheels. In the saem turbine housing (pte for example) this can make a difference. Generally, the more the boost is turned up, the more the difference in flow. This is becasue the smaller turbine wheel usually associated with a smaller compressor, isn't having much trouble keeping a favorable intake to exhaust pressure ratio. As the motor begins to move more air (either through V.E. changes or raising the boost pressure) the samller turbine wheels will have more trouble and the larger turbine wheel will allow more air to flow through the motor.

With all of the different compressors on the market, how do I know which one is the best for me?

The first suggestion to someone that doesn't have much knowledge is read up, or ask a professional. However, we all now Brian and Robert @ FP are busy people, so we will see if we can shed light on the topic for you to do it yourself.
We all have heard the saying "an engine is basically just an air pump." This is a good way to look at it for these purposes. This said "air pump" is going to have a demand, and the compressor wheels job is to meet that demand. In the DSM community people have grown very fond of the 50 trim, 60-1 and 56 trim 'gt40' compressors. They are rated at 48, 60, and 62 lb/min repectively. Incidnetally, the gt40 compressor is also used in the gt35r, as well as the smaller gt40r (there are two 40rs).

All airflow are appoximate as they can differ with a change in intake temperatures and/or elevation. However, they are commonly datalogged and generally accepted. YMMV

At 20psi, a typical 2.0 dsm will flow 33-35 lb/min of air with a mitsu exhasut manifold and mitsu style turbine housing. As you can see, there isn't a lot of room for you to raise the boost on some of the smaller compressor wheels (s16g, big 16g) without reaching the maximum amount of flow for the wheel. This is commonly seen as boost taper in the high end. The turbo can't keep up with the airflow demand of the motor, and can't keep the intake pressurized the the same amount as rpms increase. Not all boost taper is caused form maxing the compressor, but if you are near the flow limits of the turbo, that is what I would suspect.
For people with larger compressor wheels, there are two options on how to get more air through the motor. Raising the boost pressure will allow more air to flow, but I like the idea of boosting V.E. Adding cams onto the same car flowing 33-35 lb/min @ 20psi will generally bring the flow level up to 38-40 lb/min at the same psi. Now, if we wanted to we could start raising the boost pressure and start to approach the advertised flow rating of the mighty "20g". with 5-7 more psi, you should be flowing around 45 lb/min. Remeber now, the more the boost is cranked up, the more you would most liekly benfit form a larger turbine wheel, even if you are limited by the same housing. This is whay most people run "clipped" turbine wheels on the bigger compressors (before the bolt on garretts came out). That way the same turbine will be less of a restriction.
The next step to boost V.E. is the now commonplace sheet metal intake manifold. Generally, a cammed car will gain an additional 4-5 lb/min just by bolting on the manifold. That will take flow to the 44-45 lb/min mark. With the additional flow of the motor aven at a relativley 'low' 20 psi, you will start to see more gains by moving away from the mitsu style housing, and switching to a garrett style turbine housing. The difference may be nominal now, but as you raise the psi on this set up, it becomes more apparent. As the boost gauge swings to 27-28 psi, you will be in the realm of 500whp and need a comprssor that can flow ~55+ lb/min of air. A 60-1 or a 'gt40' wheel is a good choice if this is the mod path you want to take as they are rated at 60 and 62 lb/min repectively (most peopel tend to rate the gt40 at 65 lb/min, but Garrett rates it 62). The larger compressors will still have the flow in them and all you need to do is turn up the boost to get it. With 33-35psi form one of these compressors you will near 600whp. With such high airflow and boost levels, you will start to see more power at less psi by switching to an even larger hotside. The same set up with a .68 t4/t67 can produce 640+whp at the same psi.

Keep in mind all of these observed airflows are from a 2.0l motor. A stroker motor will generally lfow 15-20% more air at a given psi. A cammed, SMIM will typically flow near 50 lb/min at 20 psi.

The point where the turbine housing begins and measure the cross-sectional area A at that one point. Now measure the distance between the center of this area and the center of the turbine wheel--that's the radius R. Do some division and you come up with a measurement. Now move to a different point in the turbine housing and do it again--the calculated ratio remains constant because the housing constantly gets smaller in diameter the closer it gets to the turbine wheel. When upgrading from the .48 to the .63 A/R, it's the area that changes; the radius is essentially identical. This is precisely why the .63 housing flows more air - the passage is larger.

This is a great thread - I'll probably clean it up, and make a copy of it for the Tech Guide. Thanks to all who have contributed.

I am not done with this thread, just been super busy latley. I'll get some more info up here ASAP.

just a quick piece of information, the lower your a/r your turbine housing is the faster you have spool. but if your a/r is too low, then you won't have as much top end. so if you have a .48 a/r on your turbine housing, you're going to spool your turbo a bit faster, but you won't have as much top end power as a person that might have a .63 a/r turbine housing.

EDIT
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someone already said that in an above post, but just in case you did what i did (not read the big post because that is a big post i just thought i'd mention it in short.