Turbo Education Thread - Page 2

1SloColt · 04-05-2006, 07:28 PM

Quote:

Originally Posted by tstkl

my main question is, is there any way to determine what makes a turbo a good pump gas turbo, and what makes a turbo a good race gas turbo? I was looking at the 60-1's by pte (dual ball bearing mitsu style turbine housing ones with T40E compressor housings), but was told that that turbo is very poor for pump gas use. Is this due to its high pressure ratio efficentcy range, or some other factors? What determines if a turbo, like the 50 trim, the "pump gas king" is good on pump gas or race gas. Is it just the larger you get the harder it is to run the high boost required on a lower octane fuel, or am I missing something?

You aren't missing anything. A 50 trim loves 20psi on pump gas with a good tune because its in its efficiency range to make good power. Big turbos like big boost. You don't see many guys running around with gt42r's at 20psi, whereas you don't see many people with 50 trims at 35psi either. Pick the turbo for the boost you are going to run. If you know you are going to run 30psi occasionally then go with something that will enjoy that boost pressure, a 50 trim would kinda be pushing it for that boost IMO, a 60-1 would start pettering out around there too.

spoolinawd91 · 04-26-2006, 02:13 PM

Quote:

Originally Posted by sleestack

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…

So how much of an effect does a larger turbine wheel make on backpressure within the same a/r turbine? Say going from a stage 5 wheel to a p-trim a .63 a/r t3 turbine, would that make as big of difference in backpressure as going to a bigger a/r?

tsimiz · 05-27-2006, 02:18 PM

i found this site very infomative

so would a t4 .58 turbine housing spoolup faster than a t3.82?

nanokpsi · 07-05-2006, 02:02 PM

Quote:

Originally Posted by tsimiz

i found this site very infomative

so would a t4 .58 turbine housing spoolup faster than a t3.82?

Yes it would.
.68 t4 is comporable to a .82 t3.

sleestack · 10-02-2006, 01:26 PM

Its hard to believe its been a year since I posted that. I don't know what happened to the images in my posts. I wonder if maybe anyone backed it up or saved the image tags so I can find those pics and re-upload them to my server? TIA

I'll get back into this and make a few more posts.

brute · 10-02-2006, 03:38 PM

I can help you out, Brian. I'll do my best. What all does everyone want to know?

tstkl · 10-02-2006, 08:50 PM

the meaning to life

or you guys could probably go into the compressor housing a little more. I've heard claims of up to 10 lbs/min increase just due to a change in the housing itself. I find this hard to believe, is there really that much to just a simple housing?

brute · 10-02-2006, 09:00 PM

Well it's the same with most things. You'll obviously get more flow if you get a larger area for things to travel through. Larger injectors = more flow. Larger exhuast = more flow. Larger compressor housing = more flow. However, with turbos, it is important to match everything. And more flow doesn't necessarily make it more beneficial to your specific application. This is why .a/r is so important. Larger a/r = more overall flow, but it will decrease low-end type thing. So a huge a/r turbine housing will sacrifice spool for overall flow. Great top-end, not good low end. Dyno queen. And conversely, a small a/r will provide excellent spool at the expense of top end.

DGajre777 · 10-22-2006, 06:48 PM

Quote:

Originally Posted by brute

However, with turbos, it is important to match everything. And more flow doesn't necessarily make it more beneficial to your specific application. This is why .a/r is so important. Larger a/r = more overall flow, but it will decrease low-end type thing. So a huge a/r turbine housing will sacrifice spool for overall flow. Great top-end, not good low end. Dyno queen. And conversely, a small a/r will provide excellent spool at the expense of top end.

Thanks for your help on my other thread brute. For a small a/r turbine housing (like 0.48 A/R) what would be considered as "matching everything"?
Stock TB?
Stock intake manifold?
No cams?
3" (not 2.5 before the flex) downpipe?
No cat?
Basically keep the restrictions before the turbo and remove restrictions after the turbo?

The idea to measure backpressure using an oil pressure gauge from FP is cool.

brute · 10-22-2006, 07:12 PM

Well, a small a/r like that in the turbine housing would provide amazingly fast spool, but sacrifice top end. So, if you think about what a lot of those mods do, you can do them to help top end a little bit. The majority (if not all) aftermarket cams improve mid/top end at the sacrifice of low end torque. With the addition of aftermarket cams, people generally see a couple hp/ft lbs less up to about 3000 or so, then more from there on.

Same with intake manifolds. Generally speaking, the shorter the runner, the more top. Conversely, longer runners (like stock) help out low end. There was a thread floating around recently that explained intake manifolds. You can go do a search at How Stuff Works for intake manifolds. It explains it really well. So if you get a manifold like JM or Magnus or similar, those runners are super short compared to the stock ones, so you'll gain top end.

In terms of exhaust, there is a huge amount of information to consider on exhaust theory. I'll get into that if you're interested. But if you're worried about emissions (like some of us) get a high flow cat. Some local guys have dyno proven that high flow cats and straight through mufflers don't hurt performance in the least.

DGajre777 · 10-22-2006, 07:53 PM

"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."
Is ^^ talking about selecting a turbo instead of increasing flow with a smaller a/r housing?

If you could get into exhaust theory that would be great. No emissions testing here in FL.

DGajre777 · 10-22-2006, 07:53 PM

Quote:

Originally Posted by sleestack

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.

Is ^^ talking about selecting a turbo instead of increasing flow with a smaller a/r housing?

If you could get into exhaust theory that would be great. No emissions testing here in FL.

brute · 10-22-2006, 08:17 PM

Go to the bathroom, get something to drink, put your reading glasses on, and get comfortable. Here we go. This is taken from a thread over on 300zxclub.com. Although they're twin turbo V6's, all these points are still extremely relavent.

Quote:

2.5 inch turbo exhaust theory has to go.

The thing that that frustrates me is the old school philosophy that is extremely prevalent in the z32 community. I don’t know who started it, but anyone who has read Maximum Boost by Corky Bell, knows that it states that a 2.5 inch exhaust does not become a restriction until 450-500hp is achieved.
Corky’s chart:

I guess it's backwards that people get better e.t.’s with a open down pipe then a full exhaust.
And to back this up: From KO racing (http://www.koracing.net)

Unwilling to simply accept that for granted, we have been conducting our own testing, to determine where 3 inch diameter pipe becomes an advantage on the 3S-GTE, found in the MR2 Turbo (SW20), and Celica All Trac (ST165, ST185 & ST205). After extensive testing, we have found that point to be 300 rear wheel horsepower, which is substantially lower than Corky would have us believe. At 300 rear wheel horsepower, we were able to make the same RWHP at one less PSI of boost, and reach 200 foot-pounds of rear wheel torque 300 RPM sooner by upgrading from 2.5" to 3" down pipe and exhaust.

I know that a Z32 is a v6, and running a true dual exhaust means that each exhaust has 1.5 liters, however 2.5 inch diameter is not even equal to 3.2 inches diameter on a single system.

Turtleboy here on these forums is thoroughly convinced that 2.5 inches is the right thing over three inches, and his one word: Backpressure

The following excerpts are from Jay Kavanaugh, a turbosystems engineer at Garret, responding to a thread on http://www.impreza.net regarding exhaust design and exhaust theory:

Quote:

Howdy,
This thread was brought to my attention by a friend of mine in hopes of shedding some light on the issue of exhaust size selection for turbocharged vehicles. Most of the facts have been covered already. FWIW I'm an turbocharger development engineer for Garrett Engine Boosting Systems.
N/A cars: As most of you know, the design of turbo exhaust systems runs counter to exhaust design for n/a vehicles. N/A cars utilize exhaust velocity (not backpressure) in the collector to aid in scavenging other cylinders during the blowdown process. It just so happens that to get the appropriate velocity, you have to squeeze down the diameter of the discharge of the collector (aka the exhaust), which also induces backpressure. The backpressure is an undesirable byproduct of the desire to have a certain degree of exhaust velocity. Go too big, and you lose velocity and its associated beneficial scavenging effect. Too small and the backpressure skyrockets, more than offsetting any gain made by scavenging. There is a happy medium here.
For turbo cars, you throw all that out the window. You want the exhaust velocity to be high upstream of the turbine (i.e. in the header). You'll notice that primaries of turbo headers are smaller diameter than those of an n/a car of two-thirds the horsepower. The idea is to get the exhaust velocity up quickly, to get the turbo spooling as early as possible. Here, getting the boost up early is a much more effective way to torque than playing with tuned primary lengths and scavenging. The scavenging effects are small compared to what you'd get if you just got boost sooner instead. You have a turbo; you want boost. Just don't go so small on the header's primary diameter that you choke off the high end.

Downstream of the turbine (aka the turboback exhaust), you want the least backpressure possible. No ifs, ands, or buts. Stick a Hoover on the tailpipe if you can. The general rule of "larger is better" (to the point of diminishing returns) of turboback exhausts is valid. Here, the idea is to minimize the pressure downstream of the turbine in order to make the most effective use of the pressure that is being generated upstream of the turbine. Remember, a turbine operates via a pressure ratio. For a given turbine inlet pressure, you will get the highest pressure ratio across the turbine when you have the lowest possible discharge pressure. This means the turbine is able to do the most amount of work possible (i.e. drive the compressor and make boost) with the available inlet pressure.

Again, less pressure downstream of the turbine is goodness. This approach minimizes the time-to-boost (maximizes boost response) and will improve engine VE throughout the rev range.
As for 2.5" vs. 3.0", the "best" turboback exhaust depends on the amount of flow, or horsepower. At 250 hp, 2.5" is fine. Going to 3" at this power level won't get you much, if anything, other than a louder exhaust note. 300 hp and you're definitely suboptimal with 2.5". For 400-450 hp, even 3" is on the small side.

Quote:

As for the geometry of the exhaust at the turbine discharge, the most optimal configuration would be a gradual increase in diameter from the turbine's exducer to the desired exhaust diameter-- via a straight conical diffuser of 7-12° included angle (to minimize flow separation and skin friction losses) mounted right at the turbine discharge. Many turbochargers found in diesels have this diffuser section cast right into the turbine housing. A hyperbolic increase in diameter (like a trumpet snorkus) is theoretically ideal but I've never seen one in use (and doubt it would be measurably superior to a straight diffuser). The wastegate flow would be via a completely divorced (separated from the main turbine discharge flow) dumptube. Due the realities of packaging, cost, and emissions compliance this config is rarely possible on street cars. You will, however, see this type of layout on dedicated race vehicles.

A large "bellmouth" config which combines the turbine discharge and wastegate flow (without a divider between the two) is certainly better than the compromised stock routing, but not as effective as the above.
If an integrated exhaust (non-divorced wastegate flow) is required, keep the wastegate flow separate from the main turbine discharge flow for ~12-18" before reintroducing it. This will minimize the impact on turbine efficiency-- the introduction of the wastegate flow disrupts the flow field of the main turbine discharge flow.
Necking the exhaust down to a suboptimal diameter is never a good idea, but if it is necessary, doing it further downstream is better than doing it close to the turbine discharge since it will minimize the exhaust's contribution to backpressure. Better yet: don't neck down the exhaust at all.
Also, the temperature of the exhaust coming out of a cat is higher than the inlet temperature, due to the exothermic oxidation of unburned hydrocarbons in the cat. So the total heat loss (and density increase) of the gases as it travels down the exhaust is not as prominent as it seems.
Another thing to keep in mind is that cylinder scavenging takes place where the flows from separate cylinders merge (i.e. in the collector). There is no such thing as cylinder scavenging downstream of the turbine, and hence, no reason to desire high exhaust velocity here. You will only introduce unwanted backpressure.

Other things you can do (in addition to choosing an appropriate diameter) to minimize exhaust backpressure in a turboback exhaust are: avoid crush-bent tubes (use mandrel bends); avoid tight-radius turns (keep it as straight as possible); avoid step changes in diameter; avoid "cheated" radii (cuts that are non-perpendicular); use a high flow cat; use a straight-thru perforated core muffler... etc.

Quote:

Comparing the two bellmouth designs, I've never seen either one so I can only speculate. But based on your description, and assuming neither of them have a divider wall/tongue between the turbine discharge and wg dump, I'd venture that you'd be hard pressed to measure a difference between the two. The more gradual taper intuitively appears more desirable, but it's likely that it's beyond the point of diminishing returns. Either one sounds like it will improve the wastegate's discharge coefficient over the stock config, which will constitute the single biggest difference. This will allow more control over boost creep. Neither is as optimal as the divorced wastegate flow arrangement, however.

There's more to it, though-- if a larger bellmouth is excessively large right at the turbine discharge (a large step diameter increase), there will be an unrecoverable dump loss that will contribute to backpressure. This is why a gradual increase in diameter, like the conical diffuser mentioned earlier, is desirable at the turbine discharge.

As for primary lengths on turbo headers, it is advantageous to use equal-length primaries to time the arrival of the pulses at the turbine equally and to keep cylinder reversion balanced across all cylinders. This will improve boost response and the engine's VE. Equal-length is often difficult to achieve due to tight packaging, fabrication difficulty, and the desire to have runners of the shortest possible length.

Quote:

Here's a worked example (simplified) of how larger exhausts help turbo cars:
Say you have a turbo operating at a turbine pressure ratio (aka expansion ratio) of 1.8:1. You have a small turboback exhaust that contributes, say, 10 psig backpressure at the turbine discharge at redline. The total backpressure seen by the engine (upstream of the turbine) in this case is:
(14.5 +10)*1.8 = 44.1 psia = 29.6 psig total backpressure
So here, the turbine contributed 19.6 psig of backpressure to the total.
Now you slap on a proper low-backpressure, big turboback exhaust. Same turbo, same boost, etc. You measure 3 psig backpressure at the turbine discharge. In this case the engine sees just 17 psig total backpressure! And the turbine's contribution to the total backpressure is reduced to 14 psig (note: this is 5.6 psig lower than its contribution in the "small turboback" case).
So in the end, the engine saw a reduction in backpressure of 12.6 psig when you swapped turbobacks in this example. This reduction in backpressure is where all the engine's VE gains come from.

This is why larger exhausts make such big gains on nearly all stock turbo cars-- the turbine compounds the downstream backpressure via its expansion ratio. This is also why bigger turbos make more power at a given boost level-- they improve engine VE by operating at lower turbine expansion ratios for a given boost level.

In conclusion
As you can see, the backpressure penalty of running a too-small exhaust (like 2.5" for 350 hp) will vary depending on the match. At a given power level, a smaller turbo will generally be operating at a higher turbine pressure ratio and so will actually make the engine more sensitive to the backpressure downstream of the turbine than a larger turbine/turbo would. As for output temperatures, I'm not sure I understand the question. Are you referring to compressor outlet temperatures?

So for everyone spending thousands of dollars on turbo upgrades, and another sixteen hundred dollars on a turbo back exhaust, please realize that just because your dads dad said it, doesn’t mean that it's true. The only other community that even has a small amount of 2.5 inch turbo exhaust users is the VW/Audi community, largely in part to AWE tuning. A 3.5 inch turbo back exhaust on a mk3 supra turbo is about 80whp. I am positive that if people here jumped out of the 2.5 inch band wagon, we all could see a lot better hp gains for over a grand of money spent. I, if I decide to get a z32 tt, plan on running at least a 3inch down pipe, and a 3.5 inch exhaust, after all I am trying to make my car faster. And if I was to lose some low end torque, it could not be more then a couple of pounds, and with a car the weighs about a ton and a half, who would really notice, plus with the turbo spooling faster the power band would move to the left and right. After all, why do most racers run open down pipes? To save weight? No a full titanium exhaust doesn’t even weigh 20lbs.

DGajre777 · 10-23-2006, 05:12 AM

Thanks. ^^^ Awesome info!

DSM90AWD · 10-23-2006, 08:06 AM

Great stuff on exhaust theory

Quote:

Originally Posted by DGajre777

Is ^^ talking about selecting a turbo instead of increasing flow with a smaller a/r housing?

He's talking on matching the turbine housing A/R to the VE of the engine to keep the pressure ratio at or below 1:1.5. Changes to exhaust affects VE just like changes to intake.

Quote:

Originally Posted by Sleestack

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

nanokpsi · 11-01-2006, 05:38 PM

Quote:

Originally Posted by DGajre777

Is ^^ talking about selecting a turbo instead of increasing flow with a smaller a/r housing?

To sum it up, the more mods you have that increase volumettric efficiency, the bigger hotside you will probably need. Uprgrading from a .63 t3 to a .82 t3 means much more power for a car that already has big cams, SMIM, headwork, etc, than than it would on just an intake, exhaust, boost controller equiped car. For example, if your car is flowing 30lb/min at 20psi, a small turbine housing is not hurting peformance as much as it would on a car that is flowing 55lb/min at 20 psi.
Ultimately, it comes down to your intake to exhaust pressure ratio.