Explanation on Compressor maps

[Brian O Conner]

I am reading Turbo real world high performance. I did not realise how much there is to just the turbo till I started reading about a week ago. From the formulas to convert 1997cc to cubic inches and finding your CFM. It is definitely a dedicated mans game. I am trying to understand this portion of the book in big detail. Anything about compressor maps from what a good efficiency island to good turbine speeds or any pointers on the lowest reccomended percentage to a common percentage.

 

[Bud92gsx]

Repost question here..for the best answer.. http://www.dsmtuners.com/forums/turbo-system-tech/393636-questions-justin-21.html

 

[snowborder714]

Some good info on how to read compressor maps in these threads.
http://www.dsmtuners.com/forums/turbo-system-tech/362599-how-read-hx35-hx40-compressor-map-s.html
http://www.dsmtuners.com/forums/bolt-tech/410388-injector-pump-sizing-questions.html

 

[knochgoon24]

Repost question here..for the best answer.. http://www.dsmtuners.com/forums/turbo-system-tech/393636-questions-justin-21.html

That would NOT be the place to post that. The questions for Justin thread is mostly about specific turbo and their features. This is a general question that would best be served with it's own thread.


Brian posted some good info in that second link pertaining to reading compressor maps.

There's some good general info in this thread about what that info means:
http://www.dsmtuners.com/forums/newbie-forum/419834-compound-turbo-setup-plumed-backwards.html

There are some specifics in there that deal with compound setups, but the theory is still the same for a single turbo.

What are you looking exactly? How to read them? What they mean? How to calculate where your setup would fall on a compressor map?

If you're patient enough, I plan on doing a tech article dealing with compressor AND the much neglected turbine maps here in the next few weeks. I got a few PMs to do it after that compound turbo thread. I just need through finals this week and next. I have notes from my one class that I'll scan in that helps explain it all.

In the mean time, both of these are pretty good:
http://www.enginelogics.com/cmaps.html
http://www.stealth316.com/2-3s-compflowmaps.htm

 

[bastarddsm]

OK Heres the deal with compressor maps, they tell you how much the turbo can flow, how much pressure it can make, and how efficient it is at a given pressure ratio and flow.

The flow is determined by your engine. Here we go, get out your slide rule son.

Pressure Ratio (PR) = (14.7+boost)/14.7

Now onto the engine airflow,

CFM unboosted = (displacement * rpm*ve)/3456

our engines 122cu in, we have a good head, and were gonna turn it 8000 rpm, so:

CFM unboosted = (122*8000*1.0)/3456 = 282cfm

Now to add boost in:
CFM boosted = CFM unboosted * PR

Were gonna run 30psi so:
(30+14.7)/14.7 = 3.04

CFMboosted = 282*3.04 = 857cfm

On a good day, with good air 1CFM = 0.07lb/min, so CFM*0.07 = lb/min

857*0.07 = 60lb/min

Finally, 1lb/min ~10 flywheel horsepower on gasoline and about 11 on alcohol.
So this engine would make 600 - 660hp, which coincidentally is right at about what is typically seen of a well setup 4g63 at 30psi.

Notes on VE: VE is determined by many things, cam's, intake, turbo, ports, ect...
That being said you can estimate the VE like this

1. Stock turbo or (16g), stock cams and intake ~.85-.9
2. 50trim, hx35 30r ect, 272's and stock intake .9-1.0
3. Same as above, but using a good intake .95-1.05
4. BIG turbo GT40 HX52 S372, Monster Cams ect.. 1-1.0


Also keep in mind that the turbine has to extract horsepower from the exhaust flow to compress the air. This power is created by the pressure drop across the turbine. More pressure drop, more pumping losses, and the less power the engine makes.

Now at a 60lb/min flow rate, and 30psi it takes roughly 60hp just to compress the air, and rises drastically with boost and airflow. Now factor in the ~75% efficiency of most compressor wheels and your looking at about 75hp the compressor needs to do it's job. Keep in mind that the turbine isn't 100% efficient either. You can easily see how a more efficient turbo, and better flowing setup can drastically improve power.

Finally the numbers I have posted are definite generalizations, and shouldn't be used for anything other than rough planning of a setup. You can start at any point and see what it is going to take to arrive at a certain outcome.

 

[Brian O Conner]

So surge would be where your turbo is trying to compress a lot of air without much air flow? Also your wanting the highest amount of boost and air flow without going under a good efficiency of around low 70s is the goal of this? Also the efficiency island is the good boundries for this correct. Just to clear up some things.

 

[bastarddsm]

Yeah surge is where the force of the comressed air trying to escape back out the compressor intake, overcomes the torque generated by the turbine.

Now for efficiency, yeah you generally want to try and stay above 70%. In general you want the bulk of your powerband to be in the efficiancy island, and it will be ok if you go slightly to the left of it at max RPM.

Keep in mind when you calculate the lbs/min in the above equations you are only calculating it for one RPM point. The lbs/min flow increases with RPM, so what you can do is calculate it for different rpms (4000,5000,6000,7000,8000) and then plot them on the map to see where you are.

Also keep in mind that overall the turbo has a very small effect on the operating parameters of the engine. Meaning its best to start with a target power goal, use the numbers to see what RPM and Boost its going to take, then plot the flow and boost on various compressor maps to see which one is the best fit.

To clairify a bit, don't try and fit the pressure ratio, and lbs/min data to a map. Fit a map to the data.

 

[Bud92gsx]

That would NOT be the place to post that. The questions for Justin thread is mostly about specific turbo and their features. This is a general question that would best be served with it's own thread.

I know but he's a freaking turbo genious...He can explain turbo questions to a chimpanzie..

 

[twicks69]

I know but he's a freaking turbo genious...He can explain turbo questions to a chimpanzie..

Bud, please listen to them though, you have forwarded A LOT of threads onto Justin lately and it is a bit aggravating. Trust me, I know, I think I get PM's from anyone that has a transmission question even if it is a simple one, instead of doing any sort of research on our invaluable forum they PM me instead. Though it is a kind thing to do, it also takes up a lot of time we simply do not have being spent on things that have been answered before either by us or by others in prior threads that could have been found with the search button.

Thank you for understanding.

 

[Bud92gsx]

But if I do not know the answer..Shouldn't I forward the question to someone that can help?

I've had the same conversation with a couple people lately and keep getting mixed answers..I hate to be a pain..But like to help, even tho I may not know the answer..

 

[JusMX141]

But if I do not know the answer..Shouldn't I forward the question to someone that can help?

Simply-put, Bud....get off my nuts. There are others that understand fluid dynamics better and can give a far more detailed analysis of compressor maps than yours truly. Look at the detailed info that Kurt provided above for example.

That being said, this is the type of question that belongs searchable within the public eye and not buried in a conglomerate thread for random individual questions on the topic of forced induction.

I hate to be a pain..But like to help, even tho I may not know the answer..

You're not helping anyone by dumping every technical turbo question on me. That's just being f*cking annoying. If you can't provide useful information on your own, stay out of the thread and let others respond.

Wes, Tim....thank you.

 

[Bud92gsx]

Point made..

I Might just take a break from trying to help anyone for a while..Since All I do is piss people off..

 

[bastarddsm]

But if I do not know the answer..Shouldn't I forward the question to someone that can help?

I've had the same conversation with a couple people lately and keep getting mixed answers..I hate to be a pain..But like to help, even tho I may not know the answer..

I'd like to think I handled this question pretty well, meaning there are plenty of people on the board who know their shit.

Remember the #1 rule, if you don't know, don't have personal experience, don't post. I see you post on a whole lot of stuff that you have no business posting on.

When you don't know who to trust, be smart about it. Look at the green chicklets, look at the time slip, and look at the profile. Someone to trust will have a solid rep, low times, and a profile that doesn't make them look like and idiot.

This isn't rocket science, its basic social skills.

 

[GsXdSmKingGsX]

Point made..

I Might just take a break from trying to help anyone for a while..Since All I do is piss people off..

You'll be fine, Bud. You're a grown man .

 

[Bud92gsx]

You'll be fine, Bud. You're a grown man .

I'll be fine..Just a little butt hurt is all..

 

[Calan]

I'll be fine..Just a little butt hurt is all..

I think they make an ointment for that Bud.

 

[Bud92gsx]

I think they make an ointment for that Bud.

Not to self..Go to drug store tomarrow..Cause there closed now

I would start drinking but I have to go to the bar in a couple hours..I know that sounds backwards..But I'm driving..

 

[Brian O Conner]

just to comment no disrespect towards anyone but you guys were kind of rude to bud. Personally it would get annoying to awnser questions for new people but then again I have to agree with Justin and the other mods on this one. You really have to research this the old fashion way with a book and ask only the questions you cant understand. Really I dont get why people stereo type tuners as a bunch of junkies because in reality it is the people who are dedicated and willing to study the dynamics. Just a comment no disrespect towards anyone

 

[LandoAWD]

just to comment no disrespect towards anyone but you guys were kind of rude to bud.

Bud has 4000 posts with 30 posts of content. Things come to a head, eventually.