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Turbo maps...please help

2K views 25 replies 11 participants last post by  arny213 
#1 ·
Hey guys. I need help

Im running a gt2860r and i already maxed it out.

so im thinking to go to a gt2871r.
only thing is that i talked with a friend of mine that works for store that sells turbos and he can sell me a gt3071r t3 with the antisurge(like the gt3076r) for the same price with the gt2871r.

The thing now is that both turbos are similar in hp numbers.
I want somewhere of the 400hp mark with the least turbo lag.

so im posting the maps that garrett gives.
Please let me know which one is better.




 
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#4 ·
The gt3071r. The spool may be a bit slower but its a much better turbo. The gt2871r its somewhat choked by the smaller turbine. Go with .63 as well.

Also you will be flirting with safe max for the gt3071 at 400hp. I have never seen 400HP with the gt2871r.

There are other options that are actually just as good that will cost less unless you are getting a killer deal on the turbo.
 
#8 ·
The biggest mistake people make when they chose a turbo is that they look at the comp map and then go with the smallest turbine and AR for spool. You have to understand that the turbo works by using the flow created on the comp side and converts it to pressure by using the turbine nozzle. The turbine works by converting heat pressure into mechanical energy. Its the psi of the exhaust pre turbine turbine that is flowing to lower psi atmosphere.

Look at the max flow comp flow on each comp map. They are close to 45lb min. Now look at the turbine maps and their efficiency. The gt28 hits peak at 15lb min and the gt30 hits peak at 20lb min. Once you hit peak turbine flow you will get less out per psi from the comp. Basically you start to choke the turbo because the turbine can not keep up.

I have seem the gt2871 and gt3071 both on the same motor and setup first hand and at the same psi. The gt30 spooled slighter slower but made far better peak HP at the same psi.

I'm at work but I can go into this in greater detail later.
 
#10 ·
Ok. That makes sense.

However, ATP releases a twin scroll bolt on turbine housing for the GT28 series. I think that would be fun to play with, as I have not been impressed at all with the spool and response times of the GT30s on D-series engines.
 
#12 ·
Turbine maps are . . . difficult. The only good information I've seen online is the BW AR charts, mostly because they have very specific turbos. Garrett probably has done the work, but since there are eleventy trillion combos, that is a significant investment in testing. I wouldn't want to just give away that info, either. The turbine map is generally a combination of the whole turbo, as the turbine map is effected by the shaft, bearing assembly, compressor, turbine and compressor housings, EGT, etc. All of those variables make things very hard to test consistently or completely, as EVERY combination would be different.

GT28RS/2871R 0.82 A/R T3 DIVIDED Turbine Housing : atpturbo.com

Not cheap, but interesting.
 
#14 ·
Guys the first and fourth picture in the first post are turbine maps.
 
#20 ·
They are very informative if you understand what they mean. The line moving left to right is efficinecy but it does not show peak efficiency which relates to lb min comp/ lb min at turbine. You actually meet peak efficiency slighter before the peak turbine efficiency. I will get into this in great detail in a bit. Right now I just got home and am going to get a bite and take a knap.

Was up all night watching my "Eers" pound Clemson 70-33......
 
#16 ·
im curious about what you said for the gt2871r because at turbobygarrett.com says that makes 470hp...

Actually i dont really care about peak numbers.
I want a gt series turbo that will make around 400hp and still spool fast.
My car is a daily driver keep that in mind!
 
#21 ·
I'm interested in learning about them, that's for sure, because I haven't been able to find much info about the turbine side of things, as far as the maps go. I mean, I do understand what you just said, but, those maps don't seem to be as useful as the compressor maps.
 
#22 · (Edited)
The point of the turbine map is show how the turbine is being is used and how it converts flow into machanical energy and more importantly when. If you look at the turbine map you will see on the left side going up flow most likely in lb min and PR across the bottom in bar and then simply a line going from left to right. The curve of the line indicates how the turbo reacts. If it is less dramatic the turbo will be more linear. If it is looks like a circle it will be a fast neck snapping spool.

If you look at the GT3071R turbine map you will see 3 different AR's and this really shows you the difference and what to expect performance wise from each. Lets consider the .63 first. If you notice it hits peak at 20 lb min flow. This would allow you to be making peak efficiency from the turbo once the turbo is flowing 20lb min on the comp map. After that it performance will taper off. You will still make hp but you will be making less hp per psi from 20 lb min on. Look at the .82 and it peaks at 23 lb min. This would give you a little less response but more hp per psi in the midrange. The last is the 1.06 and it peaks around 27 lb min. This would spool slower but would give you the most per psi.

I know this sounds confusing but I will try to explain. Have you ever seen a dyno of the T3 60 trim on the Ford 2.3? You can make say 220hp at 12 psi. If you do the math then you should be able to make

12psi + (atmosphere) 14.7= 26.7 psi = 220hp or 8.25 hp per psi

So if you turned the psi up to say 20 psi you should be able to make

34.7 * 8.25= 286.7 hp

It will not happen. In all honesty you will most likely lose hp because you are past the peak turbine efficency. The reason is the PR (pressure ratio) between the exhaust valves and turbine exceeds the PR in the intake chamber before the intake valves. This is called pumping loss. What pumping loss is is when the exhaust does not flow past the turbine because you are past its efficiency range and it does not exit the combustion chamber properly because the turbine nozzle is too big of a bottle neck. The exhaust flowes from the combustion chamber because it is a higher psi and air flowes from higher psi to lower psi (or too the atmosphere).

Too give you an idea lets say the PR differential between the exhaust side and turbine side is 8 psi. That 8 psi actually exerts force back on the piston face and robs the crank of hp which means that turbos actually do rob mechanical hp from the motor. I have the math for this but I am sleepy (and lazy).

SO in a nutshell what I am saying is that for the hp you are trying to achieve the GT2871R turbine is not big enough to adequately handle it and you will make more hp per psi with the GT3071R as well as make more efficient hp.

If this is difficult to understand LMK what part and I will try to work on it to explain it better.

I am actually planning on making a thread with a bunch of turbo information like a tech thread that covers all this tuff and gives you examples and charts. I have been working on it but if I started typing now I would be up til 6 AM trying to get it all on there.
 
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#24 ·
My point of emphasis is this, most members buy a turbo say a T3T4 50 trim and look at its comp and say OK it will make 45 lb min and I can make 350hp with it no problem. But they make the mistake and get a Stage 2 turbine. Still they make their 350 but later want to make 400hp. Then they can't make it and sell the 50 trim and buy a larger 60 trim or 57 trim and make their goal. Had they bought a stage 3 turbine 50 trim to start with it would have worked just fine.

If you actually look at the T4 compressor maps you will realize the 50 trim is the widest and damn near the most effcient.
 
#26 ·
mhamrick is on the right track for sure. reminds me of when I pounded over countless charts and compressor maps.... I heavily considered the gt3071 also but the shape of the turbine was not conducive to my build, in other words the turbo I wanted wouldn't fit without a very expensive custom manifold. so I snagged the 2nd best turbo for my ride:wink: I love my 50 trim BB stage 3 (.63ar turbine). but with unlimited fundage gt30r ALL DA WAY!!
 
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