I got my car tuned today (Demetrios or Reactive Racing - good guy, amazing tuner). Overall we re-assured ourselves that this turbo is too small to make outrageous horsepower, but it spools very fast and the car is a great street car (the dyno curve below 5k is higher than most turbos I've seen). We peaked at 384 uncorrected rwhp (intake temps were in the 40's, ambient temp was around 60 in the shop), but the car makes a nice broad torque curve and a very drivable (and borderline scary fast) hp curve. The car drives nice and smooth and the boost comes on almost immediately. This turbo came with my A-Spec AP-88 kit. A couple points:

1) My engine has a huge street port (done by www.jprimports.com; great engine builder) which I think hurt my max hp due to too much backpressure because this turbo is so small (0.94 T3 hotside, 82 mm compressor wheel). This backpressure though, is probably responsible for the nice torque curve.

2) A-spec's manifold has very short runners, which will produce more low end whp and less up top, this is exactly what we are seeing here.

3) Car has 4" dp, 3" midpipe, M2 Duals, 1600/850's, large street port, and a bunch of other crap.

Overall I'm very happy with the set-up, although I would have liked to see more up top (but then I would have lost power down low. Can't have it all I guess ).

Matt

 

how much boost was that on?

 

Yeah, at how much boost? Also what computer are you running? I would still expect to see more power out of a ported motor with a GT40.

 

This GT4082 actually has a smaller compressor wheel than a GT35R (now known as the GT3582R), with a turbine wheel and no ball bearings. The GT40R, or GT4088R, which might be the turbo you have in mind as a GT40, is a whole different monster.

 

... huh?

Porting wouldnt increase backpressure. Porting lets air flow [i]easier[/], and short runners are better for high rpms, not low rpms.

I think youre a little confused there, lol. Anyway, backpressure would be c/o the hotside of the turbo, porting would help air flow better at lower boost ratios, and short runners would help TOP end, not low end.

 

gt4088 is a non ball berring version of a gt40r, the gt4082(which is also no BB) is the same thing with an 82mm wheel as aposed to the 4088 with the 88mm wheel

 

15.5 psi

PFC. It's not the GT40R or GT4088, it has a smaller compressor wheel (82 mm).

No, I'm not confused . The large port means that the engine in flowing more air. Since the turbo hotside is small (or "smaller" I should say) the turbo cannot keep up with the air coming from the engine and backpressure is formed by the turbo itself. A smaller port may result in less backpressure. My understanding about tube length on the manifold is the oposite of yours, not too sure what to say about that...

 

Smaller port just means less power period. The backpressure is from your turbo hotside, not the ports - bigger ports just let more air flow in at lower boost ratios, or just more air period if its N/A.

As far as intake runner length, well, basically put the pressure pulses that go from one closed valve to another (or with a rotary the side of the rotor... all the literature is made for piston engines, same principle) at the speed of sound. You want the wave that bounces off of the closed port to hit the oher intake at the same time as its open to force more air in.

At lower rpms youd want a longer runner because the speed of the pulse is the same, but the length it has to travel can be changed - at lower rpms you want it to take longer to get there so its timed right.

At higher rpms it has to get there quicker, so youd use a shorter runner.

However, its not quite THAT simple. Youd need runners that are like 10' long for it to work for just one bounce, so what you do is you have the runner at one quarter (or some other 1/n fraction) of the length so it bounces back and forth a few times, but still hits the right intake at the right time to push it in.

Also, for a very extreme example of short runner = high rpm, long runner = long rpm, look at GM's TPI motor (with long runners that cant hardly rev over 5K rpms) or the LT1, which has an intake with runners that are good to 8K! rpms, though youd still need to do some work to open it up to flow the air necessary for a 5.7 liter engine spinning that fast :P.

I realize thats not in the rotary world, but its the most glaring example I can see. For an even more pronounced example of this, read up on TPI motors with LT1 intakes swapped to them or that use other aftermarket intakes with shorter runners. They lose a little low end but they actually pull to redline instead of taking a nosedive between 4.5-5K rpms.

P.S. - my stepdad has a IROC-Z with a TPI motor and we're gonna put a LT1 intake on it sometime in the winter or spring :yeah:

 

That's what I said above in both of my posts. The engine is flowing a lot more air than a stock port and the turbo hotside is too restrictive for that much flow... hence the backpressure. I'm agreeing with you here .

Quote:

Originally Posted by Nihilanthic

As far as intake runner length, well, basically put the pressure pulses that go from one closed valve to another (or with a rotary the side of the rotor... all the literature is made for piston engines, same principle) at the speed of sound. You want the wave that bounces off of the closed port to hit the other intake at the same time as its open to force more air in.

It's not as simple as a high school physics class with pressure waves in a tube. There is a lot of interference (pressure/backpressure), mass/flow interaction with the turbo wheel itself, and the diameter of the manifold tube itself plays a role. On top of that the amount of air is changing for every pulse any time the RPMs are rising/falling causing the pressure pulses to undergo accelerations (in which case no constant length runner will be perfect).

I really am not too sure why longer runners are better than shorter at higher rpms and I'm not gonna make some crap up to explain it (maybe someone else can offer their opinions). I have simply heard from a different people that is the case.

 

the first example that pops into my mind is a NHRA pro stock motor "I know I know it's a piston engine". They run long runner tunnel ram intakes. These are 510 cid engines turning about 10,000 RPM. The way I understand it is that the velocity of the incoming air stacks up inside the runner. As the cylinder fills with air the air behind it stacks up like a colision forceing more air into the cylinder than the motor can draw in on its own. Of corse these engines are designed to operate under a very narrow power range.

Allen

 

He is not talking about a intake runner he is talking about a exhaust runner. And he is correct a longer exhaust runner is better for a higher reving engine, wich is opposite of a intake runner, wich means you are both correct

 

With a TURBO, it doesnt really matter. You just want a manifold to hold in heat and pressure on one side of the turbo and the other to be as free flowing as possible to maximize the difference so it will work better.

Also, IIRC, LT headers work better because they flow better and are more CORRECT for the length. Playing with the formulas Ive found they, too, want shorter header length in the primary tubes (or "runners") for higher rpms. Its just that you want longer tubes on the exhaust becuase the dynamics are slightly different... but for lower rpms you want longer tubes, etc. I put in a 600 rpm figure and got 300 inches, I put in 6000 figure and got 30 inches. However, you wont be doing SCAVENGING with a TURBO application anyway!

As far as those drag engines, uh, you measured the intake runner from the plenum to the intake valve? They have the runners going STRAIGHT from the carb to the intake because its a wet manifold. With dry manifolds or not-so-racey wet carburator manifolds, there are twists and turns and the runner length is coiled up somewhat. Go look at a LS1 intake sometime... see those buldges? Theyre the runners curving over the plenum.

BTW, little tidbit for you...

"# Input length is 10 inches
# For 2nd harmonic, RPM range is from 11748 to 14256 with a pulse strength of 10 percent
# For 3rd harmonic, RPM range is from 8827 to 10088 with a pulse strength of 7 percent
# For 4th harmonic, RPM range is from 6882 to 7696 with a pulse strength of 4 percent"

http://www.bgsoflex.com/intakeln.html <- play around with that a little bit and see what you find out. What LOOKS "long" to you might not be what actually is or is not 'long' as far as the harmonics go.

Heres a list of total runner lengths from some popular v8 intakes:
Stock TPI manifold ...................8” ...............runners 11.25”............... cylinder head 6”.............total 25.25”
Accel super ram manifold........ 8”................runners 7.00”............... cylinder head 6”............ total 21.00”
Holley stealth ram manifold .....6.26” ................................................. cylinder head 6”............ total 12.26”
Edelbrock performer RPM ...........................runners 6.00”................ cylinder head 6”............ total 12.00”
Edelbrock Victor Jr .......................................runners 5.50”................ cylinder head 6”............ total 11.50”

25" for the TPI. Victor JR is 11.5" total... there ya go.

 

i have a headache

 

Exactly. Nihilanthic, if you want to start a thread about exhaust runner length, be my guest.

I just wanted to show people what this turbo can do (or not do, depending on how you look at it) .

 

Threads often segway into explaining other things... why not let people learn something? :P

 

congrats on your numbers.Great looking engine.

 

Thanks

 

HOLY ****, that is a steep torque curve for a single on a 7!!

I would have liked to see the plot start at 3k though

looks awesome! 380+rwhp FD isn't exactly a slouch

interesting how your torque falls off after 6K...BB turbo? T3 .94 isn't that small either...must run more boost!! hahaha!

seriously though, a turbo that size makes better power closer to 18psi

 

That turbo isn't big enough to make anymore hp than what he already has. We couldn't break the 400rwhp mark with one of our customer's car using the GT40 (4082). The boost would just fall off at higher rpm (even setting the boost to 19psi and it'll dip down to about 16psi at 7krpm or so.

Here's a dyno chart we did on one of the car

 

well damn

 

I don't have the plot for <4k, but if I remember correctly it was about 205 rwhp at 4k and 100 rwhp at 3k. The torque and power come on early, so it makes the car fun to drive on the street. It's not a BB turbo. As pluto mentioned, I'm not too sure that this turbo can make much more on a rotary. It had no problem holding boost for me, but I didn't run it to 17-19 psi either.

 

mine made 430 no port work at 21psi done at aspec

 

21lbs to make 430 that is a lot of boost just to make 430

 

at peak output turbos function as restrictor plates in that they provide an absolute limit as to airflow.

look at any compressor map and note max flow (at standard temp and pressure) in lbs per minute.

that's it. no more. period. as such, each turbo can make X amount of hp.

compressor map link for the gt40 88 and 82:

http://www.moreboost.org/graphics/maps/GT40.jpg

the 82 maxflows 57 lbs per minute of air/. that's tops. it will not flow more.

the 88 flows approx 65 lbs of air.

for maximum rear wheel rotary hp just multiply the lbs/minute times 14.471 to get cfm.

57 X 14.471 = 825 cfm

65 X 14.471 = 941 cfm

divide cfm by 1.92 to get Maximum Rotary rwhp

825/1.92 = 429 max rotary rwhp

941/1.92 = 490 max rotary rwhp

notice i refer to Rotary hp...... the rotary is at a disadvantage in relation to the piston engine as to converting airflow to hp as set out by the following alternative method of solving for rotary hp:

use maximum airflow in lbs/minute and multiply by 10 to get piston engine rwhp and then divide my 1.3 to get rotary hp.

in the case of the gt40...

gt4082 57 lbs/min times 10 = 570 piston rwhp/1.3 = 438 Max rotary rwhp
gt4088 65 lb/min times 10 = 650 piston rwhp/1.3 = 500 Max rotary rwhp

please note that these are maximums. if everything isn't perfect, or is slightly detuned so you don't blow your motor you will make a bit less. There may be some upside to these numbers when running water/alcohol injection and tuning for a 12.5 AFR, but if you are running gasoline they should be pretty accurate.

howard coleman

 

apparently the compressor map for the gt4088 that i used is in error so i thought i better straighten out the confusion i created.

according to Garrett's map the GT4088 flows 72 lbs/minute...

doing the math...

72 X 14.471 = 1042 cfm/ 1.92 = 542 max rotary rwhp.

figured the other way... 72 X 10 = 720 piston rwhp/1.3 = 553 rrwhp.

howard coleman