GTX3076R 0.82a/r versus 0.63a/r
Oct 17, 2014, 09:36 AM
#18
i did some research last night and can confirm what has been said about our 94 octane... basically it either has 10% ethanol, or 0%. Sometimes you'll get a bad tank with water build-up which is where the car might run like crap... Then there is 91 v-power from Shell. Only two viable options.
Oct 20, 2014, 03:45 PM
#19
i have seen as many have, that thread on here of the guy comparing the gtx3076 versus the gtx3576 and finding that the gtx3576 spooled as fast, if not faster than the gtx30 and produced more power...
does anyone have any insight where these two are concerned and if this test is even accurate!?!
does anyone have any insight where these two are concerned and if this test is even accurate!?!
Oct 21, 2014, 09:53 PM
#20
With a 2.4L on low octane fuel, I would absolutely go with the GTX3576R over the GTX3076R. The only time I'd tend towards a smaller turbine wheel setup is when you are not octane limited, thus you can crank the boost to the compressor limit and you may get some slight spool benefits due to lower turbine inertia.
If you look at the turbine maps, it tells the story pretty clearly. Here is an overlay of the data from the Garrett maps of the small frame turbos.
Notice the GT35 0.63A/R vs. the GT30 0.82A/R. They both max out around 23 lb/min on airflow. The GT35 however builds up flow slower relative to the pressure ratio. Or to put it another way, it takes a higher pressure for a given flow below a pressure ratio of about 2.75:1. This means there is more drive pressure at the turbine wheel at lower airflow rates (spool/low boost) but then matches the total peak airflow capabilities. For perspective, 2.75:1 pressure ratio is about 25psig in the exhaust manifold on a car with a free flowing exhaust. Considering an intake to exhaust pressure ratio of 1.2:1 being about the ideal balance for a street car, you are looking at hitting that 2.75:1 pressure ratio on the turbine wise with roughly 22psi of boost. In other words, you are going to be around the 2.75:1 range during normal boost levels on either turbo so the only place it's going to have an effect is on spool up.
Of course, there are secondary effects that come into play here, but realistically, a 0.63 A/R GT35 is going to match the peak power of the 0.82 A/R GT30 turbine wheel.
The GT35 provides a better tip speed ratio though than the GT30. Thus the GT35 turbine wheel has better mechanical advantage over the compressor wheel, helping improve transient response. The closer speed match also generally means improved efficiency of the turbo assembly.
What's more, should you find you desire more power...all it takes is a jump up to the 0.82 A/R housing on the GT35R and you are up to the same flow you would be seeing with the 1.02 A/R GT30 but again, you'll have the advantage on spool efficiency.
IMO, get the best wheel match first then tweak the A/R to match your response goals.
If you look at the turbine maps, it tells the story pretty clearly. Here is an overlay of the data from the Garrett maps of the small frame turbos.
Notice the GT35 0.63A/R vs. the GT30 0.82A/R. They both max out around 23 lb/min on airflow. The GT35 however builds up flow slower relative to the pressure ratio. Or to put it another way, it takes a higher pressure for a given flow below a pressure ratio of about 2.75:1. This means there is more drive pressure at the turbine wheel at lower airflow rates (spool/low boost) but then matches the total peak airflow capabilities. For perspective, 2.75:1 pressure ratio is about 25psig in the exhaust manifold on a car with a free flowing exhaust. Considering an intake to exhaust pressure ratio of 1.2:1 being about the ideal balance for a street car, you are looking at hitting that 2.75:1 pressure ratio on the turbine wise with roughly 22psi of boost. In other words, you are going to be around the 2.75:1 range during normal boost levels on either turbo so the only place it's going to have an effect is on spool up.
Of course, there are secondary effects that come into play here, but realistically, a 0.63 A/R GT35 is going to match the peak power of the 0.82 A/R GT30 turbine wheel.
The GT35 provides a better tip speed ratio though than the GT30. Thus the GT35 turbine wheel has better mechanical advantage over the compressor wheel, helping improve transient response. The closer speed match also generally means improved efficiency of the turbo assembly.
What's more, should you find you desire more power...all it takes is a jump up to the 0.82 A/R housing on the GT35R and you are up to the same flow you would be seeing with the 1.02 A/R GT30 but again, you'll have the advantage on spool efficiency.
IMO, get the best wheel match first then tweak the A/R to match your response goals.
Last edited by 03whitegsr; Oct 21, 2014 at 09:57 PM.
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MasterNater (Feb 28, 2019)
Oct 22, 2014, 09:26 AM
#21
In practice it seems that the 0.82 GT30 turbine wheel maxes out well before the GT35. I suppose without a bunch of backpressure monitoring it would be difficult to quantify in the graph but since backpressure decreases VE I know I end up pulling more fuel out the top on a 3082(3065) vs a 3582 at the same boost level. Our 92 allows 26-27psi pretty easy but I would guess based on some monitoring we have done that backpressure is only barely over 1:1 at that point in most housings.
Oct 22, 2014, 11:47 AM
#22
Are you recommending the 0.63a/r with the GTX35 for my goal and expectations given previously a (naive, I've learned) hope for 500-550whp on the GTX3076R with 94 (or supposedly more like US 92) octane pump gas?
One thing worth mentioning is that while I do have 9.5:1 pistons, the head gasket I am leaning toward (Power Enterprise 87mm bore) is 1.5mm, which should lower the compression ratio a bit, is that true?
In practice it seems that the 0.82 GT30 turbine wheel maxes out well before the GT35. I suppose without a bunch of backpressure monitoring it would be difficult to quantify in the graph but since backpressure decreases VE I know I end up pulling more fuel out the top on a 3082(3065) vs a 3582 at the same boost level. Our 92 allows 26-27psi pretty easy but I would guess based on some monitoring we have done that backpressure is only barely over 1:1 at that point in most housings.
Thanks for all of the help everyone, very much appreciated.
Last edited by doncarbone; Oct 22, 2014 at 11:51 AM.
Oct 22, 2014, 01:56 PM
#23
^ you need to first answer this question: who is your tuner? No point setting up your car in a way that your tuner doesn't like tuning.
Also +1 on gtx3576 over gtx3076. Transient response on the gtx3076 suuckks in my experience. True mismatch of compressor to turbine wheel. An old school gt3582 0.63 a/r had better transient than a gtx3076 0.82 a/r and made more power on a built sti with petro94 I had experience with.
Also +1 on gtx3576 over gtx3076. Transient response on the gtx3076 suuckks in my experience. True mismatch of compressor to turbine wheel. An old school gt3582 0.63 a/r had better transient than a gtx3076 0.82 a/r and made more power on a built sti with petro94 I had experience with.
Oct 22, 2014, 02:23 PM
#24
^ you need to first answer this question: who is your tuner? No point setting up your car in a way that your tuner doesn't like tuning.
Also +1 on gtx3576 over gtx3076. Transient response on the gtx3076 suuckks in my experience. True mismatch of compressor to turbine wheel. An old school gt3582 0.63 a/r had better transient than a gtx3076 0.82 a/r and made more power on a built sti with petro94 I had experience with.
Also +1 on gtx3576 over gtx3076. Transient response on the gtx3076 suuckks in my experience. True mismatch of compressor to turbine wheel. An old school gt3582 0.63 a/r had better transient than a gtx3076 0.82 a/r and made more power on a built sti with petro94 I had experience with.
Oct 22, 2014, 03:30 PM
#25
i am beginning to lean more toward the GTX3576 as it's a bit more responsive than the GTX3582 / FP3586 and should still get me close to 500whp on pump...
Where I live there are small highways with lots of hills and bends, and I am not sure a large/slowish turbo in an environment with technical bends and not a ton of room is going to be particularly fun. Not to say we don't have long roads, but it's not freeway stuff you'd see outside of a large city.
It also snows a decent amount where I live and I intend on driving this vehicle in the winter sometimes.
Where I live there are small highways with lots of hills and bends, and I am not sure a large/slowish turbo in an environment with technical bends and not a ton of room is going to be particularly fun. Not to say we don't have long roads, but it's not freeway stuff you'd see outside of a large city.
It also snows a decent amount where I live and I intend on driving this vehicle in the winter sometimes.
Oct 22, 2014, 04:07 PM
#26
Or are you saying the 0.82A/R GT30 chokes even before the 0.63A/R GT35?
With the GTX3576R, it is hard to say which housing would be better. The 0.82A/R housing has shown good power gains over the 0.63A/R housing and the boost threshold shift on the dyno is minor. That said, I've driven the same car on both housings (2.0L GT3582R) and while the response appeared similar on the dyno, IMO the transient response on the 0.82A/R housing was noticeably slower.
Oct 22, 2014, 04:26 PM
#28
Exactly as the chart shows. The GT35R matches the GT30 turbine when using a step smaller A/R housing.
Or are you saying the 0.82A/R GT30 chokes even before the 0.63A/R GT35?
With the GTX3576R, it is hard to say which housing would be better. The 0.82A/R housing has shown good power gains over the 0.63A/R housing and the boost threshold shift on the dyno is minor. That said, I've driven the same car on both housings (2.0L GT3582R) and while the response appeared similar on the dyno, IMO the transient response on the 0.82A/R housing was noticeably slower.
Or are you saying the 0.82A/R GT30 chokes even before the 0.63A/R GT35?
With the GTX3576R, it is hard to say which housing would be better. The 0.82A/R housing has shown good power gains over the 0.63A/R housing and the boost threshold shift on the dyno is minor. That said, I've driven the same car on both housings (2.0L GT3582R) and while the response appeared similar on the dyno, IMO the transient response on the 0.82A/R housing was noticeably slower.
https://www.evolutionm.net/forums/ev...e-hta3076.html
We have tested the 3586 in 2 different T4 housings on a LR2.4 VIII (0.68 and 0.81) and so no spool difference but 70whp more out the top on the 0.81. Transient response didnt feel any different on the shifts in it either. Cold NW night on the road with 600+ ft lbs? Maybe that was why it felt better but to me it wasnt noticable enough to talk about a small housing.
All of our testing in the various high boost cars we do says that a small housing is never the answer, neither is a small turbine wheel. Running mismatched in favor of a larger turbine wheel with the appropriate housing is the best option. In single scroll this the TiAl V-band housing. In a twin scroll and 35R "class" nothing smaller than a 1.0 housing.
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seeaich (Apr 24, 2017)
Oct 22, 2014, 04:41 PM
#29
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I'm interested in knowing this as well. I'm in the process of having my head surface machined to smooth it out and add the PE HG due to my Cometic leaking. Car is going to be dyno tuned once everything is put back together but at the same time I'd like to know whether my CR is going to change. I'm 9.0 pistons.
Oct 22, 2014, 07:51 PM
#30
i am beginning to lean more toward the GTX3576 as it's a bit more responsive than the GTX3582 / FP3586 and should still get me close to 500whp on pump...
Where I live there are small highways with lots of hills and bends, and I am not sure a large/slowish turbo in an environment with technical bends and not a ton of room is going to be particularly fun. Not to say we don't have long roads, but it's not freeway stuff you'd see outside of a large city.
It also snows a decent amount where I live and I intend on driving this vehicle in the winter sometimes.
Where I live there are small highways with lots of hills and bends, and I am not sure a large/slowish turbo in an environment with technical bends and not a ton of room is going to be particularly fun. Not to say we don't have long roads, but it's not freeway stuff you'd see outside of a large city.
It also snows a decent amount where I live and I intend on driving this vehicle in the winter sometimes.
You may want to downsize even further to something like a gtx3071r or stock location turbo. Both will get low to mid 400s on 94 pump easy with great spool for tight roads. Where exactly in BC do you live?
Another variable is your heads and cams. Are you going to build your head?