Best Turbo For Autocross
[quote=" Dori Dori Honestly, I think you just have a hard time taking criticism... you're probably an engineer or something so it's like a straight shot to the nutts when anyone opposes your ideas. [/quote]Hah - well I am an engineer. It just appears to me that you dismiss any ideas with a sarcastic smilie, which is smug in my book. But oh well.
Quote »Oh, and according to this page ( http://www.awe-tuning.com/page...AQ=22 ), load application is adjustable on their dyno and a Dynojet to lessen the load at the wheels, effectively lowering inertia, right?
As for your curiosity about a GT28rs w/ a .64a/r, don't bother because AFAIK, they don't exist.[/quote]
The dyno you linked to is a Mustang dyno that uses hydraulics to steplessly vary resistance. There is no inertial forces involved(well, they are negligible). The only way to change load on a Dynojet is to change the gear the run is done in or change the rollers out to heavier/larger ones.
The 0.64 A/R turbine option is listed on the GT28RS page of the Garrett catalog, it's just that most places(including SCC) use the 0.86 A/R. Here is a link where you can DL the catalog:
http://www.turbobygarrett.com/...s.jsp
Also interesting is that the corrected turbine flow for the 0.64 vs. the 0.86 is only about 1-1.5 lbs/min less at any pressure ratio the manifold will be likely to see. Shouldn't pose a huge restriction in flow, but spool up even quicker. The 0.86 A/R housing probably isn't all that stressed by the time the T04B compressor gives up the ghost. 0.64 A/R looks like the better match to me, but I do tend to always arrive at turbos that have a slightly higher stressed turbine than compressor.
The FP Big28 looks sweet, but is it just me or has that turbo already fallen flat on its face after 6k RPM? It'd probably be making only around 150 ft-lbs of torque at 7.5k, which is pretty weak. I guess there's no getting around breathing through that tiny T25 back end.
Quote »Oh, and according to this page ( http://www.awe-tuning.com/page...AQ=22 ), load application is adjustable on their dyno and a Dynojet to lessen the load at the wheels, effectively lowering inertia, right?
As for your curiosity about a GT28rs w/ a .64a/r, don't bother because AFAIK, they don't exist.[/quote]
The dyno you linked to is a Mustang dyno that uses hydraulics to steplessly vary resistance. There is no inertial forces involved(well, they are negligible). The only way to change load on a Dynojet is to change the gear the run is done in or change the rollers out to heavier/larger ones.
The 0.64 A/R turbine option is listed on the GT28RS page of the Garrett catalog, it's just that most places(including SCC) use the 0.86 A/R. Here is a link where you can DL the catalog:
http://www.turbobygarrett.com/...s.jsp
Also interesting is that the corrected turbine flow for the 0.64 vs. the 0.86 is only about 1-1.5 lbs/min less at any pressure ratio the manifold will be likely to see. Shouldn't pose a huge restriction in flow, but spool up even quicker. The 0.86 A/R housing probably isn't all that stressed by the time the T04B compressor gives up the ghost. 0.64 A/R looks like the better match to me, but I do tend to always arrive at turbos that have a slightly higher stressed turbine than compressor.
The FP Big28 looks sweet, but is it just me or has that turbo already fallen flat on its face after 6k RPM? It'd probably be making only around 150 ft-lbs of torque at 7.5k, which is pretty weak. I guess there's no getting around breathing through that tiny T25 back end.
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the idea is that the next turbo will be an external wastegate controlled by an electronic controller.
My big thing is that I don't want to make massive power numbers. Autocross isn't about that, but a little extra juice sure would help.
The Big28 and the S15 T28 look to be my main choices right now.
EDIT: Of course, if I go with the S15 T28, I can kiss the idea of an external gate goodbye.
My big thing is that I don't want to make massive power numbers. Autocross isn't about that, but a little extra juice sure would help.
The Big28 and the S15 T28 look to be my main choices right now.
EDIT: Of course, if I go with the S15 T28, I can kiss the idea of an external gate goodbye.
Def, I wanted to tell you what I found out about the GT28rs on that 1.8t...it is actually a 'QS' version. QS meaning quick spool. I asked the folks at ATP what the specs where (like the turbine a/r), but they didn't know. Kinda weird but whatever. They did say that the standard gt28rs should spool 3-400 rpm later but won't fall flat on it's face after it peaks.
300-400 RPM later than that? Yeesh...
If it's an actual Garrett GT28RS, then there are only two configurations available. The 0.64 and 0.86 A/R turbine housings.
That torque graph looks like a triangle to me the more and more I look at it. Seems like it'd be hard to control wheelspin when the turbo spools on the exit to a corner, then it drops off in a hurry up top. The SCC car exhibits a very similar torque graph(I know... I know... I'm not even taking the tuning into account here, just the method of the power delivery).
If it's an actual Garrett GT28RS, then there are only two configurations available. The 0.64 and 0.86 A/R turbine housings.
That torque graph looks like a triangle to me the more and more I look at it. Seems like it'd be hard to control wheelspin when the turbo spools on the exit to a corner, then it drops off in a hurry up top. The SCC car exhibits a very similar torque graph(I know... I know... I'm not even taking the tuning into account here, just the method of the power delivery).
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float_6969
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Ok, so I'm rehasing an old thread, but you don't really need to change the turbo to reduce lag for autocross. It will take some practice (a lot to do it well) but start using a techniqe called trail braking (left foot braking). It puts a pretty decent strain on your drivetrain and brakes, so make sure they're up to par, but if they are, it will keep the turbo spooled and you'll have the power on tap all the time. Try it, you'll like it, I promise
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heel toe has been saving my butt in auto cross this season.
one thing i didn't mention way back when this thread first started was that almost all of our tracks in this region are designed for low end torque and to make the STS and street prepared classes competitive with street mod, super stock, etc etc. The last event was set up that i never even had a chance to upshift into second. it was first gear the whole way. by the time i needed to shift, i had to start braking for the next turn.
one thing i didn't mention way back when this thread first started was that almost all of our tracks in this region are designed for low end torque and to make the STS and street prepared classes competitive with street mod, super stock, etc etc. The last event was set up that i never even had a chance to upshift into second. it was first gear the whole way. by the time i needed to shift, i had to start braking for the next turn.
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MrIllegalX
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Re: (tenkawa_akito)
The answer to your question is simple. Learn how to drive better. It's not the turbos fault you can't keep it spooled. Granted, in some turns it could be impossible, but 98% of the time you can keep it spooled enough so on your exit there isn't any lag.
The T25 turbo is just fine for autocrossing. If you really want to make into an autocross car, get a smaller turbo. The Audi 1.8T is something work checking out. (I believe it's a Garrett T-12, entire thing fits in your hand)
I don't know your experience level but something worth trying is brake boosting. Heel-toe is basically pointless in autocross, don't even bother. You shouldn't be shifting more than a few times anyway, and should never be higher than 3rd gear. Try to keep it in 2nd most of the time, even if you have to hit the rev limiter, it'll save you time than shifting to 3rd. When you downshift, do so as late as possible before the turn, and start accel. early so you can get the boost up and maximize your corner exit speed.
Hope this helps.
The T25 turbo is just fine for autocrossing. If you really want to make into an autocross car, get a smaller turbo. The Audi 1.8T is something work checking out. (I believe it's a Garrett T-12, entire thing fits in your hand)
I don't know your experience level but something worth trying is brake boosting. Heel-toe is basically pointless in autocross, don't even bother. You shouldn't be shifting more than a few times anyway, and should never be higher than 3rd gear. Try to keep it in 2nd most of the time, even if you have to hit the rev limiter, it'll save you time than shifting to 3rd. When you downshift, do so as late as possible before the turn, and start accel. early so you can get the boost up and maximize your corner exit speed.
Hope this helps.
You don't pick up torque by having a smaller diameter exhaust on a turbo car. Any benifits in exhaust velocity helping scavange the head are nil beucase the big *** turbo is in the way.
I have had my S15 T28 for about 2 months now. It works GREAT at the autocross. Of the last 3 events I've won one, came in second at another and had a blast in the rain at the third.
(SM by the way)
I have had my S15 T28 for about 2 months now. It works GREAT at the autocross. Of the last 3 events I've won one, came in second at another and had a blast in the rain at the third.
(SM by the way)