stantaur

Dialing the car for autocross & street and (reason footnoted below) have to rebuild the engine. Welcome people's thoughts on how I can get quicker spool and fatten the curve in the 3500 - 7500 RPM range. Options being considered are below, as well as the prior setup.

Goal is to make the car snappier in autocross's spastic on/off/on/off 40-turn/trasition-per-minute format. Auto-x seems even more dependent on quick spool than drifting, since drifting does 25 turns/transitions per minute, and tracking even more gradual at ~ 12 turns in a minute). Need more torque out of tight turns, even if I give away some redline to get it. Considering the % of time I spend btwn 3500 - 6000 on tight courses (& Oregon roads) vs. time btwn 6000 - 8500 on tracks, either more compression and/or stroke seem attractive. Autocross has so many short transitions, I'm often at a disadvantage vs. stock 11:1 CR S2000s (risk catching no end of grief if a NA car gets close to the time of my car w/2x the power) Plus, Oregon buries you under the jail for 20 MPH over the speed limit ($1000 fine), so insta-boost & torque outweigh the warp-speed 7000-9000 pull I've enjoyed at the strip (high RPMs als scream "exhibition of speed" to the Law). The fresher rings/tighter motor being assembled by PSI in Portland would up my current leaky-ring setup to 450-460 RWHP/ 315 RWTQ, which is already too much for the 295 A6 Hoosiers, so the goal now is to shift the power curve leftward.

Options being considered

1. Stay 2.0L, up the compression slightly (no more than 9.4:1) and keep current GT3076R/.82AR turbo / ID1000 / Walbro setup
2. Stay 2.0L, up CR slightly, swap GT3076R for a quicker spooling turbo (open to all ideas here - GT3071R, _____, etc.)
3. Stay 2.0L, stay 9.0:1, swap GT3076R for a quicker spooling turbo (open to all ideas here - GT3071R, _____, etc.)
4. Stay 2.0L, stay 9.0:1, keep GT3076R
5. Go 2.2L, maybe up compression slightly ~ 9.4:1, keep GT3076R
6. Go 2.2L, 9.0:1 CR, keep GT3076R
7. Go 2.2L, maybe up compression slightly, smaller turbo
8. ____________ (other ideas - pls post or write in)
9. Advance the current AP1 cams, or alter cam phasing to open up LSA
10. Replace current AP1 cams & optimize cam phasing to open up LSA
11. Crower 2.4L stroker kit (unsure what the reliability is; would require dropping redline to 7K to keep same FPS redline of F20C at 9K or F22C at 8.4K)
12. Add an E85 tune (& drain system) to any of these options for autocross, but I'd prefer to stay pump gas due to the fact that the car's driven to events. Also want to stay within my fuel flow capacity / duty cycle, so this option might require the Aero 340 pump or an inline adder (adds noise & failure/variable).

Options 5 or 6 seem attractive if I have budget. Guessing 400 RPM earlier spool + more TQ through where I spend most of my time. Dropping redline from 9K to 8.4K to preserve pistons/pins/rods is OK tradeoff (and easier on valvetrain). Curious if cam timing tweaks would help here too.

Option 7 in theory seems good, but might run out of boost (and budget). (I have limited experience w/ turbine & compressor efficiency mapping.) If it was insta-snappy (3400 RPM ramp vs. current 4100 ramp start) and still pulled 430/285 on 92 oct, that might be worth the cost.

Option 1 may be the most cost-effective, might get 200 RPM sooner spool than 4, but isn't acceptable if it compromises reliability/longevity on 92 oct at the 450/320 level.

Goes without saying I can re-gear pretty easily - the Cobra 8.8" diff in the car allows me to do a 4.56 for 69 MPH in 2nd at 8400 RPM with the 2.2L setup, or I can run 4.77s with the 2.0L. Also nets me upper 120s in the traps if the car hooks up (ran 122 on a gentle 2500 RPM launch & 2.3 sec 60')

Welcome this forum's collective thoughts. Is there a super-quick spooling turbo that can support 430 or so to the wheels, or is the GT3076R as good as it gets w/o overheating the charge?


Prior build / background (car's set up as a fun street car that tows its own race tires to autocrosses & track days, great AC, full interior, but plenty of power & pristine stock interior / looks). 9.0:1 2.0L (F20C) Laskey build with Benson sleeves, 9.0:1 87mm CP pistons, Pauter rods, Full-race tubular mani, GT3076R (.82 AR), 3" exhaust, Precision 600 HP intercooler, stock AP1 cams at stock cam timing. Trans/diff gearing ~ to AP2 gearing, 9000 RPM redline observed, 435RWHP/295TQ at 16.8 PSI, 5100 TQ peak.

"Why rebuild something that's served me well since 2007?" The car hauler crew that transported our S2000 turbo AUS-PDX evidently joyrode the car (datalogs confirmed, plus rocks in the ducts) and it's not run right since this summer. Compression tested 140s (should be 170 PSI for a 9:1 motor on stock cams). So off to PSI to conduct a rebuild. Very good people there from what I've seen.

DFWs2k

What manifold are you using?

stantaur

Thanks guys. Yes, its a Full-race original (not the uber cool twin scroll that came out later) style. Mega PITA to swap turbo, wastegate spring, etc. on, but has (knock on wood) been a solid, reliable, leak-free piece and made decent power.

Really appreciate the idea on the custom pistons saving me the rod cost. That would be a nice cost-saver I can factor into the 2.2L path.

Read up a little on the GTX setup last night too. Looks like the GTX is an updated compressor that expands the output outline in the charts, so basically a GTX3071R makes almost as much huff as a GT3076R. If there's any (spool) benefit to doing that tweak, I might consider it. Otherwise I can stand pat with the current GT3076R or upgrade its compressor to the GTX wheel (I'm thinking the 76R vs. the 71R are different turbines & frames, but please correct me if I'm wrong).

Thunder-rush

I have a ap2 with the gt3076 and the spool is almost the same as the graph you posted but with about 20-30ft more tq under the 4k rpm mark of turbo spool. The GTX71 wheel maps looks like it can flow quite bit more than the regular 76r and since its smaller and billet its supposed to spool faster.

Touge Master

what is the hot side you have on your turbo right now???

stantaur

Good point & good question - my current setup is .82 AR. Thanks again for these ideas & discussion.

passmans2kny

go 10:1 on a 2.2, i would keep that turbo, how much power did u make on your old set up?

stantaur

Prior build was 435/295 at 16.5 PSI, specifics listed in original post. RC1000s may have washed it though, as compression was 145 in 2007 and 135 recently. From what I've been told, should be in the 160-175 range with 9.0:1 built motor.

spdracerut

I'd go 2.2, keep your current turbo, and swap on a 0.63 A/R turbine housing. The increase in displacement should reduce spoolup about 8% or so and the smaller turbine housing another 15%; the smaller A/R housing will add about 10% more backpressure hurting topend power, but I think it's definitely worth it for the spool in your case. If money were no object, I'd go ahead and upgrade to the GTX3071 also. It will spool-up a smidge faster than the GT3076, and also have much better transient and make a smidge more power.

riceball777

i have a ball bearing t3 50 trim turbo on my mase manifold with the .63 hot side and i think it spool pretty quick on my stock 2.0. spools a good amount faster then your setup and it still makes 500whp