Infiniti G20 Racecar Turbo Undershot

Project Infiniti G20 Racecar: Even More Power

By Steve Rockwood


In kid's soccer, everyone gets a trophy, regardless of finishing order.  No winners, no losers.  Motorsports, on the other hand, is completely defined by whether you're winning or losing.  Unfortunately, our normally aspirated SR20 was not so mighty when compared to the other MPTCC cars, so we forced some air down its throat in the hopes of finally getting some hardware. 

See, even in the Tuner Under (TU) class, our car was seriously underpowered.  Really underpowered.  The rule set allows for a weight to power ratio of no less than 12lbs per horsepower measured at the wheels.  Our car weighs 2450lbs with driver, and belted out 160whp on the Road Race Engineering Dynapack at the California Speedway event.  This left us short 40-someodd horsepower with a ratio of 15.3:1.  While I'm not a mathematician, I do know that 15.3lbs per horsepower is not as good as 12lbs per horsepower, especially when you consider we have the car most likely to be confused with a piece of masonry.

Rather than continue to describe how slow our car is, I'll just show you video from Mike's car at California Speedway.




Yes, our doors remained attached.  I'd like to tell you that pass happened on the latter part of the oval.  It didn't.


Project Infiniti G20 Racecar California Speedway
X marks the spot of epic pwnage.


By the time I exited the oval on that lap, Mike and Richard had already disappeared into the infield.  Not good.

Obviously, we needed to do something about our problem, but where to begin?  First, we needed to make at least 200whp, with 204whp putting us right on the money.  Second, it had to be reliable.  Third, since we’re a privateer effort on a Lilliputian budget, it had to be relatively cheap.  Luckily, 204whp isn’t all that fast, so we weren’t looking for fast, cheap and reliable (read: impossible).  Our first thought was to rebuild our motor for an all-out NA monster.  Port the head, high compression pistons, fabricated header.  The dollar signs rolled through our head and left no room for this expensive ridiculousness.  The next set of chemical signals to wander through our brains was getting an SR20VE.  Those engines already come with higher compression and ported heads, and can now be had for less than $1000 from most importers.  Scratch that, still costs money, and we’d need to throw some more money at it to get to the 200whp level.  Constantly revving an SR20 to 8000RPM is not really good for it either, and these motors cost more to replace.  The last nail in the SR20VE coffin is its uniqueness makes it so we couldn’t just reach into our SR20 graveyard to come up with a replacement part, and overnighting parts from Japan only exists in the movies. 


Mike Kojima Dog II SR20VE
We contemplated going with an SR20VE like in Mike's Dog II, but dismissed the idea due to cost and parts availability.


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Bob Holmes
Bob Holmeslink
Wednesday, February 01, 2012 10:01 PM
I run with the same kind of weight v. power restrictions with our car. We however do have torque restrictions.

It's so counter-intuitive to kill torque and power. We usually want as much as we can get.

What are you using for fuel?
Thursday, February 02, 2012 2:15 AM
aye... what a bombshell to end off this incredible build story.
Thursday, February 02, 2012 2:30 AM
Great article... Loved it... Keep it comming! :)

And good luck!
Thursday, February 02, 2012 4:40 AM
Great write up but ... Why didnt you get directly a FWD SR20DET ? These engines come as a standard in old sunny GTIR. I believe they have piston oil squirters too, that SR20DE lacks (might be good to have). And they make 200HP as standard too.

Considering the tune, as you dont get lots of power out of it, why did you go to 10:1 ? These engines works really nicely with 12:1. 10:1 is quite near rich knock, there really was no way to cut down power with timing only ?

Your turbo setup is very clean though. congrats ! Can you get another turbo, or is this one the turbo of choice ? It looks like it is "too big", yet i must say i have trouble finding one that suits your power goal and that is not overspinning. Nearly all gt25/28 turbos have poor efficiency for the boost you are running, and they should are be on the verge of overspin at more than 7300 rpm. Best suited turbo would be the gt2252r ... your engine needs approximately 10lbs of air around 2500-3000rpm, and 25lbs at redline with 6-7psi of boost. Try matching your compressor map with that data.

If you cant change the turbo (because it costs $$$), here is a free upgrade: you should get torque gain and improved spool time by throttleing the inlet (use a restrictive air filter for example).

It will lower intake pressure, thus making the pressure ratio of the turbo going higher for the same produced boost. That will bring the turbo in a more efficient zone, and most importantly for the turbos life, will prevent overspin.
Thursday, February 02, 2012 5:46 AM
@ Edward and VP: Shanks! And I gotta keep the crack supply coming, right? ;-p

@ Crousti: Buying a FWD SR20DET would've cost a lot of money, and not much gain. A GTiR 54C motor would've been even more, and would've been even harder to keep the power down on (bigger turbo, ITBs, etc). Yep, oil squirters are nice, but not necessary at these power levels. If it becomes a problem, we'll probably just build this motor up (another installment?), as the cost is similar.

Running a combination of mega-rich and not a lot of timing advance was the only way. We were concerned about running into heat soak issues on the track if we went ultra low on timing, and reducing overall timing below 10* didn't change things much, and drastically reduced power beyond 6500 rpm (or wherever the ECU runs out of RPM-specific mapping) so ultra-rich it was.

We actually wanted a bigger turbine section (to keep heat down, again), but this is what we had. If we're going to swap out turbos, we'd probably just go for the ball bearing version of our current turbo (GT2554R) because the only reason we'd switch it out is if this one failed.

The inlet is throttled a little by the 2" piping. Right now, we've shown we don't need any more torque for the glass SE-R trans to deal with. If anything, we'll look into ways to further reduce the amount of boost we're running so we don't have to get so weird with the tune.
Thursday, February 02, 2012 7:23 AM
I'm in a similar boat, trying to keep torque (and maybe power) down. Have you removed every last bit of preload from the wastegate actuator? If your arm is not adjustable, maybe get one that is or modify your own?

Also, Forge Motorsports (and others) make internal wastegate actuators with swappable springs as low as 3 psi. This is something else I'm looking into.

I've also considered just tossing a block-off plate on the end of the exhaust, or maybe a leather pouch over the intake filter or similar to limit flow through the engine. Poor man restrictors. This way you could get that tune up to where it belongs, and still limit your overall output.
Thursday, February 02, 2012 7:29 AM
@ Ben: There is still a little preload in the wastegate actuator, which we will likely remove when we get a chance. One bummer about the custom downpipe is it's a PITA to remove the turbo when compared with an OEM setup, so we've been lazy... ;-p
Martin Gonzales
Martin Gonzaleslink
Thursday, February 02, 2012 7:46 AM
Screw the OE actuator! We'll make one of these sweet IWG actuators from Turbosmart work:

Thursday, February 02, 2012 7:54 AM
Extremely well-balanced and thoughtful approach, great article. Winner, winner, chicken dinner indeed :D
Thursday, February 02, 2012 8:06 AM
The RC Injector cleaning service is badass!
Thursday, February 02, 2012 8:33 AM
That's one lesson I learend with my divorced (but recirculated) downpipe as well. Should have made it in two pieces instead of one all the way to the cat-converter location. =(
Thursday, February 02, 2012 8:55 AM
@ Martin: Clearance for the wastegate on our car is a bitch. Not sure it'll clear holmes.

@ Steve: Shanks!

@ Khiem: Werd to your mother. ;-p

@ Ben: Yep. We need to take ours off eventually anyway, so I'll V-band it after the 3" transition.
Thursday, February 02, 2012 12:04 PM
After reading that I just realized why I like the color of the car so much...DUCT TAPE!...or I mean 200MPH tape. Very enjoyable article Rockwood, and nice approach to the coolant hardline that's a good one!
Thursday, February 02, 2012 12:17 PM
Maybe I missed your explanation of it in the comments, but why don't you go with an intake restrictor? You can limit HP but still have the torque, ala WRC cars, right? I'm sure there's some fancy formula that says with a X-diameter intake creates a max of Y-HP. Add a restrictor plate and let your tuner have fun! Of course, that doesn't fix the transmission grenade problem, which is probably the more immediate issue (WPC in your future?).
saturn racer
saturn racerlink
Thursday, February 02, 2012 12:23 PM
If you take the turbo maybe porting the wastegate port (like on the frankenmiata) would help.
saturn racer
saturn racerlink
Thursday, February 02, 2012 12:24 PM
theres spose to be an "off" after turbo. damn no edit.
Thursday, February 02, 2012 12:40 PM
@ jere: The duct-tape colored car is entirely coincidence. May have been subliminal, but still coincidence... ;-p

@ speedball3: Never did anything as far intake restrictors, mainly because we figured we weren't off by far on tune. Had I known we needed to cut out 15-20whp, I probably would've played with an inlet restrictor.

With a MAF car, I wonder where you'd put it. On the back of the MAF would be the easiest, as I could make a number of plates that bolt to the MAF, but that may be troublesome for accurate readings. Other than that, I suppose we could cram one in the hose coupling between the compressor housing and inlet piping.

@ saturn racer: I was a little concerned with losing some transient response doing that. After driving the car, that may not be such a bad thing...
Thursday, February 02, 2012 2:43 PM
Deeply affended that you would call me and and my fellow chimpanzee friends monkeys. Clearly we are apes. Legal action will be sought and a class action lawsuit can be expected from a number of members of the Hominoidea.

Pretty impressed how easy it was to make 230whp though.
Thursday, February 02, 2012 2:49 PM
Great apes?
Der Bruce
Der Brucelink
Thursday, February 02, 2012 4:14 PM
Say what? I'm crazy busy today and by the time I finish this article, there's 19 posts!

O yeah, excellent article Steve :-) I do like the idea of using a restrictor to maintain the better torque curve and make cornee power even easier.
OMG Its Weasel
OMG Its Weasellink
Thursday, February 02, 2012 6:36 PM
LOL at the soccer trophy bit. Parents these days...

I like that you guys tuned down instead of a plate. A restrictor plate would not have made the car belch fire, right? Anything to add to the spectacle of road racing is appreciated. Especially from, you know, a spectators point of view.

This car makes me smile.
Dave Coleman
Dave Colemanlink
Thursday, February 02, 2012 9:23 PM
@ Rockwood,

Porting the wastegate doesn't hurt boost response. Wiring the wastegate wide open all the time does hurt boost response. Boost response SHOULD happen when the wastegate it closed, so the porting won't matter until it opens.
Friday, February 03, 2012 7:37 AM
@ Bruce: It was certainly the longest article I've written, but a lot needed to be said... And you need to put off work better... ;-p

@ Weasel: Flames are cool, yes. Almost everyone watching the race at night came over to let us know how cool the flames were.

@ Dave: Ah, I was confoosed. For some reason, I was thinking of porting the wastegate so that it was larger than the flapper valve.
Der Bruce
Der Brucelink
Friday, February 03, 2012 10:53 AM
Haha, no putting off work yesterday! Just crazy busy having a baby :-)
Friday, February 03, 2012 12:08 PM
LOL. Just let it cry, that's what I do with my kids. Some magic fairy they call "mom" comes by and takes care of it... ;-p
Saturday, February 04, 2012 11:12 PM
ah hell no, this is not long enough, we need atleast 10 pages next time :D

But still this was an awesome write up! I do have a p10 my self and have gone and spent som $, the first I am doing is getting the fastbreak kit, new engine mounts, oil cooler, aem af guage, more poly in the suspension and a ground control coilover kit. AND THEN, I will go for the big lovely and awesome GTIR engine, 220 hp at 0.4 bar is good shit :D

as this is my plan I REALLY need you to a good build up of that tranny, as my spare tranny will be getting a make over and a lsd.

Also a big thanks for all the great links in this one, will make my vallet feel so sad, its a pain in the ass ordering stuff and have it shipped all the way over here.

Ps: make more flames, blue flames are the prettyest ones :D
Monday, February 06, 2012 4:48 AM
@Ztaal3: Thanks for the kind words. Transmission is currently being built.

That being said, for street duty, a stock trans with minor beefing should be sufficient if you're not hammering on it. Unfortunately, racing isn't kind to components.
Blair Ellis
Blair Ellislink
Tuesday, February 07, 2012 3:18 PM
@Rockwood - What kind of minor beefing are you talking about?

I'm interested in hearing more about your transmission build as I too am going to need something for my G20. Currently on a brittle B13 trans.
Wednesday, February 08, 2012 7:45 AM
@ Blair: My street transmissions with cryo/shot and some bracing to the case ("Miko brace", etc) have lasted through a fair amount of torture.
Blair Ellis
Blair Ellislink
Wednesday, February 08, 2012 12:36 PM
Yea, I have the MikoBrand TrannySaver too. Its a great piece. What did cryo/peening run you if you don't mind me asking?

I should be ballpark in the 300-350whp range with my setup when done. Is that going to be enough to prevent a 3rd gear meltdown or do you recommend going with a P11 or 6 speed gearset to bombproof the driveline?
Wednesday, February 08, 2012 5:43 PM
Is there any advantage of taking the water feeds where you have from taking them off the throttle body?
Friday, February 10, 2012 7:29 AM
@ Blair: P11/6 speed for that level of power. Anything above 250whp on a stock trans, regardless of build, is borrowed time. That, or an RS5F50V trans...

@ John: Yep. We eliminated all of those lines from the hard-pipe on the back of the block when we eliminated the hot coolant recirculation pipe for the thermostat.
Blair Ellis
Blair Ellislink
Friday, February 10, 2012 10:38 AM
@Rockwood - Thanks
Friday, March 09, 2012 12:26 PM
#Rockwood, thanks for the info, as I want the gtir engine I think I will have to do a p11 swap and rebuild it without the slave sylinder and rather old fashion waiere :P

also wondering, when spring comes and it's time for trackdays again I will be trying out some race slicks and I'm scared off running the oilpump dry under side G load, have you done something for this or am I just not remembering? or do you know if mike have done something to the dog cars?

thanks again :D
Friday, March 09, 2012 2:01 PM
Haven't really done anything for side loads other than make sure the oil was topped off. Doesn't seem to be a problem.

Hell, my dune buggy (which also has an SR20) has done engine cage scraping wheelies up insanely steep dune faces (basically, completely vertical for seconds at a time) without running the sump dry. If that doesn't do it, nothing will.
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