I ran high 11's/low 12's with a mild port and stock turbos. I blew the motor and had it rebuild with 3mm apex seals, kyro frozen, water jacket mod, clearance rotors from Atkins rotary and added the GT35/40 from A-spec tuning. My air to fuel is between about 11 to 1 and I am getting pretty high knock readings (95 on PFC and 60 on Datalogit). I have Greddy 2 row IC. On the stock turbos I was running about 15 pounds. On the new turbo/motor I also ran 15 pounds and it wasn't any faster. Shouldn't the bigger turbo be much more efficient at 15 pounds? I guess I can always turn up the boost but I would like to fix the problem if I have one. My idle is also pissing me off. I have no vacume leaks and the car idles back and forth from 500 to 2000 rpms. I don't think my port job would cause this. I was expecting to run into the 10's...please help.

Mike B

 

have you had the car on the dyno? that should tell you whats going on. If its not as fast with a single turbo at 15 pounds then the stock twins at 15 pounds then there is most likely something wrong with the tuning.

what kind of tire are you using? what is the difference in your trap speed from when you had twins to now?

10s on 15 pounds with that turbo isnt going to be the easiest thing to obtain. Its possible but you have to have the car tuned really well and be driving the **** out of it.

 

The car is "hunting for idle" I think that is too lean (the symptom) or a faulty TPS

 

Check your engine compression.

Chuck

 

double check everything as your idle shouldnt hunt that drastically, check compression... also disconnect your ISC and turn off Idle control on your PFC and see if that helps...


good luck

 

GT35/40 isn't exactly the biggest turbo, you might be expecting too much from it. But it should feel at least faster than stock turbos, pound per pound. The dyno will tell you alot

 

Yes junk the ISC, my idle hunted like that untill I disconected it. Turn up the boost a few more PSI and You will feel a big difference.

 

also tune it and take it to a dyno.. a turbo wont exactly make you any faster than before in the 1/4 mile... drag racing is very tough! and it takes a combination of many things to go right to make you go faster (and luck)

 

In some cases a bigger turbo will make your car slower. You no longer have the low end grunt of the stock twins, which you traded for a turbo with more power potential. Tuning plays a big part but it could be a number of variables. I've seen stock turbo cars run 10's and 11's and single turbo cars run 14's and 15's at the track.

 

The turbo is good for deep 11's, but unless you're John Force, it's tough to get it to crack 10's unless you're running ungodly amounts of boost - over 20psi.

It sounds like the tuning wasn't done properly.
Go a dyno graph laying around?


-Ted

 

take fuel out at idle, if you have a big port on the motor

 

Wtih ISC are you refering to the TPS (throtle possitioning sensor)?
I looked on the workshop manual but couldn't find the ISC, is on TB. Thnks.

 

We got 421hp at wheels on a friend of mines GT35/40 setup, you evidently have something amuck!

 

So am I the Anti Christ at 28psi? sorry, just watched "The Omen"

 

No, you're just using the turbo in it's sweet spot!


-Ted

 

I dont understand why People put a large turbo on their car and DONT tune for high boost. 15 PSI is not even close to where that turbo should be running. 20-22 PSI is a good start.
28 is GREAT.

 

I guess we all can't afford race gas?


-Ted

 

ding ding ding.... great point ... put some C16 in and let it rip!

 

I run up to 20 PSI on 93, I just tune on the the rich side and run WI and My engine is still hanging in there with no problems. If You can get a good tune from a Guy like Steve from Gotham or Ralph from Excessive then there is NO reason 20 PSI should not be safe. The problem with all the Guys running big singles is that they dont spend the time and money for a GOOD fuel system that can safely support 25 plus PSI and try to get by on week fuel delivery. I dont know any numbers but I would bet more engines have popped because of high injector duty and not enough fuel. Spend the money now on a GOOD pump and fuel supply or spend more money on rebuilds. I am no expert at all and have got most of My info here over the last couple of years but it seems simple, get fuel , get a wide band and then get 25 PSI.

 

I always though as a rule-of-thumb, 17-18psi safe for pump gas - 92 octane max here in Hawaii.

20psi is doable, but we're talking at the absolute edge of tuning.

Anything significantly over 20psi is going to require "race gas".
28psi is definitely in "race gas" territory.


-Ted

 

At what boost lever did you make 421?


MichaelB145 - What was your mph for those runs? The mph will tell you if your making substantially more hp. If your car had all the bugs worked out, was tuned good, and had a healthy engine then you were probably making around 370rw at 15psi.

Id expect your mph to be a couple higher than the twins but with a 35/40 its not going to be anything as dramatic as knocking a full second or more off your ET at the same boost level.

Stephen

 

The magic words here are 'water injection.' If not for that little add-on, 20 psi on pump gas would be suicidal.

 

Man, I didn't even see that part.
I dunno what to say to that reply now...


-Ted

 

Well, after my experiences running 17-18 psi on 93 Octane (and many broken apex seals, hehe) and after many in depth discussions with Ari about it, I think that for a street car, you have to keep it around 15 psi or so in order to have any sort of longterm reliability.

Rich

 

Thank you all for your advise...What it really comes down to is I need tuned and nobody in Colorado really has a reputation for doing it. I am either going to have to come up with the money myself or get a few other guys to help pitch in and get someone out here. Does anyone know someone else besides Steve Kan or Hitman?