How much boost is safe for me to run on my '97 SC300 5spd. I have a boostlogic stage 1 NA-t along with some 550s, AEM EMS, boost controller, wideband, etc.

Basically, I have it at 4.5lbs making 253rwhp and 278ft/lb of torque

I'm going to push the boost up to 9lbs and see what I can get but I'm wondering if making a race gas map on about 12-13lbs would be safe.

The motor has 130k miles but is solid to the best of my knowledge.

I'm worried about boosting too much without upgrading the headgasket.

Any opinions or recommendations? Thanks in advance.

 

what lets go on those motors with out dropping the compression?

in theory, since you have AEM and have the ability to tune the car properly, as long as its not the fact that the pistons are weak.....racegas + rich afr + low timing (i typically tune timing below MBT in this situation) you "shouldnt" have any problems.

the headgaskets just a band aid. dropping the compression (headgasket) is simply doing the same thing as pulling timing and using slower burning fuel (racegas) as it less likely to knock.


tune it on a dyno, go slow, carefully watch the graph, and check the plugs every pass.

i intentionally use "high" compression pistons in all of my personal cars. my race motor is over 10:1 and runs over 40psi.


***this is going off of car and engine theory and my personal experiences with many other cars...not specifically the NA-T set up. but from what i have seen most people are not using a true stand alone like you are, so you have a lot more control***

 

I agree with the poster above. High compression is not a bad thing so long as you are able to keep detonation away with race gas.

One statistic to consider is "effective compression ratio". This stat takes into account boost pressure as well as engine compression ratio. The equation for effective compression ratio is to multiply the engine compression ratio by the boost pressure is terms of bar (1bar = 0psi boost; 2bar = 14.7 psi boost). Here is a calculator for effective compression ratio: http://www.dragsource.com/index.php?...s&calctoview=3

On a GTE motor (8.5 compression) with pump gas, most will say that ~18-20psi is the boost level beyond which you start playing with fire or have to trim timing and increase fuel delivery to the point where the returns are diminishing. 18-20psi on an 8.5 compression motor yields an "effective compression ratio" of 18.9-20.1. On a GE motor (10.1 compression), an 18.9-20.1 "effective compression ratio" results from 12.8-14.6psi.

Moral of the story:
I would not boost over 12psi on the stock motor with pump gas. Even then, you may be playing with fire. But, with race gas, you should have no problem.

High compression is good for making power (torque, specifically) no matter which way you slice it. WOTM runs 42psi with an 88mm turbo on their drag racing Supra, and it has 9.0:1 pistons. There is no doubt that, with an excellent tune, you can boost very hard with race gas on stock 10.1 compression.

 

Thank you so much for the insight and great info on the topic from both 9sec civic and Blizzy. It really helped and easd my mind about adding a little more boost to make a race gas map.

 

There's a guy named chidoks on SupraForums with a GT42 and 1000cc injectors still running the stock headgasket. I think he's around 11-12 psi.

 

Yeah, I was excited about upping the boost and getting some more power, but now I have to worry about some new problems that the shop reported:
1) after the car is taken up into boost and you let off, the needle is dropping down in rpms as usual but then it breaks through idle and goes to almost 0 and stalls out. the wierd thing is that it doesn't do this if you unplug the idle control valve (which i just replaced thinking that was the problem)
2) the brand new AEM Tru Boost controller I got isn't functioning properly because we can't make more than 6.5lbs of boost so tomorow we're gonna pressure test the system and try to identify a leak that might be responsible for both problems (I really hope its an easy fix that we identify tomorrow cuz I want my car back with more boost!)

 

I looked up some threads on his car. When he says he has the "stock head gasket", it is the stock TT gasket...which is 1.6mm and ~9:1 compression (if memory serves me). Regardless, his set up is definitely pretty sick.

 

U sure that the boost controller is installed right? Or there is no leak? Just like the beginning posts tune out the knocks and keep and eye on your afr. for a race car I lean it out to 12.5 and for my dd i am in the 11s.

 

I'd suggest a simple progressive methanol injection kit. This will enable the car to fight off detonation and remain very streetable on pump gas. With 100% methanol being injected 17ish lbs should be very attainable on your current setup. And if you have the ability to tune timing as well with the AEM, 20+psi should be no problem on 18* total timing. I'd buy a knock monitor and watch the A/F's closely. Every car is different, but as long as you aren't detonating at all and have good A/F's your golden. Tune for the highest boost w/o out any knock. Not for a specific PSI.


Good luck, let us know!

 

Thanks to all of you. Your feedback has been bery helpful...

 

100% meth would also eat way at the o2 sensors as well. I do agree with what forcefed86 said about knock. Tune out the knock as well as watch a/f closely. It's cool to make a lot of power and boost high but if you are detonating I don't think your car will last.

 

I generally like to stick around 8 psi, though I have ran my vvti 2jz in my IS up to 12 psi before on certain occasions. 8 is a good round number and not too overboard.

I was running a consistent 3 bar on my Porsche and I am still not sure how it held together, but is alive and well in North Carolina at another CL members house right now a few yrs later still doing fine. You punch it and the boost gauge on the dash just pegs out.

 

Actually meth injection even at 100 percent has no ill effects on 02 sensors Not sure where you get your information from but it is completely incorrect. Maybe if you ran 100 percent meth as your only fuel? But I am talking about injecting it only @ boost. I've had several cars I run 100 percent meth... running for many years without any o2 problems. I always run WB 02 sensors as well.