Car runs crappy on 9 lbs. of boost

My car runs real crappy on 9 lbs. of boost from my powerdyne supercharger. My a/f gauge shows me running real lean at about 800 rpms but around 1000 it shows me running stoich. I have astock fuel system other than an inline fuel pump and an FMU. This is all on my 355, LT4 hotcam, LT1 with shorty 1 5/8" headers. Do you think that I need bigger injector and a better intank fuel pump? Also I am running 9:1 cr with forged pistons. Do you think thats too high of cr for a non intercooled charger? And I am detonating some times when I driving with a heavier foot than normal driving. Although I have close to 50 miles on the new engine setup I was just wondering what everyones thoughts were. and yes I am running super unleaded. Thanks

-Slim

p.s. this is on a stock tuned computer. Do you think thats the problem and I think that I need an LT4 knock module.

Unless it's a wide band A/F guage, you can't trust it AT ALL.

Run it with a scanner and wide-band. You have to at least see where you are before you start changing parts.

Compression ratio should be fine with 9 psi. I'm running 14 psi non-intercooled on a 9/1 motor.

Your (assumed) stock fuel injectors may be locking up under the high fuel pressure caused by the FMU. This is common. If your A/F ratio (on a wide band) goes lean on top end, this is probably the cause.

Mike

I would say the Powerdyne is outside its range of peak efficiency at 9 psi. It is probably producing more heat at that level of boost than a supercharger designed to move more air. Either get an intercooler, turn down the boost, or buy a different supercharger(think Vortech or ATI).

Skip the air to fuel guage UNLESS it is a wide band setup. Get the car to a dyno and find out what your real A/F ratio at WOT is. Standard O2 sensors can only accurately detect 14.7 to 1, too lean at WOT.

So basically the a/f gauge is just for show and a light show at night? LOL. That makes me laugh at myself for getting one. LOL. Well I will try all that and then I will see where I am at. Also, I have about 5-10 psi of vaccuum on the same engine is that aight? because my brakes seem to not work as good, although I know this is what happens when you get into changing the cam and going bigger. Thanks for your advice. Thanks

-Slim

Originally posted by SlimZR28
So basically the a/f gauge is just for show and a light show at night? LOL. That makes me laugh at myself for getting one. LOL.

Pretty much! :)

Originally posted by SlimZR28
So basically the a/f gauge is just for show and a light show at night? LOL. That makes me laugh at myself for getting one. LOL. Well I will try all that and then I will see where I am at. Also, I have about 5-10 psi of vaccuum on the same engine is that aight?

Two of my friends have the light shows even though I told them not to get them. :) It's almost useless other than telling you when you go WOT that you are not over 14.7. But note that 13-14.7 will still show rich but your engine will still go boom cause that is way lean on a supercharged engine.

At idle, 5-10 psi of vacuum is definitely really low. 10-14psi is fine with a large cam.

If you are really seeing 9# of boost, then you definitely need a dyno tune. Or some kind of mail order tune then dyno it to see actual A/F ratio and misfires data. If not, your new engine will go boom again. The most important thing in building a fast engine and car is the tuning. Once it is tune properly and you know how it runs on the dyno, the car will run great and you will have peice of mind that the engine is tuned.

good luck

I think you'll be ok w/ the powerdyne. There is an LS1 pushing 8psi with ported heads, cam, and longtubes- so his engine will flow more air than yours.

At 6psi w/ a fmu i locked up my stock LT1 injectors. Probably what your problem is.


Email me, mike@axincorp.com, i can tell ya where to get a new set of 39 SVO injectors for $200 if you're interested.