Hey guys I have a problem I need help with. First off I am driving a 2002 C5 Corvette, it came stock with a LS1 5.7 L V8 w/ 350hp. I had my local restoration/performance shop who's owner has a background in drag racing, add a cam w/springs, Kooks X-pipe, Kooks 1 7/8 Long Tube Headers, and VR-Ram Air Kit. I told the shop owner to add the largest cam possible without needing a stall. My goal was to reach 400hp. I got the car back and 0-120 is unbelievable but the car now struggles to go over 120 and 140 seems to be my new top speed. Before the mod's I could hit 160 no problem. I haven't red lined the car yet but I don't know if this is normal after adding a cam or what? I know the computer was programmed to match the mods, so it may just need to be reprogrammed, please let me know what you guys think.

 

Without a data log it's tough to say. But the first thing I would look at are injectors. You've significantly increased the air movement in and out. But it doesn't look like you've done anything for fuel. I'd put it on a dyno and see what's happening.

 

I agree; If you're running out of fuel, bad things will happen

 

It's not that I am running out of fuel, it's that it sounds like my engine is going to explode. Before the car remained smooth all the way to 160, now it feels like I am putting a strain on my engine to even go 140mph.

 

It would probably help to know what size cam he put in it, what valve springs he used, etc. You're leaving out the vital details. For all we know, you're running out of fuel, or blowing through the converter, or seeing valve float, or etc etc etc.

 

I will call and ask my mechanic what size cam he put in and what type of springs he used. I know he replaced the springs but I don't know what kind he used.
The Valve Float sounds like it might be the problem. I don't know if this is normal after removing the cats but I smell like exhaust fumes after driving my car now and my gas mileage has gone from 22mpg to 16mpg.

 

Sounds like severe spark knock due to over advanced spark timing. See that all the time.

Russ Kemp

 

Without cats, the exhaust will have an eye burning stink. And depending on the cam specs, the gas mileage will be reduced.

Russ Kemp

 

What changes and/or modifications do I need to make to correct the over advanced spark timing?

 

Maybe, try the tune/diagnostics forum??

 

Ok my mechanic added a 224R Cam with Bee Hive Springs/130 Presssure.

 

There's a good chance you are running out of injector

 

More fuel

 

scan it while going max out. bet you see very static (maxed) injectors.
Any duty cycle % over 80% and you need to upgrade injectors....and pump/hotwire kit if your fuel pressure isn't what it should be (measured with mechanical gauge at fuel rail).

 

also, you never said it, but did you change gears? 4.10s swapped in place of say 2.73s and yea, youll lose a lot of top end.

 

No the gears are stock just like the day they came from the factory. I am going to go get the car dyno'd tomorrow if possible.

 

only real way to see very accurate injector duty cycle is doing it on the street, but a dyno is the 2nd best I guess. just remember, if injectors going static on the dyno, they are even worse on the street.