v10viper04

My engine seems to run fine until about 4800 rpms where you can literally feel the car stop pulling and run like crap until it shifts.... then starts to pull again... i am wondering considering i advanced my timing a little (like 1-2*) should i be running 91 octane instead of 87? is the 87 causing detonation which in turn would make it run like crap up high?

90c350

What are your cam specs? what fuel pressure are you running? Have you had any ecm tuning done? Does it just fall flat or is it popping and backfireing?? Need more info. It could be your cam/heads/valve springs/ tuning etc.

v10viper04

everything is stock besides headers and it does backfire sometimes when its not 100% warmer up and when its warmed up it falls flat on its face. BUT when its up there if i let off the throttle a little it will pull again... full out up top it dies.....

v10viper04

any ideas?

90c350

Your cam is probably all done by about 4500rpm with a stock setup. You may be runnning lean at the higher rpm with a stock tune. Can you tune your own ecm or are you able to datalog?? You will need a better cam, higher fuel pressure and some custome tuning to get her to run better. What injectors are you using the ones from the 305 or from a 350?? If you have the 305 injectors you will need to increase your fuel pressure or swap to a set of 350 ones. Lots of things that can be done but tuning is needed for the ecm and datatlogging as well. Hope this helps.

v10viper04

they are the 350 injectors and i am running the 350 ECM.... i just don't understand why they would even let it rev that high it it falls flat on its face before the shift..? its bad for 0-60 times and accel...

90c350

Gm wasnt to worried about 60' times. You may also be a little lean at the higher RPM range do to your headers/exhaust and intake mods. Even though they are minor. Stock tbi units dont allow for much modding. Try increasing your FP a little and see what happens. Do you have an AFPR?? and what pressure are you running?? You need to get into datalogging to see what is going on though. Do you have a laptop??

v10viper04

i might be able to borrow one, i was going to see how the fuel is doing by using the O2 sensor to see what it reads when it falls on its face. should be able to tell if its lean or rich. idk what pressure its running its all stock

90c350

Factory setting should be anywhere between 11-13psi. If your going to be reading the stock narrow band O2 sensor then be carefull because they are not very accurate out of their operating window. Ex-350to500mv would probably be a normall swing point for 13.5 to 15.1Afr.