ok here is my problem my 92 GTA 305 took a crap so I pulled the motor installed a just rebuilt 350 (like 100 miles on it rebuilt) everything is now 350 parts except for the Prom...Will the spark and fuel curves makes that much of a difference that it will not pass emissions? Also it surges a little about 250 RPM's between 500 and 750 in drive stopped...Any ideas on this as well....

Background......It is basicly a stock 87 350 TPI rebuilt bored 60 over 1 month ago just finished install 2 days ago....that replaced a stock 92 305 TPI

 

Well for one, a 305 uses 19lb injectors and a 350 uses 22 lb.
And the prom will reflect this.
And I'd imagine the IAC settings are different too.
A 35x will need more air at idle than a 305.
And .060 over may play havoc with your Knock sensor.
The KS is also matched to the prom/motor too.
And the limp mode fuel is completely different between the two proms.
Not sure how well a 350 would run on a 305 prom in limp mode.

 

I agree with everything aside from the bore affecting the Knock sensor....I have built another motor and has not affected at all not only that but the other motor has a Pete Jackson Gear Drive in it........

Like i said everything is 350 aside from the prom...I do not know what KS is and i do not have time to wait til the prom gets here...I have ordered it but it will take a couple days....My Carbon Monoxide is 8 points to high and my Hydrocarbons is .10 to high....I need to pass Emissions tomorrow....

 

The 350 knock sensor (for sure) and the circuitry in the memcal for the knock sensor (not 100% on that) is different.You should get the knock sensor and the 350 memcal just so things are closer to reality. Would help with the idle and may be satisfactory. Should get it tuned anyway if you want all the "little" things to be better.The 060 overbore could change the knock signature of the engine and the knock sensor may not pick up the correct frequencies with that displacement.Guys running 383's have discussed this quite a bit.Sensors are setup to detect specific range with each displacement.Do a search for the KS and you'll find the correct p/n here somewhere.Its 3.9K ohms on the 350 sensor IIRC.

 

The KS is already from a 350.....like I said the only thing i am missing is a 350 chip.....But from my experience the bore at least going to 60 over will not affect the KS enough to fail emissions (i am not saying it does not affect it just not enough to fail emissions) I have done this exact same thing (PLUS Cam and gear drive) on my other 350 and sailed thru emissions.....I think i might need to retard timing a littleI think it might be advanced to far.....But i am sure the memcal will help....

Thanks for the responses guys!!!!

 

ok well here is the update.....Apparently the prom doesn't matter either the problem ended up being the air diverter valve.....Thanks for all the sugestions everyone