1988 IROC-Z engine was swapped from 305 to 350. Everthing was reused from 305 except new injectors were installed. I was told today that there are two sizes of intake plenum and runners and that I was loosing HP because the old one was reused from the 305. Is this true? Are there different sizes for the 305 and the 350?

 

no....the only differences are the injectors 19 lb/hr vs 21 lb/hr

 

I think the knock sensor is also different. I'm not sure how the computer will do since it still thinks you are running the smaller injectors.

 

no, there are 2 different types of plenum and runenrs.. but no size or flow diffrence really. There is ZERO difference in size of runner openings in the plenum and the runners are the same in all TPI fbodies. Injector, knock sensors, and.. ahh one more thing that is different. you could be losing power by using the 19# injectors as that doesnt dish out enuff fuel for a 350. Knock sensor will take away power as if the knock sensor takes away timing for your engine, therefor losing power. Try tuning your car up with a new PROM made for a 350 and also get bigger injectors..24#'s would give you some scaleablity on what you want to do later.

 

I DID already change the injectors (bought some 21# from JEGS). Couldn't get the car to pass state emissions inspection (Texas). So, they were changed over a year ago. AND, I purchased a stock 350 chip from a Chevy house at the same time. I was just talking to a guy at a Camaro Store yesterday and he said that there are 2 sizes for the runners and that I was loosing HP as a result of not changing it also. Was just curious if true or not....

 

As stated before, false. Only dif in Intake/runners is 85-88 which have a cold start setup and 89-92 that dont.

Size is same between 305 and 350.

But u should still grab some aftermarket intake/runners for it as u will get more power.

Personaly I'd remove the LTR setup and grab a HSR, cheaper and better for future upgrading.

 

The guy you talked to is an idiot. All stock TPI cars used the same size runners & bases, as mentioned already.