I wanted to upgrade the exhaust on my 88 305 TPI Auto - will headers from an 89 350 TPI fit? I found a dual exhaust setup from a 350 TPI (SLP Headers with flowmaster cat back) for sale, but wanted to make sure it would fit - with fit meaning no special brackets or machining for clearance.

Anyone know?

 

The recomended header size for 350's are 1 3/4. For the 305's, the recomended header size is 1 5/8. I think this is why they differentiate between the 305's and the 350's. I am not positive though. I would say call SLP and ask.

Nick

 

Using the larger header for a smaller engine, unless it is blown or you have NOS, would mean that scavenging would be reduced because it would reduce exhaust charge velocity. simply put, don't.

 

Are you talking about the scavenging concerns with both of SLP's headers (the 1 5/8 and the 1 3/4) or just the 1 3/4?

I was planning on installing the SLP 1 5/8 Headers with the Y pipe for dual cats, use the stock dual cats and a flowmaster cat back. Would this actually hurt the performance of a 305 TPI then?

 

I believe they were speaking of the 1 3/4" inch versions, plenty of people run the 1 5/8s on both 350s and 305s. I have the Edelbrock TES 1 5/8s on both of my thirdgens, they definitely did not hurt the performance of the 305 in my IROC... Just find out which it is you're looking at and decide from there, I don't think you'd want to run the 1 3/4" versions on a 305...

 

1 5/8 is fine but if you run too large a header (1 3/4) you lose some scavenging which empties out the combustion chamber. So, for a 305, 1 5/8 is fine.

 

I've always run 1 5/8" headers on my 350s. You would need a pretty stout engine to need a 1 3/4" header.

 

The one in the sig? I would go with the 1 3/4 for that, IMO. a 1 3/4 is fine for a modded 350 or larger, IMO

 

Yeah, even the supercharged LT1 is running 1 5/8" headers at the moment. And the turbocharged 383 I'm building will probably run 1 5/8" primaries to help the PT76 turbo spool up as fast as possible for fun on the street.

 

Very informative thread guys, switching headers on my 87 and was wondering about which would size/sizes would suit my needs best.