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?

 

Yes, they will bolt up to engine no problem. Brackets for 88 and 89 should be identical.

 

Any header made for any 3rd gen will fit any engine (minus LS1 or V6 applications). They are all dimensionally the same externally.

 

I've gotten some feedback that installing SLP 350 TPI headers on a 305 TPI may reduce the scavenging affect on my motor - hurting performance. I know these come in 2 sizes (1 5/8 and 1 3/4). I know scavengine is a function of exhaust velocity which in turn a function of the exhaust backpressure. Will 1 5/8" headers with the factory 89-92 dual cats with Flowmaster Catback be too little back pressure then? I would hate to invest the money into a mod just to make things worse.....

Thanks for everyone's help!

 

Don't worry about too little back pressure from the collectors on back. You can't have too little back pressure in the exhaust. You want the best flowing exhaust from the collectors back. Anyone who argues is a complete fool. There have been several discussions on this board about this topic, so don't let this turn into another.

The primary header size/length is all about tuning. Larger tubes usually move the engines powerband higher in the RPM range. And since the TPI engines have plenty low end, and lack in high RPM power, it is good practice to move the powerband higher. However, personally I wouldn't put the larger 1 3/4" primaries on a near stock 305. The 1 5/8" would be ideal.

 

Back pressure is bad anyway you look at it. You would benifit well from 1 5/8". The 1 3/4" will still work and you will see nice gains as well but they are a tad overkill for a stock 305.