I measured my pipes and they seem to be 2 1/4 but all the sizes listed in books like Jeg's say 2 1/2 as the smallest size. Anyways, is 2 1/2 what came from the factory? Maybe thats why I not very good power is from the pipes being too small. lol BTW are K&N's really worth the money and do they show a significant difference in hp?

 

2-1/4" is what the factory used.

The small exhaust is one of your performance problems. Poor flowing heads and lame cam are right up there on the list.

Fix all those things, now you'll get to learn PROM tuning.

 

Amen to that. The stock piping is garbage on TBI cars. It is really pathetic once you get it out of the car and look at it. Changing to a full 3" system will really add some umph to your car. A word of advice is to buy all of your exhayst components for a TPI car. That way they come a full 3" without any attached reducers. If you buy your exhaust a pice at a time instead of replacing it all at once you will have to buy the systems that correspond to your engine code. That way the 3" piping will have the necessary reducer to attach to your stock cat.

 

Whats the stock pipe size on a LB9 TPI motor?

 

2 1/2 I think. It still stinks.

 

My 87 IROC-Z LB9 TPI had the 3" pipe from the Cat to the muffler and then 2 1/2" outlet pipes. Factory stock and I am the original owner. Now with A 350 TPI with SLP 1 3/4 Headers, 3" in & out Catco Cat and SLP 3" Catback system.

 

3" at the cat inlet, 2-3/4" after for '86-'90.

'91-'92 single cat was the same as TBI.

 

thats my schedule.

Did the exhaust this winter, working on cam heads and intake next winter. hopefully learning to tune this summer. You forgot to add gears to your list. Most of the lo3 cars came w/ 2.73 opens which is just as pathetic as swirl port heads. 1250 rpm stall converter is no good either...

Do it all at once. If you start you wont want to keep going under there to work on an unfinished exhaust, oh and run it open headers at least once. sexy sexy.

-chuck