would the exhuast manifolds off of an L69 give me any appriacable power increase on my L03? i already have a set of these manifolds "laying around". are they worth the time or are they a waste of time? if i ever went with a tubular system i would have to make sure they have the connections for A.I.R. system and they would have to work properly with my AC lines. they are also very expensive. any thought on L69 manifold would be great

 

The L69 manifolds are certainly better than LO3 manifolds. However, without the L69 y-pipe, cat, and cat-back, they won't be much help.

 

i would plan on using a new Y pipe, cat, and cat back. what would work with L69 manifolds. how much better are tube headers than L69 manifolds, are tube headers still worth the cost if i have a set of free L69 manifolds avaible. i priced out tube headers to be in the 400-500 price range. quite a chunk of change. also i am concerned that they wont fit right. someone told me that they used tube headers on a 92 with a 350 and the a/c lines came too close. i am interested in keeping my a/c. this car is a daily driver and all options work, thats they way i like it. manifolds from the L69 would bolt right on look stock, also has A.I.R. hookups. so if i decide to use L69 manifolds, what exhuast could i use for a Y-Pipe, cat, and cat-back that would work with this setup? what size are the outlets on the L69 manifolds vs. my stock L03? i want to have a better exhuast but would rather keep it on a budget. im a poor folk

 

I don't know of any y-pipe that would "work" except an L69 y-pipe. You could have one fabricated, though. That would probably cost you somewhere between $100 (if you're good friends with an exhaust shop) to $300 (and probably more). To get one fabricated that has mandrel bends would probably cost a lot more.

Tube headers flow much, much better than the best cast iron manifolds. Whether that makes a difference on an otherwise stock LO3. . .

I have never heard of a problem with AC lines and headers. But, I haven't heard everything, I'm sure. AC bracket - yes. Lines - no.

Headers and exhaust for the '86-'90 TPI single cat application are typically the best flowing. I always recommend starting with Hooker 2055HKR headers, as they are emissions-legal, and have the best 3" mandrel-bent y-pipe out there. But, it's up to you what you want to do with your money for your car.

 

IIRC, the L98 used the same exhaust manifolds as the L69, and had about the best single cat exhaust system that GM used on these cars.

 

The L69 cars had the EFE valve on the passenger side manifold while the L98 did not, so the mount flange is different between the two.

 

I stand corrected