Track Exhaust System

[88Sleeper]

Hey Guys,

I tried searching the forum, and found a LOT of great info by A20A1, but I'm not really finding the answer to what I'm looking for.

Ok, so I have a 38.38 weber on my intake side, but I still have the stock exhaust manifold, then a replacement bosal down pipe, the stock cat, a replacement bosal resonator, back to a 2.25" inlet muffler. The pipes are all 1.75" diameter.

However, I feel that the engine would be able to rev higher if the stock exhaust was able to handle the more dense exhaust gases that the weber creates.

I was thinking I could make a "track exhaust" with a 2.25" down pipe and full-length system (straight-piping the cat) to my 2.25" muffler, for when I want to track the car. Otherwise, I could use my stock exhaust on the road for emissions purposes.

The problem, I see here is that I'm not sure if the stock exhaust manifold is an air-dam on the head?
From the down-pipe I have, I can see that the 4-1 manifold outlet is actually pretty big, at least 2" in diameter, and then the down-pipe narrows down to 1.75"

Would I be better off doing 2.25" for the entire exhaust, as an "exhaust-manifold" -back system; or should I just get a header and build an exhaust from there?

Thanks!

[conozo]

Definitely want to replace the stock exhaust manifold as part of your exhaust system. The FI manifold is bigger than the Carb manifold but both are still restrictive especially if you are going to upgrade the rest of the exhaust system.

[gp02a0083]

As conzo mentioned, yes the oem manifolds are a bit restrictive. As you found out about the taper from the factory 2" pipe, i suggest cutting further forward of the flex pipe. There is a larger restriction there in the oem setup that actually is around 1.5". Not sure about the bosal one. I cut that part out and installed a new flex pipe being i couldnt install a header at the time.

Take a look at my hatch thread, i built the rest of the exhaust with my friend in 2.25" stainless and wound up to be much cheaper than the oem replacement parts from walker, bosal, or whatever aftermarket oem supplier. Plus you get the added benifit of the larger exhaust.

The a20 has never really been known as a rev happy engine. Thats due to a number of reasons , if your looling for a rev happy engine i would suggest eventually looking into a b series swap. The A series is dtill a good sturdy engine for a daily,, cant say much for track use. If you dig around some more the real restrictive part of this engine is and as eith many other designs , the cyl head. Some members here have exprimented with that area.