- Moderator
- #1
- Joined
- Nov 9, 2000
- Messages
- 7,460
- Location
- Edgerton, Ohio, United States
- Corvette
- 1959 black 270hp (9/2/69) 1981 Beige L81(10/20/80)
I am modifying a pair of original L81 exhaust manifolds to use on my '69 stepside project. I removed the heat shields and the AIR tubes then started cutting away the access welding material in the ports to beguin the port matching process. I discovered that the openings on the manifold are quite a bit smaller than the stock ports and a lot smaller than my ported heads. They are also very misshaped due to a sloppy welding process. Also in the collector end of one manifold (outlet end) there was a huge glob of weld joining the 4 tubes together that affectively closed off at least 25% of one tube. All of this can be ground out and still leave a lot of weld for strength.
The picture shows the roughed out port on the manifold I have started and the unmolested stock port of the other one. The untouched one was by far the better of the two before I started. I still have to transfer the port shape from the head to the manifold and do the finish shaping but you can see that if you spend some time port matching your exhaust manifolds you can help your L81 to breathe a little better and pick up some free horsepower .
The picture shows the roughed out port on the manifold I have started and the unmolested stock port of the other one. The untouched one was by far the better of the two before I started. I still have to transfer the port shape from the head to the manifold and do the finish shaping but you can see that if you spend some time port matching your exhaust manifolds you can help your L81 to breathe a little better and pick up some free horsepower .