[Dick Boneske]

My friend's '75 455 Grandville needs a new exhaust. We would like to change over to duals. Has anyone done this?

I've noticed that the transmission crossover mount has no bend in it to clear the left side headpipe. We've considered having someone fabricate ours to add the "bump."

Also, you may remember these cars had only about 7.5:1 compression ratio. How much can you mill the heads to increase compression? The all stock engine has only about 3,000 miles on a complete rebuild---overbore, new pistons, etc.

[694.1]

I bet a '73 or '74 cross member would have 2 bumps. Maybe run 400 heads & advance the smog cam?

[Ben M.]

Yup, '74 and earlier crossmembers are dual hump more likely than not (I've got several sitting around of that vintage and all of them were, even the single exhaust cars).

As for milling the heads, I wouldn't bother. Just put a set of 6X-8s or 6X-4s on it and put an 068 cam in it and call it a day.

[GpFreak]

I had an Impala years ago that I took to a good muffler shop to add duals. They cut the Y pipe and welded the hole shut, added the other side and flattened the pipe to clear the cross member then added glass packs. Did a great job, but man that car was loud when you got on it!

[camerjeff]

I have a 71 trans crossmember with the duel humps, $100 shipped to you. It has even been stripped but not primed or painted. let me know if interested

[grandville455]

I’ve used Hedman shorty headers on my 74 when they first came out, was the first to use them on a b body, worked well n u could drop the engine in with them on, then later on I switched to Doug’s D 590 headers, those fit very nice too.

[camerjeff]

I know that the 1970 GTO Ram Air III Manifolds fit the 71-76 B-Body chassis with no modifications, my 71 Police car came with them from the Factory