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My GTO has the base 400 ci engine with cast iron manifolds and an 066 camshaft. It runs good but just doesn't seem as responsive as I think it should be. Plugs, points and timing are set as per the factory manual.

I looked at the exhaust pipes and mufflers after noticing that things didn't look quite right. They looked to be fairly new (stainless) but
I started measuring them.
Front pipes were 2" OD and tail pipes were 2.25 OD. Mufflers seem to be some no name turbo muffler at 14".

Does this sound like it could cause the engine to be a bit weak and not as responsive? I know I should have 2.25" for the front pipes and 2" with resonators for the tail pipes.
I am curious on how much of a bearing these smaller exhaust pipes have on performance.
 

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The 066 cam is not much of a cam and was not used in the GTO for '67. It was used in full size cars and Firebird. HP rating with that cam was 325HP. In '67 there was a low compression gas regular fuel 400 rated at 255HP which came in the GTO as well. It used the "254" cam. Now I don't know what "base 400" means to you, but if you have a low compression base 400, you won't have a lot of get-up-and-go.

Your pipes shouldn't really be the problem with the 066 cam.
 
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