[PONCHOMAN]

I helped my brother upgrade his 68 400 GTO from some 670's to some ported Butler heads. He has an Edelbrock Performer RPM intake that he has been experimenting between a Edelbrock 750 and a Demon 750 with mech secondaries. He ended up changing the cam going with a Comp Cams 51-225-4. (cam stats can be found at: http://compcams.com/Technical/Catalo...ML/210-217.asp). He also installed a Pete Jackson gear drive and a set of Rhodes lifters. When we reassembled the engine, we didn't use the special gaskets needed for the aluminum heads. As you've probably guessed, it ran great, what a difference a pair of heads and a cam can make, at least for one night and that was it.
We then determined that the head gaskets were leaking, so we yanked the engine and installed the correct gaskets(at both the intake and the block). The cam was broke in, using the specifications that Comp Cams gave with the cam. The cam was also prelubed during both installations, with prelube applied on all of the lobes and all of the lifters. Now the car runs ok (the equivelent that the old 670 car ran), but not like it did the night of the cam installation. Does anyone have some insight why this? I've heard rumors that Comp Cams have a tendancy to go flat. Could the cam have went flat? Please help!

[PONCHOMAN]

I helped my brother upgrade his 68 400 GTO from some 670's to some ported Butler heads. He has an Edelbrock Performer RPM intake that he has been experimenting between a Edelbrock 750 and a Demon 750 with mech secondaries. He ended up changing the cam going with a Comp Cams 51-225-4. (cam stats can be found at: http://compcams.com/Technical/Catalo...ML/210-217.asp). He also installed a Pete Jackson gear drive and a set of Rhodes lifters. When we reassembled the engine, we didn't use the special gaskets needed for the aluminum heads. As you've probably guessed, it ran great, what a difference a pair of heads and a cam can make, at least for one night and that was it.
We then determined that the head gaskets were leaking, so we yanked the engine and installed the correct gaskets(at both the intake and the block). The cam was broke in, using the specifications that Comp Cams gave with the cam. The cam was also prelubed during both installations, with prelube applied on all of the lobes and all of the lifters. Now the car runs ok (the equivelent that the old 670 car ran), but not like it did the night of the cam installation. Does anyone have some insight why this? I've heard rumors that Comp Cams have a tendancy to go flat. Could the cam have went flat? Please help!

[sixtee8gto]

Could It be that you had a vacuum leak first, and now you have it put together right, and all you need is to tune the carb right. Say the carb was originally running to rich but with a vacuum leak it balanced out. Just a thought..

[PONCHOMAN]

No vacuum leaks here, anything else? Nothing like dropping a couple of grand into an engine and then have it perform at the same level as it did before the payout!

[78 GHOST]

Ponchoman, re-read the last post, again.. slowly.

Your carb needs tuning. Those leaky intake gaskets may have permitted enough air to be admitted to allow the engine to be closer to the ideal mixture. Well, you fixed the intake leaks, changing the mixture and the power dropped off.. see the connection?