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Looking for a little help/ direction with my Mach one. It’s a factory s code 390 with the c-6 and before the last owner (17 yes) someone added the 428 cj heads, intake manifold, carb and shaker box.
Question 1) wouldn’t they have had to change out the exhaust manifolds as well do the ports lined up?
Question 2) it runs really well but lacks power, I want to take it apart and do a mild bore and cam, are the cj heads worth a port and polish or just go with eldebrock?
Last question) is this set up worth keeping for the years I plan on owning this car due to the numbers matching block? or should I save the money and look towards a fresh 9 engine down the road.
Thanks for the help!


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Don, the CJ heads, even unported, are just as good as the Edelbrocks. Thats Edelbrocks dirty little secret. Now, If you have those E-boks PORTED, then you'll be ahead. One wonders what pistons you have, and if the compression is on the low side with the bigger heads. It used to be that these heads were milled when this upgrade was done, your guy may not have done that. IF you have the heads milled, you have to do both the decks AND the surface that mates to the intake. Don't let anyone tell you that you have to machine the intake manifold itself, that is the wrong way to do it. The 390 exhaust manifold probably works, but they are a horsepower killer. So are the 428CJ exhaust manifolds. What is the rest of the exhaust like ? You could think about some Accufab ( George Klass ) or FPA tri-y headers, they'll help alot. Keep your manifolds in a box in the garage. Don't throw them out, but I wouldn't look for any real power with them on there. LSG
 
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