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I'm rebuilding a 1972 LM340. I'm going to be using stock exhaust manifolds. I'm wonder if doing a bunch of head porting is worth the bother. If the heads breath great but can't move the air out the exhaust then what's the point?
My info says there's very little HP difference between logs and center dumps (from a guy who converted his).
Leaking logs only put water in the last cylinder vs, center dumps that get at least 2 (or 3) cylinders on each side.
Jeff
Granted, but a manifold/ riser leak puts water in 2 or 3 cylinders; a log leak only 'waters' the end cylinder.
Jeff
Where do you get "four gaskets"? I only count three.
Jeff
PS: How on earth do you get to those inside plugs! Cripes, w! What a tight installation.
If you are rebuilding the engine, you should consider the Barr Marine center rise manifolds, CHrysler used them starting around 1985, and from what I gather they flow much better than the log manifolds, to the tune of 15 HP, combined with a Edelbrock performer RPM air gap intake, little port work and a small bump in the cam You could see an easy 50-60 HP increase over stock, maybe more if you bump the compression and create a quench with the right piston domes.
It is if you are upgrading the cam and cylinder heads. The center rise manifold is basically a 68-71 340 passenger side manifold flipped upside down and water jacketed. It has longer internal runners than the log manifolds which helps keep the exhaust velocity higher through the manifold. They are not as good as a tuned header but they are much better than the logs. Less gaskets to leak and no distribution tubes to corrode either. They also introduce the water into the exhaust further away from the valve lessening the chance of reversion if you run a cam with more duration.
Granted, but a manifold/ riser leak puts water in 2 or 3 cylinders; a log leak only 'waters' the end cylinder.
Jeff
That is a moot point. At the point of getting water in your combustion chamber it does not matter wether it's 1 or all 8 cylinders.