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I am building a 454 and using the 781 oval port heads, and really want to put on a corvette tri-power. the 69 tri-power intake has rectangle ports. I think I read somewhere that Chevy actually used this combination on some corvettes. Will I have problems with the mis-matched ports?
Tom
I'm no expert, but I'd look at what gasket you can use to achieve a good seal, especially on any water passages. The mis-match at the ports will tend to create some turbulence just inside the intake, which will lead towards a thorough mixing of the air/fuel charge and might even promote a more even mix across the cylinders. Unless you're looking at trying to eke out the last couple of horsepower or ft-lbs of torque I don't see that it will be a problem provided you can get them to seal up fully. Others who are more expert on the BBC may be able to point you to specific gaskets, or may say that it simply cannot be sealed.
I don't want the fastest 454 truck around, just want to use big block tri-power.
I had a tunnel ram that was rectangle port, and oval port heads on my 396. I was told to use rectangle port gaskets and it'd be fine. The coolant passages are in the same spots, so that isn't an issue. The engine builder I was using at the time told me the same thing you typed. He said it wasn't a surprise to see rectangular port manifolds on oval port heads straight from GM on different BBC's. I can't vouge for that as I never tore any apart in the late 60's early 70's. He sure had. I don't know if anyone has ever heard of him. Maybe you have Jerry? Larry Laveretty? He used to have several different race cars and raced at Cordova a lot.
If you study fluid dynamics, you'll find that the lion's share of the flow goes right down the center of the vessel and that silly stuff like gasket matching doesn't add that much to the mix. Matter of fact, if the port ends up looking like an anaconda that swallowed a pig in side view, the mixture will slow down there, possibly separating fuel from air and puddling fuel on the port floor, to be sucked up on the next intake stroke as a big slug of raw fuel. You can see the effect of flow by looking at a stream or river, where the majority of flow goes right down the middle of the river, with little or no movement on the banks. So it is with a manifold/head port, the mass of flow going right down the middle with little flow at the edges of the vessel.
Bottom Line......
Bolt the intake on and run it.
.
"...an anaconda that swallowed a pig..." Nice visual, Tech! I'm going to remember that one!!
while you are taking all those facts into consideration--add in the mix that the big block heads have weird combo of port shapes as the intake people outranked the cylinder head people and they made the manifold to have siamised ports while the new guys in the cylinder head dept had to reroute 4 ports to line up with manifold------
I would find some rectangle port heads to go with that intake and get rid of or use the oval ports on another engine-------sell'em--------
You may want to obtain the oval port TriPower intake that Chevy offered for the 427 400 horsepower Corvette engine option from 1967 to 1969. I have one that works a bit better than my 435 TriPower on a given big block.........both use the same Holley 2 barrel carbs
Maybe you can work out a trade????????????