440 heads

[1966satellite]

I'm considering buying a 440 from a 78 motorhome. If I do I would like to get a little more horsepower out of it. I have a set of '516 closed chamber heads that I could install to increase the compression ratio a little but they have smaller exhaust valves than the '906 heads that are on it. Any opinions on which will do more to increase the horsepower? I'll probably put a different cam in it also.
Thanks.

 

[happyjackdaddy54]

The motorhome engine will make a great choice for the block. On the head's any good automotive machine shop can open up the exhaust, and install a bigger stainless valve.

 

[Meep-Meep]

Compression increase works! Even the old 413's and 426 wedge had good power with the small valve 516 heads and will be fine for a street car. See here http://en.wikipedia.org/wiki/Chrysler_B_engine There was a 300J head that was used on the HP 413's, which may be the first to use the 1.74" exhaust valve, and possibly the predecessor to the 915 head, but even other applications using the small valve 516 heads did well. Further enhancement of the smaller valve heads can be made with a dual pattern cam offering a little more duration and lift on the exhaust side. And a set of headers will help at higher RPM's. The closed chamber Max Wedge heads are not part of this discussion, plus they have a chamber volume near the 906 / 452 heads.

My concern with using the 516's is you will need hard seats for the unleaded gas, so if you have to do that then have the 1.74"s put in. It may be a hard call to swap from an unleaded friendly 452 casting to one that needs to be reworked. You know you will be putting guides in the 516's and all that work add$ up!

If you want a cheap compression increase use a steel shim gasket under the 452's, but with the 78 pistons being so far down in the hole the small gain may not be significant by itself. On a 79.5 CC chamber and a zero deck piston the gain from a comp gasket to steel shim is about .4 point. Going from an open chamber to a factory 516 or 915 chamber is also about .4 point with zero deck pistons. To get a significant increase you may have to resort to using a closed chamber head (~80 cc's), a shim gasket and mill the head as far as reasonably possible. Only by CC-ing everything will you know for sure what you get.

Bottom line: If the 452's are off anyway and need no work other than a kiss on the seats then mill them (including the intake side) and pop in a shim gasket. This with a proper cam will make for a good runner through about 4500 RPM.