I have a forty-over 360 with alloy heads, set up at about 11/1 Scr. It has run three different cams. It is in a 68 Barracuda with a 4 speed. I used to cruise it at 65 =3000 rpm, but she used to run hot; and I couldn't cure it.
So I got to thinking that either the pistons were tight or the rings were.
So I pulled the engine and stripped her down.
I sent the Block to the Machine shop to hone out the bores about a half a thou, then opened up the gaps on the top ring about .005, and the second about .002. Then slammed it all back together. No other changes were made.
After that, she has been impossible to overheat.
My guess is that my thinking was right.
BTW
On a side note:
adequate cruise-timing is essential.
With the current cam (276/286/110), my 367 likes 56 degrees at about 2400@70 mph in overdrive. She runs at exactly 207*F as measured at the stathouse with an IR gun. Hot day/cold day/fast/slow/idling, cruising, or racing; 207*F.
>If yur timing is retarded, and you have a long-period cam running headers, it is easily possible that the combustion gasses do not finish burning in the chamber. So, two things happen; 1) the expanding gasses chase after the falling piston, heating up the cylinder walls, and 2) the Headers will pull still-burning gasses out into the alloy ports, which then transfer more heat into the water jackets that encircle it.
> if yur timing is overly advanced, the pressure peak may occur too early, and result in detonation.
>Your exhaust system has to be able to deal with the hot gasses too. Any restriction will negate the work of the headers, and the hot gasses have additional time to heat up the ports.
>If your cruise fuel mixture is too rich, not all of it will find oxygen in the chamber to react with, so it/the raw fuel, goes out with the hot gasses. If it finds oxygen in the headers up near the head, it will spontaneously combust right there! This will muck up the work of the headers by causing the exhaust pressure to spike, and so the burning mixture will probably sit right there until it is burned up. If the WOT mixture is also rich, this kind of activity, will also kill some power at WOT, from the torque peak and higher, cuz it kills the overlap cycle. So then, you gotta make sure the header flanges at the heads are not sucking air, and lean out at least, the cruise AFR.
>If/when you get the timing right, you will be surprised at how lean she will run. Don't lean it out so far that the valves burn, lol.
>If you are running a Multi-strike ignition system, try not to cruise at the switchover point, which, IIRC is 3000 rpm.
> make sure the head gaskets are not allowing pressure into the cooling system.