Posted by Todd Wilson on Saturday, December 13, 2003 at 10:42PM :
In Reply to: Re: 318 vs 360 posted by George (AB) on Saturday, December 13, 2003 at 10:08PM :
318 heads are 61 to 67 cc's while the 360 heads are 65 to 73cc. adding the 360 heads gives it a bigger combustion chamber lowering the compression probably down into the 7:5.1 range. Dumping in more fuel and air then the 318 can chew.
Decking the 360 heads will help a little but most likely to achieve a 9.5:1 compression 318 using 360 heads you will need to deck the heads and add a higher compression piston.
Then you worry about piston to valve clearance and push rod issues from the cam.
Your port and polish would work good for high rpm situations. Is this truck gonna be used to rip through the mud or lug a trailer?!?! Bigger valves would also go hand in hand with the good flowing heads. You'll need high rpms to put out power. Single plane intake which puts out power at high rpms. A dual plane would be better for low and mid range torque.
In some cases a smaller head would be better for pulling and low end grunt due to the port velocity being better. Goes hand in hand with single or dual exhaust. Sometimes engines loose low end grunt going to dual exhaust.
The "purple" cam from Mopar would probably work in a truck situation when low and medium range torque is needed but there are other RV style cams that would work better.
A stock 318 with a mild cam install and a dual plane intake and 600cfm carb will really wake it up. From idle to about 4000rpms it will twist and twist good After that you will see a drop in torque as the higher rpms require better flow that you dont have.
Its been my experience in seeing and reading 360 heads are best left on 360's.
If you can find and afford them 340 J heads are a nice addition to a 318.
Even better are the "swirl" port heads of the 80's. Found on cop cars and so forth. They flow great and are cheap and easy to find.
Sounds like your #8 piston problem was some detonation occuring and the tranny not downshifting only made it worse. 360's are famous for having a restricted water passage in the area causing that cylinder to run a little hotter then the rest.
Todd
Follow Ups: