so wayne, read anything new , that i didnt tell you in the IM? .....
....just go with the 302 heads like i told you yesterday.....
....ps: all of the info i gave you yesterday, was gathered over the past 4 or 5 years from talking to the same people that have posted above
And with Eric's permission, here is the PM he's talking about.
The quote below is my message to him, followed by his reply:
I was wondering these last few days, if I have the intake off, should I just go ahead and replace the heads too?
And will a set of 360 heads w/ lifters and all fit a 318? That would take care of the port/valve size problem wouldn't it?
I was going to post a topic on this to get the details from some that have done it, but you are the guru of all things mechanical, I figured I'd ask you if it was possible first.¬†
Reply from: intenseimages
good news and bad news on this. yep, the heads from a 360 would drop right on and bolt up. all stock 4bbl 318's used 360 heads.
now the bad news, how much power would you like to keep? yes, the 360 heads have larger ports and support more air flow, but at the same time they also have larger combustion chambers and you would drop your already anemic 8.5 or so compresion down to about a 7.9 or 8:1 compression ratio.
so in essence, if you swapped to 360 heads and slapped that 4bbl on, you wouldnt notice as much difference in the power improvment. you would still get some, but not as much.
unless you are going full blown all out performance on that motor, i would leave the 318 heads on it. yes, the ports are a bit mismatched (about 1/8 of an inch) in size, but from everything i have read and experienced, you only lose out on the effects of the larger ports at high rpm's. you actually gain a bit in low end torque by keeping the smaller port heads. which, we all know, in a truck, extra low end torque is never a bad thing.
another thing you could do, if you are really worried about the air flow on the motor wit hthe smaller port 318 heads, is to go ahead and get a set of 360 heads, have a good valve job done on them, and then have them milled to boost the compression ratio back up on them. if oyu go this route, make sure the machinist knows to check the intake angle on the heads after you have them milled. you shouldnt have to mill them so much the intake angle is thrown off, but if you do go quite a ways on them then theintake wont line up unless you ahve that side machined as well. i cant remember the exact numbers on this, but if you get ahold of Marty (evildriver-3) he could tell you real quick.
if you really want to change the heads and can locate a set of them, get a set of mid-80's 302 casting heads. they came on alot of mid=80's 318's, have a slightly smaller combustion chamber (58cc's versus 65) and also have a closed chamber swirl port design. this provides much better combustion and quite a bit of improvement in air flow and power. the only better stock heads i have read about are the magnum heads. it would also place the compression ratio real close to a 9:1 ratio.