engine math! milling heads + intake

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happster

happster

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i have a pair of 360 heads. my plan is to mill them 60 thousandths, to be put on a 318. my problem is that i don't know the formula for how much to mill the intake to fit with that much of a modified head. anybody know the formula? :scratch:
 
thanks a lot BJR! exactly what i need. would it be worth it to mill off more, or should this be all i take off?
 
happster said:
i have a pair of 360 heads. my plan is to mill them 60 thousandths, to be put on a 318. my problem is that i don't know the formula for how much to mill the intake to fit with that much of a modified head. anybody know the formula? :scratch:
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you have reached a tricky question. 318's are hard deal to boost compression on. you will probably not be happy with the comp on the 360 head even after taking .060 off . first off i have heads on stock that are ported 318 heads w/ hardened seats milled .060 that yield 11-1 comp because the chamber in a 318 head is significanly smaller than the 360 .the 3.91 to 4.00 bore 318/360 compounds this.but to answer your question. we take material off the intake side of the head as opposed to taking material off the intake itself, therefore allowing intake changes without custom intakes. either way you take that much off youll have to remove the linup pegs on the block so the intake will fit. any time you start milling over .030 things get real fun real quick 318's and 360's have a different compression height in the piston. there fore making the 318 piston at tdc sit further down the bore (compression problem) only in 1971 did chrysler put a true flat top piston in the 360 after that they dish them to drop compression (emissions) small cc eddy heads are another good solution to your problem. or buy a domed 318 piston. and while your down there you might as well put a 4.00 crank and make a 390? see it never ever ends it just depends on the $$$
 
Don't mill anymore than needed. Actually I would use a set of KB 167 pistons and cut about .030 off the heads and then cut .030 off the intake side. Or you can safely cut up to .025 off the deck and still bolt the intake manifold down without cutting the intake face of the heads. This will give a slight mismatch but not enough to worry about for a street car. By using these parts you should have somewhere close to 10.5:1 compression, or just use the KB 167 pistons and end up about 9.8:1.
 
it's funny you should mention the 167s, i am actually starting to think those are the way to go. i suppose you guys have seen the 400-horse street 318 they built in popular hot rodding, and that build is actually what i have decided to do! they used 360 heads, did not specify how much they took off, but it sounds like .030 will be enough to get my compression up. they said the heads were milled from 72cc to 60cc... i do not know how to calculate how much they took off in thousandths of an inch though. it sounds smarter to mill the intake SIDE of the heads instead of the intake itself, so i can easily change intakes if i decide and still be able to put them back on the shelf and use them for a different application. they also opened up the intakes to 2.02, and did a minor porting job. the block was bored .040 over, and that is what i intend to do with mine. i'm picking up a 318 for free, and have decided that i am going to put the stock heads back on the car for now, run the factory two-barrel, and switch out to the 400 horse engine once it's done and i have gathered everything i need to put it in. this way i can keep the car running and driving, and still be building something that will peg the fun needle. thanks for your advice guys. i think this project will be fun and unique, and really change everyone around here's opinion about my "underpowered muscle car."
a lot of the engine work i will be able to do myself, as i have a full engine rebuilding shop at my fingertips right now. just have to find time to go in and do it!
 
If they went from 72 cc's to 60 cc's then they had to cut about .060 off the deck and .072 or so off the intake side of the heads. To me it would be better to use the 318 heads and use the stock size intake valves or if your just itching to put larger valves in then go to the 1.88 intake valves instead of going to the 2.02 that they did in the mag. artical. I know that they used the 360 head castings but the intake runners are a bit large for the street on a 318's bore size. The velocity will suffer and you'll be changing the heads before you know it. I have a setup like this with the 302 heads and it makes well over 400 HP and I used the KB 167 pistons and square decked the block to be just out of the deck about .018 or a build like the 340 HP engines but in a 318 block. This works very well and without any special parts other than pistons.
 
so basically what you're saying is that instead of these 360 heads, i should run 302s with 360-size intake valves? what if i kept the 360 heads but didn't modify the intakes, kept them at 1.88, but milled them like they did in the mag? i know the runners are large, but i mean, i already have these heads, and they got good power with them in the magazine. everything i have heard about the factory 318 heads (early ones, like mine) is that they have too small of valves, despite their smaller chambers, and they just didn't flow well.
 
True they didn't flow well in stock form but with a little work they can and will perform like the 360 heads with the larger valves. I did use the 360 exhaust valves in the 318 heads and this picked up the Tq a good bit when I did this. Mind you I'm not a fan of using the larger valves from the 360 on the intake side in the 318 heads for street use. As the smaller ones will give better throttle response and more Tq.
 
i would be willing to sacrifice the low end torque for more up top. i guess you could say it would be a "street/strip" engine. usually the exhaust valves arent an issue... that's surprising to hear that you changed them but not the intakes. i should also add that i will be punching the 318 .040 over, giving room for some more serious flow.
 
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