Upgrading stock 1971 318 heads

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Slantsix64

Slantsix64

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I am upgrading stock 318 heads I have an ld4b intake mild rv cam 600 cam carb and will be adding 340 manifolds. Picking up a pair of redone 302 heads hoping to gain some more comp and power.

My question is shaving 40 thousands will not effect the intake side but we're would my comp ratio be at? I have basic flat top pistons the block is a 1971. Also the exhaust ports will match the 340 manifolds that I have?

After doing some reading I know you can add bigger valves to gain more horsepower around 50hp and keeping them stock size will be around 20 gain bolt on which is fine with me the heads redone costs 300 for the pair. Milling the head would wouldn't be too expense.
 
I'd do a 318willrun port job also, he's done a how to video.
 
Yup, your biggest gains are going to be through bowl blending and cleaning the runners. It don't have to be pretty, just well formed.
 
I would not mill the heads. Your compression may end up too high.
 
Slantsix64 said:
I am upgrading stock 318 heads I have an ld4b intake mild rv cam 600 cam carb and will be adding 340 manifolds. Picking up a pair of redone 302 heads hoping to gain some more comp and power.

My question is shaving 40 thousands will not effect the intake side but we're would my comp ratio be at? I have basic flat top pistons the block is a 1971. Also the exhaust ports will match the 340 manifolds that I have?

After doing some reading I know you can add bigger valves to gain more horsepower around 50hp and keeping them stock size will be around 20 gain bolt on which is fine with me the heads redone costs 300 for the pair. Milling the head would wouldn't be too expense.
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Just drop a slant in it
 
RustyRatRod said:
I would not mill the heads. Your compression may end up too high.
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oh man, i was thinking of going with the fel pro 0.40 head gasket along with milling 0.40 of the head. do you think i could reach 9:1 with out any milling?
 
I would cut the original 318 heads .040, then port them, and make sure you give them a good valve job/hardened seats. Me personally.
 
Yes, the exhaust ports will match perfectly with 340 manifolds. Use 360 exhaust manifold gaskets. 302 heads are usually close to 69CC what year heads did you originally have on the engine '71 318 heads???

Treblig
 
When i cc'd those heads...the open chamber heads were around 68cc the early closed chamber heads were around 66cc and the 302 heads I pulled off a factory 140k motor measured up as the advertised at 64cc.

Problem here is everyone will give a different cc, what they found or heard or believe to be correct....but the fact is they varied to a degree from the factory ...as do people's memory and testing accuracy.
 
Treblig said:
Yes, the exhaust ports will match perfectly with 340 manifolds. Use 360 exhaust manifold gaskets. 302 heads are usually close to 69CC what year heads did you originally have on the engine '71 318 heads???

Treblig
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yes original stock 71 heads. so at 69cc would milling 0.40 not allow me to run on pump gas?
 
Subscribed. If you mill that much off the head surface on your present heads, you should mill almost as much off the intake side as well. The 302's in my opinion are a nice head, efficient combustion chamber and 71 318 sized ports. With the 302's I wouldn't mill them at all just do a little chamber polishing, bowl and port work.
 
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Hit the 302's roof with a sanding roll and knock the casting lines off and maybe smooth out the valve seat to head transition if it has any ridge. Dont touch the floor. unless there are huge buggers down there, dont reshape. I would not mill 302's as they are smaller as cast.
 
Slantsix64 said:
yes original stock 71 heads. so at 69cc would milling 0.40 not allow me to run on pump gas?
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May-be someone has figured that out. (compression ratio with that combination) I have stock 273 heads (on my 273) with Egge Domed pistons. I checked the ratio and got like 9.68/1. I run 92 octane with no ping. I have ran a little 87 without issues as long as you don't crowd things.
 
We have a 72 318 with stock short block and had 360 heads on it... I checked it to be 7.6 compression...

I installed a set of 67 318 heads (66 cc chambers) that I had ported and 1.88" intake and 1.60" exhaust valves installed (stock 360 valves), and with a .040" head gasket got it to 8.6 compression....
 
Before milling, when engines apart measure what the cr will be then figure out how much needs to be milled if any.
 
Given the choice of factory 71 heads or later 302 castings, I would use the 302's. The cost to rebuild is the same. The smaller chamber of the 302's will provide a compression boost. An .040 deck cut on the heads would absolutely require a cut in the intake face and most likely shorter pushrods as well.

As for what your final compression would be, that is largely dependent on where it is now. How far below deck are your current pistons? To answer the "will it run on pump gas" question, we'd need to know what cam you plan to run. There is a thin head gasket which might be of use.

Yes, larger valves can be fitted, but the machining cost would go up. OEM replacement 360 valves cost about the same as 318 valves, but to gain anything, the bowls would need a 70 degree cut and a little blend with a grinder. In either case I would be skeptical of a pair of $300 heads. To do a decent job, that's about what the parts alone will cost (16 valves, 16 guides, 8 exhaust seats and springs). Basic machine work will be about that much as well. $500 for a quality rebuild on a pair of heads using OEM replacement parts is closer to reality, if not getting off bit light.
 
Really if you haven't got the 302 yet, I"d spend a bit more and get EQ heads.
Hp per $ spent way better value plus lots of room to grow. Heads are the biggest NA change you can do.
 
bigger valves and 302 heads are not gaining a mild cam 318 50 horse, maybe 30. as has been said-measure deck height and do the pistons have valve notches? if the heads have not been recut, cut them .010", or u will need to cut the intake side. if u cut them more than .010" and the pistons are close to the deck and have no valve relief notches-check valve to piston clearance
 
Slantsix64, I will say this once on these three subjects and I will not argue with anyone.
  1. I have cut heads .040 and .045 and NEVER required a different push rod OR milling of the intake. Never an issue either.
  2. Flow trumps compression any day of the week and twice on Sundays.
  3. Closed chamber heads do NOT perform as well as open chamber heads, all else being equal.
 
When milling for compression during a rebuild.... much more than .010 requires cc'ing the chambers 1st or you really have no idea how much you'll need to mill in order to end up where you want.

If it's a deal of head gasket changed and nothing else, mill .010 and put it together... but if you have a target...you need to know where you're shooting from.
 
318willrun said:
Slantsix64, I will say this once on these three subjects and I will not argue with anyone.
  1. I have cut heads .040 and .045 and NEVER required a different push rod OR milling of the intake. Never an issue either.
  2. Flow trumps compression any day of the week and twice on Sundays.
  3. Closed chamber heads do NOT perform as well as open chamber heads, all else being equal.
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Hey you can just call me Moe, I have made a cut on a stock 360 heads .40 and the intake bolts on correctly as you stated on another thread . I was just wondering that because these heads are resurfaced would it throw off the measurements of the cut. And being that 302 heads gave the 88 318 motors a bump to 9 to 1 compression does that mean the head milling wouldn't need to be so much? Sorry if I don't make sense
 
Yes I understand maybe just putting them on with out a mill might be safe and best
 
Slantsix64 said:
yes original stock 71 heads. so at 69cc would mill

The reason I asked about the year of the block and heads is that after '69 the 318 compression ratio kept dropping. It was 9.2:1 in '69 then 8.6:1 (more or less) in the 70s. I believe my pistons ('69 Barracuda) were .030 down in the hole at TDC. Your pistons (if it is stock) should be .060" or even .100" down in the hole at TDC. If your engine is a stock '71 318 you would have a hard time getting your compression any higher than 9:1 by changing the heads. It's pretty easy to check your piston depth before you do anything else. According to my Mopar Hot Rod Book the piston pin height was 1.77" in '69 then from '70 to '72 the pin height changed to 1.74". That means that your pistons (if they are stock) should be .060 down in the hole?? That's .030 (my piston depth at 1.77") plus .030 more for the change in pin height in '71. The problem is that someone might have changed the piston is the last 50 years??? So check your piston depth at TDC, this will tell you how low you can get you combustion chamber CCs before your compression gets too high. I don't think, if you have stock pistons you could cut the heads enough to get in trouble because 318 "stock" piston sit too deep in the bore??

Treblig
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Don't know if this posted correctly so I'm trying again............

The reason I asked about the year of the block and heads is that after '69 the 318 compression ratio kept dropping. It was 9.2:1 in '69 then 8.6:1 (more or less) in the 70s. I believe my pistons ('69 Barracuda) were .030 down in the hole at TDC. Your pistons (if it is stock) should be .060" or even .100" down in the hole at TDC. If your engine is a stock '71 318 you would have a hard time getting your compression any higher than 9:1 by changing the heads. It's pretty easy to check your piston depth before you do anything else. According to my Mopar Hot Rod Book the piston pin height was 1.77" in '69 then from '70 to '72 the pin height changed to 1.74". That means that your pistons (if they are stock) should be .060 down in the hole?? That's .030 (my piston depth at 1.77") plus .030 more for the change in pin height in '71. The problem is that someone might have changed the piston is the last 50 years??? So check your piston depth at TDC, this will tell you how low you can get you combustion chamber CCs before your compression gets too high. I don't think, if you have stock pistons you could cut the heads enough to get in trouble because 318 "stock" piston sit too deep in the bore??

Treblig
 
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