Define "stock heads". Which ones? Are you gonna try to find some 302 or magnum heads, or are you gonna run the 318 LA heads? It will make a difference.
Why are 318's low HP and torque?
- Thread starter Chryslerkid
- Start date
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Chryslerkid
Well-Known Member
They're stock 318 LA heads 646 is the last three on the casting numbers. No 302's.
Ok. Have you got the cam yet?
Ok, if you have not gotten the cam yet, go with this.
http://www.summitracing.com/parts/SUM-K50052/
I was thinking you were gonna try to get compression up by using different heads. My apologies. We have more than a few 318 build threads goin and I may have gotten them mixed up. The Crane number is a little big for stock compression in a 318. That summit cam is a good one. If I am not mistaken, Crane actually still grinds the Summit cams.
http://www.summitracing.com/parts/SUM-K50052/
I was thinking you were gonna try to get compression up by using different heads. My apologies. We have more than a few 318 build threads goin and I may have gotten them mixed up. The Crane number is a little big for stock compression in a 318. That summit cam is a good one. If I am not mistaken, Crane actually still grinds the Summit cams.
Chryslerkid
Well-Known Member
I have not purchased the cam yet. I'll look into the tamer one first. Thanks.
If I do get the 302 heads, then I'll want the previous one as specified earlier in this thread right? I'm still looking for some 302's which will dictate where I go with the cam....
Thanks.
If I do get the 302 heads, then I'll want the previous one as specified earlier in this thread right? I'm still looking for some 302's which will dictate where I go with the cam....
Thanks.
Yes, if you get the compression up some, that Crane number would be a very nice one.
Chryslerkid
Well-Known Member
I'm on the hunt for those 302's we'll see if I get lucky. Thanks for the help!
Would you be able to guestimate the HP and tq with and without the 302 heads to give me an idea of what I'm looking to make?
Would you be able to guestimate the HP and tq with and without the 302 heads to give me an idea of what I'm looking to make?
If you run the thin head gaskets and clean the regular 318 heads up with maybe a .025" cut, it MIGHT see 300 HP with headers and a hot distributor curve. Chances are...probably not, but it might. If you can get the 302s and get compression close to or a HAIR over 9:1, 325 or more with that Crane grind. But be careful gettin compression that high with no quench. You don't want to go much higher than that.
Chryslerkid
Well-Known Member
Hmmm. Okay I gotcha. I'm going to definitely want those 302's then. I'll keep it moving. Thanks guys.
Any quick tips for me about what kind of gaskets to use for my headers? I don't want them to leak the first time around. Also, can I grind the head flanges down to make the surface flat without damaging the header?
Any quick tips for me about what kind of gaskets to use for my headers? I don't want them to leak the first time around. Also, can I grind the head flanges down to make the surface flat without damaging the header?
Chances ar enot good your pistons are only .080 in the hole. That would mean the engine would have had to have been rebuild and aftermarket pistons with a 1.741" compression height installed. Possible, but not probable. The stock height is 1.720. So that means the piston is in the hole probably .101".
Don't get discouraged. Just get the compression the best you can. Plenty of 300 plus 8.5:1 motors out there.
Yup they sure do. I think 5cc is a little big on the piston volume though. It's probably more like 2. THose are some small valve reliefs. The big reliefs or trough in the KB pistons is usually like 5 or 6 ccs. That'll help a little right there. A little.
Chryslerkid I wouldn't get to caught up on compression from what I understand the rule of thumb for CR is for every point of CR is +\- is 4% Hp. So let's say you take a dead stock 150hp 2 barrel 318 with 8:1 CR and bump it up to 13:1 CR that's 5 points increase of CR which is 20% increase of hp which would be 30hp increase which a high flow exhaust could easily accomplish. Now let's say you got a 300hp 9:1 318 going one point up or down would only increase or decrease your power 12hp (4%) so 8:1 288hp and 10:1 312hp. Higher compression makes hp through more efficient use of fuel & air but the path to more hp is more fuel & air per rpm. Air flow in and out of the engine is gonna make more power per dollar than compression especially on a medium performance engine. As long you got over the minimum amount of CR for your cam choice and not over the amount of CR for your fuel requirement it's more wise to spend your money elsewhere. Also if you never intend to rebuild the bottom end then mill away but the heads will only be good for a low CR short block if you wish to install KB's later it will raise the CR too much so the heads will become a One Trick Pony.
Coronet 500
Well-Known Member
318 Compression (Pin) Heights as per Mopar Performance.
1967= 1.75"
1968-69= 1.77"
1970-72= 1.74"
1973-84= 1.74"
1985-87= 1.76"
1988-91= 1.76"
1967= 1.75"
1968-69= 1.77"
1970-72= 1.74"
1973-84= 1.74"
1985-87= 1.76"
1988-91= 1.76"
I don't trust those numbers with a ten foot pole. I've torn down too many and actually measured them. 1.720 is the number I've the most of. The best and only thing to do is take measurements and blueprint your compression ratio. That's really the only way. Anything else is only a guess.
Coronet 500
Well-Known Member
As a reference my original 1970 is 1.742"
Chryslerkid
Well-Known Member
Alright. I am seriously considering tearing into my '87 318 block and rebuilding the entire engine in my garage. IF... I do this, I'm doing it right! So I am buying KB pistons, J heads, radical cam.... Will I need a different crankshaft? If so what are the cranks y'all use? I'm going to make some power out of this 318 while it's out of my car. This is the time to do it. What are your ideas guys. I am ready to order all the parts and send the block to the machine shop.
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