engine build question

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Old Oct 19, 2009 | 10:54 AM
  #2  
78D200's Avatar
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From: Goffstown, NH
that is true because the valves are larger. You might even be able to get them enlarged some more and throw a decent size cam at it and pull some pretty good numbers.
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Old Oct 19, 2009 | 11:04 PM
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I dont want to throw a spanner into the works, and I'm new to mopars, but not hotrods, But I believe they flow better, but what about the chamber volume? Is it the same or would it drop or raise the compression ratio?

Last edited by scotts74birds; Oct 19, 2009 at 11:06 PM.
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Old Oct 20, 2009 | 03:28 AM
  #6  
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From: Goffstown, NH
I think that it would lower the compression ratio a little but not too much.
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Old Oct 21, 2009 | 03:52 PM
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67 GTX's Avatar
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definetly find out the cc's of your current heads, then of the 360 ones
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Old Oct 21, 2009 | 05:17 PM
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if you put 360 heads on a 318 the loss of compression will hurt performance more than the larger valves and runners will help. If the rest of the 318 is stock, i wouldn't put 360 heads on it. Milled heads will help, but new pistons with a better compression height is what would be needed to really make the combo work well.
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Old Oct 21, 2009 | 07:16 PM
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I think different year 318's had different compression so it would be best to work it out on paper first. 67 and 68 318's had more compression.
I personally ran a set of 360 heads on my 68 dodge pickup on the 318. It had the stock 2bbl 360 manifold and carb and a set of hedders. It ran real strong indeed. You could run the Keith Black 318 pistons to gain compression.
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Old Oct 22, 2009 | 03:45 PM
  #11  
rr69half6bbl's Avatar
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instead of the milling expenses. just use a thinner head gasket, it does the same thing and you `ll need to put new ones on it anyway. itll boost the conp. a little, the 360 heads dont have as much quench area as the 318`s do, so youll gain some comp. that way also.
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Old Oct 22, 2009 | 10:15 PM
  #12  
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From: Island Pond, Vermont
I'm in Germany and I feel your pain for getting parts over here. One thing to be careful of with the larger valves is you'll want to make sure they won't impact the top of the piston when they are open.

Last edited by crwchf16; Oct 22, 2009 at 10:19 PM. Reason: spelling
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Old Oct 24, 2009 | 12:36 AM
  #13  
blue 68 gts's Avatar
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I put J-heads on my 340.... and it ran better then stock 340 heads.... Just thought I'd throw that in...
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Old Oct 25, 2009 | 06:32 PM
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blue 68 gts's Avatar
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J-heads were heads that came on 318's in certain years...
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Old Oct 25, 2009 | 09:07 PM
  #16  
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From: Springfield NE
Actually, the "J" heads were factory heads used on 360 engines.
They have a letter "J" cast into them in the area of the sparkplug location.
{there were heads that had an "O" cast into them also.} Mostly the "J" heads were associated with the 360 engine of the 70's. Some had the 2.02 intake valve but most were 1.88 intake sized. They replaced the "X" heads for the 340 in '73, {last year for the 340}. They pretty much had the same size ports as the X but usually had the smaller valve and were intended for lower rpm operation, thus the valvesprings were not up to par with the 340's in comparison. I am not actually sure but I believe they were made from '72 to about '79. They might have been used on the 318 for the 4 bbl equipped 318's in '79 {'78?}
I believe they would work good on a 318 as long as you could keep the compression above 9 to 1 (+/-). {8.5 to 1 at minimum}
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Old Oct 27, 2009 | 06:32 AM
  #18  
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Originally Posted by theomahamoparguy
Actually, the "J" heads were factory heads used on 360 engines.
They have a letter "J" cast into them in the area of the sparkplug location.
{there were heads that had an "O" cast into them also.} Mostly the "J" heads were associated with the 360 engine of the 70's. Some had the 2.02 intake valve but most were 1.88 intake sized. They replaced the "X" heads for the 340 in '73, {last year for the 340}. They pretty much had the same size ports as the X but usually had the smaller valve and were intended for lower rpm operation, thus the valvesprings were not up to par with the 340's in comparison. I am not actually sure but I believe they were made from '72 to about '79. They might have been used on the 318 for the 4 bbl equipped 318's in '79 {'78?}
I believe they would work good on a 318 as long as you could keep the compression above 9 to 1 (+/-). {8.5 to 1 at minimum}
Good man Omaha.
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