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#1
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I recently put some swirl port heads on my 318.... From what i head they were susposed to make a huge difference copared to my old heads but they didn't. My old heads i think were a 375 casting number (if I looked at the right number) Are these heads better or just as good as the swirl ports? Also my friend has a set of 360 heads sitting there, i was thinking of pulling my swirl ports off and trying those, Allthough they would bring my compression down a little bit, would they make a difference (they have the bigger valves)
Thanks.... 318SS |
#2
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318SS. What year 318 do you have?
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#3
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Here's the only empirical info I can offer. When I did some mods to my 318 way back I intially took the stock heads and milled them to raise the compression. That made a noticeable difference, especially obvious at the higher RPM. Switching to a set of 360 heads was about the same. However, once I put on a set of 915J heads (2.02/1.60) the difference was pretty amazing. I mean you could obviously tell the engine would rev up faster, and pull stronger to higher RPM.
Now..most of the folks will tell you the bigger head will hurt peformance on a 318...I'm not so sure, maybe I just had a good combo on that car, the cam wasn't stock anymore either, etc. If you're going after low end grunt stick with the 308s, if you want higher up power go for the 360 heads. |
#4
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I'm not sure what year my block is but I know its around an 83, I got the block from a friend and freshend it up abit. I put a 4bbl intake (from a 340 or 360), the edelbrock 600cfm carb, hi vol oil pump, double roller timing chain and my cam is a sum-k6901 218-228 duration @.050 and 441 lift. The old heads were 375's i believe and i just replaced them with the 308's. I have a 727 tranny with 3.21 gears (posi) I have all of this in my half ton. It goes pretty good but with the 308s but didn't knotice any change (still a dog off the line) Once it hits about 2500 it revs up pretty good and makes all its power up there.
I smoked my buddies 91 chev short box the other night, hes got a efi 350 in it. |
#5
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318SS,sounds like you have the open chamber heads, you need to mill them a bit and I bet you can get some serious improvement. Also check your ignition timing and advance. WIth lower compression the 318 likes a lot of advance, around 12 btdc at idle on my 79 318 is about perfect. Plenty of bottom end and good acceleration on the top. Even though your heads were swirlport 360 heads, they still have larger combustion chambers and therefore lower your compression. Good luck and let us know what works. cruzerjd
[This message has been edited by cruzerjd (edited June 20, 2000).] |
#6
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on a 318 the 302 closed chamber swirl port would have shown more improvement and the 308 is a 360 head,if you decide not to use the 308 casting head let me know,I have got a use for them on a 400 cube small block.
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#7
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308 is a 360 head?? I got them off a 1988 318 (TBI) Hmm weird huh Any way cruzerjd which are the open chamber? The heads i used to have on my engine (the 375's)?? If I milled those how much should I go?
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#8
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The 308 heads are just great for a 318, but are better suited for engines with a slightly bigger cams than yours. I think your main problem now is the low compression ratio. I just built a '83 318, and measured the compression ratio of a stock engine. It was 7.8:1. With the open chamber 308 heads and possibly .040" thick composite gasket you are in the low 7's. It's so much that you can't get it up enough through milling. My suggestion is that you try to find the 302 heads, they have a heart shaped closed chamber which is about 10 cc less than the 308 chamber. They also have smaller ports for better velocity; with 360 size valves and the bowls ported these are absolutely the best performance heads for a street 318 that makes its peak power at around 5000-5500 rpm. Even with the 302's you are down with the CR, some milling and the MP thin gaskets would help. The best solution would be milling the block, since you get more cc's out of each .010" milled. And because the pistons are about .090" in the hole in a stock 318, milling .060" and the thin gasket would get you a nice quench area. Be sure to measure everything when it comes to CR and aim at about 9.5:1, not more.
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#9
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I'm sorry everyone, I wasn't paying to close attention to that casting number.... The heads that i have one my engine right now are the 302's I should have caught before but it didn't click in until reading DartGT66's (explaining the 302's)
So sorry again... 318ss |
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