smallblockGT
Well-Known Member
Is there a decent moderately priced piston with enough height to bring a 318's compression up to say 9:1 to save some machine work? Hyper or regular ole' cast either one? Thanx guys
318 compression
- Thread starter smallblockGT
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Treblig
Well-Known Member
My stock '69 318 Barracuda came with 9:1 compression from the factory. So all you should have to do is buy some stock '69 318 pistons. Your engine must have heads that go with that compression. I still have my original '69 heads sitting on the shelf because I put 302 casting heads on my engine. Most 318s have pistons that sit .070 to .100 down in the hole. My engines stock pistons were only .035 down in the hole. This is the tallest stock piston they used in 318s as far as I know!!!.
treblig
skrews
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omahamoparguy
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what I did was to use 5.2 magnum pistons (melling brand) and even with 360 heads shaved .030 I ended up at 8.9 to 1 (more or less) on a 318. it runs real good even with the mid 80's 360 heads. fel pro gaskets I think
omahamoparguy
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also used chevy valves without the tulip, that raised the compression a little.
smallblockGT
Well-Known Member
Thanks Treblig I'll definitely start looking I appreciate the link for the KB's, but that's out at least for now. I'm just trying to get this thing together on the cheap utilizing as much of the stuff I already have as possible. I just want to drive the dart again so that means the 318/727 route. The block is in great shape requiring little machine work, I'm just trying to squeeze a little more out of it on the cheap
Keep in in mind different piston weights will require balancing the bottom end, and costs on average about $250.00
smallblockGT
Well-Known Member
Already planning on a Balance job
OldmanRick
Well-Known Member
My opinion.....if you're going to balance, just spend the few bills and go here...^^^^^^.
P.S. Treblig's .035 down is like winning the lottery on most of these engines. You need to find out how deep yours are and decide whether to go with a cheap cast replacement, if you can live with it, or go with the KB's. If it's just a driver with low rpm's, the replacement slug's "may" save you the balance cost's?
OldmanRick
Well-Known Member
Not to be a pest 
, but if you decide to go the stock piston/low compression route, use a cam in the 205*/215* range @.050, cut on a 110/112 LSA with some lift.....and you can still have a strong runner up thru the 5000+ rpm range.
, but if you decide to go the stock piston/low compression route, use a cam in the 205*/215* range @.050, cut on a 110/112 LSA with some lift.....and you can still have a strong runner up thru the 5000+ rpm range.smallblockGT
Well-Known Member
Not being a pest at all rick, I came here for input! Also hearing about the 69, I wonder about my motor. It was already torn down when I got it, but it came from my uncle so I know it's legit. I remember him pulling it from a diplomat cop car. It came factory with a windage tray, Molly rings, and heads that my casting book calls out as 318 hipo heads( cast in 360). Is there maybe a chance it was a higher compression motor?? Was that an offering on cop cars? Keep in mind I'm at work right now and can't get any casting #'s until maybe tomorrow.
OldmanRick
Well-Known Member
The later cop engine may very well be closer to the specs then earlier engines. Sounds real nice and with those heads.....308's?.....might be a great build for a LA 318.
75DartSE
Well-Known Member
My 75 318 is .030 over with cast replacement pistons from way back. They are .060 in the hole. I'm using cometic .027 gaskets cause they are the thinnest I can find but pricey. My engine quest magnum heads have 62cc chambers. From what I can figure it's around 9.3:1.
2 Darts
A-body Addicted
Bear with me on this.
Casting 4323345 83-86 police car head 1.88I/1.60E 75.1cc
Casting 4323302 83-86 fast burn 1/78I/1.50E 62.6cc
Depth from block surface 67-69 0.036 / 72-86 0.056
My Demon has a 68 block & pistons with 302 heads. For a street car, I have no complaints. To do this on the cheap, may I suggest the 67-69 piston & 302 heads hogged out to accept the 1.88I.1.60E valves. While the heads are being machined, suggest a mild port and a 3-angle valve job.
Casting 4323345 83-86 police car head 1.88I/1.60E 75.1cc
Casting 4323302 83-86 fast burn 1/78I/1.50E 62.6cc
Depth from block surface 67-69 0.036 / 72-86 0.056
My Demon has a 68 block & pistons with 302 heads. For a street car, I have no complaints. To do this on the cheap, may I suggest the 67-69 piston & 302 heads hogged out to accept the 1.88I.1.60E valves. While the heads are being machined, suggest a mild port and a 3-angle valve job.
smallblockGT
Well-Known Member
Like I said I can't remember the casting# and not where I can check right now but the 75cc sounds like mine. I know they're open chamber. Was really hoping to come up with some 308s for it anyway. Speaking of.... I've got the cop car heads and a set of small valve J's. I'd trade both sets straight across for a set if anyone has em to spare. LOL. Both sets are dirty in "as pulled" condition.
If you use a 10.5 piston for a 318, then put some 340/360 heads on it, you will end up at 9.2 compression and will be able to use pump gas. I've done it.
smallblockGT
Well-Known Member
Ok made it out to garage today. My heads are actually #4027596 (81-83 hipo heads). My book just gives a range on combustion chambers for these, 66-72.5cc. Block #s are 4104230-318-2, I have two sets of rods 3418645 and 2899469. Are one of these more desireable than the other, also did mopar number the rods at the factory? Pistons that were pulled appear to be 1.755 comp height. So do I have more here than I thought or should I look for some fast burn heads? Again 9:1 is my magic number with affordable pistons and little machine work as possible. Thanx for all tour help and input guys. FABO rocks.
Valvebounce
Well-Known Member
Sorry to jack this thread, but did the small end of the LA rods fit inside the magnum slugs? (width wise)
And are they Hypers?
2 Darts
A-body Addicted
My book shows 66cc chambers on the 596. This is a late (77-86) 360 head so it should have hardened valve seats.
The 3418645 casting is an HD 74-86 pressed pin 318 rod. (74-86)
How about 2899496 for the other set of rods. These were HD rods with a floating pin.
To make these rods work without balancing, a 72 or later 318 crankshaft will need to be used. A 72 or later stock piston should be used, too. I prefer the floating pin as I don't need a press to assemble pistons and rods. I'm not crazy about the 72-86 spec piston as it sits .056 in the block. This is better than the 70-71 which sits .060, but not as good as the 67-69 at .036.
The balance issue is also why I went with the '68 spec reciprocating assembly (Light duty rods, & crank with appropriately weighted pistons) and 302 heads. It seems to me if a 9:1 compression ratio is a must, the KBs seem to be the way to go. Make certain of the crank and rod castings so that you get a piston weight that won't cause you to shell out for balancing.
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