Its been a year since I tore down a 1969 318 2 bbl. I can't remember how far the slugs were in the hole. For some reason .030 is sticking in my mind. Does anyone know for SURE?,thanks
How far in the hole?
- Thread starter Dana
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So I did some math. The average cc of a 675 casting is about 64cc. 5cc gasket with the flattop, an advertised compression of 9.2:1 puts the piston .058 in the hole., sounds reasonable
71beater
Well-Known Member
You don't think the advertised compression is what it's actually hitting, do you?
I'd bet they're .060"or more in the hole.
Off the top of my head I don't remember, but 318s are typically like .080" down the hole, and even the earlier pistons are only like .015" taller, IIRC.
I'm sure someone with better memory, or better versed on this will confirm.
I'd bet they're .060"or more in the hole.
Off the top of my head I don't remember, but 318s are typically like .080" down the hole, and even the earlier pistons are only like .015" taller, IIRC.
I'm sure someone with better memory, or better versed on this will confirm.
Well, I reckon I,all get off my lazy a$% and mock it up and check it. Thanks for the info
mderoy340
Well-Known Member
I recently checked a 68 318 and it measured .060 in the hole
DaveBonds
Garage Trash
.075" was what I had on a '73 318. .060" sounds correct to me.
Also, 64cc seems to me to be on the small side. Most castings hit 67-72cc, depending on the valves that are in it.
I checked my closed heart chamber 302s with open faced valves and they hit 62cc. They advertise 59cc with closed valves, I'm guessing they come in somewhere between 60 and 61.
If you are looking for more squeeze, get a machinist straight edge, check the block and heads with a feeler gauge against it and if it's nice, go with a pair of 1121G Mr.Gasket .028" compressed and hit the bolts with 95ft lbs.
That will get you closer to your figures by .030"-.032" ish, if your pistons are, in fact, down around .060"
I'd still be skeptical of the CC. Easy to check, though, with a piece of plexi, white grease, alcohol and water mix with some food coloring and a 100 mL / cc syringe.
Also, 64cc seems to me to be on the small side. Most castings hit 67-72cc, depending on the valves that are in it.
I checked my closed heart chamber 302s with open faced valves and they hit 62cc. They advertise 59cc with closed valves, I'm guessing they come in somewhere between 60 and 61.
If you are looking for more squeeze, get a machinist straight edge, check the block and heads with a feeler gauge against it and if it's nice, go with a pair of 1121G Mr.Gasket .028" compressed and hit the bolts with 95ft lbs.
That will get you closer to your figures by .030"-.032" ish, if your pistons are, in fact, down around .060"
I'd still be skeptical of the CC. Easy to check, though, with a piece of plexi, white grease, alcohol and water mix with some food coloring and a 100 mL / cc syringe.
Saetun
Sinister Swinger
Pistons on my 318 we down .070", I went with the 302 heads & .028" gaskets as well.
How does it run? What kind of milage?
Treblig
Well-Known Member
When I pulled my original '69 318 cuda heads my pistons measured .039 down in the hole. In the original '69 Service Manual it states that the '69 318 came with 9.2 to 1 comp ratio. I also have a '73 318 and the pistons on that engine are .100 in the hole. After 1969 the compression on most vehicles dropped dramatically. If you have original pistons you should have high compression unless somebody changed the heads. I pulled my original heads to install some 302 casting heads and also install mag truck manifold on passenger's side with 340 manifold on driver's side. I really didn't notice very much difference in performance. So now I'm going to install a 2004R with 4:10 gears...that should wake it up!!:burnout:
Treblig
Treblig
DaveBonds
Garage Trash
They also used metal shim gaskets that were super thin from the factory.
I've measured 9.65:1 with known 62cc heads and pistons that sit .011" in the hole, on ring lands that sit higher than stock, with .028" gaskets. Those 1121Gs are 4.140" diameter.
I think you could fetch close to 9:1 with the right gaskets and heads on a stock, early 318 bottom end.
Advance the cam to fetch more overall cyl pressure.
PSI is what everything accumulates to. PSI = power.
I've measured 9.65:1 with known 62cc heads and pistons that sit .011" in the hole, on ring lands that sit higher than stock, with .028" gaskets. Those 1121Gs are 4.140" diameter.
I think you could fetch close to 9:1 with the right gaskets and heads on a stock, early 318 bottom end.
Advance the cam to fetch more overall cyl pressure.
PSI is what everything accumulates to. PSI = power.
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