I'm after comppression, so how many thousands can you cut a J head? safely.
How much can you cut off a J head
- Thread starter SGBARRACUDA
- Start date
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AdamR
Big Member
The Js that were on my old 340 had about .060" shaved off them. Thats good for a half point in compression.
a friend bought a 360 that had .100 shaved and we had to machine valve reliefs deeper in pistons ,best compression gains are from zero decking block
plus you get more turbulence in combustion chamber and reduces chance
of pre-ignition -ken
My engine has dish pistons and agter i tear it down I'll cc the piston, chambers and such to find out where I'm at. But i think I'll whind up putting flat tops in it.
I finally got to the the engine and tore it down. The motor has a strangs piston that maybe someone here can ID. It is a 0.30 over flat top that is .028 down in the hole, but it has a raised part or tiny dome on the top that is .042 above the deck? I attached a photo. I also found out it was a balnced bottom end with 0.10/ 0.10 cast crank, Windage tray ,HV oil pump. Bearings and cylinders look great ( It ran great in the car, just didn't have much balls) so I will be using the short block as is. I was going to cc the heads but havn't yet. They are 2.02 J heads so I would guess the cc at 68- 70. The man that built or had this motor built, passed away so, this is the first time I know for sure what was in it. Here are some of the details, I'm looking to get 9-9.5 compression Maybe cutting the heads. Let me know what you all think. This is a 69 Dart 727 auto wiht a factory high stall convertor, and a 3.21 sg rear. just a cruiser not a racer, Oh and it wil have CPPA headers and 2 1/2 thru Magnaflow mufflers.
Some facts
4.030 bore
.028 in hole but the top portion is .042 positive
cam was installed at 112 degres, I checked it
Hughes HE2430 AL cam
Felpro 8553 PT gaskets
Gasket ID 4.195
compessed thickness .050
The lower end was ballanced, I can see the rod caps ground on and the piston bottoms with drilled holes and the crank throws have extra drill marks.
This what I'm after, A little more muscle to my muscle car, though this engine ran great, sounded great. It just doesn't make decent power. Leaving the short block alone since it is a good foundation What kind of mods do you think I should do. And WHAT KIND OF PISTONS ARE THESE?
Thanks for your time and suggestions.
Some facts
4.030 bore
.028 in hole but the top portion is .042 positive
cam was installed at 112 degres, I checked it
Hughes HE2430 AL cam
Felpro 8553 PT gaskets
Gasket ID 4.195
compessed thickness .050
The lower end was ballanced, I can see the rod caps ground on and the piston bottoms with drilled holes and the crank throws have extra drill marks.
This what I'm after, A little more muscle to my muscle car, though this engine ran great, sounded great. It just doesn't make decent power. Leaving the short block alone since it is a good foundation What kind of mods do you think I should do. And WHAT KIND OF PISTONS ARE THESE?
Thanks for your time and suggestions.
fishy68
Tyr Fryr's Inc.
Did you look the pistons over to see if their is a mfg stamp or number on them? If their aftermarket they usually are marked. I've seen some KB pistons look like that. Look for a number then check out KB's site.
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