CR Problem?

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Captainkirk

Captainkirk

Old School Mopar Warrior
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My engine guy called today.....Good News/Bad News. Seems the porting job on my J heads looks pretty good (good news). Bad news is, he checked the heads for cc volume and found them to be 67cc chambers........which gives me a 12.87:1 CR if I stick with the pistons I'm using. I'd like to, actually. This motor was a screamer before (and I know why now) and ran OK on 97 octane pump gas (leaded premium). I have access to 100 octane Avgas and could run it staight or blend it with 93 octane unleaded. Any reason why I shouldn't carry on with engine assembly?
I've already spent a boatload getting the crank, rods and pistons balanced, and bought the rings.......
This is not a daily driver, but rather, a "Saturday Night Special" car
 
LOL, If you don't mind the av-gas or race fuel to feed it, run baby run with it.
 
ive heard of thinner head gaskets. are there thicker ones? would lower the cr a bit
 
TRW's. The P/N stamped on top is L-2322

trws.jpg
 
Well, I looked up a picture of the top. If you flip the piston over, can you see a bump under the small dimple where the spark plug ends up? Or is it flat all the way accross to the valve releif humps under the dome? My first impression is to mill off the dome to eliminate that spark plug dimple. If you can knock 4-5ccs off that dome, you can drop the compression a point at least. Then you're into thicker head gaskets to get it lower than that. But with a big cam, you should be able to run that 97 no problem in an 11:1. I dont think you can in a 12.8:1. I have to run c-12 (110) in my 12.8 small chamber big block. It will create an overbalanced situation. It's not the best situation, but you could squeek by with no rebalance I think. You may want o weigh the piston after and see how much lighter it got. More than 20grams lost IMO means rebalance.
 
Captainkirk said:
My engine guy called today.....Good News/Bad News. Seems the porting job on my J heads looks pretty good (good news). Bad news is, he checked the heads for cc volume and found them to be 67cc chambers........which gives me a 12.87:1 CR if I stick with the pistons I'm using. I'd like to, actually. This motor was a screamer before (and I know why now) and ran OK on 97 octane pump gas (leaded premium). I have access to 100 octane Avgas and could run it staight or blend it with 93 octane unleaded. Any reason why I shouldn't carry on with engine assembly?
I've already spent a boatload getting the crank, rods and pistons balanced, and bought the rings.......
This is not a daily driver, but rather, a "Saturday Night Special" car
Click to expand...

What is the specs on your engine build? especially the dome CCs etc.

A thicker head gasket would seem to be in order as you have open chamber heads and with anything above 10.5CR I would be going with Cometic and they can make them in any thickness you need up to .125".
 
I would go the thicker head gasket route. Do you have E85 were you live? If you do I would leave compression as is and convert your fuel system to run that stuff. As soon as they bring E85 to my area I'm converting my drag car to street use. Being it is 85% alcohol it has about 105 octane and will also help keep your engine cooler.

Chuck
 
340mopar said:
I would go the thicker head gasket route. Do you have E85 were you live? If you do I would leave compression as is and convert your fuel system to run that stuff. As soon as they bring E85 to my area I'm converting my drag car to street use. Being it is 85% alcohol it has about 105 octane and will also help keep your engine cooler.

Chuck
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Will it have more or less power - just asking?
 
More! alcohol race cars make more power than gasoline cars do. It takes approximately twice as much alcohol as it does gasoline at 100% so you mileage will suffer. The reason it takes so much is because when alcohol burns it releases some of its own oxygen so it requires more fuel to counter act the lean condition. This is also why it is so popular with the anti-global warming community, more oxygen and less CO2.


Chuck
 
With the price of premium unleaded running in the 3.50 range here and race gas at 5.00, I would keep the compression and pay a few extra for race gas or 100LL fuel.

For an everyday driver type car then the priorities change and less compression would be a better choice.

Since it's a Saturday night type car... GO BIG!!! :headbang:
 
if you do not mind mixing your own fuel try this mix [i was in the fuel field for 30 plus years] 9 gal 100LL av gas,1 gal toluene from paint store and 6.6 gal of 92 oct unleaded the av gas by it self is too dry and the vapor pressure is off the toluene will help this and the 92 oct. gas will givew you the need additives this mix will net you a oct reading of 107.6 aand make the eng run like a rapped ape
 
crackedback said:
With the price of premium unleaded running in the 3.50 range here and race gas at 5.00, I would keep the compression and pay a few extra for race gas or 100LL fuel.

For an everyday driver type car then the priorities change and less compression would be a better choice.

Since it's a Saturday night type car... GO BIG!!! :headbang:
Click to expand...


If your race fuel has lead and you pay taxes in the on road stuff don't let the state find out you are running race fuel on the street. You would be breaking two laws.


Chuck
 
They were checking fuel here in Eastern Wa about a year or so ago and found a ton of it and the state thought they had something until they found out that most of the vehicles that tested positive were "farm" vehicles which are allowed to run dyed fuel even on the road. So they went away, I bet it was the GOV trying to get back at the east side of the state for not voting for her, the COW. If you voted for her, I mean nothing against you it's your right, but it is also my right and duty as a tax payer to call her a COW if I feel the need.

I wasn't saying don't run an "unapproved fuel" I could care less, Lord knows I may fracture a few laws here and there. I just wanted him to know it is illegal.


Chuck
 
Hey chuck was born in e-burg know about the eastern wa blues biggest part of the state with the smallest amout of people and pay the less taxes and get no respest now live on the coast same thing here
 
We swapped sides, I was born in tacoma and moved over here in 2001. I would not move back for anything in the world.

Chuck
 
340mopar said:
I would go the thicker head gasket route. Do you have E85 were you live? If you do I would leave compression as is and convert your fuel system to run that stuff. As soon as they bring E85 to my area I'm converting my drag car to street use. Being it is 85% alcohol it has about 105 octane and will also help keep your engine cooler.

Chuck
Click to expand...

Dammit Chuck!

That's was going to be my secret build! 12.5:1 408 stroker, roller cam, indy heads and E85 with the required fuel system changes.
 
ramcharger said:
Dammit Chuck!

That's was going to be my secret build! 12.5:1 408 stroker, roller cam, indy heads and E85 with the required fuel system changes.
Click to expand...


It's gonna be all good! Man I never thought I would say that about an environmentally friendly fuel. Crap I'm gonna be a tree hugger,LOL.


Chuck
 
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