Jeep Strokers

Hello all,

I just got my block back from the machine shop, and I'm trying to pick a head gasket.
I used the compression ratio calculator and the results seemed low (9.09:1), so i followed Flash's calculations in the FAQ section and got 9.19:1.
Please look this over and let me know if you think this will work for 87 pump gas.

My parts are as follows:
Scat 4.0 rods
Russ's pistons; 0.60" over dished 28cc
Scat 4.2 crank
Russ's modified 232 Comp Cam with the .435/.448 lift
The block has not been decked, and the pistons are 0.003 out of the hole as is.
The shop also gave me a good deal on an Edelbrock head that has been set up for my cam.

So the math following Flash's post and using a 0.051 gasket (for a 0.048 quench):

.7854 X Bore 3.935 X Bore 3.935 X stroke 3.895=46.41 Cubic Inches X 16.387, =760.52364cc
Head volume ..........................................................55.00cc (according to Edelbrock)
Head gasket(.051")....................................................10.45cc
CC from flat top of piston and deck suffice (-.003) ................-0.59cc
Piston dish............................................................28.00cc
Total...................................................................92.86cc

760.52(stroke volume)+92.86=853.38 Divided by volume above piston (92.86)= 9.19:1

What are your thought? It seems like it wouldn't be worth it to have anything decked off, right?

Thanks for the help!
-Mike

Almost correct but nevertheless you should have no problem running 87 octane gas.
I have displacement at 4657cc (776.2cc per cylinder) and the SCR at 9.36:1.
A 0.043" head gasket would have worked slightly better for you (0.040" quench, 9.50:1 SCR) but the difference is too small to be of any concern.

I haven't bought a gasket yet, so if I can find a .043, should I get it? Or is it worth decking the block some so I can get the quench down on the .051?

Thanks,
Mike

Hi Mike,

Regardless of what cylinder head you run you'll want to use a .043 gasket if you don't deck your block.

Your original plan was to run a factory OEM cast-iron HO Head. Your numbers with a .043 gasket 9.5:1 static compression ratio looks to be correct. Unfortunately that's going to be too low for an aluminum cylinder head.
A 19cc Piston will give you another compression point. That's where you'll need to be at.

Also if you're going to run an upgraded valve spring with the Edelbrock head there's a better camshaft choice that I'd recommend.

Shoot me a call/email. I would be happy to exchange parts if that helps

Russ

Hey Russ,

Your right, the edelbrock head was a last minute choice. My local shop offered me a deal on it that I thought was too good to pass, but it might be working against me now. I'll give you a call and see if anything can be done, but I think I'm stuck with the pistons since I had my rotating assembly balanced.

-Mike

I'm curious Russ; is it that you are missing out on power with the aluminum head if you don't up the compression, or will you actually make less power at the same compression compared to an iron head?

SkylinesSuck wrote:I'm curious Russ; is it that you are missing out on power with the aluminum head if you don't up the compression, or will you actually make less power at the same compression compared to an iron head?

Good questions Chris,

Probably too strong of a statement to say it would lose power. After all it's intended as a replacement cylinder head. At 55cc's the Edelbrock head is 2 to 3 tenths smaller than a typical cast-iron HO Head, but still isn't where it needs it be for a static compression ratio in a normally aspirated application