Hey, I have a question about using a compression ratio calculator. First off some specifics on my car. As far as I know it has stock pistons with valve reliefs, 1990 L98. I replaced the heads with some built 416 heads with 58 cc combustion chambers and am using .028 head gaskets.

This is the calculator I used: http://www.campbellenterprises.com/R...o%20calculator

And these are the numbers I used:

Bore 4.00"
Stroke 3.48"
Head 58.00cc
Gasket thickness 0.028"
Deck height 0.025" (really no idea what to put here)
Valve pocket -5cc
Cylinders 8

Results:

Displacement: 349.85
Compression ration: 10.69:1

That comp. ration look about right? I didn't expect it to be quite that high.

 

Yea I showed it as 10.6:1 as well.
-are you sure stock 1990 pistons are 5cc flat tops?
- You didn't do any work to the 416 heads at all? (why are you using them then, they aren't as good as your stock L98 heads, stock for stock...)
-no chamber work or ---hint hint--- larger valves in the 416 heads?

 

The heads were redone with bigger valves etc, but then shaved down to get back to 58cc's.

I'm not sure about the pistons all I know is that when I had the heads off they had valve reliefs.

 

Ah, then nope, that's probably it.
How's it run? Probably pretty hot, but the knock retard is probably coming on fairly often?

 

I don't have the car running yet, soon I hope.

Waiting on a set of pushrods from summit. Once they get here I will have just about everything to get it back together.

If you click on my cardomain link in my sig it shows what state the car is in, info on the heads is on the last page.

 

The bore size of the head gasket is always larger than the cylinder bore.
4.166" typical for a 350 composite gasket.

Your online cr calc does not allow for this input for the calc so the resulting cr is a little higher.

when you account for the larger gasket bore the cr will be 10.63:1 based on your other inputs.
I use this online cr calc
http://www.wheelspin.net/calc/calc2.html

 

I'm guessing with this comp. ratio the stock starter wont cut it?

 

Probably will for a little while. Mine had 10:1 and started over like a brand new car. Ran that way for a few summers, figured i'd replace it while the engine was out ( still works fine...)