Mystic_350

Using a calculator from race-cars.net I calculated that my compression ratio would end up being 12.2. That seems awfully high, anyone else running anything that high?

Perhaps I made a mistake on the calculation? I'm running a stock bottom end with a set of LE2s that were milled .030 using a set of Victor Reinz 5898 gaskets (.029).

Thanks,
Chris

Injuneer

What are the rest of the numbers you used to calculate the static CR? How big a cam are you going to run - that will affect the dynamic CR, which is what determines octane requirement.

96capricemgr

You would need to mill the heads a heck of a lot more to get that compression on a stock shortblock, you input somethingS wrong.
For one the Victor gasket is .026 but that would have made the number higher.
I am going to guess you gave it a zero deck height or got the "+" "-" wrong on the piston volume.
It is probably in the low 11s for compression, that is about average for that gasket with milled heads on a stock shortblock.

Mystic_350

Hey Fred, I used stock numbers (4" bore and 3.48" stroke IIRC) and I am pretty sure I used 53cc for the CC. I can cc them to get an actual number, but I haven't yet. I know that can have an affect on the static CR, but being that the chamber is not going to be too much different (smaller if anything?) I was ok ball parking it... that is until I saw the 12.2.

I'm guessing the calculator is wrong or I fat-fingered something. I was looking for a low 11 number. Now that I'm thinking about it, I didn't take into consideration how far the stock bottom end has the piston in the hole at TDC. I will go back and check to see if there is any place to include that in the calculation.

Also, I'm still running the LT4 hotcam I have been running for years. Just putting a new top end on it!

Chris

Injuneer

As Dwayne mentioned, what did you use for the deck height (= piston in hole) and what did you use for the piston valve reliefs?

Mystic_350

Clearly I'm messing something up...

I used -5 for the piston valve relief, and I used .020 and I ended up with 11.7 which still seems high.

I'm not overly concerned with the exact CR at the moment, I'll run 93 octane no matter what. I just wanted to make sure I wouldn't have any issues with crazy high CR (or detonation). Upon further review, the VR 5898 gaskets I picked with the heads milled .030 will get me a nice pickup in CR and HP without any risk.

I'm consumed now with an oil pan gasket replacement that I'm not looking forward to!

Thanks again guys,
Chris

Bersaglieri

I got about 11.60 with what you've given, [assuming .020 in the hole, 53cc chambers, and 5cc reliefs]. Add 3cc to the heads [56cc] and you're down to 11.1ish so, cc'ing the combustion chambers can make a 1/2 point difference.

I used wallace: Wallace Racing - Automotive Calculators "Compression Ratio".

Nice to see a decent thread in the advanced tech...been a while.

-Dustin-