Comp Ratio someone confirm my numbers please

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StrokerScamp said:
Sorry, but this is incorrect. Look at this calculator.

http://www.kb-silvolite.com/calc.php?action=piston

See where it says "Note: A piston with a positive number is either a flat-top with valve reliefs or a dish. A piston with a negative number is a pop-up."

The reason for this is because of what I stated the first time. A domed piston has a negative cc measurement since it takes away from the combustion area. A flat or dished piston has a positive number because it adds to the combustion area. It's just that simple.
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If you read my entire post you would have seen where i said to enter the number the way the calculator tells you too. The one I use states to enter a dish or valve reliefs as a negative number. It's just matter of how the formula in the program is constructed. One isn't correct and one wrong as long as they give you the correct answer.
 
dgc333 said:
If you read my entire post you would have seen where i said to enter the number the way the calculator tells you too. The one I use states to enter a dish or valve reliefs as a negative number. It's just matter of how the formula in the program is constructed. One isn't correct and one wrong as long as they give you the correct answer.
Click to expand...


I understand that......and I wasn't tryin to argue....what I was trying to figure out is, if the two ways are BOTH correct, why are they coming up with two entierly different compression ratios? I guess I shouldda included all that, too. LOL sorry bout that. SUMTHIN has gotta be wrong somewhere. whether it's the caulculator, us humans enterin info backwards or sumthin.
 
Dustedu2 said:
So, if I run felpro 1008 .039 gasket deck at .010 that should put me at 11.2:1 and a quench at .049 correct? oh yeah, there is a very slight dish.
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NO INCORRECT. You said you have heads with a full cut chamber that is .060" deep. THEREFORE YOU CANNOT HAVE ANY USABLE QUENCH EFFECT WITH ANY GASKET.
I capitalized because you seem to be looking past that fact. You have to cut the heads to get the quench area or the chamber to have any effect, and that will put your chamber size down to 59ccs...
 
StrokerScamp said:
....and on the AV gas, it's not a good idea to run AV gas in an automotive engine. They have a lot of different addives and such to deal with altitude and other things that don't work well in automotive engines. It also lacks some of the lubricants that automotive fuel has. AV gas can have a tendancy to run leaner because of this.

http://www.rockettbrand.com/techsupport/documents/TechBulletins/RacingGasolineVsAviationGas.pdf
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Huh, I never had a problem, I also wasn't at 8-10g rpm nor 10,000ft... Maybe the Avgas was different 10 years ago.....

I guess if you want to be safe, just mix some VP or equal race gas to your mix of 93octane. I am lucky enough to have a gas station down the street from me that has pump VP 100 and a Suzuki bike shop that has 110 and 112 in those gigantic drums With the hand pump
 
Av gas has always been less dense than automotive gas. It's not something that's changed recently. As such, it runs much leaner than automotive fuels. Been a known constant for as long as I can remember to NOT run av gas in cars.
 
I would be running a bigger cam that closes the intake valve latter to bleed off cylinder pressure.
I would think that the cam you chose would be used with no more then 10.5 to 1 max.
If you have the converter and gear for it,run a bigger cam @ 50.
Make sure you are positive about what the compression will be.
You could cc the heads to make sure that they are correct.
 
StrokerScamp said:
I understand that......and I wasn't tryin to argue....what I was trying to figure out is, if the two ways are BOTH correct, why are they coming up with two entierly different compression ratios? I guess I shouldda included all that, too. LOL sorry bout that. SUMTHIN has gotta be wrong somewhere. whether it's the caulculator, us humans enterin info backwards or sumthin.
Click to expand...

Don't know why the two calculators are constructed that way. The one I used (http://www.csgnetwork.com/compcalc.html) could have been as simple as a dome is plus because it adds materials to the piston where a dish is negative because it subtracts material. Where the KB calculator is looking at it from the cylinder standpoint; a dome is negative because it subtracts chamber volume where a dish is positive because it adds to the chamber volume.

To write the formulas either way is a simple algebra manipulation. Remember (+3) times (+2) = (+6) and (-3) times (-2) = (+6). So just have the right signs in the equation in the right place will make either give you the correct answer.

If you understand what you are calculating and the calcultor does not state how to enter numbers you will knwo from looking at them which is correct.

For anyone that is so inclined to calculate their cpompression ratio withou the aid of a program here is the formula.
 

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