Anyone knows how to determine what compression ratio your motor has?
Since race gas is only recommended for high compression engines, is there an easy way to find out? That way I don't waste my money on expensive gas.
Full Version: Compression Ratios
Yep... you need a compression tester. It screws into the spark plug hole, then you crank/kick the engine over numerous times with the throttle held wide open.
I think sandpusher is asking if you check compression on a two stroke the same way you would do it on a four stroke. And if that isn't why asked, I want to know. 
i belive he said "compression RATIO" which could be IE 10to1 9.5to1 13.5 to1 and so on not the compression pressure 13.5to1 meaning it can pack 13.5 cf of air fuel mix into 1cf i probablt got the measurement "cf" wrong but right now i just cant remember
Go here to calculate the proper way: http://www.cprparts.com/ci_calc.html
Of course it only works if you know measurements when your engine is apart...
Of course it only works if you know measurements when your engine is apart...
Static compression is good to know, but once the engine is complete "cranking compression" is all you can test. Plus, cranking compression tells you the real deal.
kg theres lots of factors that can eff with the readings such as carbon build up will give a higher read , and other factors i prefer a leakdown test duncan racing has instructions for doin that on a 2 stroke
| QUOTE (bansheen250r @ Mar 23 2004, 09:47 PM) |
| kg theres lots of factors that can eff with the readings such as carbon build up will give a higher read , and other factors i prefer a leakdown test duncan racing has instructions for doin that on a 2 stroke |
Well I know I'm not the smartest guy in the world, but isn't a leakdown test done to check the condition of the rings and cylinder seal? How can that give you a compression number?
I agree, a lot of carbon buildup could affect your compression ratio, but it is still a true reading of what compression you have with the carbon. A mathmatical compression number does not account for carbon build up or ring/cylinder wear.
Compression RATIOs is what I was looking for as stated by bansheen250r.
Rick that link is pretty cool. Since the engine is all apart, I can actually try using this calculator.
KingGlamis, assuming cranking compression gives you the real numbers, at what compression level do you consider your engine to be a "HIGH" compression engine?
Again, I am trying to determine if what LRD calls a "high" compression engine really is. That way if it is, I will use race gas, if not, I don't want to waste my money.
LRD tells me I should use 108 octane or higher.
Rick that link is pretty cool. Since the engine is all apart, I can actually try using this calculator.
KingGlamis, assuming cranking compression gives you the real numbers, at what compression level do you consider your engine to be a "HIGH" compression engine?
Again, I am trying to determine if what LRD calls a "high" compression engine really is. That way if it is, I will use race gas, if not, I don't want to waste my money.
LRD tells me I should use 108 octane or higher.
Sandpusher, is this a two-stroke? I don't recall the exact numbers, but I think anything above 185psi of cranking compression is bordering on needing race fuel. 200psi for sure.
those numbers dont mean eff*ing s*** kg go read a book abot it
Since every engine is different, you can calculate all you want, but testing (actual seat time) will really tell. Invest in 5 gallons of race gas and try it. Then try mixing down different ratios until you find the mix that works best for your engine and your wallet.
If you are trying to build your engine for a specific fuel, that get's pretty complicated and you will probably go through several building/testing/cussing/tearing apart iterations before you get it right.
If you are trying to build your engine for a specific fuel, that get's pretty complicated and you will probably go through several building/testing/cussing/tearing apart iterations before you get it right.
I use race at 25/75 for knock suppression but I don't notice much of a power increase.
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