I was looking at the specks for the cannondales and I noticed that they all had 12.5 to 1 or something close to that compresion ratios which means that you have to run race fuel in cannondales , right ??

 

No, u dont have to run Race Gas, 93 pump gas will, do. I run 93 pump with fuel booster.

 

We only have 92 octane, NOS makes 3 boosters, I've tried both their off-road and race formulas, they both work fine but havn't had much time on the race formula.

 

How is this possible ? if you put a 12 to 1 ratio in aany motor it should detonate without race gas how come the cannaondale doesn't

 

I imagine its due to the fuel injection. It must be able to manipulate the air/fuel mixture to an acceptable ratio using only premium fuels.

 

I don't see that being the reason because fuel injected cars can't run 12to1 without race gas.

 

Really? A friend of mine from work runs 12:1 in his 351 Windsor powered Mustang ('85) on pump gas and its carbeurated. I've heard of people running 8#'s of boost through 11 and 12:1 302's on premium and a DFI setup. I dont see where it would be a problem with more fuel and less timing and obviously it isnt because they are running it like that.

 

I imagine it has a lot to do with the cam. If you have a radical cam in a 12:1 engine the cam can open the valves sooner and later and make the motor really run like an 11:1 motor. This is probly why they can afford to run such a high compression but with a wild cam.

 

With correct spark plug and a hair slower timing it's not a problem. I haven't looked but I'd wager they're running a hair smaller than all out open throttle body, which keeps the cylinder from running at true 12.5 to 1, while still retaining the increase thermal effeciencies of the setup.

 

It probably has better cylinder head design than most car engines. Part of the problem with high compression is that there are hot spots or places where the pressure is higher and detonation begins. A better head design will not have as many or as severe hot spots.

Since two strokes don't have valves in the head, the combustion chamber is smooth and they do not have hot spots (bad squish band design will have hot spots). When I researched how much I could bump up my compression, I found that 180 psi static compression was doable on 93 octane. I bumped mine up to 170 psi to leave a little room for bad gas. I have been running Mobil 93 in it for a long time with no problem.

A very rough calculation not factoring in cam timing, intake efficiency, ...:

(12.5 - 1) x 14.7 psi = 169 psi.

Someone could check their actual static compression or maybe it is in the manual. It is probably lower. If Cannondale says it will run on premium pump gas, I would have no problem believing it.