| Author | Message | ||
     Ezblast  |
Running 91 octaine - whats the highest compression piston in a stock Blast would you run? 11.5 - 12.5 - how high would you go?I know some performance cars are running 12.5, but what could a stock Blast engine handle? GT - JBOTDS! EZ  | ||
| Jlnance  |
EZ - I don't know the answer to your question, but I will tell you what I do know. I dug this up doing research on water injection. You probably know this already, but I thought it was interesting, and I'm sure someone will enjoy reading it. And I'm sure someone will correct the mistakes I am sure I will make. You have to heat a higher octane fuel to a hotter point before it will explode. This is good because you want the fuel to burn in a controlled manner, not explode. If the fuel explodes, you get engine knock, which is bad. Raising the compression ratio raises the temprature. But the ignition timing also affects the temprature, as do things like the outside air temprature and how far open the throttle is. So I suspect the answer to your question is going to depend on whether you are willing to alter the timing and whether you need to be able to ride in death valley in the summer. | ||
| Ezblast |
Probably 10.5 to 1, however, there is the new Blast track group forming, and the bike I could use would be the red my dailly commuter, the black being too modified - lol - but the only thing on the red I'd have to do would be a piston swap and she'd be ready! I should probably leave well enough alone - but thats never been my style - lol - probably pick up some laverda bars as well. GT - JBOTDS! EZ | ||
| Steveshakeshaft |
Actual effective compression ratio is determined by the intake valve closing point too. So the "high performance" cars running 12.5:1 CR may have an effective CR significantly lower, as they'll be running radical cam timings. HTH. Steve. www.ukbeg.com steve_s@ukbeg.com | ||
| Jlnance |
EZ - Interested in playing with water injection? | ||
| Ezblast |
Naw - not for a hobby racing venue - if I where drag racing - probably - lol GT - JBOTDS! EZ | ||
| Chris_mackay  |
A standard Sportster style motor will handle 13:1. I have both an aluminum and an old cast iron motor running this ratio and they both do fine. I run pump gas in both. But you do have to keep it tuned well and it's rather rough on starters. Will the Blast motor handle it? It's the same base so it should. | ||
| Rick_a |
I know a few people running only 10.5:1 on premium having serious detonation issues. It all depends on the set-up, though. | ||
| Fullpower |
depends on the cams. if you go above 10 to one you will NEED longer duration cams. i have a sportster that makes 205 PSI cranking pressure and it really runs strong on methanol. gasoline is a bit of a problem, with retarded spark, a slightly rich mixture, and various blending with acetone, toluene, methanol,and leaded aviation gasoline it can tolerate pump gas, in a marginal way. next time i tear down the engine, i will either lower the compression some, or run a lot more cam.. currently using the andrews N6, and mechanical compression ratio is 11 to one. |
