| Author | Message | ||
     Holling |
An easy way to build more power is by raising the comp ratio. Why are xbs' limited to 10:1 when most sportbikes run 11.5:1 to 12.5:1? I read that even the XBRR runs 12.5:1. The air cooled Ducs even run higher comps. | ||
| M1combat |
Detonation. High octane fuels are less volatile. The "RR" uses some "high" octane fuel. another way around the problem is cooling. If you keep the combustion chamber cooler you can run higher compression, but this is at the cost of efficiency. For our engines, you don't want to go much higher than about 10.75:1 compression, and it'll be a little troublesome on a hot day. | ||
| Fullpower |
Air cooled Ducatis are 10 : 1 compression, and due to longer duration cam timing run lower cylinder pressure than the stock XB | ||
| Spork |
Air cooled engines retain more heat in the cylinder heads compared to liquid cooled mills that have coolant circulating thru water jackets in the heads. Excess heat in the combustion chamber can lead to pre-ignition, better known as pinging. This is when the air/fuel mixture is ignited prematurely and collides with the piston as it is coming upward toward top dead center, and results in power loss and the "pinging" noise. Fuel octane is also a factor. Octane is a measure of resistance to pre-ignition. The higher the octane, the less prone to being ignited. Therefore, high compression (like the XBRR)or highly boosted engines need very high octane gas to run properly. The standard 91 octane swill limits compression ratios on street ridden bikes. I hope that answers your question. | ||
| 45_degrees |
Direct-injection would allow for a higher compression ratio on pump gas. |
