Just like the topic states I am looking for more of a technical answer as to why bikes can get compression ratios of 12:1 and more where as car motors start detonating around there. I mean what gives bikes that ability to run 91 octane at those compression ratios? Any technical knowledge on the topic would be great. Its really been boggling my mind for quite some time now. Thanks in advance.

 

There is no reason why a car engine can't run the same state of engine tune as a bike. There are a number of firms which put Hayabusa and similar motors into racing cars.

The key issue is that the higher the specifc output of an engine the less flexibility and torque down low.

For a motorcycle this is not such an issue as the power to weight ratio is still high enough lower down in the rev band, even though most highly tuned bike motors are still pretty gutless down low.

For a car, however, the lack of torque, and need to frequently chane gears is something that most drivers are not prepared to live with. As is the need to be running pretty high revs by comparison with a larger capacity, lower tune motor. Witness the S2k - a classic example!!

 

Ferrari and Honda's F1 cars go into the 19,000s!

 

Also, longevity plays a factor, Not as many bikes hit the 100,000 mile plateau where as most cars do. Those compression ratios place hell on a motors durability. But for the most part, what was mentioned above and the main reason.

 

Since nobody has actually answered the question yet, I'll give it a try.

Motorcycle engines can have higher compression ratios because the flame front doesn't have as far to go in the smaller combustion chambers, so it's easier to avoid detonation. The big V-twin engines can't get away with as high of compression because their cylinders are larger in diameter. The more cylinders you have, the smaller they are and the higher the compression ratio you can run without detonation.