Honda Accord 4 cyl Vs. Audi 4 Cyl (Another Gas Question)
 

2005 Audi 4cyl has compression ratio of 9.3 to 1

2005 Honda Accord has compression ration of 9.7 to 1

WHY does Audi recommend premium fuel ( http://auto.consumerguide.com/auto/n...x.cfm/id/37495 )
and Honda does not? [since I heard a lot of talk here how compression ratio has ALL to do with what gas to use].

Thx

"Audi recommends premium-grade fuel for all A4s."
1.8T engine has a turbo. So pressure at the end of compression will be higher.
AUDI Engine is 1.8 vs. 2.4 on Honda so turbo puts noticable pressure.

3.0 engine has 10.1 ratio.

I would imagine that is why.

Compression ratio is important, but it's not the only thing that matters. Combustion chamber shape, spark location, cam profiles, spark timing, turbo (of course). Compression ratio & boost are probably the most important, tho.

Ignition timing is typically the main factor there. Shape of the combustion chamber and piston are also important.

I have a 12.5:1 compression ratio on my motorcycle and it runs OK with 89 octane.

bet it'll run better with a higher grade gasoline though