C/R on a m20b25 / somebody please explain ?

[robmespeedy]

OK guys heres my question .
Why do people say that 10.5 compression is too high for the m20b25 on 91 oct. ?

While my 2001 325ci has 10.5 c/r stock runs on 91 oct.

[rs4pro3]

24 vlave head versus 12 valve head, better fuel injection setup, and the list goes on

[trent]

Re: C/R on a m20b25 / somebody please explain ?

OK guys heres my question .
Why do people say that 10.5 compression is too high for the m20b25 on 91 oct. ?

While my 2001 325ci has 10.5 c/r stock runs on 91 oct.

Electronics play a big part. That engine also has knock sensors, much more advanced engine control The flow is also a lot better as well as the dual vanos on that engine. M20 ain't got shizzie.

[AdamF 88iS]

The shape of the M20 combustion chamber is also more prone to hot spots and pinging than the DOHC motors are.

[mspiegle]

do any BMW motors use hemispherical combustion chambers?

[bkelsey86]

engines such as the s14 and s38 do hence the spark plugs being in the center of the head.

[StereoInstaller1]

cam profile and overlap make a HUGE difference in detonation resistance too. C/R is static, actual pumping pressure is far more relevant.
Luke

[AdamF 88iS]

cam profile and overlap make a HUGE difference in detonation resistance too. C/R is static, actual pumping pressure is far more relevant.
Luke

This is true. A very agressive cam lowers the effective compression raito as the motor runs, and can relieve some detonation issues.