Timing query

Hopefully you would advance it to take advantage of the higher c/ratio.

Don't forget that you will be more susceptible to detonation (pinking) on lower RON fuels.

Peter

-- Peter & Rita Forbes snipped-for-privacy@easynet.co.uk Engine pages for preservation info:

Yep - Advance - You can only advance the timing until the car pings.

Nowdays its not a good idea to increase the CR as the fuel does have a lower rating. Even mine is struggling with 97 octane fuel.

Unless you have a LC engine in the first place then you will need to change the pistons to increase the CR.

Depends upon a number of unquantifiable variables. The reason for timing advance is to allow some of the combustion process to take place before the piston reaches TDC. Combustion takes a time to complete, therefore more advance is needed at higher engine speeds. ISTR that flame propagation is faster at higher pressures therefore less advance is needed. There may also be better squish at a higher CR. That may give a faster burn, hence less advance. However, squish is largely determined by combustion chamber shape which may be altered when the CR is changed. Of course, you may carry out other changes while you are raising the CR. Even a "good" decoke can alter flow characteristics. How much are you raising the CR? The chances are that you will not change it enough to make any appreciable difference. An increase of around 5% is the norm for A and B series engines unless you are very radical or are starting with a low comp engine. Generally, I would leave the timing alone or set the engine up on a rolling road or dynamometer.

John