Is detonation more likely to occur running high boost in hot weather or cold weather, my current boost was set mid summer. I know that the boost level drops a bit when the air temps are hot , is it safe to run the same boost when air temps are cold or do i need to knock it down a bit.

 

when its cold, the air will be denser so it will contain more oxygen so the car will probably produce slightly more boost (more than likely just feel more lively). Whether or not you would need to adjust your boost levels is another matter but I would imagine the ecu would be able to cope with it.
Detonation is more likely to occur in hot weather running high boost, due to the air being less dense, therefore less oxygen to burn with the fuel

 

Cheers, thats what I thought just wanted to be 100% sure.

 

I've actually noticed up to about 1.5psi difference between a hot summer day and a cool evening.

 

both depending on how cold or how hot.

Cold air will be denser, and even at the same boost, you will have more air going into the engine, which means higher cylinder pressures and possibly increased det. However, if the car was limited by excessive temperatures in the past (say small TMIC and hig boost), and you cool the inlet charge you will more than like decrease det.

Paul

 

To be precise, detonation is more likely in warm weather as the overall inlet charge temp is higher. There is a temp at which the fuel air mix with either fully or partly ignite in an uncontrolled manner during the combustion cycle.

Nothing to do with there being insufficient oxygen for the fuel. If anything just the opposite. Where there is too much oxygen for the fuel, ie an overly lean condition is where detonation is more likely to occur. Excess fuel will in most cases reduces the probability of det as it absorbs heat from the inlet charge, reducing the overall charge temp and hence the risk of det. Hence why turbo cars (Impreza included) are invariably mapped from the factory to run excessively rich on boost for safety.

The answer is still the same though. Hotter days more risk.

If concerned on det risks, fit a knocklink and if necessary reduce boost in warmer weather or increase fuel octane level with appropriate octane boosting products