Rule of thumb ?

Bassman/NZ

Bassman/NZ

Well-known member
Generally speaking, when compression is raised on an otherwise stock engine, does the ignition need to be advanced, retarded, or stay where it is. I've done a search, but cant find anything on this.
 
Ignition advance has more to do with the shape of the combustion chamber, fuel used, etc. Compression would become an issue if you are getting into a "pinging" situation and needed to back the advance off. Compression is related to the burn rate of the fuel and higher compression requires a slower burning fuel.
 
What Talkwrench said - retarded. I learned that driving various elevations from 15,000 feet to below sea level. Always have to advance the timing going up (less air = less compression) and retard it going down (more air - more compression) to keep the engine running right.
 
Agree with above - the rule of thumb would be that more compression would require the ignition to be retarded. But that would infer that was at it's maximum advance beforehand. As said, it may run fine as is or even take more advance if the timing was not particularly well set up beforehand. If it was previously set at the ragged edge of detonation, the raised compression may require the ignition to be backed off a tad.

The message is, don't just retard it because it is what you are "supposed" to do.

Mart.
 
If you read my book, again, you will find a complete explanation of the impact compression ratio elevation has on ignition requirements including why things happen the way they do.

JWL
 
JWL said:
If you read my book, again, you will find a complete explanation of the impact compression ratio elevation has on ignition requirements including why things happen the way they do.

JWL
Click to expand...
Oops.... back to the book! :o
 
I re-read JWL's treatise on the matter, and it made sense. Increasing compression slows down the flame (increases the lag time), so reducing advance would be the rule of thumb.
 
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