The Ford Barn

Bassman/NZ · 02-24-2016, 10:48 PM

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.

Talkwrench · 02-24-2016, 11:01 PM

Rule of thumb retarded I'd say , but .. It might run fine the way it is.. ?

JSeery · 02-24-2016, 11:30 PM

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.

Old Henry · 02-24-2016, 11:32 PM

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.

Mart · 02-25-2016, 04:00 AM

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.

JWL · 02-25-2016, 06:26 AM

Sponsored Links (Register now to hide all advertisements)

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

JSeery · 02-25-2016, 09:03 AM

Thanks for the reminder JWL, I don't remember reading that part!

Bassman/NZ · 02-25-2016, 02:52 PM

Quote:

Originally Posted by JWL

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

Oops.... back to the book!

Talkwrench · 02-25-2016, 07:36 PM

Are you having probs Bassman , or was it a general question?

Bassman/NZ · 02-26-2016, 02:45 AM

Quote:

Originally Posted by Talkwrench

Are you having probs Bassman , or was it a general question?

No mate, just a general question.

Bassman/NZ · 02-26-2016, 02:52 AM

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.

02-24-2016, 10:48 PM	#1
Bassman/NZ Senior Member Join Date: May 2010 Location: Napier, New Zealand Posts: 2,001	Rule of thumb ? 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.

02-24-2016, 11:01 PM	#2
Talkwrench Senior Member Join Date: Aug 2012 Location: Perth, Western Australia Posts: 2,687	Re: Rule of thumb ? Rule of thumb retarded I'd say , but .. It might run fine the way it is.. ? __________________ *"Came too close to dying to stop living now!"*

02-24-2016, 11:30 PM	#3
JSeery Member Emeritus Join Date: Nov 2012 Location: Wichita KS Posts: 16,132	Re: Rule of thumb ? 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.

02-24-2016, 11:32 PM	#4
Old Henry Senior Member Join Date: Oct 2010 Location: Orem, Utah Posts: 5,762	Re: Rule of thumb ? 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. __________________ Prof. Henry (The Roaming Gnome) "It is good to have an end to journey toward; but it is the journey that matters, in the end.” *Ursula K. Le Guin in The Left Hand of Darkness

02-25-2016, 04:00 AM	#5
Mart Senior Member Join Date: May 2010 Location: Solihull, England. Posts: 8,744	Re: Rule of thumb ? 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.

02-25-2016, 06:26 AM	#6
JWL Member Emeritus Join Date: May 2010 Location: Fitzgerald, Georgia Posts: 2,204	Re: Rule of thumb ? Sponsored Links (Register now to hide all advertisements) 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

02-25-2016, 09:03 AM	#7
JSeery Member Emeritus Join Date: Nov 2012 Location: Wichita KS Posts: 16,132	Re: Rule of thumb ? Thanks for the reminder JWL, I don't remember reading that part!

02-25-2016, 07:36 PM	#9
Talkwrench Senior Member Join Date: Aug 2012 Location: Perth, Western Australia Posts: 2,687	Re: Rule of thumb ? Are you having probs Bassman , or was it a general question? __________________ *"Came too close to dying to stop living now!"*

02-26-2016, 02:52 AM	#11
Bassman/NZ Senior Member Join Date: May 2010 Location: Napier, New Zealand Posts: 2,001	Re: Rule of thumb ? 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.