Hot Rod Forum : Hotrodders Bulletin Board - View Single Post - lean mixture?
Thread: lean mixture?
View Single Post
  #41 (permalink)  
Old 01-29-2013, 04:32 AM
cobalt327's Avatar
cobalt327 cobalt327 is offline
WFO
 
Last wiki edit: Intake manifold
Last journal entry: 1980 Malibu Wagon
Last photo:
Join Date: Mar 2009
Location: Atlanta
Age: 59
Posts: 5,037
Wiki Edits: 1616

Thanks: 128
Thanked 597 Times in 546 Posts
Quote:
Originally Posted by jeepers creepers View Post
Thank you, i have Edelbrock performer alu heads on so i believe it's better a little more advanced, are 36* ok? Because the total timing with vacuum plugged in is way more of that, i think was close to 45*.
What a 45* or too much total advance would cause to the engine?
Total advance is initial plus mechanical, without vacuum advance added in. This should be around 36 degrees. Too much total advance causes detonation, and detonation will kill an engine- no two ways about it.

You want another 10-12 degrees to come from the vacuum advance. That means under light throttle cruise/low engine load conditions you'll see upwards of 46-48 degrees of advance.

A common problem we have is the cam wants a lot of initial timing, but if you give it enough initial timing, the total timing is now too high. The way around this is to limit the mechanical advance to an amount that, when combined w/the initial timing, equals the 36 degrees total timing target. An example would be 18 degrees initial timing, plus 18 degrees mechanical timing. Or any combination of the two that equals 36 degrees. Remember- this is w/o vacuum advance added in. It will be disconnected and the hose to the carb plugged. Only reconnect the vacuum advance after the initial and mechanical is set.

The exact way to go about limiting the mechanical advance depends on what distributor you're using. The following link covers GM-type HEI and MSD distributors: Ignition advance
Reply With Quote