Timing a Weber-based engine

[Steve Toner]

Howard,

We've got 85/88/91 here because of the altitude (valley floor is around 4000-4500 ft). We do get crappy winter gas but the summer blend seems pretty good. I'm running 88 in it right now, in th ehopes that if I do take it back down to Las Vegas (about 2000 ft), I can run the highest octane pump gas there and not have to mess around with it too much. Because messing around takes time, which I may not have (though just backing off the timing a few degrees is no biggie)... But that's also why I was asking about the MSD 8680 timing control. Everything's a compromise...

[Steve Toner]

Howard,

From your post in the engine cost thread, it appears that you're running a 4bbl carb, not Webers. If what Dan at Inglese told me about IR Weber setups wanting more initial timing is true, then I don't think we can expect any correlation between your results and mine. If you're not running vacuum advance, then that disputes my vacuum advance theory as the explanation for wanting more timing, but that was just a theory.

Clearly, the "Webers need more initial timing" is still in dispute here, but I've seen references to plenty of people running something like 18 degrees initial with Webers.

Perhaps I should jsut switch to fuel injection and just leave it up to the computer [img]/ubbthreads/images/graemlins/smirk.gif[/img]

[Howard Jones]

Steve, You are correct I am using a holley 4 barrel. I also have a mech advance only dist. and a fully mech secondary carb. I guess I just don't understand enough about webers to see the need for a difference in timming advance given a static AF ratio. I will be following this thread in hopes that someone who really knows can teach me somthing. I assume that the difference in air density, your's being higher and thus less dense, is the reason you can run lower octain gas. The result is a smaller volume of A/F to be compressed IE: lower effective compresson ratio. Could this be why my Audi seams to run stronger at 6000 ft around lake Tahoe and Nevada. I thought it was the better gas and cool air. Wouldn't the computer continue to ask for max allowable boost without detonation resulting in a more or less contant effective CR? This computer stuff really make my head hurt! That's why "I just got me a holley"