Timing advance with engine RPM

BottleFed70 · Post by **BottleFed70** » Sat Aug 05, 2006 5:10 pm

Hi guys,

Can anyone tell me why nobody has their spark timing advance all the way up to redline? I always see timing graphs that show the timing to be "full in" at between 3000-4000rpm.

Wouldn't it make sence to have the timing advance all the way up to 6000rpm?

pete · Post by **pete** » Sat Aug 05, 2006 8:29 pm

You want all your timing in as soon as the motor can accept it. You'll find that each combo will be able to take a diffferent amount of advance and the amount of advance the motor can take will not increase above ~3500 RPM. This is at WOT.

So in short. If you get best power with 35 degrees at 3500 RPM you won't get any more power with 40 degrees at 6000RPMs. Why this is I don't know but this has been shown over and over on engine dyno's and at the track.

BottleFed70 · Post by **BottleFed70** » Sun Aug 06, 2006 12:12 am

pete wrote:You want all your timing in as soon as the motor can accept it. You'll find that each combo will be able to take a diffferent amount of advance and the amount of advance the motor can take will not increase above ~3500 RPM. This is at WOT.

For the most part I think I know what I want my timing to be. My gueation was about why "If you get best power with 35 degrees at 3500 RPM you won't get any more power with 40 degrees at 6000RPMs" is true. My initial thought would be that "the higher the rpm the more ignition advance you need. I was wondering why this isn't the case.

bluetrepidation · Post by **bluetrepidation** » Sun Aug 06, 2006 8:42 am

Cylinder pressures are so high above 3500 RPM that the fuel burns much must faster so more timing is not needed. The increase in pressure kinda does the advancing for you if you get what I mean.

A.J.

Jarmo · Post by **Jarmo** » Sun Aug 06, 2006 11:54 am

I have usually gained a few hp on top rpm by pulling a degree or two from max ignition advance after peak power. (NA rally motors)

pete · Post by **pete** » Sun Aug 06, 2006 4:49 pm

I found this
http://www.jcna.com/library/tech/tech0013.html

Seems there are many factors, which makes sense, but for higher RPM's it seems increased VE requires decrease in timing for a given RPM. Seems like if your VE is steadily increasing with RPM it stand to reason you won't need any more advance.