Idle timing

3liter914-6 · Post by **3liter914-6** » Fri Aug 25, 2006 10:05 am

Hi,

I just got my MS'd 355ci SBC running for the first time a few days ago. I've been bleeding the cooling system for the last couple of days, and now that I have all the air out can get to the serious tuning.

I'm running MSnS-E with the 8-pin HEI, and I'm having some issues with getting a good idle. My main question is, how much timing is normal at idle? Engine is running a fairly mild cam, and AFR 195cc aluminum heads with CR of 9.6:1.

Here's what's gotten me the best idle RPM so far:

Idle started at 6-700rpm, and I kept bumping up the timing, and the idle kept on climbing and smoothing out, and the map kept dropping. 30-40* of timing just seems like a lot, and I'm not really sure whether having those bins at those values is going to cause a problem down the road.

Anyone with some input?

Thanks!

Jon k · Post by **Jon k** » Fri Aug 25, 2006 1:15 pm

When you say map keeps dropping, you want the LOWEST numerical KPa value, not the highest. 30 degrees does sound like too much advance at idle to me as well.

3liter914-6 · Post by **3liter914-6** » Fri Aug 25, 2006 1:48 pm

Jon k wrote:When you say map keeps dropping, you want the LOWEST numerical KPa value, not the highest. 30 degrees does sound like too much advance at idle to me as well.

Yeah, that's what I was shooting for, lowest KPa reading. With the timing up around 30* I was getting ~49KPa. It bounces around a lot though 49-59 KPa.

It just seemed like everyone else has timing maps that have 10-19* of timing in the spaces where I have 30+, so I just wanted to make sure there wasn't some other issue causing my engine to be happy with so much advance. Requested and Actual timing seem pretty spot on, but timing bounces around so much it's hard to get anything but a vague idea that it's in the right area.

Thanks for your input,

Adam

krisr · Post by **krisr** » Fri Aug 25, 2006 4:44 pm

Are your input and spark edges correct?

I used to run about 30* of idle advance to get a smoother idle and more vacuum but dropped it down to 20* so I can feel the idle

My timing map for my 400 Pontiac, mild 240 @ 0.050 solid cam, ported heads yada yada..

coyoteboy · Post by **coyoteboy** » Mon Aug 28, 2006 12:55 am

I also get best idle around 20-30 (lowest kpa and smoothest) but it seems whacky so i run 20 to be at the lower end of whacky. But then when the stock ECU runs and I use a timing light the mark vanishes out of view so I assume 20+ is fairly standard.

If you look at these maps of my car (supposedly stock ECU maps) and look at the tables (load bins are upside down) you will see they have 27 in the idle area.

http://member.newsguy.com/~gtfour/stockmap.htm

J