Timing advance setting with Engine Management System

[nlowe79 at gmail.com (Nate Lowe)]

> >  On 5/3/05, Dan Bubb <jdbubb@ix.netcom.com> wrote:
> >>
> >> For full throttle I think what you have is pretty close.
> >> Full advance by 2500 seems a little fast to me, so I'd lower the value at
> >> 2440 somewhat.
> >>
> >> Couple general comments about spark timing and setting up load points on
> >> an aftermarket engine
> >> management just cause I can't help myself.
> >> 1. I don't think these engines need a huge amount of total advance at WOT
> >> based on input from both
> >> TT and NGP. I would think 32-34 max would be good. Plus you have a higher
> >> than normal compression
> >> ratio and that speeds up the burn rate meaning you need even less advance.
> >> 2. The burn rate in the combustion chamber varies with throttle opening.
> >> More throttle=higher
> >> density in the chamber=faster burn rate. So, at partial throttle (cruise
> >> conditions) you need to
> >> have more advance. So, you might try adding more advance in the lower load
> >>  positions. As an example,
> >> if your engine cruises at .5 bar/15"vac then you probably want to have
> >> 12-15 deg more advance at
> >> that RPM point then you do at WOT for that RPM. In other words you want to
> >>  emulate the vacuum
> >> advance of mechanical distributors.
> >> 3. Engines are generally linear in their requirement for fuel or ignition,
> >>  but with some exceptions.
> >> One is around idle where some monkey business , mostly with the ignition
> >> timing, can improve idle
> >> quality especially if you have wild cams. The second is engines with wild
> >> cams tend to have weak low
> >> speed performance and at a certain RPM "come on the cam".
> >> The TEC II (and also Megasquirt) has 8 load and 8 RPM points. I would
> >> adjust the RPM points so you
> >> have a couple close to the idle speed, and several around the RPM where
> >> the cams kick in to handle
> >> the drastic change in fuel required there, of course one at your max RPM,
> >> and last one or two in
> >> between those points.
> >> For idle, one at the desired idle speed, then one RPM point a few hundred
> >> below that. This lets you
> >> put in the actual idle advance at the idle RPM and really bump up the
> >> advance if the idle should
> >> falter some. So, say 6 deg across all load points at 1000 RPM and 20 deg
> >> at all load points at 700
> >> RPM. Idle drops down, advance kicks in and helps to bump the idle back up.
> >> Let's say your cams kick in around 4000. If it's a big change in power
> >> then you may want an RPM
> >> point at 3700, one at 4000 and one at 4300. The ignition requirements
> >> don't change drastically when
> >> the cams come in (or maybe it just doesn't matter that much) but for good
> >> drivability the fuel will
> >> change quite a bit and that's why you need a bunch of RPM points around
> >> non-linear behaviour.
> >> Also, since you're running ITB,s I'd also bunch the load points towards
> >> the higher end of the range
> >> especially if your using MAP (manifold absolute pressure) for load. Maybe
> >> if you're running throttle
> >> position for load this would be less important.
> >>
> >> I'd put in an ignition map here but the formatting will be all hosed. So,
> >> if you'd like my idea of
> >> an ignition map LMK and I'll send you one in Excel.
> >>
> >> And one last comment. You are going to run more than 7000 RPM?? I bet your
> >>  power peak will be that
> >> high and you need a few hundred RPM beyond that for maximum performance
> >> through the gears.
> >>
> >> Anyway, that's what I think. Most of this is based on experience with a
> >> 2.0L 8V with ITB's and a 306
> >> cam using Megasquirt running to 8000 RPM.
> >> Hope this is clear for all that read this far.
> >> Dan
> >>

I'd like to see that excel sheet if you don't mind Dan, I'll just
pretent I know what I'm looking at :)
As far as reading "that much" technical, it's all relative. Now if I
had to read a page description of the meaning behind a painting,
that's when I would get a headache.
Nate