Tuning ignition and fuel

[E30godz]

As im not an expert on tuning engines, i thought id try to learn some basic principles.

When you advance timing, does the engine want more fuel?

Should i advance the timing as far as it will go at each point RPM band, for the best power?

I have been advancing it slowly over the entire band and notice a little pick up. As for now ive left the fuel alone.

[rwh11385]

Re: Tuning ignition and fuel

As im not an expert on tuning engines, i thought id try to learn some basic principles.

When you advance timing, does the engine want more fuel?

Should i advance the timing as far as it will go at each point RPM band, for the best power?

I have been advancing it slowly over the entire band and notice a little pick up. As for now ive left the fuel alone.

Timing changes when the spark fires in relation to the location of the piston to TDC. Firing a lil early makes for a better burn and better power.

I'm not sure if it uses more fuel or not.

But be careful too far and you'll fuck you're engine. :shock: And we don't have knock sensors, so you could really mess things up.

I'm planning doing MAF/SMT6 this summer, but I still have a JC chip on order. Jim spend hours upon hours getting the timing just right, it's silly to think we could ever get the timing as good as or as safe as him.

But good luck and be safe and smart with the timing advance.

[E30godz]

yea i know ; )

Im not sure what the arbitrary numbers on the SMT-6 fuel/ignition plots are. But i advanced it up to 13 at full throttle from around 4500-6500 and it wouldnt go past 4500, my guess was it started to ping (the car bucked and shuttered) i instantly lt off the gas and set it down to 11, and it ran fine again.

[darien28]

WOAH, +11 timing? that sounds like a lot to me... but maybe it's just me... i dunno.

try tunig it on a dyno?

[peerless]

"When you advance timing, does the engine want more fuel?"

Fuel is a matter of consumption based on RPM, Displacement, Injector Flow and Pulse Witdth. Timing will not directly effect fuel consumption.

Should i advance the timing as far as it will go at each point RPM band, for the best power?

I am not sure whether your spinning a distibuter or programming timing in a chip. Heres how I know it based on a distributer. This applies in both cases as you are doing the same thing either mechanical or electronicly. You have initial advance and centrifigul advance, as well as vacumn advance if so equipped. Changing initial advance will have little effect on performance except maybe a little crisper off idle response. The power comes from the centrifigul curve. Starting at the beginning of the power band you start increasing advance in a smooth curve getting more aggressive to full advance at the peak power point.

"I have been advancing it slowly over the entire band and notice a little pick up. As for now ive left the fuel alone."

Adjustable Fuel Regular to increase pressure and high flow injectors will help feed additional power requirments. Also on some E30's the DME has a Fuel Qaulity Switch. This will allow you to increase/decrease the injector pulse width 3% and 6% respectivly.

Remeber an engine is nothing more then a complex airpump. The more air that can pass through in any given moment defines the power output.

Robert
85' 325e

[peerless]

Ok, I wan't thniking, you obviously don't have a distributor. I tried to look up some specs for the timing, but since its controlled by the computer I can't find any. Heres what I did find, as well as some experiences I have had with timing.

First off the older 4 cyl 318 with a distributor had a total advance of 26 degrees @ 4000rpm.
Now based on my work with american V-8's you generally have about 32-34 degrees total advance at about 3800-4000 RPM's. My freind had a built 350 pushing about 480HP, he was set up at 38-40 degrees max timing.

I made a mistake with my 68 Mustang one time and had full advance just off idle, It wouldn't go past 3500 RPM's without running like shit with no power. This was a 289 that pushed 400HP at 6800 RPM's. So timing is crucial. I was running 12 initial and 36 total @ 6800RPM.

From your post about it crapping out, it looks like you have your max timing coming on way to soon. Is your car a Turbo? The higher the RPM the sooner the spark has to arrive. The faster the engine rpms the more aggresive the spark timing curve.

I would think 28-30 degrees at max power would be a safe place to start. I would imagine initial would be any where from 4-8 degrees advanced. I am just theroizing based on the numbers between the 4cyl and 8cyl. The 6cyl has got to be in the middle ground.

You did note the stock timing points before changing everything right?

Robert
85' 325e

[peerless]

ah, and here is a good article that should shed some light in your situation:

http://www.sdsefi.com/techign.htm

The whole website is packed with great information.
It's not BMW specific, but it is fuel injection specific. Lot of turbo information too.

[E30godz]

There is no way to judge where the baseline timing is at. The ignition maps on the SMT-6 are all set at "0" from the get go. So i assume that to go back to the way it was stock i would just enter in 0 again for all the points. I wish someone with more experience with the SMT-6 could pop in!

I'm also running with a Dinan chip, so the advanced timing is ocurring on TOP of what the chip has already done. I think its running right on the edge of performance right now as it seems fairly quick. When i get the piping done from the turbo to the intake, I'll reset all the timing points to 0 and start from there.

This question is mainly directed at people familier with the SMT-6. As you know, there are 3 maps you can modify the "analog fuel" map, "injection" map and the "ignition" map.

What exactly does the injection map do? I've played around with it and have seen no change in engine performance at all (good or bad).

[skat 325is]

As far i know, u can only advance or retard 12 degrees with the smt6.

[mspiegle]

something you should probably know before you screw something up...

I have yet to 100% verify this, but the SMT6 ignition may seem "backwards".

I believe (however haven't tested) that negative numbers advance your ignition. Why? Because you are attempting to move the signal BEFORE 0. Firing before top dead center means taking points off, not adding points.

When you set it to a high number at a high rpm, you essentially created a rev limiter for yourself.

My buddy has a gtec, and i plan to borrow it and test my theory out. Also, test and see if i got anything from that MAF conversion.

[E30godz]

thats VERY interesting. Im going to have to check this tonight..Maybe it was just all in my mind that it felt a little quicker!

[E30godz]

I have the SMT-6 software installed on my computer and i do believe that the positve numbers advance the ignition. My reasoning for this is because in the Global Settings,, under the Ignition tab it shows 2 sliding bars half way down. it says "Ignition Adv. Limit:" and gives a 0 to 12 (selectable up to 45) and below it, a "Ignition Ret. Limit." and gives 0 to -12 (or whatever between 0 and -45). Clear anything up?

[DaN]

I believe under boost, you will want to retard timing a bit depending on how many psi.
If you are running full advance you are bound to have detonation/preignition problems under full boost.

[E30godz]

i believe peak torque is where timing will need to be retarded the most.

[mspiegle]

that's a very good point.

I'm at work right now, so i can't test this, but how about you drive around with the log running, and see what the ignition signal is, then what the modifer is, and what it gets modified to. That *may* shed some more light.

I really need to get a copy of the developer manual or something... i think it will explain alot about how this thing works.