Idle tuning for lowest MAP

[panel]

How are you guys doing this? I saw a post from Fastback re tuning not for AFR but for lowest MAP. Is it just a matter of adjusting the AFR +/- etc till it gets the lowest or? This is a quote from the MS site but I'm asking anyone who has an EFI system. I've always set the AFR for my ECU to tune around this at idle but I take it that's wrong.

To set the VE table entries near idle, you should try to achieve the lowest MAP (in kPa) that you possibly can, at your chosen idle speed. This will give the highest idle vacuum and the most efficient idle. Don't try to get to a target idle mixture (stoichiometric, or some other number), instead adjust the VE table entries around your idle rpm and kPa to achieve the lowest MAP reading as seen in MegaTune. As you work to lower the MAP, the rpm will likely rise, and you'll have to reset the throttle stop to lower the rpm to your desired idle speed. When you have it set so that either raising or lowering the VE table entries increases the MAP, then you have the best idle mixture for your engine (it will require the smallest throttle opening).

[miniman82]

I ignore AFR readings at idle, tune for best idle quality/stability. Same things generally goes for the low RPM/MAP areas, only place I really worry about AFR's is WOT and cruise. I tried to tune AFR's everywhere before, all it got me was an unstable lurching popping pig of an engine. Mine seems to like high 12's/low 13's for idle at 16-18* timing, most of that is static compression/cam spec dependent.

[Piledriver]

What Mini said, I also go for what runs best.

Mine will only idly stably at ~11-11.5:1 and seems to prefer richer AFR targets at lower maps than cruise even.
I can play with the mix vs. vacuum until I'm blue in the face, that's ~best lean mixture at idle on this motor combination

Remember-- you don't really get a vote what the motor likes.
Do what it asks or it will be unpleasant.

Having a happy idle mix and timing (and the final 500-700PM line) is how you make for a hard-to-stall motor.
I can just about dump the clutch in second and it will easily "climb out of the hole."

The downside is I can tap the key in gear (accidentally) it will do the same on a hot restart.

[MarioVelotta]

The sqareback I am working on with the type 4 in it idles at 31kpa... I almost want it to be more

[miniman82]

31? Must be a short ass cam.

[Piledriver]

I get ~40-42 with a web73 on a 1.8,would probably be 35ish on a 2L.
(not fully optimized or min vac)

[Munchhausen]

Dont get idle map under 45? 2L with mild cam (schleicher 296)
around 16°timing. AFR ~14

[supaninja]

Yup, most vac is how you do it. If you buy some dyno time and tune all the cruising cells for most vacuum you will get the best mileage/crisp throttle too The motor talks, you just need to know how to listen

[panel]

Are you supposed to adjust the timing (eg: 10*) in conjunction with the AFR to achieve this or strictly the AFR?

[Piledriver]

Timing will have some effect.

With MS2 (at least) idle timing and the actual cells in the timing map (as in with throttle open some) do not have to correlate.
I run a lot more timing in that area of the map that at actual idle, the idle timing settings/curve keeps the idle speed quite steady.

[MinamiKotaro]

You might have to run a hair-raising amount of timing.

Some SBC guys report 60+ degrees timing at idle and very lean mixtures to achieve the lowest idle kPa reading.

[Munchhausen]

Looks like i have to advanced my timing. 16° was alot for my gut feeling. Just tried with less.
But have nearly stable idle at 950rpm with no loop adjustments like timing or idle valve. Plus, still have vac ref. at pressureregulator (first thing i want to change) . Drops to 850rpm with all electrical consumers on.
Hope i will find the time to fiddle around with it the next days. Dont have much time for the Type3 this year. (wife, second kid coming, bought old house and starting own buisiness ) I am happy when i find the time to drive it once a week.

munch

[Steve Arndt]

I was able to make the engine pull more vacuum at idle by tweaking the idl AFR. It pulls 1 inch more vacuum at 14:1 AFR than it does at 16:1. (about 3.4 Kpa more vacuum).

I'm running 48mm CB throttle bodies and 86B cam. I wish I had more vacuum.

I tested the vacuum with just one throttle body vac port, and all 4 tee'ed together and fuel filter. Same values.

Steve

[Piledriver]

I was able to make the engine pull more vacuum at idle by tweaking the idl AFR. It pulls 1 inch more vacuum at 14:1 AFR than it does at 16:1. (about 3.4 Kpa more vacuum).

I'm running 48mm CB throttle bodies and 86B cam. I wish I had more vacuum.

I tested the vacuum with just one throttle body vac port, and all 4 tee'ed together and fuel filter. Same values.

Steve

if you have ms2-extra or ms3 you can specify the sample angle and duration to find the lowest vacuum point.
On ms3 you can vary that with rpm via a small table, which would work at more than just one rpm.

[Piledriver]

You might have to run a hair-raising amount of timing.

Some SBC guys report 60+ degrees timing at idle and very lean mixtures to achieve the lowest idle kPa reading.

True, but a many older design, not LSx SBC chambers need 40++ degrees at WOT.