Max AFR and Ignition Advance on stock 1600 Beetle?

[paullanzarotti]

Does anyone have an opinion on the max AFR and ignition advance for 1600 Beetle?

[Piledriver]

Does anyone have an opinion on the max AFR and ignition advance for 1600 Beetle?

At WOT, 32-34 BTDC, checked at ~3600 RPM, after verifying TDC mark.(mechanical advance only, vacuum disconnected)
Vacuum advance should pull in another 15 degrees or so , at light loads, the burn is slower, so it actually helps keep CHT and EGT down.

The factory jetting ran as rich as 11:1 AFR on some models.
WOT should probably not exceed 13:1.

[paullanzarotti]

Ah - I should have been clearer - I meant with a programmable ECU and FI rather than mechanical dizzy and carb.

[Piledriver]

Ah - I should have been clearer - I meant with a programmable ECU and FI rather than mechanical dizzy and carb.

Around stock is still a very good place to start.
You'll probably find it likes a lot more initial advance than "spec".

You will also probably be able to pull 16-17:1 AFR at cruise, it will need MUCH more timing advance at lean AFRs.
This headshots CHT/EGTs, and you may not be able to do it in winter, even with a Tstat I have to target ~stoich during the "cool season"* here in Texas to heat up properly.
(The engine, not me, I have a BN4 in the frunck so driving with the drivers window 1/2 open on the coldest days is typical)

*I won't call it "Winter" as I have lived where that actually means something.

[gtmdriver]

I am running my 1600 twin port standard Beetle engine with a maximum advance of around 34 degrees including vac advance and AFR ratios between around 12.5 to around 15 but it has not been on a rolling road yet so I have been very conservative with the settings.

[Marc]

The less-efficient your combustion chamber shape is, the more lead will be needed - but assuming you aren't running hemi-cut heads or huge piston deck height you probably should not stray too far from the conventional wisdom of keeping the advance below ~32° under full-load @2500 RPM - that's typically the "worst-case" scenario. The popular "SVDA" distributor (stock on `74 USA 49-state 4-speed 1600s) has a centrifugal curve that doesn't come all in until 3500 RPM or so (compared to the ubiquitious centrifugal-only 0 231178 009 which tops out around 2500) but the vacuum-advance component riding atop that can yield ~45° total under high-RPM/light-load conditions. A few degrees more advance may be tolerable and yield better efficiency under ideal conditions, but the added load of an upgrade or headwind can be enough to cause damaging issues - so it's wise to be a little conservative rather than go for the absolute maximum if you don't have a dashboard control to back it off when needed.

[Piledriver]

A programmable setup with a MAP sensor has much finer control than a vacuum canister: it the load increases the timing automagically backs off.(assuming the advance tables are sane)

I'd post mine up (I have previously many times) but 2L 914 t4 combustion chambers are not like T1, and I'm running very very lean at cruise, so it might hurt your motor, assuming it ran at all.
(A stock T1 would probably need more timing than I run...)

[paullanzarotti]

Thanks for the replies. So it sounds like I can lean out to about 16 AFR with an advance of 44 with a light load MAP 40-55?

[Piledriver]

Thanks for the replies. So it sounds like I can lean out to about 16 AFR with an advance of 44 with a light load MAP 40-55?

Might want another 10 degrees of timing.
Everywhere.
(based on the timing tables posted in the other thread, which really should be merged with this one)
Stock T1 heads have great turbulence/swirl going but the chambers aren't the greatest for burn speed...
...nor the worst.

Under ~70 KPA you can pretty much get away with murder, ignition timing wise, esp at leaner AFRs.
At cruise, too little timing hurts your efficiency and CHT/EGTs far more than a little too much.

[paullanzarotti]

Interesting - I have been making some wholesale changes as the car felt a little growly and over advanced for my liking. When you say "another 10 degrees of timing" do you mean it's over advanced by 10 degrees or under?

These are the tables I was working with as of last night (and based on a lot of research in to what other people are using in VW's)

Does this all look a little conservative?

Screenshot 2016-12-07 09.19.47.png

Screenshot 2016-12-07 09.19.26.png

Screenshot 2016-12-07 09.19.15.png

[Piledriver]

Very, very conservative.

I suggest:
Ditch 10-30KPA lines unless you live on Everest or at the top of Pikes Peak.
Use those extra lines for some finer control around cruise an/or WOT.

My AFR table everything over 2800 rpm and under 87 KPA is at 19:1 (or at least it was until this week when the temps dropped) Cruise for me is ~60-80 KPA depending on speed and hills. I am not running a T1 based motor, but this should be ~conservative for a stock T1... I'm running a MS3, 1.8L T4 with 2L Porsche heads and a Web 73. 8.6:1 CR. (49cc chamber heads are cut a bit, step cut, the step cut is most of the deck space)

[paullanzarotti]

Ok let me try that. What advance do you run on 19:1?

[Piledriver]

Sorry, switched to my tuning laptop so I had TS available
this is table1 for gasoline, table3 has a little more everywhere for e85.
The firmware blends between the two based on the GM ethanol sensor input.
MS2E can do this as well, just not quite as flexible.
There is a very slight blend in the row and column adjacent to the lean cruise area.
This mirrors the AFR table, note the close transition bins so it doesn't get interpolated wrong.
(Th blue numbers area was 21:1 but I know thats too lean so I changed it, hasn't been burned to the ECU yet)
With a stock t1 chamber/compression and std ignition <17:1 is likely lean misfire limit.

[CBDZ]

Piledriver - What is your MAP at idle?. I also assume you have a separate cranking ignition setting. I would think that timing in the 20's could cause kickback at cranking?

[Piledriver]

Piledriver - What is your MAP at idle?. I also assume you have a separate cranking ignition setting. I would think that timing in the 20's could cause kickback at cranking?

from memory 55-60ish warm ~70 when its reaaly cold.

Re: cranking timing...
I do, but it really doesn't, it just hits a little more instantly at 0.
(I have it set for a 3 second priming delay to get a little oil going, max "ignore pulses" so it cranks a couple rotations before it lights the spark etc... so it cranks for a couple seconds before it hits, then is ~instantly at idle speed.).
The instant its above cranking speed its at ~20btdc, it accelerates briskly.
I'm running a 2KW Jetta TDI starter so YMMV.
There's absoutely no sitting there cranking waiting for it to catch... It cranks at ~360 RPM, and gets there RFN.