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Fri Apr 14, 2023 2:46 pm

So, I have read here and on other sites, that the way to set the timing on a type 1 engine is :vac disconnected, set to 7deg BTDC at idle, and look for 30-35 deg total advance at 3000 RPM.

My engine is a 1600 DP, stock, except for dual Empi 34EPC's, and a Pertronix SVDA electronic distribuitor.

When I use the above mentioned procedure, I end up at 40 deg total advance.

After some looking around on the web, I found this table, which says to set the timing at idle to 5 deg ATDC, for a 1973 1600 engine:

http://volksconversions.com.au/VC_TimingFigures.pdf

What is it then ?

Fri Apr 14, 2023 2:52 pm

your pertronix distributor should not have more than ~22 degrees or so of mechanical advance. this will make for maybe 5~10 degrees BTDC advance at idle when set up correctly

. If you are getting up to 40 it is out of spec due to manufacturing issues or being worn out. Very common issue with new production distributors.

5ATDC is a spec for a factory/OEM DVDA,with both vacuum retard as well as advance. It does not apply to your SVDA. That chart is also not accurate, as the timing depends heavily on the carb or EFI, as well as transmission options and depending on destination country.

Fri Apr 14, 2023 3:00 pm

Pertronix distributors are based on the Bosch 034, so you're timing spec is for the 034.

Problem is that Pertronix and all of the aftermarket distributors are poorly made and have large variance from unit to unit.

Try this, set the timing to 32* BTDC with the engine rpm at 3500 rpm and the vacuum hose disconnected.

That will limit the mechanical total advance to 32*.

Also you have aftermarket dual carbs, so the vacuum they produce might not be the same as the original stock Solex 34PICT-3.

Fri Apr 14, 2023 3:12 pm

Quote: Also you have aftermarket dual carbs, so the vacuum they produce might not be the same as the original stock Solex 34PICT-3.

You are probably right about that...
I removed the vac hose from the distribuitor with the engine running at idle, and the was no difference..

Fri Apr 14, 2023 3:54 pm

MTT3107 wrote: So, I have read here and on other sites, that the way to set the timing on a type 1 engine is :vac disconnected, set to 7deg BTDC at idle, and look for 30-35 deg total advance at 3000 RPM.

My engine is a 1600 DP, stock, except for dual Empi 34EPC's, and a Pertronix SVDA electronic distribuitor.

When I use the above mentioned procedure, I end up at 40 deg total advance.
Are you seeing this 40deg (40BTDC?) with the vacuum hose connected or while it is still disconnected but you rev higher than 3000rpm?

The idea of setting the timing at high rpms (>3000rpm) and vacuum canister disconnected is to make sure the distributor's mechanical advance does not take you into detonation at any engine rpm. You rev the engine until the distributor stops advancing. If this happens at 3800rpm instead of 3000rpm you need to rev your engine higher. Watch the timing marks under the strobe light while you increase the engine rpms. Once the mechanical advance has fully advanced the timing (timing marks stop advancing, adjust the distributor to 30BTDC (just to begin with). Allow the rpms to drop to idle (<1000rpm). Tighten down the distributor clamp and rev the engine once more to make sure you adjustments haven't changed and the timing still maxes out at 30BTDC. Let the rpms drop to idle and note what the idle timing is. This can be your baseline. Usually it is somewhere between 5BTDC and 15BTDC. Add or remove a couple of degrees here at idle will change the max timing advance the same amount... and you won't have to bother your neighbors any more with a 4000rpm rev ;) .
With the vacuum advance still disconnected, and take her out for a drive. Accelerate hard to the rpm where your timing advance was maxed and listen for pinging or detonation. If you hear anything, retard the idle timing a degree or two and try again. If you don't hear anything you could try increasing the idle timing a degree or two but no more. 32BTDC is a good max total timing (initial + mechanical). Most find that 28BTDC or 30BTDC is good enough. Don't go more than this or you could encounter detonation at high rpms under a load.
Once you found your sweet spot, reconnect the vacuum advance. If you rev the engine in the driveway (no load) with the vacuum advance connected you should expect it to add 8-12deg of timing advance to the 30BTDC. 40BTDC+ is not unusual with vacuum advance connected. There is no spec for max timing with vacuum advance because vacuum advance adjusts for engine load. When accelerating under a load the vacuum advance basically removes any advance it was adding leaving you with just the advance from the mechanical advance which is RPM dependent. Mechanical advance does not sense the engine load. It only adjusts based on rpms.

28-32BTDC is the safe upper limit for rpm-based timing advance on ACVW engines. This is why the timing on SVDA distributors is set w/ the vacuum advance disconnected. Once you know your mechanical advance will not over advance at higher rpms, you re-connect the vacuum advance and let it auto adjust based on engine load. More vacuum advance under low load. Less/zero vacuum advance under higher load.

The SVDA distributor was designed to be connected to ported vacuum on the carb. Ported vacuum has no vacuum at idle since it is tapped from just above the closed throttle plate. As soon as the throttle plates are cracked open ported vacuum is exposed to intake vacuum and follows the intake vacuum curve.
If you test the vacuum on your carbs, you should see no (zero) vacuum at idle, then as soon as you open the throttle plat the vacuum level should jump up to nearly 20in-Hg. The SVDA vacuum advance will typically max out to 8-12deg of advance at 12-20inHg.
You can check this by connecting the hose to a vacuum hand pump or intake vacuum at idle and watch how many degrees of timing advance are added to the idle timing when there is vacuum on the vacuum advance hose. The hand pump and a vacuum gauge will allow very accurate incremental increases to the vacuum so you and confirm a smooth increase in timing as you increase vacuum. Connecting the hose to strong intake vacuum only confirms the max vacuum advance can be reached.

MTT3107 wrote: After some looking around on the web, I found this table, which says to set the timing at idle to 5 deg ATDC, for a 1973 1600 engine
What is it then ?
That is the stock timing with the OE DVDA distributor that came on the '73 1600 US Spec engine. Since you don't have that distributor that ignition timing does not apply to you.
Timing is set based on the distributor installed.

The DVDA distributors had a vacuum advance as well as a vacuum retard system that would retard the timing at idle by up to 12deg. This would take a normal 7BTDC idle timing down to 5ATDC. For this reason the timing was set at idle with both vacuum hoses connected. The vacuum retard hose was connected to intake vacuum at idle and would pull the vacuum canister into retard. The idea was to force the ignition event much later so the heat of combustion would be carried past the open exhaust valve and take more heat into the exhaust. This worked to burn up any unburnt fuel that made it into the exhaust, reducing the exhaust pipe emissions to satisfy mid-'70s emission laws.
Unless you need to be emission compliant for your model year, this idle timing retard serves no performance purpose. It just gets your exhaust pipes really hot at idle. :shock:

Sat Apr 15, 2023 12:08 pm

I've seen aftermarket vacuum canisters for the 034 allow more advance than the VW specification.

Sat Apr 15, 2023 6:30 pm

Heimliech, can you deliver more insite on the SVDA diversity of canisters avaliablle?

Sat Apr 15, 2023 7:02 pm

I only tested that one because a customer sent it to me with it on it.

Sun Apr 16, 2023 6:50 am

@ashman40 :

Thank you very much for that detailed explanation !

The 40deg total advance I mentioned is with the vac hose connected.

I will tinker with it some more, following your procedure.
I have noticed no pinging/detonation so far.

Sun Apr 16, 2023 10:34 am

MTT3107 wrote: The 40deg total advance I mentioned is with the vac hose connected. Then there is nothing to worry about as long as the initial + mechanical advance doesn't take you above the safe max of 32BTDC. This is the more important measurement.

Mon Apr 17, 2023 6:42 am

So, should I set the total advance at 3500 RPM to 32BTDC, and let the advance at idle fall to where it may ?

Mon Apr 17, 2023 10:00 am

yes, basically. However- if the idle advance ends up too low, for example 5 degrees after TDC, then you should repalce the distributor. I wouldn't settle for less then ~5 degrees before TDC.

Mon Apr 17, 2023 5:37 pm

MTT3107 wrote: So, should I set the total advance at 3500 RPM to 32BTDC, and let the advance at idle fall to where it may ?
I would state it slightly differently...
Start with an ignition timing of 30BTDC at "what ever rpm the mechanical advance is all in". Regardless whether this is 2500rpm, 3000rpm, 3500rpm or 3800rpm. Rev it until it stops advancing, then set it to 30BTDC as a starting point.
Test it at 30BTDC and go up to 32BTDC (or down to 28BTDC) thru testing. The range is because differences in engines result in different max timing.

Once done, note the idle timing as your baseline for future tune ups.
As long as the idle timing is in the TDC~15BTDC range you are good. It is more important to make sure the max mechanical remains within the safe upper limits than what your idle timing is. Less than TDC or more than 15BTDC and you will have a hard time starting the engine.

Tue Apr 18, 2023 7:18 am

Did that, and car runs well, maybe a little better than before. Advance at idle ended up being just a little BTDC.

Wed Apr 19, 2023 3:52 am

This is exactly why I never time at idle anymoe. Wayyyy too much variation with distributors and units installed in different than designed setups over the years. I always go for max advance then you know you're safe.