DVDA retard function

[theKbStockpiler]

Hi all!
Can anyone tell me if the retard mechanism on a DVDA works against the advance side and cancels this out only ,or does it actually retard the timing past where the centrifugal advance is? Example; if the centrifugal part has the spark timing at 15 BTC can the retard part counter act this and set the spark timing at 10 degrees BTC?

Thanks for your expertise!

[Clonebug]

Hi all!
Can anyone tell me if the retard mechanism on a DVDA works against the advance side and cancels this out only ,or does it actually retard the timing past where the centrifugal advance is? Example; if the centrifugal part has the spark timing at 15 BTC can the retard part counter act this and set the spark timing at 10 degrees BTC?

Thanks for your expertise!

Almost every distributor is a little different so if you really want to know what it is doing you will have to document it yourself.
I can't remember what mine would do it's been so long. I haven't searched for that either since 2011.
Install the distributor and put air to the correct fitting, then use a timing light to note how much retard you get per pound of air applied.
I ran a DVDA for about two weeks and only 6 lbs boost. The first thing I bought was a MS-1 and crankfire trigger to give me loggable and infinitely adjustable ignition.
I bought it because I didn't like not knowing what I was getting for ignition advance.

If you stick to 6-8 lbs boost a distributor like that would probably work well enough but any higher boost numbers....especially if you don't have intake cooling....would give a pretty good chance of hurting the engine.

Any intake temps above 130-150*F will start to give detonation without boost retard. That is not much especially in the summer when your ambient intake temps can be over 100*F non boosted.
My turbo heats the air about 20 degrees from ambient just going through the turbo nonboosted.
So 80* weather gives me 100*F cruising air intake temps.

[theKbStockpiler]

I found a Dave and Robs ;or whatever page that has this to say about it:
This distributor it timed at 5 degrees after top dead center (ATDC) at idle, which jumps to 7.5 degrees before top dead center (BTDC) above idle, then normal advance after that.

It sound like it does actually retard the timing instead of back off of the vacuum advance only.

[Clonebug]

I found a Dave and Robs ;or whatever page that has this to say about it:
This distributor it timed at 5 degrees after top dead center (ATDC) at idle, which jumps to 7.5 degrees before top dead center (BTDC) above idle, then normal advance after that.

It sound like it does actually retard the timing instead of back off of the vacuum advance only.

Its a Dual (V)vacuum Dual (A)Advance diaphram....DVDA
The second nipple is used with only boost and it will retard the timing a set amount of degrees.......apparently you can file the linkage for clearance to gain a little more retard if needed....how much has to be determined by trial and error.
Do you have one on hand that you can look at???


While they will work...I myself didn't like the fact that you can't tune it and are stuck with what it gives when installed.

I spent about $350.00 to install a MS-1 with crankfire ignition.....it was worth every penny.

You can do a Megajolt for about the same price but you can't upgrade to FI with Megajolt.

I realize you can''t do Megasquirt for that price now but in the long run it is still worth it if you plan on going to higher boost levels.......You know you want to......

I have taken apart at least ten of the DVDA distributors and about eight of those had bad DVDA diaphrams. They would not hold vacuum and therefore were junk.....In fact....most VW distributors are worn out rusted pieces of junk and don't work like they are supposed to.
Make sure you test them before putting any serious amount of boost to them.

If you go thru my build you can see I didn't take long before I upgraded to a better ignition setup........it was no more than a couple weeks..

[theKbStockpiler]

Did you have the DVDA connected the same way as stock using a turbo?

[Clonebug]

Did you have the DVDA connected the same way as stock using a turbo?

The inside connection on the diaphram gets hooked the the carb connection like stock and the outside larger connection gets hooked the turbo wastegate outlet if it has one. Otherwise give it a boost reference only....no vacuum.

[theKbStockpiler]

Wouldn't the vacuum side have to be connected to a pressure higher than boost reference for the retard side to work?

[Clonebug]

Wouldn't the vacuum side have to be connected to a pressure higher than boost reference for the retard side to work?

I was wrong....You only hook up the inside connection to the carb advance port....it will take care of advance and retard because the dual diaphram allows the advance plate to travel both ways.

It's been so long since I dealt with a distributor I can't even remember most of it.

If you are serious about boost....get a boost referenced programmable ignition with logging capability....it's worth every penny.
That way you can log where the detonation is and lower the advance in only that area instead of guessing.

Trust me....it will be the best money you spend.