Bosch DVDA distributor question

aeromech · Posted: Sat Jul 20, 2013 2:00 pm Post subject: Bosch DVDA distributor question

Guys,
I'm in the final stages of building a 1776 for a 1971 bus. Currently the engine has a SVDA distributor but I found a DVDA in my parts pile and was wondering if that would be a better choice. The number is 043 905 205C which from what I can tell originally came on a 1974 Thing. What would you do? The carb is a Solex 34PICT-3 that I'm in the process of rejetting for the larger engine size.

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Randy in Maine · Posted: Sat Jul 20, 2013 2:48 pm Post subject:

Stock camshaft?

Is the 34Pict 3 set up for a DVDA based on the flange number?

aeromech · Posted: Sat Jul 20, 2013 3:37 pm Post subject:

airschooled · Posted: Sat Jul 20, 2013 3:51 pm Post subject:

That model you have sounds like it will give you much more vacuum advance and much less mechanical advance. From OVH:

205C - bug and thing
9-12deg Adv, 11-13deg Ret; Centrifugal: 6-12deg @ 1500rpm, 22-25deg @ 3800rpm

205Q - bus and pickup
2-5deg Adv, 11-13deg Ret; Centrifugal: 12-16deg @ 2200rpm, 22-25deg @ 3800rpm

Be careful of the vacuum can specs. Busdaddy informed me of the different treatments given to different cans that share the same part number. The dimple prevents over-advance on the bus units. I accidentally installed a non-dimpled version and had pinging once the engine reached a nice operating temp. Drove like a bat out of hell though Twisted Evil

EDIT: Flange info can be found in this thread…
http://www.thesamba.com/vw/forum/viewtopic.php?t=185095
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aeromech · Posted: Sat Jul 20, 2013 4:58 pm Post subject:

Here's some more information. I just set the timing. The Bentley says for a 1970 bus with single carb it should be 0 degrees at idle with vacuum hose disconnected and plugged. This yields 27 degrees total advance. When the hose is hooked back up I'm getting 37 degrees total advance. Is this correct? Seems like it could run a bit better than it is. I used 1970 because they didn't have the DBDA distributor so I thought the specs would be closer. Am I wrong?
Additional info. The valves haven't been set yet. I'll need to do that tomorrow and I'm not sure how much that might affect things right now.

I accomplished the cam break in today. Tried to purchase the correct jets for the 1776 but they were out of stock so I just drilled the main one numbered drill bit larger.
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Lead Mechanic: San Diego Air and Space Museum
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Boeing 727,737-200-300-400,757,767
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BAe146
Fokker F28/F100
VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
Capable of leaping tall buildings in a single bound

busdaddy · Posted: Sat Jul 20, 2013 4:59 pm Post subject:

Unless it has to smog the SVDA is likely just as good depending on what model it is (what's the number on it?), the DVDA makes that super retarded idle that keeps the exhaust hot but really doesn't have much of an effect at speed. It does play well with the 34PICT3 without modifying throttle plates, etc..
As Asaib3 mentions total vacuum advance is a factor as the bus lingers in a RPM range that a light beetle accelerates through quickly.
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aeromech · Posted: Sat Jul 20, 2013 5:01 pm Post subject:

I don't know the number of the SVDA
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Lead Mechanic: San Diego Air and Space Museum
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Boeing 727,737-200-300-400,757,767
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DC9/MD80
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VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
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Capable of leaping tall buildings in a single bound

aeromech · Posted: Sat Jul 20, 2013 5:08 pm Post subject:

Answers:

Flange number is: VW325-2

SVDA number is: 0 231 167 070
113 905 205 AN
_________________
Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
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Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
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VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
Capable of leaping tall buildings in a single bound

Randy in Maine · Posted: Sun Jul 21, 2013 5:56 am Post subject:

That is the factory carb/distributor set up for a 72 beetle.

It should work fine.

aeromech · Posted: Sun Jul 21, 2013 9:09 am Post subject:

busdaddy · Posted: Sun Jul 21, 2013 9:22 am Post subject:

I'd set it to 30 degrees full mechanical advance (hoses off) and see if you can hear any pinging when really hot and you suddenly speed up.
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Wildthings · Samba Member Joined: March 13, 2005 Posts: 50352

Either a SVDA or DVDA dizzy needs to be timed in the 28-32°BTDC range at 3500+ RPM's hoses off. Start with 28-30 and see how it runs and if pretty weak give it another couple of degrees.

aeromech · Posted: Sun Jul 21, 2013 9:30 am Post subject:

Sounds good. The engine is going in today so I'll know more later after my first run.
_________________
Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
Capable of leaping tall buildings in a single bound

Joey · Posted: Sun Jul 21, 2013 9:43 am Post subject:

Just to add... the reason that the DVDA distributor must be matched to the correct carb is because on the carbs that came with dual vacuum distributors that were timed to 5*ATDC at idle the hole in the throttle plate was larger. 5/32" compared to 1/8" in the single vacuum carbs. The larger hole was to help with the idle because of the retarded timing.
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borninabus · Posted: Sun Jul 21, 2013 10:26 am Post subject:

I would test drive it w/ both and see which one feels best.
I have found that some beetle vac/mech dists can cause a bus engine ping under hot load.
A 205C not being one of them.

They will both be pretty soggy on a "performance" engine, IMO.
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aeromech · Posted: Sun Jul 21, 2013 10:35 am Post subject:

Well I wouldn't consider this to be a performance engine. When I started on the rebuild I thought it was a stock 1584 but it turned out to have 88mm pistons which made it a 1700. Couldn't locate replacement 88's so we decided to up it to 90.5 which I had a good set of in my shop. So here we are with a 1776 with a stock cam as well as everything else mostly stock.
_________________
Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
Capable of leaping tall buildings in a single bound

raygreenwood · Posted: Sun Jul 21, 2013 11:32 am Post subject:

Bear in mind that the dimple in the can is not a great way to identify one can over another. The dimple and the ring around the dimple have more to do with the seating plate for the spring than the spring tension itself.

Bosch cans had a stamped # on the arm. I wouldd give my front teeth for a chart of those #'s as it identified the specs of the can. The dimple area was used for numerous things and I have found identical cans with the identical arm # that have dimple and no dimple...so always test the cans with a hand pump and note the draw length on the arm at various vacuum settings.

Also note the total arm length, the depth of the notch in the arm on the can side of the arm...which is what allows the arm to draw to a pre-set maximum stroke, and also note teh notch length and spacing for the vacuum retard on the arm...as well as the retard stop pin diameter. these are the items aside from internal spring pressure...that differentiate one can from another.

Years ago I disected about a dozen differnt dual vacuum cans. they all had roughly the same springs.

The real differences werein the thickness of the bakelite block in the can that sparates the vacuum diaphram from the retard doaphram. that item will change the stroke ....taking more stroke from one diaphram and giving it to another. for the most part...the springs and bakelite block were the same.

The differences were primarily in arm length...notch length for vacuum and retard arm stops...and retard stop pin diameter and placement.

Of course there are obvious differences...like the placement of vacuum nipples...and there are some units that are idnetical in every way saave for the nipple placement.

keeping all of this mind....I have found that if you find a working can that has the same vacuum pressure characteristics...and the nipples are in the right places....but the vacuum arm stroke is simple shorter....if you are skilled with a dremel tool and files you can open the notch up to make a short stroke can identical to a longer stroke one. You can also tune retard rate by increasing the diamter of the retard stop pin by drilling a small hole in it and installing a setscrew...or...grinding the pin to decrease its diameter, or wrap it with a metal band. You can also open up the retard notch if for some reason you want to increase retard stroke.

There is no mystery to these cans....just a lack of manufacturere documentation as to the specs of each can and a map of the arm #'s.

Oh...and by t way...the coolest dual vacuum can I have found...is the arm #917 which came in some 411/412 and most 914 with 1.7L. It has an adjusting screw in that dimple...which allows limiting the vacuum advance. You can install that screw in about 20 minutes in almost any dual vacuum can. Ray

aeromech · Posted: Sun Jul 21, 2013 3:55 pm Post subject:

Well the engine is installed and I test drove it. Ran pretty good and thankfully there are no oil leaks yet. Now I can go on vacation this coming week without having a project unfinished. Here's a couple pics.

As a side note the owner is a retired teacher and lives in a $1m cliff house overlooking the ocean. I guess he just likes driving that bus.
_________________
Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
Capable of leaping tall buildings in a single bound

airschooled · Posted: Mon Sep 30, 2013 10:33 pm Post subject:

borninabus · Posted: Tue Oct 01, 2013 8:56 am Post subject:

i have a 205Q w/ can #853.
i believe it's OG.
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88 Van WBX, A/T - 13 JSW TDI 6M/T - 2012 Touareg TDI Sport


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