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Hi guys.

I think i may have decided to change the old Bosch setup on my M20B25 to a set of sidedraughts. I have done alot of theese back in the day on both 4 and 6 cylinder engines, so the tech stuff is not an issue.

However, converting the M20B25 to a carburatted version may be. I have the complete ignition set of the old carburated M20B20 and are planning to use this. On the M20B25 the hole in the block exist for this, but will the ignition run if i installe it? I have googled it a bit and it seems that the Germans call it the "zwischenwelle". Its the shaft that runs the oil pump. Will i need to change this ?

Hope some of you M20 guys know your stuff or maybe someone has done a similar setup.

On the other cars i have owned i have never experienced a power increase when installing Webers or Dellorto´s under 10bhp. Even a 1,3 liter VW got another 10hp. How does the M20 react to a set of sidedraughts ? My old Opel Monza 3,0 (179bhp) got just over 200 with this setup, a better flowing exhaust manifold an 2,5" exhaust). So expectations are a bit high

Yes it is possible to put the m20b20 dizzy in, it will drive the oilpump.
So that won't be the problem, but another problem is the place the distributer takes, it might interfere with your planned carburettors.

Do you change the camshaft as well?

BertjeConti wrote:Yes it is possible to put the m20b20 dizzy in, it will drive the oilpump.
So that won't be the problem, but another problem is the place the distributer takes, it might interfere with your planned carburettors.

Do you change the camshaft as well?

Thanks for the answer. I was unsure wether the oil drive shaft had the lobes for the drive on the pully.

Its seems that the distributor will fit, anyway i can see that others have made it work. I have flat head ignition cables and that free up much space. The next concern is the thermostate housing. It may interfere with carb # 1 but there are ways around that too

I am planning a camshaft at some point, but i´d like to see what i can get just on the stock engine as it is. 180bhp would be awsome.

you should be capable of just removing the blank and installing a mechanical distributor off another m20 engine without any mechanical problems. the only issue I see here is the possibility of ignition timing and retard rates. all m20 distributors offer different timing curves so finding one suited for your b25 could possibly be a bit hard with the proper timing advance properties.

Dammizi wrote:you should be capable of just removing the blank and installing a mechanical distributor off another m20 engine without any mechanical problems. the only issue I see here is the possibility of ignition timing and retard rates. all m20 distributors offer different timing curves so finding one suited for your b25 could possibly be a bit hard with the proper timing advance properties.

Are you reffering to the vaacum controlled ignition advance mechanism ?

Are you suspecting any Brakebooster problems? or is it a rhd car where the brake booster is located in a different place.

The carbs need a lot of space in the engine bay, but dizzy is possible like this E30 conversion below:



Looks very nice

I think a conversion only makes sense when the camshaft profile is changed also.

BertjeConti wrote:Are you suspecting any Brakebooster problems? or is it a rhd car where the brake booster is located in a different place.

The carbs need a lot of space in the engine bay, but dizzy is possible like this E30 conversion below:



Looks very nice

I think a conversion only makes sense when the camshaft profile is changed also.

I am going to loose the brake booster and drive without it, so that won´t be a issue.

The tripple sidedraught makes sence no matter what. I have done it alot of times on other cars over the years, from a 1,3 litre Polo Mk1 to a Opel Monza 3,0 straight 6. I have never had any bad experiences, and every car i have made the sidedraught conversion on has made alot more power afterwards even with no other tuning done to it. The reason is simple that elder cars typically has a very restrictive fuel injection system, and especially the old BOSCH injection systems are pretty much analogue and not-tunable and almost unadjustable. This also goes for the M20. 200bhp is near impossible with the Bosch fuel injection system still on the car.

Regarding the overall tuning it will of course make even more sense to add a high lift / high durability camshaft, and that can always be done later. It will require a tuneup of the doublecarbs and may or may not require a larger diameter set of venturi´s.

ruh wrote:

Dammizi wrote:you should be capable of just removing the blank and installing a mechanical distributor off another m20 engine without any mechanical problems. the only issue I see here is the possibility of ignition timing and retard rates. all m20 distributors offer different timing curves so finding one suited for your b25 could possibly be a bit hard with the proper timing advance properties.

Are you reffering to the vaacum controlled ignition advance mechanism ?

yes, you can read up on the differences in m20 distributors on this site:

https://sites.google.com/site/e21323i/b ... ng-numbers

Thanks for the info. My dizzy comes from a 82 320-6 and that seems to be good. Either 23 or 26 degrees. It should be easy to adjust this. It seems that the worse of the ignitions are the ones from the 323 and i am wondering if this is due to the 323´s old Bosch injection system?
I need to go find the dizzy number to make sure though as the ignition needs to be adjusted spot on before adjusting the triple carbs.

Once again thanks for the extremly usefull info