Drouin Supercharger

I have a long term project to fit a Drouin to a Commando.

I have a new, unused late model Drouin and a variety of bike's/motors it will fit. (see signature).

The questions I would like to pose are:-

1. What would be the best stock motor. I am leaning to a standard stroke 850 mkII or MkV 750. Keep the revs down and use the torque.
2. What is the best cam for a supercharged commando. ?
3. Compression ratio ?
4. For fuel Bruce's lectron was a nice solution. Are there any improvements such as injection etc ?

This will be a street bike and ridden twice a month. Not a racer.

Any help appreciated.

Thanks

There was a discussion in the now closed Other Classic Bikes" Forum, over to you Hobot

I recall a magazine article on the Drouin when they came out, and they said that the stock cam worked better than the Combat cam. A stock 850 with 8.5:1 compression is the best starting point.

Hi, Stock 850 with stock cam works well. Even with the stock cam, there is a little too much valve overlap that will be evident with bluing of the exhaust for the first foot or so regardless of richness. I also sugest going with the Total seal piston rings and use valve seals on all 4 valves.
:roll: No you will not have any problems by doing the seals that way!
Bruce MacGregor

I know a fella that has a few of these superchargers. I've read a little on the bearing issues and ceramic replacements. I would love to build a mild engine to handle one, rod bolts, good head work and the best suited compression ratio. I have an MK111 which as I understand it is low on hp due to CR decrease and maybe a milder cam?? I'm sure a few extra pounds slowed them down as well.

I'll be keeping an eye out here for comments and progress!

Rusty bucket said:

I have an MK111 which as I understand it is low on hp due to CR decrease and maybe a milder cam?? I'm sure a few extra pounds slowed them down

Click to expand...

The MK3 has the same compression ratio as the earlier 850s.
It also has the same cam profile as all other Commandos, Combat excluded (and the handful of production racers that exist).
The Commando profile is the same as was used on the first 650, the Manxmam and then the SS, then the Atlas. It's a really good profile for the street, so they never changed it.
What really slowed the stock bike down were the "whisper quiet" stock mufflers. An electric starter is not heavy enough to make a great deal of difference.

Glen

Rusty bucket said:

I know a fella that has a few of these superchargers. I've read a little on the bearing issues and ceramic replacements. I would love to build a mild engine to handle one, rod bolts, good head work and the best suited compression ratio. I have an MK111 which as I understand it is low on hp due to CR decrease and maybe a milder cam?? I'm sure a few extra pounds slowed them down as well.

I'll be keeping an eye out here for comments and progress!

Click to expand...

The Drouin kit only fits pre-MK3.

Can anyone provide a cam ground for supercharger use ?

Thanks

Nortiboy said:

The Drouin kit only fits pre-MK3.

Click to expand...

Say it's not so...

:cry:

Nortiboy said:

Rusty bucket said:

I know a fella that has a few of these superchargers. I've read a little on the bearing issues and ceramic replacements. I would love to build a mild engine to handle one, rod bolts, good head work and the best suited compression ratio. I have an MK111 which as I understand it is low on hp due to CR decrease and maybe a milder cam?? I'm sure a few extra pounds slowed them down as well.

I'll be keeping an eye out here for comments and progress!

Click to expand...

The Drouin kit only fits pre-MK3.

Can anyone provide a cam ground for supercharger use ?

Thanks

Click to expand...

Suggestion
Could possibly use radiused lifters since result will be less overlap but won't affect lift.
I'll check (profile) the "QR" norton cam. It might also be a suitable grind to reprofile on to a 20M3S+ 06-1084 commando core.
The QR cam is a pre 20M3S cam shaft. It came in my 1959 88 engine.
sorry for all this pre commando mumbo jumbo

I have 3 drouins but have not installed one yet.
http://atlanticgreen.com/ndsc.htm

Bernhard said:

There was a discussion in the now closed Other Classic Bikes" Forum, over to you Hobot

Click to expand...

Where is Mr H.

The nicest supercharged Commando I've seen was featured earlier this year in an Aussie publication "Retrobike". It was built by a kiwi by the name of Ray Coleman. It uses a small Aisin blower (about six inches tall, four or so wide and about eight long) originally designed for use on a small Subaru car. The supercharger sits directly behind the head and is mounted onto a custom inlet manifold. Drive is via a small belt, with the drive taken from a beefed up points housing behind the cylinders, with the actual points located as per later Commandos. The carb is a 32mm Bing. The whole bike has been customised (later Japanese forks, wheels etc) and looks the business. The owner's estimate from the 750 engine is around 70hp, with very snappy response. I think it looks brilliant - very elegant and quite unobtrusive. I'm now keeping my eye out at swap meetings for a similar Aisin blower (I have also seen them on ebay).

Hi Nortiboy.
Seen this site?
http://commando.yolasite.com/drouin.php
Ta.

[quote="dynodave
Suggestion
Could possibly use radiused lifters since result will be less overlap but won't affect lift.
I'll check (profile) the "QR" norton cam. It might also be a suitable grind to reprofile on to a 20M3S+ 06-1084 commando core.
[/quote]

The radius or offset radius seems an elegant solution to reduce overlap. I know little about building boosted engines so any help is appreciated.

As far as I know, all norton twins had radiused lifters from 1949 until around 1959-60... so not really that exotic,, but could be useful to revert to earlier configuration in this case.