Pros and cons of the Drouin

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Dec 22, 2006
I have read some of the old threads on Drouin Superchargers and it sounds like this is a pretty risky thing to do to an old Norton. I wouldn't install one on my current bike, but I am planning on building up a msimatched bike using an 850 motor and various parts. I am considering installing a Drouin on that one.

Does anyone here currently run a Drouin, and if so have there been any big problems with the unit or with the engine as a result of the extra power output?

I have no experience with the Druin but have a little bit of experience with car applications for both turbo charging and supercharging. I'm sure that you have already seen the various negative comments about this modification, although I'm sure that most of these refer to a simple
bolt-on application. I would recommend that you consider a compression ratio drop down to at most 7:1 and possibly lower depending on the boost provided by the setup that you are using. This can be achieved by piston or combustion chamber machining or simply putting a compression plate under the cylinder barrel flange. I would also have thought that starting this project with the final iteration of the 850 crankcases - possibly even strengthened round the main bearing area - would also be the way to go. You should also consider boring the crankcase mounting holes to size and fitting brass inserts and sized bolts to ensure minimal flex of the cases.

Good luck

Anything can be done with enough money. Consider this before proceeding.
If the system has a 1-5 pulley set up you will be hitting 40,000 rpm on the blower bearings at max rpm. The bearings provided are rated at 20,000 in oil and 15,000 in grease. I have been told that there are bearings that can handle it but they didn't post a price. Will these bearings be packed in grease or have a re-cycling system with oil or a total loss system for the oil required? this will need more time and money. A carb with a guillotine slide will be very helpful cha chig, Maybe some new pulley's to get a belt that works, a waste gate or blow off for safety, and on and on the money flows...
Jim Comstock who knows, once told me that when you hit 100 hp the output end of the crank falls off.
norbsa48503 said:
Anything can be done with enough money.

Jim Comstock who knows, once told me that when you hit 100 hp the output end of the crank falls off.

:lol: :lol: :lol: :lol:

Don't take offense, I just couldn't resist.
If you do the Drouin, I would be interested in your prpogress.

Sounds as though buying a Drouin is buying a hole to throw money into.
Since I sold my boat for that reason, I will think twice about going this route. Thanks for the info.
I've been running a late model Drouin on my stock 850 Norton for 3 years with no problems. Go for it!
Dont listen to these people who don't know what they are talking about! A lot more power than stock. But you will have to balance the rotating assembly, install new bearings and get rid of the Drouin fuel injector set up. I have been runnng a harley C.V carb . But this winter I'm going to get a new 40mm Lectron with a power jet as the CV has its limits.
Bruce MacGregor RI :D P.S. dont buy the one on Ebay today, The impeller should have 18 blades.
Hi Bruce, good to hear from someone who is using the Drouin.

I have been looking at the one on Ebay, but it appears to be missing a few things. My understanding is that there were three versions of these built (for the Norton) . Is the ebay one the second version? I have seen photos of the third version, is this what you are running?I am thinking yours must be the third and final as I seem to recall the final unit came with fuel injection and twin belts, the others with a large carb and single belt.

Could this ebay unit be the second iteration and as such have a different impeller than yours?

Yea what he said. [Dont listen to these people who don't know what they are talking about! ] Just so ya know Bruce I owned one, running it just didn't seem worth the effort all things considered. Glad your happy with it ,you may have had better luck than I ,mine was one of the first models impeller bearings alone just made me shy.
(sorry if this auction was already posted somewhere else... !)

drouin 850, ends in 2 days. for a lot of scratch: ... 0192183692

my hats off to all of you who feel that the stock norton is underpowered!!! i converted my '71 750 to a front disc, and still feel like i am going supersonic at 80 mph... (on my friend's bsa, i get the same feeling at 60 mph!)


22 bids, and well over $5,500.00!!!

I could do a lot of nifty stuff to a Norton for less than that, and have it run pretty much the same speed, only a lot more reliably and a lot less ugly.
if you have not ridden a norton with a drouin you have not lived. they are a pain in the ass to get to work at all and they might not not last long but when they work they really work. they do not just bolt on in a few hours-the mounts are a joke. the value of the damage you can do to the bike can easily exceed the cost of the blower so beware-this is not for the faint of wallet. there was a saying that went- you always get a screwin with a drouin. still holds true today. like for bearings..... i am looking at using a slightly different bearing-same od and id but .5 mm wider-skf 2901 or nice 2601-there should be enough room to narrow the driven pulley or bore the mount deeper.
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