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 Marshall J50 Supercharger		  Forum Locked  Topic Locked
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doctorbob

United Kingdom
145 Posts
Posted - 17/04/2008 :  12:20:11  Show Profile
Would this size of blower be the correct size to run at the same rpm as the engine on a J2, or would it need gearing up? Similarly, does a volumex unit need any specific modifications to run directly off the front of the engine?

David Allison

United Kingdom
665 Posts
Posted - 17/04/2008 :  13:58:36  Show Profile
From memory - the J series blowers were all designed to be belt driven (I will have to check) but the most often used sizes by the works were the 75 (for larger engines) and the 85 for the (smaller engines) although I am less than sure of this fact.

The swept volume of the blower is the key - that is the amount of air displaced on a single revolution.
The swept volume should be more or less similar to that of the engine - smaller and the thing will not produce enough boost to be worth driving it - too big and you will need special brew fuels.

A Volumex blower is designed for an engine of around 1600 cc - similar in size and swept volume to the Marshall 75 this blower gives up to 15 lbs boost on a 1100 cc 6 cylinder engine.

The modification to convert the Volumex to shaft drive is not complcated but there are a number of specialists offering the service which includes supply of the blower and the fitting kit.

The drive has to be altered from the Fiat system (belt driven) - pressing in a new drive shaft machined to take the MMM universal jointed drive.

I know Peter Green has converted a number of these blowers (he has one on his K3) Oliver Richardson has just fitted one to my sisters NB racer and the kit of bits was very tidy.

The work done by Fiat on the supercharger was very helpfull! - giving us a supply of replacement units for 15 years following production plus a continued parts supply for an additional 10 years.
This service is comming to an end but the units still seem to be in circulation - who knows in 20 years it might be Lancia-Alfa owners comming to US for spares?

Hope the info helps
Regards David
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George Eagle

United Kingdom
3240 Posts
Posted - 17/04/2008 :  18:15:42  Show Profile
My NB is fitted with a front mounted Volumex. The pulley for the original belt drive has to be removed and replaced with a coupling which has it's own universal joint and is splined to take the drive shaft. As I recall the only machining required was to have the Volumex shaft machined to fit a woodruffe key. The couplings and all the fittings are readily available from suppliers.

With regard to fitting the Volumex to the J or P types, it is possible to reduce the swept volume by machining the rotors and having a distance piece made. I believe Ken Robinson in Slough has done this mod for several owners.

George Eagle NA0960
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Richard Hardy

United Kingdom
2159 Posts
Posted - 18/04/2008 :  13:33:21  Show Profile
Ken Robinson (Slough Gringing Services 01753696989) has Volumex blowers in all the time that he is working on for customers. He keys rotors/ gears, and keys the shaft and undertakes the necessary machining for the drive coupling arrangement as well as reducing capacity is required. He is worth talking to.

Rich H
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Bill Putnam

USA
64 Posts
Posted - 16/05/2008 :  19:45:12  Show Profile
We've been running Marshall J75 and J100 blowers on J2s. Drive is at crank speed by a direct shaft off the front of the crank. Displacement has varied between 847 cc and 939 cc. Boost has fallen in the range of around 5 psi for a somewhat worn J75 and 15 psi for a J100 in good condition with the smaller displacement (847 or a bit more).

I would expect that a J50 driven at crank speed would be somewhat undersized, and either a larger blower or stepping up the blower speed would be needed to realize much improvement over normal aspiration.

Bill Putnam
J3488

bputnam@cityofmadison.com
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