Supercharge!
0 to100 m.p.h. in 14 seconds in a HR Holden
by Eldred Norman
Chapter 9 - A Clutch For The Supercharger
People often ask if it is possible to fit a clutch to a supercharger so that it does not have to operate all the time.
As far as I know I am the only person in the world at present offering a unit with a clutch which can be operated from a button on the dash as standard equipment.
The fitting of the clutch involves more than just the mechanism for disconnecting the supercharger. It is also necessary to provide a by-pass system for the air/fuel mixture.
With an engine of small capacity a clutch has not the advantages it has with the larger motor.
In general, supercharging causes a slight increase in petrol consumption, partly because it takes some power to drive the supercharger itself over and above the power saved in the motor by the reduction in breathing effort, and partly because use is always made of the extra power available. Even if a person drives no faster there is always the tendency to accelerate faster.
In the larger car the rise in petrol consumption is more noticeable simply because it amounts to more money than it does with the small car.
Also there is the question of performance. The average three litre car of today is capable of around 90 m.p.h. and since few people drive at anything like this speed even on the open highway, the supercharger would appear to be superfluous much of the time. This is in fact so, as is the case with a large V8 motor.
My own Holden utility with a 186S motor and fitted with my 110 deluxe supercharger, which has a clutch, and pulling 3.36 rear end, has a top speed unblown of about 100 m.p.h. (Blown it will reach 135 m.p.h.). On long runs in the country I hardly ever engage the supercharger unless I use it to pass a timid motorist who is enjoying the diesel fumes of some semi-trailer. I use it a great deal in the city where the additional acceleration available is a big advantage.
Of course where big mileages are being covered the clutch saves supercharger wear as well as saving fuel.
In the past all my clutch models have been operated hydraulically. They have been quite satisfactory but expensive to make.
Quite recently I have been experimenting with an electric clutch of Japanese manufacture, which appears to be equally satisfactory and is a great deal cheaper. Of course there is still a considerable amount of work involved in fitting the clutch since the by-pass between the two manifolds is still essential. Roughly speaking the whole clutch set up for a small to medium supercharger is likely to cost about $100 more than the non-clutch version.
For demonstrating the effect of supercharging the clutch has no equal. You simply floor the accelerator unblown in say second gear, and then watch the bonnet line lift two inches when the supercharger engagement switch is thrown.
As I have said, in addition to the clutch itself it is necessary to provide a by-pass for the air/fuel mixture. If this is not done, although the car is still drivable the performance will be very much down on that of the normal unblown car the motor will have to operate either on leakage past the rotor of the supercharger, or it will cause the rotor to rotate slowly. In the latter case the supercharger is in effect turned into an air motor, and this of course offers a considerable impediment to the car's performance.
I am often told by the knowing that it is not possible to use the same carburetor and jet set up with both the blown and the unblown motor. This is rather amusing. You might just as well say that it is not possible to operate the same engine on both half throttle and full throttle. A large enough S.U. carburetor for instance will simply not open the dashpot/ choke assembly fully when operated without the supercharger, even on full throttle at peak revs. Of course with the supercharger engaged the extra volume passed through the motor will open the dashpot controlled choke further. With a large carburetor with fixed venturies and no progressive linkage arrangement it might well be that choke velocities could fall so low at low revs. unblown, that fuel starvation did occur, while the same motor operated satisfactorily with the supercharger in operation. This of course simply indicates that not all carburetors are suitable for supercharging as I mentioned in the chapter on carburettion.
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This is a special Technical Info article, reprinted from the original (and rare!) book that was supplied with superchargers purchased from Eldred Norman, Aussie racing legend and manufacturer of Norman Superchargers.
Although not a common method of modifying an FE or FC, the theory and information about fuel induction, carburettion and so on is fascinating. Many thanks to Tony (IhadaV8) for obtaining the book and providing it to us. Tony in turn thanks Mike Norman, for supplying a copy of his father's book.
Important Note: This document is intended as a guide for those persons interested in repairing or modifying their vehicle. The FE-FC Holden Car Clubs of Australia take no responsibility and accept no liability for the information contained herein. You must ensure that all work carried out and/or modifications made to your vehicle are legal in your state, and we recommend you contact an engineer or your local Traffic Authority for further information.
If you have a technical question about repairs or maintenance on your FE or FC, please post a question on our Discussion Forum.
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