MG Midget Forum

Hi guys and girls,

Recently started to bring my 73 midget back to life after 5 years off the road. Rebuilt suspension and brakes front to back and a few engine mods.

I've got a rotrex supercharger hanging round the garage and wondered if anyone has ever attempted to fit one to an a series?

Positioning on the engine could be an issue as it needs to be in line with the crank pulley, I have an alternator on the one side and the exhaust side seems cramped.
Would the engine cope with the additional load of an extra crank pulley?
Cheers for any help,
Ant

Hi there Anthony,

I have never owned a blown Spridget, but back in the U.K I had a pal at uni who had one - a 1275 mk4 .

As far as could be worked out at the time it is not worth the effort of fitting, discharging the heat build up etc.

You can get the same power and better reliability with off the shelf bits and bobs.

I remember his blower getting hot under the bonnet, and getting air out of the engine bay without using tin snips was a real issue.

There is a twin cam 4 valve head available from ( I think ) Aldon or Burton and that comes with Webers or EFI and with a few better sparks can get 125 hp reliably and it looks so cool. And the bonnet does not get paint burn from the heat.

I have a pal here in the land that time forget that has one of these jobbies, the car goes well, and all he does twixt races is wash it and check the tyre pressures.

Kind regards to the old dart,

Chris.

My fake plants died because I did not pretend to water them

.???

Never heard of this issue with supercharging. Turbocharging......yes. The same issues don't arise with a supercharger as there are no additional exhaust plumbing issues to deal with.
I've never heard of the rotrex, so not familiar with its design/size, but as long at its delivery volume is correct for the A series 1300cc displacement, it should be doable.

The twin cam deal is pretty involved, and the one I'm familiar with, uses a BMW R1200 head IIRC.
A significant amount of machine work is involved, and it adds enough height to the engine to require a bulge in the hood.

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Andy

NAMGBR# 20-7738



Edited 1 time(s). Last edit at 2014-07-23 06:34 PM by 7mg2.

OHHH it is very doable, but is it worth the effort ?

The heat eminates I think from the speed and mechanical movement of the vanes in the blower. These things have very large and deep cooling fins for a good reason.

I think it may be a rotax blower, or perhaps an shorrock.

They were the only two I remember in the U.K that we used for the dragsters on Santa Pod back in the olden days.

Of course one fun advantage with a blower is that you can fit a clutch ( like an air cond clutch ) that can then be switched on and off at will, and the resultant high pitched whine from the motor when it is engaged can be used to startle the passers by !!

It seems to me that if forced induction was really a reliable way to get power there would be more of it about and the big manufacturers would have persued it more vigorously. Good for torque on trucks of course.

My daily driver Benz has a blower, but it is scarcely noticeable and I reckon it is only there because Jag offer one!!

Kind regards,
Chris.

The Judson supercharger I sold a few years ago was a vane type compressor and increased heat levels under the bonnet considerably. Got hot!

Now the Eaton type supercharger kit for the Midget currently being sold by Moss doesn't have this shortcoming I've been told.

The cylinder head conversion is as follows -

It is made by Jack Knight Developments- jacknight.co.uk - ( the works Imp people ) and is a straight bolt on bit- all the pulleys and stuff come with the kit.

It requires no alteration to any body panel, and various extra sooped up internal parts can be added later if required.

The only thing is you have to use a good quality coolant as the new head is aluminium, and it can safely run unleaded ( preferably the high octane stuff ).

My pal uses the waterless coolant, and runs on avgas.

It do go!!

Kind regards,

Chris.

hm, the Jack Knight web site doesn't include any information (that I can find) about the cylinder head conversion you are mentioning

There are a couple of guys over at the mini mania forum who have fitted 4 valve, twin cam BMW motorcycle engine heads to their 1275 A series engines. There is a fair bit of engine machining (not to mention a custom cam necessary). I was not aware of anyone offering a kit to make this a DIY option.

The result is beautiful, and goes really well, but it sounded like a very major undertaking. It sounded much more involved than simply bolting on a supercharger.

Norm

I'm curious Chris.

Jack Knight have been known for many years for their excellent gear work. Jack Knight gearboxes particularly, but I have never seen anything else from them.

If you could provide more detailed info on this twin cam set up for the A series, I'd appreciate it.
As Norm says, there isn't any info on the web site.

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Andy

NAMGBR# 20-7738

Hi, I think the twin cam head is from Kent Auto Developments (KAD) and they're not cheap by any standards!!

http://www.kentautodevelopments.com/shop/category/16v-cylinder-head-kits-and-installation-parts/

I think the BHP gains are quite staggering but it makes the Moss supercharger kit a bargain in comparison.

Mark

We have a Rotrex on an inline 6 302 motor here in the shop. They take a fair amount of hp to turn. The required lubrication is $125 a pint. Other than that, the planetary gear design WILL make more power off idle than an Eaton style screw charger, but its power output is capped based on sizing. Which size unit do you have? One off a 6 cylinder Jeep? Keep in mind you don't want to blow through carbs, so figure the cost of fuel injection into the overall cost, or you'll need to make a sealed box for the carbs. By sealed I mean 100% sealed, and I'm not sure how SUs will respond to that.

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jeff@advanceddistributors.com

Hi, if you wanted to keep it on carbs you could use a HIF44 from an MG Metro as I believe they were 'blow through'

Thanks
Mark