Supercharging pre-WW2 MG Midgets – 130 MPH!

 

A slight digression from the current bike projects….

I was recently thumbing through an ancient copy – June 1935 - of The Motor

when I came across 2 adverts relating to MGs of the period - I take an interest in these because I have one. The first of these was from MG itself advertising the MG Midget and its racing prowess

and the second was from Zoller superchargers, again advertising the speed that could be obtained from an MG Midget by supercharging.

What caught my eye was the fact that both adverts are claiming over 130 mph (209 km/h), presumably the same car and event. With a 750cc engine this will almost certainly have been a J4. I am not an expert on the different variants of MG Midgets so I have to resort to Wikipedia which tells me:

“The J4 was a pure racing version with lightweight body work and the J3 engine, but using more boost from the supercharger to obtain 72 bhp (54 kW).”

Just for the record, the “8 H.P.” referred to in the Zoller advert is not a measure of the actual power of the engine but rather a value assigned for purposes of taxation based loosely on the size of the engine – see here for details.

As anyone that has read my blog in the past will know, I also put a supercharger - a Marshall blower - on my MG PA some years ago (see here and here) which is why these articles caught my eye. The claimed power of 72 bhp is substantially more than the 42.6 bhp that we measured on the dyno after fitting and setting up the blower on my car; admittedly, I am running with around 3 – 4 psi maximum boost pressure rather than the much higher boost that these early midgets would have been using. Incidentally, the J4 engine only has a 2-bearing crankshaft whereas the PA that I have with 847cc has a 3-bearing crank.

However, 130 mph! Assuming this is not a complete fabrication (and the magazine is dated June 4 1935, so it’s not an “April Fool”), I cannot imagine being in one of these little cars at a speed even approaching this sort of figure. This is my little MG PA at a classic car event at Amberley earlier this year

and this is my installation of the Marshall compared to the Zoller in a PA.

I find that driving my little car at 55mph (on 4-inch-wide tyres) is quite exciting enough - they were brave men back in 1935!

Nevertheless, after 5+ years of driving with the blower fitted I have found it to be totally reliable and a great performance booster - especially for improved torque at lower engine speeds. Barry Walker still has these kits for sale for anyone interested.