Jones Supercharged 4 cylinder Pictures
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Thanks to Paul for this picture of a Dennis Jones Supercharged 4 cylinder two stroke built during the war to race, but was made obsolete with the banning of Supercharging post war.
I met Mr Dennis Jones and his machine in October 1946. I was 15 and returning from compulsory Sunday walk to my school – Trent College. He was standing, looking at his bike outside the school driveway gates. I said “This is a four cylinder 2 stroke isn`t it?” He said “Yes, how do you know that”. I said “Well I can see it is!” Then we had a brilliant conversation about it. He had built this magnificent machine at home and cast the crankcase in his back garden;- well that`s what he told me,but of course he couldn`t say it was done at Rolls Royce could he?
Yesterday I came across a letter card I wrote to my father that evening. It is date stamped 7pm 7oct 1946 Long Eaton. I quote from it.- ` This afternoon I saw a motorbike which was a shaft driven 4 cyl 2 stroke, HOME MADE !!!!. It was supercharged !! So you can imagine what a beautiful thing it was. It had front and rear springing. The frame was beautifully constructed. The owner is a racing specialist and I had a good talk with him. I do wish you could see the motorbike an hear it running. The owner said that he has done 119 mph on it and is going to put it into racing soon.`
I feel that you could find this interesting. I wish I could afford your magazine ! R S. PH1 1QJ
Good day to you,
This looks really good and well manufactored. But what can supercharging achieve in a two stroke engine since the piston controlled exhaust slot is still open after the inlet slot is already closed again exept the scavenging with fresh air. In my opinion, no supercharge, means above ambient pressure, is possible in this design.
Have a great time, Rolf
Consider 2-stroke Diesels (Detroit Diesel). “Naturally aspirated” engines were supercharged. One could, IN ADDITION, opt for a turbocharger.
On 2-stroke bikes, it used to not be unusual to modify the crank with vanes, resulting in a “pull-through” supercharger. I used to do it, myself.
The bike is a nice piece of art! Such a priviliege to meet the builder…
Two stroke SI-engines with piston controled ports terminate the gasexchange process from exhaust side so any boost pressure available for the combustion needs to be based on the pressure level from the exhaust side as Rolf points out in his comments .
It also looks like this bike have exhaust megaphones which will lower the exhaust pressure even more within certain engine speeds.
However, if the exhaust pressure can be managed some power increase may be obtained. This can be done by utilizing a tuned exhaust pipe including a baffle cone at least within a certain speed range.
A more convinient way would be to use a turbocharger were the exhaust pressure comes as a part of the package which can be taylord to the proper level by careful turbomatching. Another upside with turbo is that no crank power needs to be spent for charging purposes.
Re the DDC they use an external scavenge pump but to my knowledge the purpose is not to create boost pressure at a significant level. Just obtain scavenging.
Ciao Lennarth