Supercharging the Triumph Drag Bike - AMR500 Supercharger

Published on 24 December 2023 at 09:42

I should point out that I haven't even finished putting the engine back together yet but I have become fascinated by the prospect of supercharging it. All the most successful bikes at the time were either supercharged or had twin engines, I have no doubt mine was quick but I don't believe it set the sprint world alight. My dilemma is that I really wanted to keep the bike as close to it's original state as I can but the lure of extra power is keeping me awake at night. Last night, I couldn't sleep because of impure thoughts of boost and how to fit an intercooler but the question of whether I should was the thing that really exercised the grey matter.

In the end I thought - what would the original builder have done if money had been no problem and the tech was available? I think the answer would be he would have done anything and everything to make the bike as fast as possible so that he could win more races.

Back then there were only a few manufacturers of superchargers - the likes of Wade, Shorrock and Weiand, most of what they made were for cars of at least 2 litres capacity, they were way too big for bikes. This is where the Japanese have made such a massive contribution to the wellbeing of petrolkind, they invented the Kei car. For the unfamiliar, in Japan they brought out a set of regulations for micro cars that are cheap to run, cheap to insure and will fit in the tiny parking spaces found throughout Japanese cities. They are restricted in size, power and engine size, rather fortunately for the Triumph owner the engine size is restricted to 660cc - virtually the same as our twins - and a power output of 65ps, which is about 63bhp. What all this means it that the clever Japanese had to find a way of extracting good power from small engines, the solution that many chose was a small, simple supercharger, the AMR300 and it's larger brother the AMR500 were born. These tiny chargers were compact, light and fairly efficient, they quickly became very popular indeed.  Customers loved them because with a simple pulley change to make the charger spin faster fairly decent boost could be generated, performance was similar to a much more expensive Eaton units of similar size. The one big problem they tend to have is the temperature of the air leaving the compressor - I have heard of temperatures in the 200 degree range, which totally kills any of the benefit derived from the extra boost - engines love cool, dense air, hot thin air is no good at all.  

 

There are two variants in common use, the smaller 300 that delivers 300cc of air per rev and the bigger brother the 500, which coincidentally delivers 500c per rev. Because of the heat issues nearly all the kei cars run an intercooler, lubrication is very important. The chargers are filed with oil, the type of oil used is vital to get the maximum performance, you also need the body of the charger in cool air.

This thing looks like it was made for the Triumph, it could live at the front of the engine in free air, it can take it's drive off an adapter welded to the engine sprocket, pipework should be fairly simple, a plenum could be made to feed the twin carbs. The best thing about these is that they are very cheap - less than 200 quid will buy you one. A few years back they were really hard to find as the manufacturers would only supply to the car makers but gradually a lot of reconditioned ones and good used ones found their way on to the market. The Chinese now make copies of them. I wouldn't expect one to last 100,000 miles but for the quarter mile used half a dozen times a year they should be just fine.

in terms of performance the unit should be able to supply about 0.7 bar of boost, I reckon power should be adequate.

The Triumph left the factory with 42 bhp, I think with the mods on it so far it should produce about 50-55 bhp, maybe as much as 60. I think I should be looking at an extra 30 per cent on top of that so hope it would be in the 80 bhp sort of range, with the bike weighing so little it should be a solid performer. So that is what I intend to do, I will get the bike running properly first and will then have a go at supercharging, after all I'm pretty sure it's what George will have wanted. 

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Vincent Brossy
2 months ago

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Dave, it's a very good idea to fit an aisin AMR 500 to a twin triumph. The picture is my pre war 1939 500 Triton, blowered. The bike is very fast and I think the power is 50 HP .