Diesel Bikes? Don't talk daft!

I suggested in a previous article at OD-Racing about a Triumph Trophy Diesel as a possible future bike. A few of you out there probably thought I’d totally lost my marbles, but the idea is not as daft as it sounds.

Diesel engines are being heavily promoted in the car world now for a number of possible reasons – less harmful emissions, easier and cheaper to make (less reliance on the Middle East for the right sort of oil to make petrol), etc. Diesel can actually be made from many things very easily, the commonly talked about being used cooking oil from the chip shop.

This year Audi won the Le Mans 24hr race as usual, but this time it was with a diesel powered car with a very impressive spec. Layout – 5500cc V12 Turbo Diesel Power – over 650bhp Torque – over 1100Nm This might not look that impressive, but bear in mind it was breathing through two 39.9mm diameter restrictors and had a maximum turbo boost of 2.94bar(absolute – 1.94bar above atmospheric) to comply with endurance racing rules.

It also had a usable rev range of 3000 to 5000rpm (diesel doesn’t burn that quickly compared to petrol, so the engines don’t rev very high). During the race, lap records were broken, the race pace was higher, with more laps achieved during the 24 hours and Audi used less fuel than previous years.

The engine was also the first large capacity, all aluminium cased diesel, to keep the weight down to racing levels. The engine was reported to be very smooth, with no vibration (a V12 is a very well balanced configuration), and was remarkably quiet. Take off the air restrictors and raise the turbo boost, and more performance is easily available. Re-engineer the engine as a standard road going unit, and the performance will probably drop down to just below the race version.

JCB are also trying to break the land speed record for diesel powered vehicles, using two modified digger engines. The world’s fastest JCB, you’ve never seen a road dug up so quick. While I’ve been typing this, they have succeeded in breaking the record with a speed of 328mph, and are still going to try and go quicker.

There are some diesel road cars with equally impressive figures, and civility built in (they don’t sound or drive like a tractor). A good example is the BMW 5-series.

Diesel Layout 3000cc 6cyl Turbo Power 190bhp @ 4000rpm Torque 410Nm @ 2000-3200rpm Av. Fuel Consumption 39.8mpg

Petrol Layout 2500cc 6cyl injected Power 189bhp @ 6000rpm Torque 245Nm @ 3500rpm Av. Fuel Consumption 30mpg

So, with a bit of Audi’s race winning technology, we could possibly see a 1200cc turbo diesel bike with: Power – 130bhp @ 5000rpm Torque – 220Nm @ 2000rpm Av. Fuel Consumption – 70mpg This wouldn’t replace any petrol engined bikes for top speed performance, but for a lazy tourer or custom cruiser, this could be ideal.

For a comparison, BMW’s R1200 has just over 100Nm of torque at over 3 times the revs. Imagine also an off road version for riding around the world on. Enough power for a decent top speed on the tarmac, with loads of low down torque for taking a mountain of luggage up the steepest of climbs.

The other advantage being that diesel fuel is nearly always easily available in remote countries compared to decent quality petrol. This is all sounding a bit too good to be true now, so you’re probably all wondering what the catch is.

Unfortunately, diesel engines are heavy. Due to the huge cylinder pressures involved, the engine has to be very strong, which results in it being heavy. Audi had the same problem when they were building their Le Mans winner, and so took the brave move of developing an aluminium block, rather than the commonly used cast iron.

A motorbike engine could be made lighter and stronger by adopting the monoblock principle as used on the Hart 415T formula 1 engine in the 1980’s. This engine was a 4 cylinder 1.5litre turbo engine, with the block and head cast as one piece, with no head gasket or head studs. There were no problems with the compression blowing the head gasket, so the boost could be wound right up.

Building the engine could be a bit tricky, as the valves had to be fitted through the bottom of the block and up through the bores into the chambers. So, if we used a monoblock construction, the head, cylinder block and upper crankcase could be cast as one piece, giving us a very strong and light structure.

This engine would also be strong enough to be used as a fully stressed member, enabling the frame to be minimised. The mass would then be centralised (the bike design word these days), and the bike could claw its weight disadvantage back.

Now, all we need is a manufacturer to take the plunge and produce such a bike. Some engineers in Holland have already built a diesel racing bike, using a 1200 VW Lupo engine, with some very encouraging performance figures. So come on Triumph, why not join forces with a company like JCB, and put Britain back on the map with something revolutionary. Don’t imitate! Innovate!

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