Question: Is it possible to run a 3600rpm diesel at 4500rpm?

[phsystems]

Hi,

Why is it that automotive diesel engines run so much slower than petrol?

I want to run an industrial diesel (say a kubota) engine at 5400-5000 rpm, whats likely to go wrong?

Thanks

Paul

[jacquesm]

well, you could run a diesel at 10000 RPM if you wanted to...

The catch is of course how long do you want it to live ?

All the pressures and wear figures are good only until you 'redline' an engine, any type, be they diesel or gas powered that does not mmatter.

besides totally wrecking your engine, why do you want to increase it's RPM ?

After all it's horsepower you're interested in, not RPM, a simple gearbox will increase the RPM for you to anything you could possibly wish for

[phsystems]

I am trying to convert a motorcycle to diesel, I want the minimum changes to the bike, and would prefer to run the engine faster rather than modify the gearbox. I dont need any more power, in fact I dont mind if theres a slight loss of power, I just need the revs!.  The old petrol engine runs at approx 7500rpm max at 110 mph.

Thankz

Paul

[jacquesm]

It would have helped if you gave full info the first time

Ok, so there are things called 'inline' gearboxes, a small set of planetary gears that you bolt to your outgoing shaft on your engine to give you higher or lower rpm.

Mess with the governor on an industrial diesel and hear the cash register chime !

[elvin1949]

if it is chain drive

change the final drive sprokets

later

elvin

[DanB]

I could be wrong about this, I'm not an expert.... this is my best guess though.

Diesel engines run at much higher compression.  Normally I believe they have a longer  stroke that gasoline engines.  At combustion, the forces on the crank, main, and rod bearings are greater than a gas engine.  I believe it's for these reasons that they are normally a bit slower, and heavier than their gasoline counterparts.

For the motor bike... I think you should probably change the gearing.  Wouldn't just changing the rear sproket make it all pretty easy?  I think if you buy a diesel and run it past it's 'redline' it wont last long...

[finnsawyer]

It's also likely the injector pump won't work properly at the higher rpms.

[juiced]

"its HP, not RPM you want."

 I disagree. I just think we dont know how to collect properly from RPM.

 I never won a bikme race trying to power my way through. Alwas by 'spinning'.

 Love to hear comments on this.

[TomW]

juiced;

This is pretty similar to your high volts low to no amps generator problem. RPM without torque is like volts without amps, you need both to get "power".

Common misconception that you have taken to be truth.

T

[juiced]

I have been thinking about you reply for some time now.

 When i ride, well when i want speed; i go into granny gear!

 Why?! I start 'spinning' at a rate yet to be measured, but bystanders say its almost too fast to see. I can get up to about 15-20KPH like this. Then i throw my front ring to 2nd and my rear to 2nd or 3rd. This propells me to about 35. By the time i throw my front ring into 3rd, the momentum of my legs (probably about 60lbs each) sends me flying to 46-50. Only then do i apply the rest of my gears, achiving an average max speed of around 67, avg speed 33. (all time max was more then the 3 digits my speedos(not shorts! :p ) can handle)

     I really REALLY try not to pump but rather like an engine with off set pistons, I propel a leg forward and one backwards (simplest neuron sequence to 'program') as fast as i can. The result is SPEED.

  So, now the only torque values i see would be the 'forward' leg because the rear follows suit and retracts according to tendon/nerve reaction.

   Im not so much challenging you but trying to learn.

 I thought i fully understood my biking techniques due to the results i achieve.

[DanB]

I think it's an issue of your engine Juiced.

Tom is right though.

When you want to go fast on your bike, you have to gear things way up - because humans are not very efficient high speed engines.  You could be in 2nd gear cruizing 20mph and peddling really fast (but not putting much torque on the pedals) so you have high rpm and not much torque, or... you can goto 10th gear and pedal real slow but find yourself pushing a good bit harder on the pedals (more torque).  10th gear will seem much easier basicly because humans are not very efficient high rpm low torque engines - your legs are much better suited to low rpm/high torque.  In either case your producing the same power to the back wheel, but one case is much more suitable to the design of humans.

[nack]

Don't run the engine past it's rated top speed, go to a larger primary chain crankshaft sprocket, and/or a larger front sprocket on the final drive chain.  Also plan on some kind of vibration isolating mounts - a diesel is likely to put vibration cracks in everything on the bike and maybe the rider, too.  If you finish the project, and want to ride it a second time, start checking for cracks in and around the frame welds as part of your pre-ride safety check.

[nack]

juiced,

In the mechanical world HP = Torque X (RPM/5252).  The actual definition of 1 HP is 550 pound-feet over one second.  The simplified equation has converted RPM to radians per second (60 seconds in a minute, 2pi radians in a rev) and divided 550lb-ft by the resulting number, 550/(2pi/60) = 5252.1131220... drop the fraction (resulting in an expected error of a milli-percent or whatever) and you now have a constant that encompasses most of your unit conversion ratios.