what limits diesel max rpm?

[matt-max]

talking with my dad (retired gm engineer) tonight, he asked what limits diesel maximum rpm.

our trucks usually redline around 3500ish although, according to those that have aftermarket power-adding devices that change rev limit, this can be increased to around 4000 with substantial power gains.

in motorcycles, lighter reciprocating parts (waisted bolts, knife edge rods, etc) are used to increase max rpm and power. (stock 600cc yamaha r6 redlines at 15,500rpm!)

is it just the additional weight of the diesels that limit them? does the compression ignition mandate heavier parts?

with a 6.5 or similar motor obviously the breathing is poor, but with a 32-valve dmax i would think a higher rpm would be beneficial and desirable?

what is the highest factory and non-factory rpm for a diesel anyone is aware of?

thanks for any info and opinion!
matt

[NH2112]

I think the main reason diesels tend to be held to lower RPMs than gassers is because the pistons can outrun the combustion at higher RPMs.

[EWC]

A couple of years before the Dmax came out there was an article in Autoweek with a vice pres of VW talking about diesels . One of the points was how the mechanics of the diesel combustion process limited RPM's to about 5000 .

Bill Heath had a 6.2 drag truck and broke something on a pass ( rear end ? ) and had the tell tale go to 8460 ! Article was in TDP a few years back . Upshifts @ 4500-5100 and through the traps around 4600 .

[More Power]

These engines are really just big air pumps, and are designed to be most efficient over a predetermined rpm range. The Duramax 6600 is most efficient at 3100 rpm - less above and below that, according to a 2000 SAE paper I have.

Certainly the heavier reciprocating components in a diesel engine tend to limit the max safe rpm, but flow and diesel combustion efficiency also enter into the equation.

The new Ford PSD has a higher governed limit than the Duramax. I contend that this higher rev limit is the key to its performance edge over the Duramax. Higher rpms tend to coincide with higher HP potential, and a broader rpm range means you can stay in a lower gear for a longer period of time while accelerating or pulling hills (torque advantage due to gearing).

I read once in the TDR that the 5.9 Cummins comes apart at 4250 or thereabouts. That's why Banks limited its Bonneville truck to 3800.

We know the Duramax is factory governed at a max of 4800 while in grade-braking. We hope to discover if it can run at power to 4800 in the Duramax project truck.

MP