RPM Limit

[Trippin]

Forgive my diesel ignorance. I've been a gas guy all my life. This board convinced me I should own a D-max. Bought one, love it. That said, what is the "hard part" limiting rpm factor of a D-max? Valve springs? Rods? Oiling system? I see in the build-up article in the members area a 5500 rpm statement. Just "idle" curiosity. :rolleyes:

[Heartbeat Hauler]

Well I'm not one of the engineering types, but it seems to me that when you build a heavy duty engine everything in it is heavy duty. The key word is heavy. I would suspect that the internals of the DMAX, for purposes of longevity, are heavy (weight wise) parts and some sort of law of physics may limit the speed at which all of these parts can move (there is probably a margin of safety built in for future enhancements). When you get that much weight spinning the faster you go the heavier it gets (E=mc2). That puts a ton of stress on the crank, bearings and main caps, not to mention heads...blah blah blah. So I guess you could build stuff out of titanium, but then it would cost so much no one could afford it...well almost no one. Now there are guys out there that will build these babies to the MAX (pun intended)but I doubt the survivabilty of the engine for extended periods of time. Anyhow, that's my $.02 worth.
JP

[ 12-31-2002: Message edited by: Heartbeat Hauler ]</p>

[Maxter]

I always wondered that myself. I know that big 18 wheelers are in the 2000's rpms and that a humongus oil tanker is in the 100's rpms but the Dmax is able to do well in the 4000's rmp when engine braking. Why not when pulling itself?

Everywhere you can read that it's normal to go 4500 rpm down a hill while engine braking. It doesn't say not to do it often it only says that if it becomes unsafe for the engine, it will upshift.

Now, seing the power curve of the Dmax, it's doesn't make much sense to be wanting to go at 5500 rpm, My Mazda used to go at 7200 rpm but I like my diesel cruising at 1500 rpm just the way it is. I would even enjoy a 6th speed anytime to lower those rpms when going 70 mph.

I just wanted to know why it's like that with this particular engine.

[cowboywildbill]

The Duramax will turn 4,000 rpm with out any problems. It is a well balanced engine. The tow haul mode will let the engine rev to 4,800 rpm while it is grade braking before it kicks out the downshift, correct me if I'm off a couple hundred rpm, but I think that is what I remember reading in the manual. I don't think GM would let it run at that amount of sustained rpm on a long downhill if the motor couldn't hold together. As far as longevity, I wouldn't think that a few hundred rpm wouldn't really make much difference. But keep in mind that more revolutions are like more miles, and that is what wears things out. Just a thought.Happy New Year!

[ibelyea]

While our trucks are unbelievable engineering marvels, they do not approach the law of physics. E=MC^2 is the law of relativity and is the basis for atomic energy. The law we should be thinking about is F=MA which involves mass and acceleration. Just for grins.

Ivan and my space rocket :D

[Oongawah]

Diesels are high compression and burn the fuel by achieving enough temperature via this compression to bring the fuel past the flashpoint. This higher compression can be made with a longer stroke. With a longer stroke the inertia involved with higher RPM's can compress and rip parts apart pretty quick. We do have technology integrated in our trucks like Split Fractured Aluminum Rods, Pilot Injection, Valve Design and so on, to help get those parts up and down quickly, but still there is that F=MA thing to deal with. Sorry for getting technerlogico, Chuck.

[csimo]

One of the main things that limits high RPM's on a diesel engine is the nature of the fuel. A reciprocating diesel engine "outruns" the flame front at about 4000 RPM's. It's possible to make more RPM's, but the curve will drop sharply above 4000. Diesel fuel burns slowly as compared to say gasoline or other fuels. With gasoline you outrun the flame front at about 17000 RPM.

[AzKevin]

I heard BMW's F1 engine this year redlined at 19500rpm, most likely not gas powered. Supposedly, incredible power but had a knack of blowing up before the race ended.

[hdmax(mike)]

The new Powerstroke 6.0L has a red line of about 4200 rpm. How can a diesel hold up long term with those high rpm?

[TLA]

As a teenager, one of my dreams was to design race cars and race engines - but, math sucks! I recall that one limiting factor to engine rpm was piston speed. Obviously, the longer the stroke, the higher the piston speed for a given rpm.In practice, there are other limiting factors, especially reciprocating and rotating mass.
A 4200 rpm red line may or may not adversely affect engine life - it depends how one uses it.
Sort of rambling here - Happy New Year everyone.
Tom

[mtomac]

the 6.0 PS shifts @ 3500rpm and redlines @ 4250rpm

the smaller PS has to rev to make power

The 6.0 makes peak hp 500rpm higher than the 7.3

The 6.0 makes peak TQ 400rpm higher than the 7.3

Any people thought the Duramax was a high rpm diesel

[AzKevin]

If I'm not mistaken the Dmax tach shows the redline at 3250rpm or 1000rpm lower than the new 6.0L PSD. That's over 30% more spins than the DMax with just a 10% smaller displacement motor.

Could it be said that Ford pushed the envelope more than GM's initial Dmax design? Or do spins grow much faster for slightly smaller displacement diesel motors?

[NWDmax]

Just to show how ignorant I am I thought one of the limiting factors to diesel rpm was not just reciprocating weight and stroke(piston speed)but was the rate at which diesel burns.I know that diesel has more BTU's per gallon than gas but how fast does it burn compared to other fuels?
Blake

[mdadgar]

TLA,

Can you shoot me at email at md@pdc-racing.net?

I'd like to ask you some stuff about your Kelderman air suspension.

Thanks!

- Mark