For those wanting to spin them faster...

[dansvan]

Copied from DieselPowerMag

Another reason the output of a diesel engine per cubic inch is less than that of the gasoline engine is because a spark-ignition engine can operate at a higher rate of speed. This is due to the combustion burn rate of gasoline being faster. Diesel fuel has a reduced combustion efficiency at high speeds because of the longer ignition delay, longer injection duration (in crankshaft angle degrees), and from the slow mixing rate. In diesel engines, the government-mandated smoke limits are very hard to meet at high speeds since the engine doesn't have enough cylinder event time to burn all of the fuel. Since the diesel engine has a high compression ratio, the energy required to revolve the engine itself, or what is known as friction loss, is greater than that of the gasoline engine. Therefore, when speed is increased to boost horsepower output, the friction loss raises enough to offset the output component of the engine. For a production-style gasoline race engine, a practical maximum speed is around 10,000 rpm. A similar diesel engine would only be able to achieve approximately 5,000 rpm.


So with our heavy internals where is the point of diminishing returns?

 

[PwrSmoke]

Depends on what you want to do. Powerwise, 3300 IMO. Not much is happening past that point. Torquewise under 2000. Economywise 1400. My truck has spend a bunch of it's highway time at 3000 rpm, so I don't think that level is all that harmful. long or short term.

 

[kas83]

And your point is? For a practical, everyday driver, with low emissions, keeping the RPM low is where it's at. For a more performance minded daily driver, with slightly elevated emissions, a few more RPM is going to help. For an all out performance truck, one used for drag racing or sledpulling, more RPM will help tremendously, IF the engine is built to make power at the extra RPM.

One thing you have to remember, is that most people who build 'hot street' vehicles aren't running the thing to redline and beyond every single shift, they usually drive them sanely and know there's a time and place for the power to be used. For someone to continually wind it out when they aren't on the dragstrip or pulling track is beyond stupid, IMO. You are gaining nothing except a bad image.

And if 5,000 rpm is the ceiling, how come sledpulling tractors, semi's, pickups all can turn 6k+, and still be making power? The right setup increases power as the RPM goes up.

 

[sle2115]

And your point is? For a practical, everyday driver, with low emissions, keeping the RPM low is where it's at. For a more performance minded daily driver, with slightly elevated emissions, a few more RPM is going to help. For an all out performance truck, one used for drag racing or sledpulling, more RPM will help tremendously, IF the engine is built to make power at the extra RPM.

And if 5,000 rpm is the ceiling, how come sledpulling tractors, semi's, pickups all can turn 6k+, and still be making power? The right setup increases power as the RPM goes up.

I'm doubting they are running stock anything. If you wanted to "re-engineer" an engine, as many of these guys have you are talking about, anything is possible. I've told the story about SBC in Outlaw cars, they are only Chevy in appearance, Brodix makes the engine, valve spring pressures are 4+ times that of a stock SBC, crankshaft weight is substantially less, etc. They also don't care if they have to rebuild them every week if they win in competition...they seem to have unlimited pockets. We worked on many pulling tractor engines and the first thing I noticed was they weren't near as sooty...I asked a couple of the guys that ran DT466's and they said they run a diesel/alcohol mix. I thought they were pulling my leg until my neighbor showed up with a tractor (Dirty Sally's Alcoholic Sister - feel free to google it) and it pulled on total alcohol.

I'm not arguing with you, or anyone else, but don't believe everything is bone stock turning those RPM's, even in gassers. You want horsepower from either, all it takes is a wallet full money! I'm sure Brodix would build you a diesel engine to your specifications if you front the money!

 

[kas83]

I'm not arguing with you, or anyone else, but don't believe everything is bone stock turning those RPM's

Where did it say stock? It said production style race engine. Based off something that was mass produced, and widely available, like a SBC, DT466, 6BT, or other base platform commonly used in motorsports of this caliber.

 

[sle2115]

Burn rates of gas versus diesel don't change, stock or otherwise...add a fuel modifyer and anything is possible!


And based could be just like the Brodix engines we worked on, wasn't much stock in them, or coming out of them.

 

[kas83]

I'm not arguing burn rates of either fuel by any means.

But you guys are really starting to split hairs lately when it comes to the RPM of any diesel. Did you know that there were small diesels in the 80's, with oldschool mechanical technology, that turned 5,000 rpm off the showroom floor? And that in todays world, the same holds true. That article from Diesel Power is a blanket statement that doesn't hold up. Larger diesels won't handle as much as the smaller ones will, I'll give you that, but it still holds true that a diesel can turn some high RPM.

 

[sle2115]

Not splitting hairs either, just saying that these engines, as all engines, were designed to work at a specific rpm range...running it more rpm's isn't a quick power fix. It takes more than just a governor spring...that's all I'm saying.

 

[Jake S.]

I've owned in the past a ford ****** diesel with a 2.0 I-4 n/a and a volvo 2.4 I-6 turbo. Both ran to 6k rpm, but there wasn't much power there. They were just noise after 4,000. But they turned it, and if it was tuned right they would make power at the upper range. But they were smaller motors. I think that there is a need for modified stuff. I wouldn't do it, or could afford it. I am happy with what my truck can do as it is. But if I every built a mud/offroad truck, then a high-revving diesel with an auto would be the ticket.

 

[punkmechanic]

I have three diesels and a gas burner in the driveway right now. We own all of them. Two are 6.9 liter navistar/ford trucks that redline around 4000 and arent doing much of anything but smoke and noise past 2500 or maybe three. One is an automatic N/A and the other is a worn out turbo with a zf. The turbo pulls harder higher and the auto has grunt off the line. The gasser is an 06 scion xa that wont get out of its way till 4000 and stuff starts to feel like it may actually do something at about 5500 with a redline of just over 6000, its a 1.5 liter toyota vvti inline four. The last vehicle is a 78 mercedes 300d non turbo inline 5. It has some grunt low but really doesnt do much till 1000-1500. At 60 mph all four have decent power and cruise nicely. The scion and benz or spinning for the stars and the auto idi is getting up there, the zf is just purring along. punching either auto isnt going to take you from 60 to 75 in any hurry, itll rev and sound like its gonna grenade but not much else, the scion will come to life and breeze away, same for the 7600lb crew cab flat bed.

All engines arrive to use in stock or nearly stock form. changing this or that can get you more power, revs, fuel economy, longevity, etc. The thing is that we are going from a "stock" base and working out. The "stock" base is a balance of the whole list. When we start changing that balance then we are sacrificing in another area. Even the magazines dont tell you that the "4000 hp cummins quad turbo bliggity blah" when its makeing that power its not doing the internals any longevity favors nor is it getting mpg (gpm would be the correct measure there).

If you wanna rev it and build power at that rpm range then it will cost money, it will change the "stock" base and it will cost you in another area (my bet would be some economy, the longevity, and the power increase will be slight if any.

I like my truck to run as long as possible, with as much power as I can get without killing myself in fuel bills. I have been driving a worn out diesel for two years and the turbo helped. I got by fine and only pulled it due to it blowing oil from EVERY spot it could. I dont need clouds of smoke and gobs of power. I need a usable dependabl truck that works as hard as I do.

The stock 6.9 with a hypermax fits the bill fine for me. Now I wanna see what one with good compression can do.

punk

 

[dansvan]

My question was why turn our motors to 4k if the majority
of the bennifit of it is lost to frictional losses? Large bearing journals, piston side loads, massive reciprocating weight are going to cost you alot on Hp at those rpm. Spend alot of money on custom this and that for minimal gains. and I'm talking street driven trucks.

 

[kas83]

It takes more than just a governor spring...that's all I'm saying.

Almost every post I've made over the last couple months says this exact same line.

The right setup increases power as the RPM goes up.

Hell, I've even eluded to it in this thread.

Turning more rpm, and making power at those extra rpm, are two completely different things. I know this, and I've elaborated in other posts that my main concerns are getting it to make power, hold together, and be reliable. Turning 4000+ is not a simple thing, it will take time to get it right, alot of research, and tuning.

Spend alot of money on custom this and that for minimal gains

Show me the proof that makes this statement have merit. Yet another blanket statement, based off the Diesel Power rag article referenced at the beginning of this thread. I know what diesels are capable of when spun high AND tuned right, and minimal gains doesn't exactly describe it.

 

[icanfixall]

Ok... At 3000 rpm the piston is making 50 rotations or trips...... Per second... At 4000 rpm its doing this 66 times per second. A indy motor turns up around 12,000 plus rpm.... Thats 200 trips to tdc per second. The piston is moving really fast in the 1 1/2 inch stroke. Our stroke is around 4.180 with a 4.110 bore.... Thats a lot of metal being pushed around. I don't have the piston speed in feet per second but probably can find it... I personally don't like to turn my motor to a red line but others do.. And to them I say have at it... I'm just not comfortable "up there".

 

[kas83]

While you're at it, figure out the piston speed, weight and so on, with a DT466 and it's 4.68 inch stroke at 6,000rpm. Those blocks and reciprocating assemblys are used as the basis in many pulling trucks and tractors, and can make more power in one cylinder at that RPM than an IDI can produce total. So much for frictional losses and minimal gains with added RPM.

 

[emmer]

IMHO, high rpm's on a diesel are about as usless as **** on a chicken