How often does your 617 diesel see 4400 RPM? - PeachParts Mercedes-Benz Forum

Brian Carlton · #1 08-02-2007, 01:30 PM

Quote:

Originally Posted by ConnClark

However, at higher rpms your power and torque drops off due to a drop in volumetric efficiency and prechamber design not to mention the governor cutting back on fuel. The OM617 just wasn't designed to generate optimal power at these rpms because it didn't need to. You might be able to improve on volumetric efficiency with a custom cam and porting the heads. You can also adjust the governor to get more fuel at higher rpms, but redesigning the prechamber is going to be a lot of trial and error.

I think you can redesign forever but cannot overcome the limitations of the burn rate for diesel fuel. It takes a certain amount of time for the flame to propagate and once you get over 3800 rpm or so............torque starts falling off in a big hurry.

ConnClark · #2 08-02-2007, 06:57 PM

Quote:

Originally Posted by Brian Carlton

I think you can redesign forever but cannot overcome the limitations of the burn rate for diesel fuel. It takes a certain amount of time for the flame to propagate and once you get over 3800 rpm or so............torque starts falling off in a big hurry.

Upping the boost will increase the burn rate and reduce the ignition lag.

Edit: I suppose upping the compression ratio would do the same thing too.

larry perkins · #3 08-02-2007, 07:22 PM

did you high revers ever think of what it happening at the top side of your cyl walls as the piston and rod assy stretch at these high rpm's? every one i take apart has a ring groove formed at the top and as the components elongate it would seem to me that you are forcing the piston rings to a position where the bore is at origional demensions and doing damage to rings and pistons.
larry perkins lou ky

#4 08-02-2007, 09:50 PM

Quote:

Originally Posted by ConnClark

Upping the boost will increase the burn rate and reduce the ignition lag.

Edit: I suppose upping the compression ratio would do the same thing too.

It may increase the burn rate slightly, but not enough to change the peak torque rpm significantly. The important parameter is the piston speed, if you really want a higher rpm diesel, design a diesel engine with a shorter stroke.

Brian Carlton · #5 08-02-2007, 09:52 PM

Quote:

Originally Posted by Craig

It may increase the burn rate slightly, but not enough to change the peak torque rpm significantly. The important parameter is the piston speed, if you really want a higher rpm diesel, design a diesel engine with a shorter stroke.

I'm not sure that a shorter stroke will get you that much more rpm. With a given burn rate, you're limited by time. Sure, you can get a bit of a benefit, but, I don't think you'll find any diesels with a torque peak much above 3500 rpm. There is just insufficient time for the fuel to burn.

Anybody know the torque peak for the new CDI's? Presumably, they've pushed this envelope as far as current technology will allow.

#6 08-02-2007, 10:07 PM

Quote:

Originally Posted by Brian Carlton

I'm not sure that a shorter stroke will get you that much more rpm. With a given burn rate, you're limited by time. Sure, you can get a bit of a benefit, but, I don't think you'll find any diesels with a torque peak much above 3500 rpm. There is just insufficient time for the fuel to burn.

I theory a shorter stroke will give you more rpm at the same piston speed, which should raise the rpm corresponding to peak torque. However, I believe you also need to keep the bore/stroke ratio pretty square in a diesel. I guess that means you would have to go to more cylinders to get higher rpm from the same displacement engine. Does anyone know the specs on the audi tdi racing engine, I think it runs about 6000 rpm.

DslBnz · #7 08-02-2007, 10:40 PM

Quote:

Originally Posted by Craig

I theory a shorter stroke will give you more rpm at the same piston speed, which should raise the rpm corresponding to peak torque. However, I believe you also need to keep the bore/stroke ratio pretty square in a diesel. I guess that means you would have to go to more cylinders to get higher rpm from the same displacement engine. Does anyone know the specs on the audi tdi racing engine, I think it runs about 6000 rpm.

No less than 6600 rpm.

http://www.exoticcarsite.com/pages/audi-r10-2006.htm

#8 08-02-2007, 11:12 PM

Quote:

Originally Posted by DslBnz

No less than 6600 rpm.

http://www.exoticcarsite.com/pages/audi-r10-2006.htm

Thanks, that's good info. The article also says, "The usable power band lies between 3,000 and 5,000 revs per minute." I guess that's just about the state of the art for diesel engines.