Redlining a Diesel - PeachParts Mercedes-Benz Forum

cirrusman · #1 11-21-2009, 04:16 PM

I've noticed that Diesel tachs don't show a redline as gassers do and I'm wondering how come? I watched a video on youtube of some crackheads trying to kill a 240D over revving it, and they had a hard time doing that. Since I don't want to use my engine as a guinea pig, I'd like to know what's the max RPM I can run through my engine ('83 300SD OM617) before starting to harm it.
If you want to see the video, here's the link: http://www.youtube.com/watch?v=wTdC3LC2lW0&feature=player_embedded
Those guys had to resort to a sledgehammer in order to kill the engine, that's how strong they are

okyoureabeast · #2 11-21-2009, 04:47 PM

I think it has something to do with the way the fuel is atomized making it much hard to redline a diesel since the engine runs at a much lower speed.

Please feel free to correct me.

snookwhaler · #3 11-21-2009, 05:07 PM

I'm curious about this too. In my Truck (Dodge 3500 Cummins) it shows the red line at 3300 RPM.

No red line mark on the tach in the MB. Mine sees 4,000 RPM on a regular basis. Hope thats ok?

mytmousemalibu · #4 11-21-2009, 05:11 PM

The injection pumps have a governer inside that defuels at a certain point. Hi revs are still hard on them. Diesel internals have alot of mass and that combined with the compression/cyl pressures and the burn rate of diesel effectivly lowers there operating rpm. But as things advance, they are more revy today than ever. We have Dmaxes reving between 6-7000 RPM, thats screamin!

toomany MBZ · #5 11-21-2009, 05:41 PM

No red lines with auto trannies, but 4700-5200 rpm is the recommended limit. With maximum bhp at 4350 rpm.

Brian Carlton · #6 11-21-2009, 05:42 PM

Although several on the board will push the 616 or 617 above 5,000, I'd consider 4,400 rpm to be the limit if you want the engine to provide reasonable durability. It really doesn't make any sense to run the engine higher than 4400 rpm because you're over the point of peak horsepower and the torque curve is falling like a stone.

rcounts · #7 11-21-2009, 05:56 PM

I know our MBs are a lot more tolerant of higher revs than most diesels. My F250 redlines at around 3500 RPMs. I was talking to a pro diesel mechanic about the engine in my F250 and why the redline is so low the other day and, without him even knowing I have the MB, he made the comment that "it isn't like these (Ford 6.9 IDI) engines are one of those high-revving old Mercedes diesels that can handle running at 5000 rpms..."

Brian Carlton · #8 11-21-2009, 05:58 PM

Quote:

Originally Posted by rcounts

"it isn't like these (Ford 6.9 IDI) engines are one of those high-revving old Mercedes diesels that can handle running at 5000 rpms..."

Don't believe everything you hear.

It might "handle" the speed for about 5 hours...........

leathermang · #9 11-21-2009, 06:26 PM

It is my opinion that the major limiting factor is the basic lack of valve overlap.

rcounts · #10 11-21-2009, 08:09 PM

Quote:

Originally Posted by Brian Carlton

Don't believe everything you hear.

It might "handle" the speed for about 5 hours...........

The point I was making is not that you should go for an extended run at 5k rpm. Like you said - what would be the point since output peaks at 4400 rpms and starts to drop off rapidly above that.

The point I was making is that these MB diesels can, will, and are in fact KNOWN for being able to handle higher revs than other diesels of their era...

Hatterasguy · #11 11-21-2009, 08:18 PM

My old 603 and my friends 606 are screamers, they will happily rev to 5k or in the 606's case just over. Thats screaming for a diesel!

The Finn's run them up to like 7k!

Skippy · #12 11-21-2009, 08:54 PM

As others have stated, the injector pump includes a governor that precludes over revving the engine under power. However, it's still entirely possible to overspeed an engine by an untimely downshift. Several years ago I heard about a duece and a half that suffered a destroyed engine by a newb picking too low of a gear at the wrong time. The test center I worked at later also had the same thing happen with a fairly large (and $$$$) Cat in a semi. It happened just before I started working there and there was still considerable debate whether it was the fault of the driver actually did it, or the engineer who told him to.

brandlj · #13 11-21-2009, 09:15 PM

If the engine speed in a 603 diesel increases above a certain engine speed, I imagine the speed that the engineers destined to be a safe RPM, the governor takes care of shutting the car down.

This quote is from the governor description for a 603 Diesel. " If the engine speed increases above a certain engine speed, the spring retainer is over-compressed followed by the governor spring. The control rod is thus brought into the STOP POSITION (deceleration fuel cutoff).

pawoSD · #14 11-22-2009, 12:05 AM

I usually keep mine under 4k (usually well under) but yesterday I was in a pinch on an uphill section of freeway, so I dropped to 3rd and ran 73mph uphill with it for about 20-30 seconds at around 5100rpm or so.....it was pulling strong! My engine has always been a "freely revving" 617 IMHO....my brother's 300D doesn't like going over 4k, nor does my dad's '82....his '83 likes revving though. Very odd.

Either way, I rarely rev it that high....no point.

I don't know about the "runs out of power over 4400" idea....mine pulls strong to the governor....then it just kinda holds there until I shift. It's faster revving it to max in third than it is to go to 4th at 4400 and keep on it.

awsrock · #15 11-22-2009, 01:09 AM

Not sure on the 617s, but some (Dave M, I believe) have adjusted the max rpm setting on the fuel pump of the 603 to get up to just over 5000 rpm. I guess with the added fuel of the full load screw adjustment, there was some more power to be made above the stock setting. However, as Brian has already said, the power drops like a rock after a certain point.

Point being, the true redline of the engine may be higher than what the factory is set at, but there is little reason to go into that zone. (Or above the power peak, for that matter)