I believe that max boost for the OM697.95X is .9 Bar which, for the metrically challenged is, 13.0533964 PSI.

For some strange reason mine, despite the fact that they're are sporting two different kinds of turbo (KKK and Garrett), are both cranking right about 9 PSI at full chat.

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Never a dull moment at Berry Hill Farm.

If your 300SDL is running at 5500 rpm then PLEASE drive with retraint OR hope that the tach is not reading correctly (they are adjustable - and aren't completely stalwart). If the clock's been repaired, the tach is likely to have been disturbed (don't ask how I know this ;-).

The design limit for the wastegate is 0.95 bar or ~14 psi. Many OM617.95s don't improve much as the boost is raised above about 10 psi. (and I'm NOT exactly sure why) while the OM60x turbo engine are more responsive as boost rises. The overboost switch is set for 1.1 bar and this is the simply a safety device in case the wastegate fails. You CAN (with a lot of luck) run an engine for years with the boost well in excess of the design limits and with the ALDA spooled up if you don't ever push it for very long, but some large number of such engines WILL fail without ANY warning within minutes in a full load situation. When they let go, a rebuild is seldom possible or economically practical.

Marshall

My 82 300sd measures 10.5 from 2000 rpm up to 4000 rpm. But, at 4000 it's blowing out some pretty black smoke. I never rev over 4k. I hate to hear an engine run so fast. I spent years behind Mack diesels turning 14 to 1600, and later Caterpillars with a top rpm of 1900.

If you're blowing smoke you need MORE air (boost) or less fuel!

The engine was designed to wind out to 5100 rpm without problems - if you don't like that - don't do it, but you waste a lot of what Mercedes provided for you.

Marshall

Here's a pic.


The car is in second gear. It doesn't want to pull off much more engine speed than this. This is pretty much about where the "big drop off" occurs at full load. PSI cuts back from a solid 13'ish to a measly 8 and it won't accelerate any further. Hints of the drop off occur after 5K rpm.

Oh yeah...BTW. Clock works sporadically. Whenever it feels like it, really.:p

Too bad I can't go 120 all day long. This beast is turning a good 4500 rpms at those speeds and is nearly as quiet as a gas car.

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1987 300SDL (324000)

1986 Porsche 951 (944 Turbo) (166000)

1978 Porsche 924 (99000)

1996 Nissan Pathfinder R50 (201000)

Your picture shows the tach at 5200 rpm (well within the 5100 +/- 150 rpm MB limit). And at that point fuel is limited. Sounds like you mighht be also triggering the overboost protection (when boost get near 15 psi) and that will shut off all fuel enrichment liming power by about 30%.

What's the problem? The machinery is simply trying to keep you from destroying your engine. You can probably break it if you REALLY try, but why would you? I can make any of my cars go well over the 5100 rpm limit by downshifting into a low gear at too high a speed, BUT THAT WOULD BE STUPID!

Marshall

No kidding,:p

Understood, and I am certainly not trying to destroy the engine in my car; Good God, no!

At no load though, it IS set to about 5450.

__________________
1987 300SDL (324000)

1986 Porsche 951 (944 Turbo) (166000)

1978 Porsche 924 (99000)

1996 Nissan Pathfinder R50 (201000)