Questions: The things I think about at work - PeachParts Mercedes-Benz Forum

PanzerSD · #1 10-19-2007, 12:40 AM

Someone once said, in this forum that "our engines are governed to about 5300RPM"

Governed by what? something internal to the IP or by the physical design limits of the engine?

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When rebuilding an engine (617 spacifically) is it absolutely neccessary to remove or replace the prechambers? where can I buy Pre chambers and how likely am I to need to replace mine at 440,000km?

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and finally, some clarification about wastegates.

if the sctuator is set to 18PSI that means that the wastegate is FULLY open at 18PSI? is there any wastegate valve movement approaching 18 PSI?
would this amount of movement be more if the wastegate were set lower?

the REAL Question: Does a BOOST CONTROLLER block ALL signal pressure till it's set PSI? or do I still get that valve "flutter" lag?

Cervan · #2 10-19-2007, 01:22 AM

The engine is governed by the injection pump alone. the engine can go well over 5k rpms. the reason they set it to that low is because diesels have problems with high rpms.

The wastegate starts to crack open at about 15 psi and then is fully open at 18.

prechambers dont have to be replaced. but its a good idea if any of the balls are missing.

PanzerSD · #3 10-19-2007, 02:21 AM

Quote:

Originally Posted by Cervan

The engine is governed by the injection pump alone. the engine can go well over 5k rpms. the reason they set it to that low is because diesels have problems with high rpms.

The wastegate starts to crack open at about 15 psi and then is fully open at 18.

prechambers dont have to be replaced. but its a good idea if any of the balls are missing.

Balls?

so if it's set at 10PSI it's probably starting to open at around 6 or 7PSI?

Dee8go · #4 10-19-2007, 09:27 AM

Boy, THAT takes some BALLS!

Brian Carlton · #5 10-19-2007, 10:05 AM

Quote:

Originally Posted by PanzerSD

Someone once said, in this forum that "our engines are governed to about 5300RPM"

Governed by what? something internal to the IP or by the physical design limits of the engine?

----

When rebuilding an engine (617 spacifically) is it absolutely neccessary to remove or replace the prechambers? where can I buy Pre chambers and how likely am I to need to replace mine at 440,000km?

----

and finally, some clarification about wastegates.

if the sctuator is set to 18PSI that means that the wastegate is FULLY open at 18PSI? is there any wastegate valve movement approaching 18 PSI?
would this amount of movement be more if the wastegate were set lower?

the REAL Question: Does a BOOST CONTROLLER block ALL signal pressure till it's set PSI? or do I still get that valve "flutter" lag?

The governor inside the IP will prevent any more fuel from being delivered to the engine above the setpoint. I cannot recall the exact spec on the setpoint, but, 5300 sounds a bit high for a 617.

At 440K kilometers, you can be assured that the prechambers are toast. The shafts are loose in the walls and you'd be foolish not to replace them. Since you'll have the head off anyway, I'd recommend you send it to Metric and they'll do the full job including the installation of the prechambers.

The actuator setpoint is not a fixed number. It's a dynamic system. The wastegate begins to open at a certain pressure........say 10 psi. This serves to reduce the exhaust pressure to the turbo slightly.........but not enough to overcome the increase in volume from the engine........and the manifold pressures rises to 11 psi.........further causing the wastegate to open a larger amount. The rise in pressure is slower now and equilibrium is slowly approaching. The manifold pressure rises a bit more to 12 psi with more rpm's and the wastegate opens a bit further. Finally, the wastegate opens sufficiently at 13 psi so that the turbo cannot accelerate any more due to insufficient exhaust gas and the engine/turbo has reached equilibrium.

A boost controller is designed to block all flow until the setpoint. But, it's also a mechanical device that is not a switch. So, the "setpoint" might happen over 1-2 psi.

deerefanatic · #6 10-20-2007, 09:12 PM

Brian nailed it on the head......

But, governed max speed is actually 5450 rpms..... Brandon had his to that and had it pegged there..... I've got the video of it....... That's before he modded it AFAIK..........

lietuviai · #7 10-20-2007, 09:35 PM

5450 sounds about right. I had tried to see how high my 85 300D could rev while driving it in 2nd and that's around where it seemed to be the limit. It didn't seem to have much pull at those rpms.

deerefanatic · #8 10-20-2007, 09:41 PM

The rev limiter is cutting fuel at that point... That's how it governs engine speed....

Brandon claims now that he's raised his rev limiter up, he has more pull at hi rpms..... But now the car is no longer idiot proof either.........

PanzerSD · #9 10-20-2007, 09:46 PM

Quote:

Originally Posted by deerefanatic

The rev limiter is cutting fuel at that point... That's how it governs engine speed....

Brandon claims now that he's raised his rev limiter up, he has more pull at hi rpms..... But now the car is no longer idiot proof either.........

So don't let an idiot drive it!

lietuviai · #10 10-20-2007, 10:07 PM

Are we talking about the same Brandon who lives in Oregon whose former SD is RIP?

Hatterasguy · #11 10-20-2007, 10:29 PM

I wouldn't recomend spooling a 25 year old engine that high..but it would be a great way to learn about the rebuild process.

I could never do that to my car, I'd be worried about all the old sloppy parts moving really fast, those really expensive parts getting ready to break....

My 617 sounded like it was about to throw the pistons threw the hood near 5k rpm.

At those miles the prechambers are shot.

lietuviai · #12 10-20-2007, 11:09 PM

Perhaps this is what would happen?

Hatterasguy · #13 10-20-2007, 11:14 PM

It could.

I have no problem running our engines up to 4,800ish, but pushing them above that at this point... I don't have $8k cash sitting around at the moment to rebuild my 603 if a rod goes through the block.

But if you have $6k burning a hole in your pocket, see if you can't run your 617 up to 6k.

With a diesel its pointless, I beleive the combustion starts to chase the piston around 4,500. Diesels are not high RPM engines, nature of the beast.

lietuviai · #14 10-20-2007, 11:36 PM

I wasn't responsible for the damage pictured in that engine. It was a freebee thrown in with my $150 300D.
I've yet to open it up to see the actual damage inside.

PanzerSD · #15 10-21-2007, 03:25 AM

Quote:

Originally Posted by lietuviai

Perhaps this is what would happen?

Cool! a self-ballasting boat anchor!!

what did THAT sound like?