Diesel Performance? - PeachParts Mercedes-Benz Forum

#1 01-08-2004, 12:16 PM

I was talking to someone who fixes up mercedes diesels and he said that he can make them alot faster by bypassing a regulator. He said that theres a line that goes from the manifold to the reulator then to the turbo ( i think i dont remeber i will ask him again) and he said that if you just bypass the regulator it will run completely different and "it dont hurt the car at all". Is this poossible im assuming it probably more for the 5 cylinder rather than the 6. However has anyone tried this? do you think its a good idea. I dont want to experiment on my engine . All opinions are welcome. Thanks
Bob

psfred · #2 01-08-2004, 01:19 PM

That is the overboost protection switchover valve, and if it is bad, yes, bypassing will give you better performance. However, cutting the line from the turbo to the wastegate servo will, too -- at the expense of engine life. It's there to prevent engine damage from overboosting if the wastegate control fails. One common mode of failure at the switchover valve is to leak, venting off the pressure signal to the IP, so that it doesn't provide the extra fuel noramlly injected when the boost goes up.

Make sure the lines are clear and that the overboost protection switchover valve is working (holds pressure unless energized) and you will be getting all the performance you need.

Peter

#3 01-08-2004, 09:48 PM

I wonder if replacing the line from the manifold to the ALDA with a smaller insde diameter tube to match the hole in the banjo bolt would decrease the power delay? The air won't have to expand after the bolt, then recompress as it passes through the aldo bolt . I can't find the site that explains the physics behind the idea, but it has to do with air slowing as it expands after going from large tube-small hole-large tube.

shane83SD · #4 01-08-2004, 10:17 PM

Weak spring in the wastegate will degrade the turbo boost in two ways. One is slow build up of the boost pressure. Another is lowered maximum boost pressure. Hook up a boost pressure gage and you can observe the current state of the wastegate. There is a boost pressure vs RPM curve at maximum load shown at the 123CD. It shoots straight up near max boost at 2K RPM at maximum load.

My 83SD was getting max boost around 8.5 psi and boost pressure build-up is slow. I think the wastegate "leak" some pressure so that the build-up is slow. There is also some "roughness" perhaps due to the modulation of the leaking boost pressure.

Out of curiousity, I clamped the wategate hose. The boost came up much faster and the maximum boost pressure is around 15 psi. This totally changed the dynamics of the car.

Rather than fooling around with the wategate spring (a PITA job for the Garret), I made a pressure regulator using a vaccum/pressure relief valve (part#48935, MacMaster-Carr) and some brass fittings out of Home Depot. Now I can dial in the desired maximum boost pressure while getting a fast boost pressure build up. Total cost less than $20.

JHZR2 · #5 01-08-2004, 10:29 PM

I am curious how you did this with mcmaster # 48935... Looking at the picture and reading the description, which is (with a few snips to keep this messagew short):

They also convert to pressure-relief valves (not pop-safety) for low-pressure applications. Pressure adjusts from 0-20 psi with the knurled adjustment screw. Valves have a Type 302 stainless steel spring.
Connections: NPT male bottom inlet and vented top outlet.

It seems to me that this walve would have to essentially take place of your wastegate completely. Why I say this is because it says nothing of the outlet being threaded... Unless of course Im reading the sentence the wrong way

Looks like a great alternative to the dawes one, since its probably more or less the same item, I just put it together myself...

Thanks,

JMH

shane83SD · #6 01-08-2004, 11:19 PM

"It seems to me that this walve would have to essentially take place of your wastegate completely. Why I say this is because it says nothing of the outlet being threaded... Unless of course Im reading the sentence the wrong way "

The valve is designed to "vent", so there is this vent hole. I used a 1/8" hose barb to MIP adapter (Home Depot part# A-85). Cut off a few barbs and punched it into the vent hole (may want to add some thread sealer). The wastegate hose can fit part# A-75 (Flare to female pipe coupling).

So total BM for the boost controller is one pressure relief valve, one A-85, and two A-75. It will fit the exsisting wastegate hose.

I think Dawes device is similar in concept, you may have to make some sort of hose adapter.

JHZR2 · #7 01-08-2004, 11:21 PM

Thanks very much for the clarification... And pardon my ignorance, but what is 'MIP' in the 1/8 barb to MIP adapter?
Thanks again,

JMH

shane83SD · #8 01-08-2004, 11:54 PM

It is 1/8" hose barb in one end and 1/4" pipe fitting in the other. Go to Home Depot and check out the listed parts (A-75, A-85).

#9 01-09-2004, 11:42 AM

So do you think that this is worth experimenting with? I mean the SDL gets pretty good pickup as it is and i am a poor college student and dont want to endanger the life of the car anymore than i already do. It doesnt seem like there would be that much of a noticable difference. Am i correct to say this? thanks
Bob

JHZR2 · #10 01-09-2004, 11:54 AM

Well, my car, granted its lighter than yours, has good pickup despite the 8-9 psi that Im getting. I figure even if I dont turn up the ALDA (Im trying to get max longevity from my car), ANY fuel that might be put in there to follow a turbo working at 11 psi or so, which isnt getting burned at my boost level will. And if nothing else, at least I am back to OEM boost level... nothing wrong with that...
Id say for $43, the dawes device is a good deal. If you keep the setting conservative, like 11 or 12 psi, which is the factory wastegate setting, youre not going to hurt anything, and I suppose you could allow more complete combustion and get a tiny bit more power at full throttle.
Ill rport when I install some boost controller setup.

JMH

Merc_Missy · #11 01-09-2004, 12:28 PM

Quote:

Originally posted by JHZR2
Well, my car, granted its lighter than yours, has good pickup despite the 8-9 psi that Im getting. I figure even if I dont turn up the ALDA (Im trying to get max longevity from my car), ANY fuel that might be put in there to follow a turbo working at 11 psi or so, which isnt getting burned at my boost level will. And if nothing else, at least I am back to OEM boost level... nothing wrong with that...
Id say for $43, the dawes device is a good deal. If you keep the setting conservative, like 11 or 12 psi, which is the factory wastegate setting, youre not going to hurt anything, and I suppose you could allow more complete combustion and get a tiny bit more power at full throttle.
Ill rport when I install some boost controller setup.

JMH

Sorry, new here, but not to mercedes in general, what is a Dawes device?

JHZR2 · #12 01-09-2004, 03:40 PM

dawes boost controller, from www.dawesdevices.com

JMH

psfred · #13 01-09-2004, 06:45 PM

Bob:

Keep ignorance away from your car. What is being suggested (wrongly, because the idiot doesn't know Benz) it to disconnect the wastegate on the turbo. This will destroy the engine (this isn't the first time I've heard this story, by the way.... not the first time someone got a new vehicle and wouldn't say why, either!).

You get amazing power out of that car in the first place. If you want a road racer, get a cheapo Jap car and hop it up, don't mess with your Benz.

Unless you are having trouble keeping up in traffic, there is nothing wrong with you SDL, and you don't need to mess about.

Peter

shane83SD · #14 01-09-2004, 11:24 PM

For OM603 (aluminum head) engine, I would think twice about increasing boost pressure. Also I would be extremely cautious to make sure the cooling system is in tip-top shape first.

For the iron head (OM617), go ahead and increase the boost pressure (factory setting 8-9 psi is very conservative) and "drive it like you stole it".

rwthomas1 · #15 01-09-2004, 11:40 PM

Since the factory fuel cutoff occurs at 1.1bar or about 14psi I don't see how increasing the boost to about 13psi is going to harm anything. If it was damaging to the engine then the cutoff would be at 9psi...... I say crank it up and let your engine run as it was designed to. If you are only getting 8-9psi there is a good chance that the IP is not fully increasing fueling or reaching maximum fueling under boost. Adjusting the boost to the maximum allowable factory spec should allow for maximum power without causing any harm. RT

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