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Go Back   PeachParts Mercedes-Benz Forum > Mercedes-Benz Tech Information and Support > Diesel Discussion > Diesel Performance Tuning

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  #1  
Old 02-15-2011, 03:42 PM
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350SDL power

So ive been trying to do things to increase top speed and power in the 350. When I got the car it barely did 95mph downhill. I cleaned the air intake manifold, lines to the ALDA and unhooked the EGR and now im able to hit 115mph on a straight. I want to get more power and speed still. I unhooked the vacuum line to the wastegate today. Before hand the boost was max of 0.9bar now I am getting all the way up to 1.5bar. However the strange thing was when the boost started getting higher towards 1.7bar the needle started twitching back and forth and as I got to higher speed it felt like the turbo kicked in and out? Anybody have some good ideas what I can do?

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Old 02-15-2011, 03:57 PM
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What year?

The line on the wastegate iin a '90/'91 SDL is pressure, not vacuum.

If you're getting to 1bar, the overboost protection should be shutting down fuel enrichment as if there's no boost (via ALDA pressure line / switchover valve).

I'm not sure that the original turbo is capable of holding up to 1.7bar, my local turbo shop tells me that it's easily good for 1.2bar though.

Just FYI, according to Mercedes the factory settings on the .970 are .85bar, and that's good for 135,000rpm.
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Old 02-15-2011, 05:42 PM
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The car is a 91 and I think youre right about the over protection shutting down the fuel mixture. Any ideas on what I could do to up the power possibly adjust where the wastegate turns on at? I constantly read about guys turning the ALDA screw up on their cars, but as fat as I know thats not possible in my car as there is no screw on the ALDA

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Originally Posted by babymog View Post
What year?

The line on the wastegate iin a '90/'91 SDL is pressure, not vacuum.

If you're getting to 1bar, the overboost protection should be shutting down fuel enrichment as if there's no boost (via ALDA pressure line / switchover valve).

I'm not sure that the original turbo is capable of holding up to 1.7bar, my local turbo shop tells me that it's easily good for 1.2bar though.

Just FYI, according to Mercedes the factory settings on the .970 are .85bar, and that's good for 135,000rpm.
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Old 02-15-2011, 05:45 PM
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so.. hook your waste gate up . Get a plastic vacuum tee (smaller the better) cut the vacuum hose to your wastegate and install it inline and then as long as you have a boost gauge you can meter the leak to the waste gate to allow for more boost. Unhook the vacuum lines from your over boost protection and run them into eachother . doing both of those things will give you more power with less risk than just removing the wastegate line.
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Old 02-15-2011, 05:57 PM
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That seems like a good solution. My uncle also said something about turning up a fuel screw on the side of the IP to get max fuel injection. Any idea where that screw might be or if this IP has it? I did some research and havent come up with much.

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Originally Posted by josha37 View Post
so.. hook your waste gate up . Get a plastic vacuum tee (smaller the better) cut the vacuum hose to your wastegate and install it inline and then as long as you have a boost gauge you can meter the leak to the waste gate to allow for more boost. Unhook the vacuum lines from your over boost protection and run them into eachother . doing both of those things will give you more power with less risk than just removing the wastegate line.
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Old 02-15-2011, 06:06 PM
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You will have to search for tuning your pump but i do not believe there are any that are external, I believe they are all behind the cover at the rear of the ip.
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Old 02-15-2011, 07:33 PM
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The wastegate doesn't have a vacuum line unless it is '92-up W140 body, which I believe is called an S300 diesel.

If you want more boost, you can adjust (shorten) the rod from the actuator to the wastegate on your Garrett T-30 turbo. Initial settings can be made with a Mityvac or other air source and pressure gauge, setting the wastegate to start moving at your intended max. boost. A boost controller can work also, but is an additional failure item.

Changing the overboost protection to protect the engine at a new boost-pressure setting can be done I'm sure, but you'll have to replace the 1bar pressure switch with a higher-pressure switch (I'm looking for one also). Eliminating it as Josha prescribes is the only other option, by bypassing (or unplugging) the switchover valve or removing the ALDA.

Increasing boost without increasing fuel is just going to waste power, you will need more fuel to get more power. Yes, there is a way to adjust the fuel also (again presuming you're talking about a '90/'91 as you still haven't given that information) on the mechanical M-series pump. There is a torque adjustment and a max-fuel adjustment, both (along with several others) under the governor cover on the pump (rear cover).

Apparently however, there isn't much more fuel availble on that pump without getting into end-of-injection timing problems, plus the issue with your engine (the "rod bender") already having problems with the stock power destroying rods.

If you really want to push the engine, best to buy a 3.0L block (I have a spare) that can be pushed, install that and begin tuning, some 7mm elements in your IP, aftercooler, and something purty like a Holset HK35.

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