Bigger exhaust for 300D turbo
 

Hi All,

I have read about increasing the power output of the 617 engine (manual trans, intake, intercooler--Ridge). However, I have not found any threads about improving the exhaust. Almost all the *big* diesel mods start with increasing the exhaust diameter for better flow.

I recently put 3" mandrel bent exhaust from the turbo to tailpipe on my Diesel Scout with the Nissan SD33T (3.3 liter) engine. It made a huge increase in bottom-end and mid-range torque. Throttle response is also much improved. Granted, I was going from 2" pipe to 3", but I made no other modifications outside of a K&N air filter.

Anybody tried this on a Benz?

Bigger pipes
 

I'd be very interested in some specific figures on your installing larger exhaust pipes on your Nissan diesel. My son and I are the ones who've done the intercooler and are about ready to install our first 5 speed manual transmission, after which we'll dyno the rig and see just what we get.

Ben
www.reproduce100s.com

Ridge,

We don't have any specific numbers off a dyno--yet. It is more of a seat of the pants feel that a number of us Scout Dieselers have noticed.

Our engines use an Airesearch turbo T-3 with an A/R ratio of 0.62--boost is limited to 6.5 lbs (bad things happen to this engine when going to higher boost pressures). The M/B 617 uses the same turbo with an A/R ratio of 0.48--boost at 11lbs. [Future installation planned with the 0.48 housing to reduce turbo lag while keeping the 6.5lb waste gate]

Without increasing the boost and no intercooler, the bigger exhaust helped out with mid-range and bottom-end torque. The big problem with the factory exhaust is the cast iron *elbow* to reroute turbo exhaust away from the starter. Mercedes exhaust flows smoother out from the turbo, but it is still not 3" in diameter.

Here are some links:

Diesel Scout forum

Diesel Scout 3" exhaust install

Elbow Eliminator--3" exhaust flange for turbo

I think a free-flowing exhaust will make a noticeable difference in a properly running MB diesel. Exhaust mods are the most commonly performed upgrade on all the other diesels that get "tweaked" on so why not a Benz? The big question is how much of a difference will it make.... The VW TDI's seem to flow well enough that most just perform a "mufflerectomy" and are more than satisfied. The Dodge/Cummins trucks seem to have a pretty good system from the factory, most just remove/replace the muffler. The Ford/PS and Chevys cat-back, or removal of cat-complete systems are very popular. These mods have produced proven power gains on dynos so again why not a Benz? I have a 3" downpipe and 4" exhaust on my truck and it made a very noticeable difference when I installed it. Now I know some will chime in "you gotta add fuel to make more power in a diesel". While this is true it doesn't take into account how much restriction is in the exhaust system already sapping power that has to be overcome. The difference in driveability experienced in the Scout is due to the fact that the engine revs/responds to throttle input and the turbo spools up much faster when there is little or no backpressure/resistance from the exhaust system. Free-flowing systems also run much cooler which is another reason the pickup guys like 'em for towing. The factory MB system has fairly smooth bends and looks to be at least 2.5" I am planning on removing/replacing the center muffler with straight-pipe and replacing the rear muffler with a free-flowing design like a Flowmaster, etc. A custom exhaust shop should be able to do this for under $200. I have heard quite a few turbodiesels without mufflers and they are not loud at all however most states require a muffler even if not needed for sound control. RT

rw, I thought that most states didn't require a muffler if it's a turbo.... I know they do require one for non-turbos. Maybe that only applies to trucks and not cars.....?

Well my buddy's Dodge was failed in TX for no muffler...... Not sure about RI where I am now but I would be very suprised if they didn't require one. Bottom line is with no muffler some may find it too loud or offensive. If you want it as quiet as stock put a muffler on it, just make sure its a high-flow design. RT

Guess it just depends on how strict they are... and how loud the car is. Here there are lots of Dodges and Fords with no muffler but they don't seem that loud either... I've heard some that are loud too.

I ditched the muffler when I did the 3" exhaust on the Scout. It made the exhaust note sound like a big truck, but not overly loud. I would still run a high flow muffler on the wagon if I go to 3" exhaust.

I still have a few projects left on the Scout before I do anything to the Mercedes. :)

Phil, the factory boost spec on the OM617 is 0.85-0.95 bar (12-14psi). If yours is at 11.5, adjusting the wastegate may help a bit. The overboost circuit shouldn't kick in until 1.15 bar (+/-0.1), which is 16-17psi...

Dave, you think a bigger exhaust would benefit our 87 300D's at all? I've already replaced the 5 way vacuum fitting at the vacuum pump with a 3 way (no more air recirculation).

On our cars (1987 300D) the pipe is already 3 inches all the way back, I think... or at least it's really freaking large. I have considered removing the oxidation catalyst which was added into the front pipe when the trap oxidizer is replaced. You can either rod it out, or buy the old style pipe designed for the trap since it has no catalyst. I don't know what the power gain would be since I haven't done this. If I knew it would work, I'd do it in a heartbeat! But it's pretty low on my list of things to experiment with. There is a plug on the manifold by cylinder #1 where you can connect a backpressure gauge, I wonder what the stock reading is... and if it would mean anything, since it's before the turbo, not after...

BTW, I totally removed my EGR valve. No more oil seeping out the EGR body! Here's the photo:

Dave,

Thanks for the correction. I was misinformed to the max boost on the Mercedes. I don't have a gage on the car, nor have I checked its pressure. Pyro and boost gages only on the Scout for the time being.

MB & Scouts
 

So what are the odds of 2 members having this mfg combination? 1984 300 CDT and 1980 Scout II..Scout was originally a diesel but was converted to 345 Auto w/dana 300, thermoquad, Tri-Y headers, etc. by prev owner.

3+ yrs w/ MB, 10+ yrs w/ Scouts

MikeL

Re: MB & Scouts
 

Not many! I have only found one other guy (on the Binder Bulletin) that also has a 300D.

John McNeil
'72 Scout II w/ '80 SD33T
'83 MB 300SD
'82 MB 300SD

There has also been specualtion of installing the 617 in place of the SD33T in the Scout. :eek: The 617 is a great engine!

Exhaust measurements
 

I just checked the diameter of my factory exhaust. It measures 2.36" dia (60mm). Going up to 3" would be a big difference.

On my Diesel Scout, I had quite a bit of hesitation off idle--well before the turbo spools up. After going to 3", throttle response is much faster off idle. Turbo is still not a factor, at least until it winds up past 2,000 RPM. I think the smaller Mercedes turbo housing will help the Scout even more.

I believe the 3" exhaust will help the Mercedes a bunch, especially with the auto trans I am still running. Off idle response is horrible with an auto. I don't want to say a prayer each time before I cross an intersection anymore. ;) I know Ridge doesn't with his intercooled, manual tranny roadster. :D