slow acceleration, how much can I up the boost & such, limiting factors? - PeachParts Mercedes-Benz Forum

michaelwoodcock · #1 10-01-2012, 04:57 PM

Hello guys,

I had a sluggish 300sd for a few weeks. I finally got around to installing a boost gauge, and I had no more than 8 pounds of boost! The ALDA screw was already turned almost all the way CCW when I bought the car so I turned it just a 1/4 turn ccw. I used vice grips to pinch the wastegate actuator line, and the car would build up to and over 11 lbs of boost easily, I was letting off the diesel pedal at 11 psi to prevent any engine damage.

If I want more gains, what are the limiting factors, and what do I have to monitor? My engine is very healthy, almost no blowby hot or cold, valves adjusted, etc. I believe I should add an EGT gauge and monitor the EGT's? Will excessive boost harm the engine? Can I turn up the boost on the stock turbo to, say, 14-15 PSI, and just monitor EGT's, and/or add water/methanol injection? I have tuned lots of gasoline engines, but diesel tuning is new to me! I know all the preignition concerns are mostly eliminated, so I just have to worry about EGT's, correct?

Secondaries · #2 10-01-2012, 05:10 PM

Search; this very question has been asked many many times...

Stock boost is around 10-12psi, turning it up to there should be fine. 14-15psi is all the air the stock pump can provide fuel for. Again, searching for pump mods (and checking the Super Turbodiesel forums) will find you all the information you will need.

Edit: This thread here was two lines below yours and contains most, if not all, the information you will need on finding more horsepower.

winmutt · #3 10-04-2012, 05:45 PM

Verified your linkages are set properly?

michaelwoodcock · #4 10-09-2012, 04:56 PM

Hello,

if anything I overdid the linkages, I have to give a very firm press to hit the kickdown solenoid, I am about to have a buddy give me a hand to get them just right.

Cheers,
Mike

Simpler=Better · #5 10-09-2012, 06:14 PM

Is your transmission short shifting into 4th and then lugging down? Does it rev completely and shift through all 4 gears when you floor it from a stop?

Secondaries · #6 10-10-2012, 11:10 AM

Quote:

Originally Posted by michaelwoodcock

Hello,

if anything I overdid the linkages, I have to give a very firm press to hit the kickdown solenoid, I am about to have a buddy give me a hand to get them just right.

Cheers,
Mike

You overdid the linkage? Care to elaborate?

At zero pedal the pump arm should be on the horizontal throttle stop/idle adjuster, and the roller bushing should be at the beginning of its slot. At full pedal the pump arm should be on the vertical throttle stop, the roller bushing at the end of the slot, and the pedal pressing on the kickdown switch.

oldsinner111 · #7 11-09-2012, 05:59 AM

I drove two years on 3/4 throttle , till I found out my linkage was not going all the way.

ngarover · #8 11-22-2012, 11:59 AM

First off, I would go in and do a Valve adjustment very first thing. While in there I would check the timing chain stretch, and correct it if there is any, then, drip timing the IP would be next. Then upon putting it back together, I would verify that the linkages are adjusted correctly. I would then clean out the banjo bolt, and related tube. THEN, I would have this injectors pop tested and repaired if need be.

AFTER I knew all that was correct, I would recheck and enjoy the power acceleration the car has at that point and then decide if anything else need to really be done.

Thing is, all the above con be done extremely cheap, and in a hour or so of work. Maybe 2 if it's your first time. (except for of course sending out the injectors)

Basically, fix the issue causing the problem instead of looking for a way to bandaid it and cause yet another issue. Having driven a brand new om617 engine, I know how powerful they really can be when tuned correctly. Most of us are only use to the tired, old, abused engines puffing around and think this is the norm.