2.5T (602) power enhancement
 

Today I lost a stoplight race to a kia rio. I spooled up and took him off the line but he caught and passed me near the top of second gear - very embarassing. I noticed that my car seems to bog a bit at high rpms and from 4-5K there is a significant amount of black smoke. After each full-throttle shift it's back to no smoke until the RPMs come back up. I think this means there is an air restriction at high RPM, maybe the factory exhaust is partially plugged? The car still makes decent power (for what it is).

How much boost can these cars handle without a head gasket upgrade? I am already making the stock 11psi. Is there an easy way to make a manual boost controller? I know my wastegate is vacuum-operated and I can't think of an easy way to increase the boost to, say 14psi with a simple mechanical device. All I know how to do is hook constant vacuum to it for max boost, which I don't want to do for fear of blowing up the motor.

Also how much can this particular car benefit from larger exhaust? I have the factory muffler and resonator in the rear - can one or both be eliminated or replace with high-flow versions? How about 2.5" pipe? Should I disconnect the exhaust and go for a test drive? :wacky:

You can ditch the vacuum controlled wastegate for a simpler boost controlled wastegate. A turbo rebuilding shop should be able to do that.

Straight exhaust should help too.

You should get familiar with the ALDA and EGTs before you introduce more boost.

If you really must race and feel badly when you don't win, trade your car for a 400E. You won't even have to add any money since Diesels hold their value well vs same body style gassers.

Sixto
87 300D

As much as you'd like to, you won't beat a Kia Rio (Or many other modern gas cars except for possibly a Toyota/Honda Hybrid). It's 0-60 is 9.3 seconds vs your 12 seconds and 2365lbs vs your 3200lbs.

You would have to be into the 180hp range to beat it.

Heh, even a Prius will take you. 0-60 in upper 9's, low 10's. They actually have a buttload of torque thanks to the electric motor. Honda Insight is similar at 10 seconds :)

That's depressing. And I think my car is more like 3400lbs but you're probably right. Even if I could come close, say 10-sec 0-60, I would at least not be embarassed. I am looking around for a nice '87 6-cylinder but can't find one that doesn't have a multitude of problems, and I would likely have to give up my black interior since I have never seen an 87 with black interior.

Thanks - I appreciate the advice (except for the 400E part! ;). Does the whole wastegate have to be swapped or can you just swap the actuator? I have already removed and adjusted the ALDA so I am familiar with that. No EGT gauge yet.

Lower rearend gears.....
 

If you want to win more drag races, the cheapest route may be to swap rearends. The factory 2.65 ratio in the 2.5T cars is the "tallest" (lowest numerically) ratio available in a W201. Even a relatively small step to a 2.88 rearend will be noticeable. With a 3.07, 3.27, or 3.42 ratio, you will really notice a difference in accelleration (and an increase in highway rpm's).

I'm using a 2.88 rearend in my latest 2.5 turbo 5-speed project. It hasn't hit the road yet, but should offer a good compromise between low end accelleration and highway rpms.

SteveM.

Ooops, sorry.
 

Sorry, I thought you had an '87 190D 2.5T. I don't know what the ratios are for the W124 diesels.

Steve.

Standard Diesel performance is:

More fuel = more HP BUT...
More fuel also = higher EGT's so you need more air to counter it.

This can be accomplished by tweaking the wastegate for more boost, installing a larger turbo or compounding two or more together. You can also install low restriction intakes and exhausts for more air flow.

You mention a "vacuum operated" wastegate. I don't know if this is a MB thing or if you actually mean a manifold pressure controlled wastegate. Lord knows MB likes to do things their own way so I'm not judging... If the wastegate is boost or MAP referenced, you can create a "calibrated leak" in the control line by inserting a brass fitting with a tiny hole in it open to the outside atmosphere. This in effect, stiffens the spring and makes it require more boost to open up. A neater solution is to tighten the wastegate rod so there's more pre-load on the diaphram spring. I don't know if your particular model has an adjustable actuator rod but it's worth a look.

It also goes without saying that you need an EGT and boost gauge to monitor performance before you go tweaking around with fuel and boost levels.

Bottom line on your car, I'd do the following:

1. Get yourself some gauges.
2. Do some research and find out if your IP can be adjusted for more fuel.
3. Adjust your wastegate for more boost to compensate for the fuel.
4. Install free flowing exhaust and intakes for more air.

As far as boost is concerned, I don't thnk 15 PSI would hurt but then again, I'm speaking about Diesels in general as I'm not familiar with the limits of this particular engine.

Since your smoking the answer is not more fuel. You need more air.

First and fore most make sure the cars engine is working right. Check your air filter. Also check for leaks between your air intake back to your air box. Mercedes is one of the few companies that does make an attempt to use the ram air effect and it helps a little provided that there aren't any leaks. You might also check to see if your EGR valve is closing all the way. At higher rpms it is supposed to be totally closed. Your injectors may be fouled so a good diesel purge treatment might be a good idea. Check your timing too.

With out major surgery your looking at some of the right places to improve things. A free flowing exhaust makes the turbo's job easier so it doesn't burden the engine as much. You'll also get boost a tad sooner. It won't help boost once the waste gate is open though lower exhaust back pressure will help some by allowing more exhaust to be evacuated from the cylinders. Keep the resonator it can actually help torque at some rpms and eliminates the low end drone. I put a cherry bomb on my 85 300SD and it helped give it some more spunk with a very very minor increase in noise. The fiberglass in it will eventually get packed with soot and it will be in effect a straight pipe, but its still a muffler in the eyes of the law.

The best thing you could do is brainwash the computer and install an intercooler but this might be a bit beyond your skill level.

Replace the actuator and tap the compressor outlet for a boost signal fitting. Keep track of which way is open and which way is closed for the wastegate lever.

Sixto
87 300D

At 242K miles you have already out run the Kia....big time:D.

And overgearing a turbocharged vehicle will not let you hit full load in lower gears. Not what he's after.

True - I know the rearend gear is tall but so must be the gears in the tranny because the overall ratios are pretty low. Topping out at 25mph in first gear tells me that I do not need "more" gear, just more power. :dizzy2: Thanks for the suggestion though!

-David

Thanks - I will try and find the proper actuator. Any reason why I can't just tap into boost at the intake manifold? Do you need a dedicated line at the turbo for reliability?

-David