What is the stock bar-psi measurment in an 87 300D Turbo? Can this be adjusted easily? How much hp can be increased by doing so? What is the maximum boost capability of the stock engine? Has anyone messed with this? Would the CD service manual describe how to do a procedure for this? Also what else can be done to increase performance??????????

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Elliot Easton
1987 300D Turbo 151K
1996 C220 stock (Mom's car)

I've got a 603 Manual and I'll get you the numbers as soon as I get a chance.

But on a different note I'll give a little anecdotal info to ponder!

I got my 87 SDL/603.961 in November 2001 at 197K and with an engine that supposedly had 80 - 90K on it after a complete rebuild. The first week I did a 3000 mile/ 53 driving hours round trip from Boston to Boca Raton Fla. Never burned a drop of oil or lost a drop of coolant. Since then I've put an additional 8K on this car. About a month ago now I did a 600 day trip where I experienced a noticeable loss of power enroute. I attributed it at first to a half tank of bad fuel. After reading plenty on this forum I deduced that the lack of power was a turbo boost related problem and did a cleaning of the boost circuit and man oh man I think that since I've had the car it was the first time that the turbo boost/ALDA system was 100%. This car will jump from about 2300 RPMs and upwards. Life is good!!

Now the bad news in the last couple of weeks I noticed a small consumption of oil and I've started to experience coolant system symptoms that in toto are starting to feel like the dreaded blown head gasket syndrome that the aluminum block on this engine is fairly well known for. I've got the car sidelined as I'm waiting for the tool to pull the head bolts and the head to check the gasket. I'm praying the head is not warped or cracked but only time will tell. I'm expecting the worst and hoping for the best while reading every 603 head thread or post on this site!

And for you I have these words of wisdom from a likely fool! As this engine can quickly and expensively go from a fire breather to a smoldering derelict I would caution you to take the time and a LITTLE money and before you take advantage of the impressive stock turbo charging capabilities and very seriously before you opt to explore the upper limits of turbo tweaking, to check or have someone you trust examine and check the basic destructible engine elements such as your engine’s head, its' bolts, and gasket and a similar check of the associated valve train including your engines timing chain componentry and coolant system would be cheap insurance that could prevent a disaster. Personally I will eventually do some boost modification to my engine because its there! but I will only do that after I'm sure the important parts, pieces, tolerances and spec are in order so that I can enjoy stomping on that pedal, hearing that turbo spool up moments prior to feeling the superb leather seat my 4000 lb autobahn sled propel me ever closer to nirvana. Then life will be GREAT!
:p

TurboD,

Whoa, there! One thing at a time! Now, let's see:

1- Stock boost should be 0.85-0.95 bar, at full load, in third gear, at 4000rpm.

2- This can be adjusted, but not particularly easily. If you have the KKK K24 turbo, you can adjust it with the screw in the end of the wastegate (accessible from underneath the car). This turbo has a small metal pipe going to the wastegate. If you have the Garrett turbo, you need to adjust the length of the rod between the wastegate pressure canister and the valve itself. This turbo has a rubber hose from the intake to the wastegate canister. Sorry, I don't have more info or photos of the Garrett (yet). Pictures of the KKK turbo can be found here:

http://www.meimann.com/images/mercedes/head_gasket/



3- I don't know for sure what the HP gain would be. I do know that the engine is rated at 148hp when running as Mercedes intended it to run. It depends how "bad" yours is now. The best test, IMO, is to clock the car 0-60. At sea level, on a flat road, the spec is 10.9 seconds. If yours is 13 seconds or less it's pretty good. Slower than ~13-14 seconds means you need to fix *something* - the trick is to figure out what! Note: At higher elevations (over 2000-3000 ft), there will be a significant power loss off idle. Not much you can do about that though.

4- The max boost capability of the stock engine is whatever it will take before melting the pistons. The overboost switch on my car is stamped "1.1 bar +/- 0.15". So, Mercedes put a safety rated at 1.25 bar max. I don't know if I'd want my car running at that amount on a daily basis, though. That's asking for a blown motor ($8000 for a new BARE longblock, or $8000 for a rebuilt with injectors, IP, and turbo.)

5- I'm about to mess with mine a little, but haven't had time yet. I want to set mine around 1.0-1.1 bar max. I tested my overboost sensor by hand with a MityVac and it engages at 1.2-1.25 bar.

6- No, the factory service manual does NOT specify how to adjust boost. It is supposed to be set by the turbo manufacturer. The only procedure is how to test the boost pressure. You need to figure out how to adjust it yourself.

7- There's not much else to increase performance over the factory rating. What you want to do is make sure you are actually getting the full rated 148hp. That means having the trap oxidizer removed (factory recall) if it hasn't been already, disabling the EGR and air recirc valves, making sure your injectors are good (can be tested for ~$30-40 at a diesel shop), cleaning out the intake manifold if necessary, cleaning out the hoses, tubing, and valves between the intake manifold and ALDA (on the injection pump), making sure you don't have brakes dragging, using synthetic oil in the engine, tranny, and rear end, keeping tires inflated properly, etc, etc. One thing I have heard, but not verified, is that the "cruise control surge retrofit" can reduce power output. If your car has 3 switchover valves in the pressure/vac tubing near the washer reservoir, your car has the retrofit. If you only have 2 it doesn't. My one '87 has this but I haven't removed it yet as a test. It's designed to compensate for the air recirc valve, but if that is disabled, it's not needed.

8- If the car is slow off the line (and you are near sea level), you can either remove the injection pump (I/P) and have it calibrated (big job), or try tweaking the ALDA on top of the I/P. Search the archives for details on how to do this. This will NOT, I repeat NOT improve top end power. It will ONLY increase "off idle" power. But it makes a big difference if yours is weak off the line! Remember, this applies at sea level more than at higher elevations...


Please post again if you experiment, to let is know what happens. Good luck!

__________________
Dave
Boise, ID
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