I am putting my supercharged 16V engine back together after burning a second set of pistons. This time I decided to lower the compression ratio a little by having 1.5mm removed fromthe top of the piston (should be about 9:1). I am also installing a VDO EGT probe into the exhaust stream to monitor the exhaust temperature in an attempt not to repeat my past errors.

My question is, what should be the "full output" temperature (extended full throttle)? What should be the maximum temperature? I read one of SpeedTech's postings where he used the range 1200-1300 as target range. Does anyone have any experience with measuring exhaust temperatures?

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Jim Villers
190SL, 230SL 5-speed, 95 E320 Wagon, 01 E320 Wagon, MGB, Boxster 'S', 190SL "Barn Find"

Jim, this is strange. I have run my turbo at 14lbs of boost on a stock engine and headgasket. I did blow a headgasket because I did not let out when I had some detonation. That was MY fault.

Anyway, I wonder why you are burning pistons. You almost HAVE to be running Very lean or way too much timing.!!!!!

Use a timing controller and take out a few degrees under boost and make it run at 12:1 fuel ratio under boost and you will be fine.

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Benzmac:
Donnie Drummonds
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS

Donnie .... I agree with everything you say. I set my injection up on a dyno at 12:1 fuel air and retarded the ignition to 20 degrees advance under boost. My fuel air gauge was always in the very rich part of the scale so I thought that I was "safe". I was the surprised guy when I opened it up and found the pistons burned. I thought that I had broken a ring or something like that. I could have had detonation; my ears do not hear it and I have not gotten a knock sensor to work on this engine (no good place to mount it).

Do you run your car on the track as well as the strip? I was thinking that the long full throttle back straight at VIR could have been part of my problem.

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Jim Villers
190SL, 230SL 5-speed, 95 E320 Wagon, 01 E320 Wagon, MGB, Boxster 'S', 190SL "Barn Find"

Jim

I used to run a pyrometer on a couple of my vehicles ( for R & D purposes ) a long time ago.
The target range you mentioned in your post above seems about right, maybe even a little bit conservative ?
How much exhaust back-pressure are you getting ? Just a thought.

P.S. Are you running an intercooler ?

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2007 C 230 Sport.

Jim I'm also playing with the idea of mounting a knock sensor (connected to say i light that flashes when detonation occurs) on the engine but I've come up with nothing yet ;( . I was also thinking of lowering the compression by takeing a bit off the top of the pistions but wouldn't that make the pistons weeker ?

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190E 3.0-24v (M104 980) turbo @ 0.8 bar
1/4 mile: 2.483 / 13.540 / 175.17 km/h (street tires)

Manny ..... I believe that I have very little backpressure. The cat converter is empty.

Joreto .... I don't believe that I have weakened the pistons. The piston had an initial dish of about 1mm (picture in a previous post) and I just had them take off the shoulders plus another 0.5mm, hardly enough to worry about. My calculations indicated that the center dish compensated for the over bore, the shoulder was worth about a half a compression point and the extra mil was another half. I'll let you know what I think when it runs in a couple of days.

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Jim Villers
190SL, 230SL 5-speed, 95 E320 Wagon, 01 E320 Wagon, MGB, Boxster 'S', 190SL "Barn Find"

Jim,

When to machine the outer edge of the piston you are inceasing the piston to head clearance in this vital area and reducing the A/F opportunity to generate turbulance for better burn rates and higher detonation protection. You always want to strive for a tight Piston to head clearance in the squish band area to increase cylinder turbulance.

The Long back straight at VIR does put a very high strain on the motor. You need to do some plug chops in the this area of the track and look at the spark plugs for signs of detonation.

Is'nt building motors that live on the edge fun!!

Jeff

Jeff ... I am sure that you are correct on the shape of the combustion chamber. I just didn't see an "easy" way to lower the compression and keep everything in balance. Deeping the dish was my first thought but after talking it over with the machine shop guy, I agreeded that a flat top would be the most consistant between the four pistons.

On building engines, my fun was getting the supercharger stuffed in and working through the "sorting out" process. I gave up on CIS and instaled a digital engine management system that provides all of the control and flexibility to keep the process interesting. Changing pistons is just WORK.

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Jim Villers
190SL, 230SL 5-speed, 95 E320 Wagon, 01 E320 Wagon, MGB, Boxster 'S', 190SL "Barn Find"

Jim.

I have run it long and hard. One thing is, I think max timing was 16 under full boost....HMMM. I wonder if these are prone to detonation from combustion chamber design and if so, could we cool the head more to help>?

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Benzmac:
Donnie Drummonds
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS

WATER INJECTION ! cheaper & easier than replacing pistons.
http://www.aquamist.co.uk/cp/cp.html

Jim, I would definately make sure your air fule ratio and timing curve are "within spec",,,, then maybe do some reading up on water injection.
I have an aquamist system that I plan to put on Priest's turbo car as soon as it comes back from the body shop. (he is having an evo 2 body put on it this winter).
We got it from an outfit in Arizona for around 500 bucks.
Will be using the stock washer fluid tank since it has a low level light and will use 1/2 distilled water 1/2 methanol mixture.

What I like is the fact that the water injection fights detonation without needing to over richen the mixture & it helps keep the combustion chambers clean of carbon.

I'm not suggesting you use this as a bandaid to cover another problem, but it is great insurance & gives a little bit of "buffer" on any forced induction set up.

I don't think I'll add a turbo or supercharger to anything again without also installing a water injection system.

Remember that your "kompressor" has one disadvantage since it has a tendency to heat the air it compresses, so the water injection seems like a natural solution to fight that heat.

my 2 cents.
Good luck,
Alain

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Alain
independant MBZ tech since 1981
http://www.motorsportlegendsks.com/

Jim,

If you run your car really rich, there is a chance that you will build up carbon deposits that can cause detonation on your pistons.

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George Carstens

Alan ... Good to hear from you again. I really didn't think that I had a problem was part of my problem. I thought that running less than 10psi and a 12:1 air-fuel and 20 degrees advance was very conservative. The only item that I can think of that I didn't do that I should have was to install colder plugs (possible problem).

The engine is running now and I am breaking it in. My first impression is that I lost a lot of power by lowering the compression. I'll put it on a dyno in a couple of weeks to see what is real verses "gut feelings".

I installed an exhaust gas temperature probe so I have one more way to observe what is actually happening in the engine.

I thought about water injection but I still don't believe that my inlet air temperature is high enough to worry about. My gauge is not easy to read but I have never seen it over 200 degrees.

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Jim Villers
190SL, 230SL 5-speed, 95 E320 Wagon, 01 E320 Wagon, MGB, Boxster 'S', 190SL "Barn Find"

In supercharger mode expect EGT temps of 800 to 900 degrees. Sometimes 1000, also this is dependant on where you put the probe. Most race cars have probes no more than 8" from the exhaust valve.

Turbos due to the restriction make the EGT higher. Try not to exceed 1350 degrees before turbo. If you mount the probe after turbo expect a 200 degree drop in temp.

Jim.

After blowing a stock head gasket, I did stud the head to the block and add water injection. I built the whole kit for under $100 using factory Mercedes parts. It works so well!

I have it to come on above 12psi boost. I do not have any detonation now.

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Benzmac:
Donnie Drummonds
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS

Donnie ... What spark plugs are you using in your 2.3-16? I think that it might be wise to use a colder plug than the stock plug.

The engine is now broken in and I just finished a compression test. I read 175 psi in each cylinder. That is very close to the compression with standard pistons and I was expecting to drop the compression ratio by about a point. I had guessed that the compression should have been about 160 psi since I had shaved 1.5 mm from the piston crown.

Any thoughts?

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Jim Villers
190SL, 230SL 5-speed, 95 E320 Wagon, 01 E320 Wagon, MGB, Boxster 'S', 190SL "Barn Find"