Coating Prechambers - Page 2 - PeachParts Mercedes-Benz Forum

libbybapa · #16 04-13-2006, 01:28 PM

The two reasons that direct injection engines get approx 10-15% better fuel economy than indirect injection diesels are pumping losses in and out of the precombustion chambers and the increased heat losses from the greatly increased surface area of the precombustion chambers as opposed to the direct injection combustion chambers. This decrease in fuel economy of the IDI's is despite their better combustion characteristics. The heat loss of the pre-chamber is also the primary reason that IDI engines are harder to start. There is very little that can be done about the pumping losses, but modern thermal barrier coatings can greatly decrease heat loss to the head and so increase efficiency and cold starting. It is my understanding that current ceramic coatings can be applied that do not significantly add dimention and will easily withstand the temps and abuse without self-destructing. Yes, one could go buy a TDI for fuel economy, but coatings are not cost prohibitive and seeing how the Mercedes prechambers are removable with the head on I thought I would ask if anyone else had done so. I cannot imagine that coating the five would cost $100. It might be worth it in fuel savings. It might also be worth it if the car will start easily with marginal compression and so extend the rebuild interval. It might not. That's why I asked if anyone else had done so and what their results were...

Andrew

imdavid28 · #17 04-13-2006, 01:49 PM

Quote:

Originally Posted by Craig

trying to re-engineer these little bits and pieces just seems a little silly to me.

Silly, but fun to talk about.

Quote:

Originally Posted by libbybapa

I cannot imagine that coating the five would cost $100.

My boss had the bottom of his intake done for $200. I think you will be paying quite a bit more.

#18 04-13-2006, 01:50 PM

Interesting concept, but I can't imagine that you would be able to coat the old pre-chambers and new ones cost about $100 each, so you are talking about a $600 experiment. It might be worth considering if you were going to replace them anyway, but $600 is about half the cost of a remanufactured head. I may be wrong, but this doesn't sound very cost effective.

Bajaman · #19 04-13-2006, 02:11 PM

First of all, I don't think that new prechambers are in order for coating. A combination of sand blasting and or chemical etching should create a surface amenable to ceramic coating. On pumping losses, if more heat is retained with a heat barrier, couldn't one take advantage of this extra heat and lower the compression ratio a tad by "opening up" the prechamber pinholes. This would decrease the heat retention in the prechamber, but may be a feasible tradeoff (more heat from thermal barrier/ less heat retention with enlarging pinholes). There was some discussion on this very topic on another forum: http://www.binderbulletin.org/forums/showthread.php?t=34650&highlight=prechamber+ceramic+coating
Though 617 uses a different prechamber design, I think that the same logic is applicable.
BB

ConnClark · #20 04-13-2006, 02:16 PM

Well, the way fuel prices are going up it may become more attractive. Really if your going to do it you would want the piston crowns, intake valves, and head chamber done as well. If it got me 1.5 mpg more I would spend the $600. I bet it would only get you 0.2mpg more though.

libbybapa · #21 04-13-2006, 03:32 PM

On a 1.6TD VW rebuild I was quoted $300 for piston crowns, combustion faces of the head, prechambers and exaust manifold inside and out. Agreed, that all of those would be beneficial, but other than the exhaust manfold and prechambers, the head would need to be removed adding a whole lot of labor. Certainly the prechambers would be the important part to aid starting.

With regard to enlarging the pinholes, the compression would be lowered almost insignificantly.

As mentioned, there would not be any need for new prechambers unless the old ones were unserviceable in which case they should be replaced anyway.

Andrew

#22 04-13-2006, 03:46 PM

Quote:

Originally Posted by ConnClark

Well, the way fuel prices are going up it may become more attractive. Really if your going to do it you would want the piston crowns, intake valves, and head chamber done as well. If it got me 1.5 mpg more I would spend the $600. I bet it would only get you 0.2mpg more though.

Well, if it actually increased your mileage from 30 mpg to 31.5 mpg you would get your $600 back in only 126,000 miles (assuming $3/gallon). However, I also suspect the change in mileage would actually be negligible. If you spent that $600 on new/rebuilt injectors, a valve adjustment, checking the IP and valve timing, a new air filter, and some high quality 5W40 synthetic oil you would probably do better with regard to both mileage and cold starting.

ConnClark · #23 04-13-2006, 03:50 PM

Actually your compression ratio would go up with the coating. This is normally a good thing. I have no idea why on that other forum they wanted to lower compression. I also wonder how their experiment turned out. I assume it wasn't good as the thread ended.

As far as the cost goes, $300 is to the point where it might start getting attractive if you are already rebuilding an engine.

ConnClark · #24 04-13-2006, 03:57 PM

Quote:

Originally Posted by Craig

Well, if it actually increased your mileage from 30 mpg to 31.5 mpg you would get your $600 back in only 126,000 miles (assuming $3/gallon). However, I also suspect the change in mileage would actually be negligible. If you spent that $600 on new/rebuilt injectors, a valve adjustment, checking the IP and valve timing, a new air filter, and some high quality 5W40 synthetic oil you would probably do better with regard to both mileage and cold starting.

I have a Kalifornistani 300SD that gets only 21 mpg if I keep my foot out of it, so my payback would be a lot more rapid. I think that the atomizer pin change I mentioned earlier would be more effective than the ceramic coatings.

#25 04-13-2006, 04:15 PM

Quote:

Originally Posted by ConnClark

I have a Kalifornistani 300SD that gets only 21 mpg if I keep my foot out of it, so my payback would be a lot more rapid. I think that the atomizer pin change I mentioned earlier would be more effective than the ceramic coatings.

I still think that you must have something else wrong to only get 21 mpg. Have you ever checked your IP timing, condition of your injectors, compression, etc.? Do other Cal. cars get that kind of mileage? I would look at all the basics before I started changing things.

ConnClark · #26 04-13-2006, 04:19 PM

yep, 85 Kalifornistani 300SDs typically get about 21 mpg (in town driving). I can get 24.9 on the highway in cold weather. EPA rating is 22mpg highway.

#27 04-13-2006, 04:23 PM

Quote:

Originally Posted by ConnClark

yep, 85 Kalifornistani 300SDs typically get about 21 mpg (in town driving). I can get 24.9 on the highway in cold weather. EPA rating is 22mpg highway.

Wow, I didn't know there was that much difference from the federal model. Do you know what causes the difference, and can it be changed?

ConnClark · #28 04-13-2006, 04:34 PM

Mainly the trap oxidizer( cat if you had the recall work done). Kali cars also have higher EGR ratio and an air recirculation valve on the turbos compressor housing.

To de-californate it you have to replace the intake and exhaust manifolds, the turbo, and the exhaust down pipe. A little super glue or a BB will take care of the rest. You might as well change out the air filter too since they run about $60-$70 for the 85 Cali version.

Edit: If I ever get my hands on a 76 W115 intake manifold this stuff is gone.