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  #16  
Old 10-29-2008, 01:25 AM
ForcedInduction
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Quote:
Originally Posted by OM616 View Post
Question: so if there were five engines lined up on the floor and one was uprated how would you pick it out?
By serial number if you can find out when the changes were made.
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  #17  
Old 11-02-2008, 04:10 PM
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Location: Michigan
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I am looking for a head with PCs to use as a mock-up for porting, a new cam, and PC mods for my 616 turbo research project over the winter. I saw one for a 616 in the parts section & sent a PM but no dice so far. I think a 617 would work as well for what I want to do with it. If anyone knows of a junk or really cheep one that would help with my research. Some old pistons dished pistons would be helpful as well extra cams to mock up.

I am going to cut a slot accost the three burn holes that point towards the center of the cylinder and parallel to the head & piston. The slot will start at the right and cut accost to the left. This will direct the fire horizontally over the piston and head.

For this set up I would prefer to use the new uprated type 2 PC in combination with a standard power type 1 dish piston. I will need to machine the piston for the longer PC and make the valve pockets deeper for a new cam. With the modified PC the star chambered pistons that are required with type 2 PCs would see fire directly on the piston star groove walls, ( can't think of a good way to describe it) where the dish would be open.

Depending on what I can get for parts, and a donor engine, I could start with a standard power engine and cut the PCs to get an idea of the difference. The flat bottom of the type 1 PC is not as strong as the type 2 PC but the slot should reduce the pressure in the PC, ( less restriction ) that is where some of the power would come from. MB increased the hole Dia to get more power so the slot would flow even more. My thought is that the thicker bottom of the type 2 PC would handle heat better and it appears that the PC ball is supported on both ends.

My thinking is that getting enough fresh air into the cylinder is not the problem although the cam is not the best. I think the problem is getting enough fresh air in to the PC and the rapidly expanding gasses out with minimal resistance. I think the " over fueling" and associated rapid and high EGTs are from the PC loading up during full power. They can't get the gasses out, there is very little time to get fresh air in and fuel builds up in the PC. I think that is why 617s need to run so much boost for so little increase compared to DI engines. If the slot will allow more air into the PC faster and the " over fueled" gasses to get out of the PC and into the combustion chamber faster so they can use the air in the combustion chamber that currently is not taken advantage of before the piston has traveled too far. This would be as close to a DI as we could get and still have the PC benefits.
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  #18  
Old 11-03-2008, 02:46 AM
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Originally Posted by OM616 View Post
[FONT=Times New Roman][SIZE=3][COLOR=black]

My thinking is that getting enough fresh air into the cylinder is not the problem although the cam is not the best. I think the problem is getting enough fresh air in to the PC and the rapidly expanding gasses out with minimal resistance. I think the " over fueling" and associated rapid and high EGTs are from the PC loading up during full power. They can't get the gasses out, there is very little time to get fresh air in and fuel builds up in the PC. I think that is why 617s need to run so much boost for so little increase compared to DI engines. If the slot will allow more air into the PC faster and the " over fueled" gasses to get out of the PC and into the combustion chamber faster so they can use the air in the combustion chamber that currently is not taken advantage of before the piston has traveled too far. This would be as close to a DI as we could get and still have the PC benefits.
Experts say that the PC is getting small above 300 HP. Never heard that the Finns modified the PC.

Tom
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  #19  
Old 11-03-2008, 03:14 AM
ForcedInduction
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I asked on Mersu forum and Mauri H. replied that they don't need to be modified.
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  #20  
Old 11-03-2008, 12:28 PM
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Is it that they were able to get XXX Hp with out modifying the PC. or that they tried modifying the PC and there was no benefit? MB modified their PC (Referenced from my MB engine manual) and found a benefit. They also kept increasing the burn hole dia and number of burn holes as time passed.

We put bigger valves in high power V8s to get more flow. I want to increase the flow in and out of the PC.

If some one has tried to modify the PC, can we get the specks on what they did and the test results? I have heard of other people wanting to try drilling out the burn holes but never any results.

In the absence of " this is what I did and this was the result" I will press on and find out if there is some efficiency to be had. I like to say there is one way to find out. It will be better, worse, or make no difference at all. Better living through modification.

Please do not think I am being argumentative. I am just following the progressive changes the MB has done and going further to see if there is indeed a sweet spot with the burn holes.

If some one has done this and has the technical data and test parameters and results we could evaluate what was done, the result, and perhaps put this to bed. And it would save me from potentially wasting a lot of time
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  #21  
Old 11-03-2008, 03:04 PM
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Originally Posted by OM616 View Post
I want to increase the flow in and out of the PC.
Why? Power is made in the combustion chamber not the precombustion chamber. The PC's reason for existence is to pre-heat and accelerate the fuel for better (smoother and quieter) combustion, MB probably restricted flow in/out for a good reason.
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  #22  
Old 11-03-2008, 03:58 PM
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MB probably restricted flow in/out for a good reason.[/quote]

With out a doubt. They had several parameters they need to stay within when they designed the 616/617 engines. Emissions played a huge role at that time along with smooth and quiet operation. I have spent may hours in a engine test cell trying to get every bit out of a new design so the engineers know what they have to work with when they detune it to meet the regulations.
The result was more often than not a slug that met emission regs.


I may be wrong in my thinking. And that is ok, I have been wrong before and I will be wrong again with out a doubt. This may be a perfect set up for an " I told you so"
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  #23  
Old 11-04-2008, 09:53 AM
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I think an accurate measure of the prechamber volume vs. the combustion chamber volume at tdc is in order. This will give you an idea how much of the air is actually going in and out of the prechamber. I am inclined to believe that the combustion chamber volume is rather small compared to the prechamber. This would support the need to open up the prechamber for better flow. Cold start and noise are probably the two biggest negative outcomes. Who knows maybe power will also be negatively affected?? We won't know until someone tries. I would do it if I had a spare engine lying around.
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  #24  
Old 11-04-2008, 11:26 AM
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I know where a car is in Ohio for $400 -- supposedly the engine is good, just no radiator (got stolen out of the car)
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  #25  
Old 11-04-2008, 12:17 PM
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I would take it!! I have been looking for a donor car but haven't come accost anything as close and as cheep.

I even still have an old radiator!!

PM me with more details please, year if known, and is it drivable?.
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  #26  
Old 11-04-2008, 01:52 PM
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Originally Posted by Bajaman View Post
I think an accurate measure of the prechamber volume vs. the combustion chamber volume at tdc is in order. This will give you an idea how much of the air is actually going in and out of the prechamber. I am inclined to believe that the combustion chamber volume is rather small compared to the prechamber. This would support the need to open up the prechamber for better flow. Cold start and noise are probably the two biggest negative outcomes. Who knows maybe power will also be negatively affected?? We won't know until someone tries. I would do it if I had a spare engine lying around.


I get the feeling that there are a couple schools of thought regarding what the PC dose, is meant to do, and how it works. This is my hypothesis as to what is going on in the 616.912 PC.

If you take the name pre-combustion chamber literally that implies that it is a "before combustion" chamber, as in no combustion takes place in the chamber. I can see this type of operation as a method of atomizing the fuel and using the holes to disperse the fuel throughout the combustion chamber where it ignites and burns. In this case the PC is merely an extension of the injector, and the hole dia would be sensitive as the velocity of the fuel being expelled would only be pushed by the pressure difference created by the injection it self.

I am seeing the PC as a Primary or Initial Combustion chamber. Where the actual timed ignition takes place in the PC. If that is the case then a couple things need to happen.

First the rapidly expanding gasses need to get to the combustion chamber as easily as possible to push on the piston. If the pressure is trapped in the PC then that energy is not used to make power and is a loss. If the PC volume is not sufficient enough to hold enough air to mach the amount of fuel being injected, then at some point the fire will go out due to lack of oxygen. Under full load this would situation would leave raw and partially burnt fuel in the PC, essentially it would be flooded. The pressure wave in the PC would expel some of the unburnt fuel into the CC where it could be burnt, but if the holes are to restrictive, at high speed there may not be enough time to equalize the PC and CC pressures before TDC. My thinking, given this scenario, is that larger less restrictive holes will allow more gasses to flow over the same time or the same volume of gasses in less time. (Bigger valves in an engine)

Now that the injection and ignition has taken place, the PC needs to be cleared out for the next ignition cycle. Since the pictures in the manual do not show any way for gasses to flow through the PC, I have concluded that the only way to get fresh air into the PC is through the holes, during the compression stroke. In that case there is very little time for that to happen and I can see a flooded PC getting enough air to perhaps burn the fuel that was left from the last cycle, but if there was not enough oxygen ( due to the volume to injection A/F ratio, which I am guestimating and do not know for sure) to completely burn the last fuel charge then with each full load ignition cycle the PC would lode up more and more. The PC burn pressure would be lower and the lower pressure would require more time to expel the fuel through the holes, and at high speed could be continuing to expel fuel well after TDC. If this is even close to what is happening then any changes that help gasses flow from the PC to the CC would be beneficial. By increasing the PC VE, the amount of completed PC combustion could be increased, the time it would take to get the PC pressures to the CC to perform work would be lessened, and the fuel that was not burned in the PC would get to the CC faster where it could be burnt in time to be beneficial to the power stroke instead of being burnt in the exhaust manifold creating high EGTs.

My thinking is that the 616.912 PCs are adequate for a low power application. Where the VE of the PC is sufficient for the amount of fuel being injected. Smooth, Quiet operation with low CC temps, low EGTs and no smoke. Now the car finds it self in the USA where gas mileage and pollution be dammed, we want power!! So we start turning up the fuel and that troughs off the PC A/F ratio and EGTs go up as well as smoke appears. So we turn up the boost and that helps the PC VE so the EGTs go down and smoke goes away. So we turn the fuel up even more, and the cycle continues.

My thinking is that if the VE of the PC is increased by modifying the only way in and out of the PC then the amount of boost needed to artificially increase the PC VE could be reduced thus reducing exhaust back pressure. The amount of PC pressure that is used to push the piston could be increased, and the amount of unburnt PC fuel that is burned in the CC to perform work could be increased as well.

I am not worried about cold starting because the glow plugs are still there and if the PC can breath better, the PC pressure rise time will be lessened and the pre injection air temp may be higher that it is now. One side effect is that the PC post injection pressure drop would be grater and happen faster. If the PC needs the additional pressure caused by small holes to get through the warm up phase or low speed operation, opening up the PC holes may cause the engine to be cold blooded.

I welcome any thoughts.
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  #27  
Old 11-15-2008, 03:55 PM
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I am picking up a guni pig use for my PC tests. It is a 300SD engine so it is the uprated engine with the star chambered pistons and not ideal IMO for the slot mod.

First I will get it mechanically sound and instrumented up to get a good base line. Then I will start turning up the pump until I have reached the drivability threshold ( EGT & Smoke). With this less than ideal fueling set up, any pros and cons of any PC mod should be very easy to notice, basically better or worse EGTs with less or more power, nailing, and smoke.

With the star pistons I will start by just enlarging the burn holes in an effort to keep fire directed away from the vertical piston surfaces. MB increased the burn holes and saw a power increase so this should do something without putting the engine at that much risk. I would rater not cook a piston if I don't have to. If the EGTs go down and nailing is not an issue I will get new base line for another series of PC mods. If the EGTs go up, it is nailing, or smoking like crazy, and the problems can not be addressed with timing alone, than we have a good idea that this is not a good mod. If everything looks good I will turn up the pump again and so on to find a line. I am thinking that the stock turbo will be a limiting factor if the engine responds well the mod.

I am also thinking about putting a reflective coating on the inside of the PC ( except on the atomizing ball) to help reduce the thermal transfer to the head and cooling system. With the ball not coated it would remain hot and be able to cool itself via the chamber to head. Coating the out side of the PC would be easer, but the PC would not be able to transfer heat to the head and I am thinking it could melt down like a valve that dose not get enough seat time or when the lash is too tight and it doesn’t seat tightly. It will be tough to get the coating on with the ball in place. I looks like the newer PC balls are a rod type that is pressed in and supported at both ends. It might be able to be removed for the coating process and pressed back in after.

Again, any constructive thoughts?
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  #28  
Old 11-15-2008, 09:03 PM
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the ball can be pushed out from one side. Mark the position before.

What are your plans for PC mods?

Tom
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  #29  
Old 11-15-2008, 10:25 PM
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Quote:
Originally Posted by tomnik View Post
the ball can be pushed out from one side. Mark the position before.

What are your plans for PC mods?

Tom

See post #26. Main objective is to increase PC VE and possibly reduce some thermal losses to the cooling system( keep the heat is the gasses not the block).

Regarding the reflective coating:

If the thermal coating was on the outside of the PC, the PC temp would remain at a higher temp between ignition cycles due to the reduced thermal conductivity to the head. This would help vaporize large amounts of fuel quickly which is one of the benefits of the PC, (allowing for a higher operating RPM compared to DI engines) but it might cause the PC to over heat.

I have two theories:

One theory I have is that if the outside was coated and the PC body could not transfer as much heat to the head, the PC would, 1) only reach the max burn temp, and 2) the PC would be cooled by the vaporizing fuel. The more fuel the more heat and the more cooling. It might be the way to go but if the material that the PC is made from can't take the temps, a different material could be used.

The other theory I have is that if the inside of the PC was coated, the PC would not get as hot and preheat the air inside the PC, (before compression). Cooler air is more dense=more oxygen. This is a difficult argument with a diesel because it relies on hot air. It would be the same argument for an inner cooler. Keep the air as dense as possible. But there is so little time from the point where fresh air starts being pushed into the PC to the point that the pressure raises the temp that it really is not even practical to even consider it .

Having just reviewed this, my new thoughts are that coating the inside would not be beneficial, even with a hot ball. I bet it would run like a cold engine all the time and would not handle lots of fuel well.


If it seems like I am contradicting myself , it is because I am. I try to identify as many sides and aspects of an idea (pros and cons) before I decide on a plan of action. That is where everyone comes in. Any thought or idea, regardless of how frivolous it may be, helps insure that as much as possible has been thought of.
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  #30  
Old 11-16-2008, 04:53 AM
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I also started to think about PC modification a while ago.
I got the fab drawings for the 616, rounded end PC, the 617a PC and the 606 (177 HP) PC.
Unfortunately the 606 is not interchangeable but the differences were obious.
Increased inner volume, increased bores (angled injector/ ball axes which came with the 60x engines). The location of the glow plug whole is different. Geometrically there is a triangle build by PC glow plug and piston centre, while the 61x engines have these parts in a line.
My ideas are to increase the bores square in relation of fuel increase (or HP increase).
Next make the centre bore inlet (from piston side) funnel like to decrease flow restriction.
The swirl in the PC is caused from compression air flowing into the PC where it hits the flat side of the ball and swirls in the "gallery" of the PC until fuel is injected. Here it could help to have increased volume and good geometry for the swirl. The PC body is made from 2 parts and welded afterwards. The surface quality is not very fine (and hard for us to rework).
The flow velocities are huge so it makes sense to me to optimise the geometry. Coating could be helpful for decreasing the flow restriction inside the PC.

BUT, I am sure there is potential in the PC although I was told that the C111 had no PC mods. The PC will become a bottleneck >250 HP.

Personally the PC is on my list but not on top.

Speaking of temperatures I think injection timing and duration is more important and on top the initial source than the PC.

Beside my progress in IP mods I am looking with one eye only at the possibility to get a set of PC 617a for studying but I will never buy them new.

Tom
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