Very cool stuff. Who is going to build one up?
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New pre-cup idea?
- Thread starter THEFERMANATOR
- Start date
6.5L
Old Iron Runner
Would you even have to have a protrusion that large? I was thinking a instance where the whole precup was a slightly hemispherical shape with a 5 hole pattern. Think cup with holes drilled in the bottom. Small protrusion and something the pistons wouldn't have to be that different for. Please see crude attached drawing I just made in paint. You get the idea. 
After Ferm posted I was think along those lines also.
I know Dennis's precups are pretty big and he had had very good results. He said you can easily see the injector from the valve side.
I know Dennis's precups are pretty big and he had had very good results. He said you can easily see the injector from the valve side.
Chevypoor
Active Member
Been thinking on this one and thought I would share a few thoughts. Kinda new to diesels so I am still learning but here is an idea. Small ports equal great velocity and swirl. That is a given. This equates to low speed power and mileage. So a smaller port in the cup gives us better efficiency but as others have demonstrated they do not play with well big turbos and restrict power at higher speeds. Stick with me a minute on this one guys. The problem I see with using the Mercedes design with our 6.5 is the pre cup is obscured by about on third by the block and cylinder head. If we were to make a bump or bulge into the chamber we would have to reduce the size or the center of our cut out in the piston would have to be almost directly on the edge. This affects rings and would almost require a notch in the block itself to form a chamber like those used by Mercedes in the piston. The essence of the idea with the Mercedes pre cup, and I could be wrong on this is to keep mixture velocity high with a small port, ie the tiny holes but give volume for power by drilling multiple holes. Since the velocity is higher in theory the combustion should be more vigorous and efficient. I am sure the extra "chamber" in the piston top helps by giving more squeeze to mixture. What if we made a cup with no port and placed it into the head. Using a head gasket as a template you could scribe the combustion chamber orientation onto the pre cup. Then take an old pre cup and do the same thing. Then you could measure from this "chamber" line to the throat opening. Then you could scribe this same point on the new blank cup. Then drill a series of angled holes in a radius that are equi distant to the chamber arc that match the throat angle. This should in theory be a cruder form of the Mercedes design that requires only the cup itself to be machined. You could tune the cup by drilling larger holes but the mixture velocity should still stay alot higher than hogging out one massive opening.
Chevypoor
Active Member
- Staff
- #26
The simplest idea to try to me would be to make a precup with 2 small chutes coming out of the bottom of it. I'm not very good with paint or else I would do up a sketch. But instead of one large opening, why not try a precup with 2 small openings? It would be the simplest to try as you wouldn't need a drastic piston change, and it could easily work within the confines of the current head design.
Dreaming now, but what about a variable dia orifice precup? Anyone know how?
6.5L
Old Iron Runner
Wouldn't the piston design have to change regardless since the precup design is changing and the flame front is exiting in a completely different manner
schiker
Well-Known Member
I have thought similarly guys just day dreaming.
Yeah, wondered about variable nozzle before could have a pintle type device maybe but not sure how to seal an adjustment to outside mechanism. A thermal movement of a pintle or other blocking device might be possible and neat. But soot would probably foul movement.
Also thought immediately of nostril like holes. Did not know about olds precups but good to know. I would think sum of opening should start about the size of smallest turbo precup opening.
I have always wondered it some type of 3rd small valve behind the precup that could flush out any CO2 or other gasses and help cool precup would be something in a new design that would be beneficial.
I am still wondering about just how they get that much more power out of the precup and piston shape. Is it they have better ventilation of the precup with cross flow or just the stronger vortex of mixed gasses? OR other other some nozzle effect that doesn't cool the precup gasses.
Maybe they have sized them to choked super sonic flow of expanding gasses as the piston crosses over TDC so its not all pop at TDC or other neat effect of a nozzle. I am thinking its something with burn rate or timing effect????
Yeah, wondered about variable nozzle before could have a pintle type device maybe but not sure how to seal an adjustment to outside mechanism. A thermal movement of a pintle or other blocking device might be possible and neat. But soot would probably foul movement.
Also thought immediately of nostril like holes. Did not know about olds precups but good to know. I would think sum of opening should start about the size of smallest turbo precup opening.
I have always wondered it some type of 3rd small valve behind the precup that could flush out any CO2 or other gasses and help cool precup would be something in a new design that would be beneficial.
I am still wondering about just how they get that much more power out of the precup and piston shape. Is it they have better ventilation of the precup with cross flow or just the stronger vortex of mixed gasses? OR other other some nozzle effect that doesn't cool the precup gasses.
Maybe they have sized them to choked super sonic flow of expanding gasses as the piston crosses over TDC so its not all pop at TDC or other neat effect of a nozzle. I am thinking its something with burn rate or timing effect????
The people who came before us in the precup design have retired. We are having to re-invent the wheel just to understand what GM did with the many precup designs out there. We do know it was "cheap" aka low pressure injection etc. for the low bidder government contracts and civilian stuff had to meet some emissions specifically NOx as listed on the emission label.
It is a interesting science to get the precup in a sweet spot. It is like playing a flute with too much air speed or too low air speed not making the proper or any sound. Tuning the precup requiring the high swirl for the most complete combustion for emissions, have it all burned by specific number of degrees ATDC for peak torque/economy, RPM, load, and the variable to different amounts of air via turbo boost. IMO some (myself included at the bottom of the scale) have used brute force via lots of boost PSI to burn the fuel on smaller precups. Don't forget the piston is a balanced part of the precup system. If you install the pistons upside down in a 6.x engine the precup hole will burn away the aluminum under the precup. So drilling holes without the proper matching reliefs in the piston would be turning a blowtorch loose on those areas of the piston.
Great White posted up a lot of info on IDI engines awhile ago. The most interesting of his posts was a small precup with a high power (fuel) applied, although known for high MPG, would accelerate the burning air fuel charge coming out of the precup so fast that it would separate the fuel and not mix or burn well. So the small precups were limited to low fuel rates otherwise the engine simply quit burning all the fuel when it is useful to do so. IMO the fuel can continue to burn when the exhaust valve is open, but, it isn't doing any work at that point.
At low fuel rates the small precups burns everything it can due to a lot of mixing of the burning fuel and air.
Unless you are putting on a lot of miles and fuel cost comes out of your paycheck the MPG Gap between old IDI and DI isn't that big: about 20% for Modern DI with a bigger gap for pre emissions DI. An 2008 emissions strangled 2WD crew cab long bed Duramax pickup SRW gets 18 MPG. My hopped up 1995 3/4 ton, 4x4, 1986 6.2 smaller military 6.2 precup equipped repower, Suburban with a large turbo and spool valve gets 16 MPG driven the same on the freeways. For the frugal 6.5 owner this may not pay for the mods.
I am curious as to the TQ the Mercedes IDI's are getting. 400HP sells cars... No question there is a big gap there.
The OP can comment on other things needed to handle high power in our body styles. Since some have already gone down that mod rabbit hole... :agreed:
It is a interesting science to get the precup in a sweet spot. It is like playing a flute with too much air speed or too low air speed not making the proper or any sound. Tuning the precup requiring the high swirl for the most complete combustion for emissions, have it all burned by specific number of degrees ATDC for peak torque/economy, RPM, load, and the variable to different amounts of air via turbo boost. IMO some (myself included at the bottom of the scale) have used brute force via lots of boost PSI to burn the fuel on smaller precups. Don't forget the piston is a balanced part of the precup system. If you install the pistons upside down in a 6.x engine the precup hole will burn away the aluminum under the precup. So drilling holes without the proper matching reliefs in the piston would be turning a blowtorch loose on those areas of the piston.
Great White posted up a lot of info on IDI engines awhile ago. The most interesting of his posts was a small precup with a high power (fuel) applied, although known for high MPG, would accelerate the burning air fuel charge coming out of the precup so fast that it would separate the fuel and not mix or burn well. So the small precups were limited to low fuel rates otherwise the engine simply quit burning all the fuel when it is useful to do so. IMO the fuel can continue to burn when the exhaust valve is open, but, it isn't doing any work at that point.
At low fuel rates the small precups burns everything it can due to a lot of mixing of the burning fuel and air.
Unless you are putting on a lot of miles and fuel cost comes out of your paycheck the MPG Gap between old IDI and DI isn't that big: about 20% for Modern DI with a bigger gap for pre emissions DI. An 2008 emissions strangled 2WD crew cab long bed Duramax pickup SRW gets 18 MPG. My hopped up 1995 3/4 ton, 4x4, 1986 6.2 smaller military 6.2 precup equipped repower, Suburban with a large turbo and spool valve gets 16 MPG driven the same on the freeways. For the frugal 6.5 owner this may not pay for the mods.
I am curious as to the TQ the Mercedes IDI's are getting. 400HP sells cars... No question there is a big gap there.
The OP can comment on other things needed to handle high power in our body styles. Since some have already gone down that mod rabbit hole... :agreed:
schiker
Well-Known Member
The direction and swirl probably does get help from piston shape and may have been cost prohibitive with GM. And or not needed at original design for power levels intended nor emissions reasons. They were still trying to maximize profit and easy mfg. The Diesel wars had not really heated up yet.
I think everyone is just thinking of easy mods to start research at lower cost.
I think everyone is just thinking of easy mods to start research at lower cost.
I like to look at MPG vs. power because under high load you get more MPG and power with specific mods done to the 6.5's. This is an exception to the rule of more power usually decreasing MPG. Some mods pay for themselves in fuel saved.
I love to see new ideas and some are fun to try. Even if it is old ideas applied to our even older engine.
- Staff
- #34
From research I have done, there is a little ramp inside of the precup under the injector that creates a swirl effect before the flame front leaves the pre-cup. The nostril idea sounds promising as MERECEDES used a simliar design on the earlier OM617 5 cylinder with a basic ricardo bowl in the piston. The pre-cup extending just slightly down into the chamber, and had teh opening in the side of the pre-cup to direct the flame outwards instead of downwards.
The torque numbers are pretty close to the HP numbers on these engines due largely in part to there short stroke high RPM design. theres a few of the inline 6 2 valve per cylinder OM603's out there that have dyno'd just over 400HP to the wheels with torque numbers i nthe mid 500 range. Considering the cubic inch of these engines that is pretty good I think. Heres a comparison of what the MERC can do VS a 6.5. This is one of the 3.0L inline 6's running an HX40 turbo at 30 PSI of boost, made 350/350 out of it.
http://www.youtube.com/watch?v=J3Q3diU7sVU
I realize it's just pipe dreaming, but with all of the talk of people trying cutting edge design to furthur the 6.5 I would think the first place to start would be to get away from the 100 year old technology portion of the engine and step up to as modern as you could.
The torque numbers are pretty close to the HP numbers on these engines due largely in part to there short stroke high RPM design. theres a few of the inline 6 2 valve per cylinder OM603's out there that have dyno'd just over 400HP to the wheels with torque numbers i nthe mid 500 range. Considering the cubic inch of these engines that is pretty good I think. Heres a comparison of what the MERC can do VS a 6.5. This is one of the 3.0L inline 6's running an HX40 turbo at 30 PSI of boost, made 350/350 out of it.
http://www.youtube.com/watch?v=J3Q3diU7sVU
I realize it's just pipe dreaming, but with all of the talk of people trying cutting edge design to furthur the 6.5 I would think the first place to start would be to get away from the 100 year old technology portion of the engine and step up to as modern as you could.
ak diesel driver
6.5 driver
all that precup modifiying is worthless without more fuel. The merc pumps obviously pump more fuel per cylinder.
NVW
Well-Known Member
Unless work is done to the bottom end, more hp is out for me.
- Staff
- #37
The pumps can be modified for more fuel on the MERCS, but the 6.5 can get a good sized DB2. The reasoning for me bringing this up is seeing how much more power potential they are getting with this design. They seem to be getting much closer to direct inejcted efficiency while still being IDI.
Like the above example, any way you slice it a DI is going to be roughly 15-20% more efficient. If a different pre-cup could bridge that gap then it would be worth it from an efficiency stand point alone. Also if in the process you can get a cleaner more controlled burn, you could probably push teh HP higher without damaging the bottem end. Tuning and making everything work together is the key to making an engine live. 8 years ago a 500HP stock bottme end DURAMAX was over the edge, now with current technology and tuning more than a few are going 650-700 on stock bottem ends. If a different precup could increase the efficiency of the engine, it could help people on frugal budgets with making power and mileage.
Like I said though, it's just an idea I've been kicking around while being laid up.
Project57idi
New Member
The other thing not mentioned is that, sure the db/ds pumps may not put out a ton of fuel in stock form, if you increase the efficiency of the combustion, you require LESS fuel to hit your target/goal so a wussy pump is less of an issue.
Ferm and others keep the ideas rolling. Thanks.
Will L.
Well-Known Member
The pre cup was a known soft spot in the design, why do you think there are so many styles of it out there. Various emission / power / efficiency changes could be made without major retooling. Low cost in manufacturing and ease (speed) of assembly had a bit to do with it also. Look back at the pre cups Mercedes used in their truck engines if you want to see the same basic design as our pre cups. when MB had to step up their game in the truck engines, they dropped compression, upped the turbo and went to the domed pre cup. Viola they dominated their market, just like they did with this design in their diesel passenger cars.
The MB's that are hopped up to 600 ponies with 3.0 liter. That would be 1300 hp from a 6.5- not gonna happen, but I dont think that's what Ferm is saying. We are leaving $ on the table by not correcting this known weak link. how much smoother and less abuse does the lower end go through with a better balanced and flowing upper end? Having spent more time in big diesels than small ones I kinda feel ashamed I never thought of trying to fix this a long time ago. I learned all this years ago, I just never put the puzzle pieces together. Got me to thinking about a refractory injection nozzle used in some underground equipment before they got the exhaust scrubbers worked out. I have a call in to an old friend that might have one laying around he could send to me for dissecting.
More fuel? Yeah, dual pumps can make it happen, and a stronger lower end is the p400. All the same torque an hp numbers are probably possible with less fuel with proper atomization and burn flow rates. For the 10 people out there who are determined to get monster numbers from the 6.5, a p400 and twin db's probably isn't scary. But for the rest of us, the moderate power gains and fuel savings have real potential. What was the difference of better cups with the ATT vs the wrong ones WarWagon mentioned a few times? Way bigger potential gains here than I think most realize.
The MB's that are hopped up to 600 ponies with 3.0 liter. That would be 1300 hp from a 6.5- not gonna happen, but I dont think that's what Ferm is saying. We are leaving $ on the table by not correcting this known weak link. how much smoother and less abuse does the lower end go through with a better balanced and flowing upper end? Having spent more time in big diesels than small ones I kinda feel ashamed I never thought of trying to fix this a long time ago. I learned all this years ago, I just never put the puzzle pieces together. Got me to thinking about a refractory injection nozzle used in some underground equipment before they got the exhaust scrubbers worked out. I have a call in to an old friend that might have one laying around he could send to me for dissecting.
More fuel? Yeah, dual pumps can make it happen, and a stronger lower end is the p400. All the same torque an hp numbers are probably possible with less fuel with proper atomization and burn flow rates. For the 10 people out there who are determined to get monster numbers from the 6.5, a p400 and twin db's probably isn't scary. But for the rest of us, the moderate power gains and fuel savings have real potential. What was the difference of better cups with the ATT vs the wrong ones WarWagon mentioned a few times? Way bigger potential gains here than I think most realize.