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Pre combustion chamber design research

Twisted Steel Performance

Anything worth doing is worth overdoing.
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I have run low compression in several motors, all have used the piston top design I offer, granted all these used DB2's that were putting out more fuel than a DS4 can, and all were using HX35/40 hybrid's with different than stock Holset blades. I found in all instances the motors were quieter and had more power than needed towing @20K plus..

All the motors are still in use and performing like new.

I think when looking at the stock precup & piston design everything else also needs to be considered, small turbo that was used, built to conserve fuel not make loads of power, pass smog tests, etc. For what the motor was designed to do the high compression, cups, piston design worked well, but...

Now more than double or triple the amount of air & fuel along with boost pressures that same design might not be optimum.

It's a fact that a larger container will hold more product, air & fuel in this case, what makes the power we all look for??? more air & fuel...

The cylinder pressure calculator in the download page on my site will spit out pressure numbers for an array of different setups, cylinder pressure, or toooo high of pressure will effect everything, and end up with a motor replacement sooner or later...

I too have read most everything on the interweb about IDI motors, I consider it somewhat out dated and not really apples to apples for most builds where more fuel & boost are being added, more power requires a motor that breathes well... but it's just my opinion based on my builds and R&D... I say build what you believe in...
 

Twisted Steel Performance

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Also, I have posted pics of a piston with the designed top I offer, it's here somewhere, in every instance the burn pattern travled across the top and into the other side of the piston, both sides were even. I know the piston rock @TDC was less their by decreasing the rattle and giving a more even load on the piston..

This piston was cleaned a bit but the burn can still be seen to a extent...

56423
 

n8in8or

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I think when looking at the stock precup & piston design everything else also needs to be considered, small turbo that was used, built to conserve fuel not make loads of power, pass smog tests, etc. For what the motor was designed to do the high compression, cups, piston design worked well, but...

Now more than double or triple the amount of air & fuel along with boost pressures that same design might not be optimum.

It's a fact that a larger container will hold more product, air & fuel in this case, what makes the power we all look for??? more air & fuel...
This is very true and important what you have stated. There are many variables when designing an IDI diesel engine: compression ratio, injection pressure, precup passage size and shape, pre-combustion chamber shape, combustion chamber shape, fuel injector angle.....many options. The OEMs make choices for specific reasons and I would guess that their main concerns when choosing options for the 6.X engine were easy starting, low emissions and fuel economy. A lot of us here like those things, but would trade some of those factors for performance. Dropping compression ratio is pretty much a no brainer here - reasonable cold starting capability can be retained while dropping compression. This will allow more fuel and air for more power and take some stress off of the engine mechanically. The 18:1 piston top design is interesting. I appreciate the theory of it distributing the burn across the piston more - I could see that, but does it sacrifice the turbulence the Ricardo cup provides that helps mix the fuel and air for a more complete burn of the fuel? I don’t know. I have no doubt the design works and I would not tell anyone to not buy the pistons, they’re for sure a quality item, it’s just interesting. There’s more than one way to skin a cat.

At this power level there are a lot of things that can be changed and have negligible effect - for instance, changing my injector pop pressure from 2500 to 1700 and seeing basically no power change on the dyno. What I did see though was a negative change to cold start characteristics, certainly from the courser spray not lighting off as well when it’s cold. However after doing more reading a courser spray is preferable for power because it leaves more fuel available for consumption in the main combustion event in the combustion chamber rather than in the pre-combustion chamber. So what if at this power level the coarse spray has no apparent effect on power, but try putting even more fuel in the engine and maybe that’s where the coarser spray shines? Won’t know until we try it.

So I think that’s where we are....there are theories and some things tested, but not a lot on the 6.X platform, so we want to take some of this general IDI theory and apply it and see what happens. RR and I hope to get some things around and then spend a day on an engine dyno and see what they do on a 6.X. We’ll see what happens and share what we find out...hopefully we find some good stuff or maybe we won’t....at least we’ll have some definitive answers.
 

Rockabillyrat

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Couldn't have said it better myself.

Most of the information and books I find are older than the 6.2 and 6.5 platform. And any of the newer stuff applies to smaller single cylinder engines found overseas. Its impossible to find much about the 6.2/6.5 platform and why changes in the injectors, cups, and pistons were made. So learning more about how the combustion process works seems to be the only way to figure out how to set it up or modify it for more power. And even then it's all guess work. I'm just trying to put my best educational guess into my build. That's my favorite part about the 6.5. No one truly knows what's the best way to build power. It's like the old days where you build it your way and see what it does. Hot roding at it finest.
 

Will L.

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We had multiple water loaded engine dynos at the oil
Company doing the stress tests. It was more difficult to get it to load the turbo compared to them running gas engines.
No clue what brand/ type they were, sorry.

Oh yeah, there was a couple that were electric motor with mechanical braking on them. They were good for creating constant drag or work load, but not consistent for measuring power on turbo engines
 

n8in8or

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Do either of you know of a engine dyno that can and will or has run a turbo 6.x?
I’m going to ask the local one that’s doing the machine work on my LS. If they aren’t interested and we can’t find another one, then we much just make a simple chassis that can run on a chassis dyno - not ideal, but at least it will be easier to do parts swaps.
 

Will L.

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A bunch of us have various precups that are cracked, but still would work for testing. We could pool in for head gaskets too- I am sure I have a set of odd ball brand that may not be great for the long haul but certainly would work for dyno runs.
 

Jaryd

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A bunch of us have various precups that are cracked, but still would work for testing. We could pool in for head gaskets too- I am sure I have a set of odd ball brand that may not be great for the long haul but certainly would work for dyno runs.

Id be in on the donating when the time comes. Just let us know ahead of time so we have time to dig out our parts stashes or send whatever might be needed.

I think it’s pretty dang cool what y’all are trying to do for these old engines. A simple chassis with the necessary gauges would be pretty much perfect and easy to use especially for fast changes to different parts. Keep up the good work fellas
 

n8in8or

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A bunch of us have various precups that are cracked, but still would work for testing. We could pool in for head gaskets too- I am sure I have a set of odd ball brand that may not be great for the long haul but certainly would work for dyno runs.
Using cracked precups for testing is a great idea!
 

n8in8or

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Id be in on the donating when the time comes. Just let us know ahead of time so we have time to dig out our parts stashes or send whatever might be needed.

I think it’s pretty dang cool what y’all are trying to do for these old engines. A simple chassis with the necessary gauges would be pretty much perfect and easy to use especially for fast changes to different parts. Keep up the good work fellas
Thanks Jaryd. We’re still a ways off from this endeavor, but for sure, when the time comes we’ll put feelers out to see if there are any orphan parts out there that are good enough for testing.
 

Will L.

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Back on my quest, compiled these part numbers so far. Hopefully helps on this thread.
Square -10230426
Circle - 10149629
T - 10149630
Diamond - 10183926
triple square (6.2)- 10149688- not sure but believe stock not oversize
GEP Diamond Over sized - 12550985
Square .010 over is 10230425

Knowledge of “best” may turn to a moot point. Availability might be bigger factor.

We might need to figure all the dimensions of each part and record for the future. Anybody have access to one of those cool 3d scanners that downloads into the computer?
Face opening is one thing, but how it is inside and angles count for a bunch.
 

wirenut450

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Hopefully I am not going backwards, I am having a set of the military triple square ID ones opened up to match the diamond just on the opening no machine work to the internal side of the cup, Head gasket to lower compression to 18:1 or so.
 

Will L.

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That’s what I am doing now. Same Precups being machined, then will have them and other parts sent to chryo. Then a whole stack of metal stuff getting coated.

Always faster and cheaper to do it right the first time...
 
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