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porting precups

I think that we are just beginning to explore some new possibilities with pre cup modification. Hopefully exciting new things on the horizon
 
Then i would be happy to share information on what I have done and see what you have done. Have you done larger than the ones I posted a pic of. did you change the floor or just the exit volute exit angle, width, diameter? I am interested. I am not sure how big the cups can be before they are past the point of diminishing performance.
 
Thanks to another thread here I am wanting to twin turbo my 6.2 in the 69. So motor will come out after header mock up. studs, crank,Kings bearings. I have many sets of precups. Gonna leave one set of diamonds alone. and cut 2 more sets. after fine tuning and all the bugs worked out it would be a good time to play and test!
 
Well Woody my but dyno says I like them, but that being said there are other people that seem to have all the answers at another place. So I will give you a little of what i know to be true from my observations only.

HAND ported pre cups will have issues, NO QUESTIONS ABOUT IT.

I like my pre cups and live with the fact in some rpm ranges I have higher EGTS, I don;t think the under load pulling power is there like the diamond or slightly larger diamond cups that are being used by some, but mine are as large as we physically could would go.

Their is a limit to porting based on a number of events, In the normal pre cup all or the vast majority of the fuel is burned in the pre cup and this spills out into the cylinder through the opening or exit: as the fuel burns any unburned fuel / fuel droplets are then supposed to be atomized or vaporized into a gas where it mixes with the cylinder air and the fuel is burned completely by the already ensuing flame front.

The short story is you can only get so much air through a fixed orifice in a specific amount of time. So if the fuel can not get out quickly enough you lose power and get a lot of latent heat in the head. Large openings let the gases expand at a greater rate unimpeded by the pre cup exit. NOW here is where it gets funny, (these are my observations) larger is better at lower rpm and better at higer rpm. GETTING the fuel to burn completely in the other rpm range is the trick, and that is where the experimenting comes in. I am sure that there are better experts out there that have all the answers, but these are my observations.

I think that the larger than diamond pre cups will be a good thing for those that are looking for power. The slight trade off is slightly higher (very small amount) egt at some driving conditions, low rpm towing. The slight mileage gains at highway speed (I experienced with my particular setup) are another trade off. I am still learning, but since my funds have run out for RD I am done for awhile. I am lucky enough to have access to two of the best machinists, that a person could have. these guys do top notch work and are involved in racing for large commercial ventures, and proto type work. They have a wealth of knowledge that still humbles me, without their knowledge it would be a futile effort at best.

HAND PORTING your pre cup WILL give you poor performance and a multitude of other problems that may or may not be evident. The pre cups MUST be UNIFORM or they WILL NOT work properly and will not be consistent from cylinder to cylinder. ANYONE that has ported their pre cups by hand in my humble opinion can not get consistent repeatability from their modification to be useful for data collection.
 
What are the effects of ceramic coating on pre-cup funtion? I had thought Heaths LST used ceramic on his as well as exhuast ports.
 
skypilotj said:
What are the effects of ceramic coating on pre-cup funtion? I had thought Heaths LST used ceramic on his as well as exhuast ports.
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Ceramic coating in general resists/reflects heat away from the surface, so your heads would absorb less and more go to expansion pressure into the cylinder.
 
buddy said:
Ceramic coating in general resists/reflects heat away from the surface, so your heads would absorb less and more go to expansion pressure into the cylinder.
Click to expand...


So that would be a good thing? Would the results be quantifiable?
 
Well narrow & wider over short & fat in my mind would be better at moving the flame path into the cly but I don't know...... We will see how they work later this year when I finish the motor..
 
Actually the angle of the flame front is probably most critical.
 
ak diesel driver said:
so how does one shape the mouth to achieve that?
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The wider picture of sctrailrider, didn't change the angle of the pre cup exit, as it is in relation to the piston. As you go wider you actually should probably angle it more towards the piston rather than towards the opposing cylinder wall. The idea is to get the flame front to roll across the piston and out at the same time. I am sure that recardo did a boat load of studies on the pre chamber before deciding on the design. We might get lucky, and hit on something, a little better, but that is yet to be seen. Any small change like .850 will not make a noticeable change, at least that is my opinion for what it is worth. Also I would not be messing with the floor of the pre chamber not sure how that is going to affect it. Will be interesting, the little dent left in the center where the old pre cup exit was, might be something that will affect the exit shape of the flame front, not sure, more for the fluid dynamics guy. Just my humble opinion.
 
Slim Shady said:
The wider picture of sctrailrider, didn't change the angle of the pre cup exit, as it is in relation to the piston. As you go wider you actually should probably angle it more towards the piston rather than towards the opposing cylinder wall. The idea is to get the flame front to roll across the piston and out at the same time. I am sure that recardo did a boat load of studies on the pre chamber before deciding on the design. We might get lucky, and hit on something, a little better, but that is yet to be seen. Any small change like .850 will not make a noticeable change, at least that is my opinion for what it is worth. Also I would not be messing with the floor of the pre chamber not sure how that is going to affect it. Will be interesting, the little dent left in the center where the old pre cup exit was, might be something that will affect the exit shape of the flame front, not sure, more for the fluid dynamics guy. Just my humble opinion.
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Dennis... I know we have chatted a few times before on the phone, BUT that IS hanks work..;) SCtrailrider didn't machine those "himself"...
100_5123.jpg
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Mike K3500 said:
Dennis... I know we have chatted a few times before on the phone, BUT that IS hanks work..;) SCtrailrider didn't machine those "himself"...
100_5123.jpg
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Actually I knew that going into what I said in my post. I have been working on these with Hank for sometime. I have found that if I say that I had a hand in the development of something it becomes controversial. Hank and I did a lot of practice and what most don't know is Hank is one of the best machinists and prototype guys I have ever met, He is no slouch when it comes to what he does. We have used these long before anyone was ever given the chance to get a set. THEY WORK and WORK WELL, ok now people can flame me, on how we know, data dyno and the rest now you see why I didn't say more than that.

The little indentation ("we think") actually helps the flame front get some turbulence and we "think" may help the flame front swirl and mix with the remaining air.

My precups were an experiment between (Hank and I) in how large could we go and what would the effects be, so we know what the possible limits of the modification are and how it affects the base line.

IF ANYONE HAS A SET OF PRE CUPS THEY WOULD LIKE TO DONATE I NEED MORE SETS so that I can get more versions in,swapping heads in the truck is not for the faint of heart.

HANK was the person that came up with how to mount the A_TEAM TURBO to our trucks. He designed the down pipe and I put the rest of it together, it was a collaboration. SO you are in good hands. We never sell anything that we have not driven or tested on our own trucks first. REST EASY those pre cups will work just fine.

:)
 
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