Pre-cup size fuel charge ratio request for review and ideas

[NMB2]

also, if your IDI was anywhere near a 24v.... either your BIL is retarded, or his truck is a pile. There is no comparison.

[82f100swb]

I think you are failing to realize how worn out 22,000 hours actually is. Figure an average speed of even 45mph that is the equivalent of 990,000 miles. My IDI would eat this thing for lunch after it warms up(hpop is worn out,) and pulled better n/a with 3.55's than this thing does with 4.10's. BUT, it was free....

I seriously think that monkeying with the precups isn't really worth doing at this point, there are still too many other things that can be changed before we add another variable to the mix.

[hairyboxnoogle]

Originally Posted by 82f100swb

I seriously think that monkeying with the precups isn't really worth doing at this point, there are still too many other things that can be changed before we add another variable to the mix.

That i can, and do agree with. At the same time i interested out of curiosity as much as i am performance. Im not looking for the "holy ####, ive done it" answer, just AN answer. Better or worse, out of curiosity really. Would be interesting to know.

As far as the guy opening the mouth and seeing better bottom end and a level top... lemme see some dyno charts before / after and that will actually help, otherwise im testing the stock cups first and maybe one altered set. The effects mentioned tell me that he is not getting enough turbulence, as in the fuel is not mixing as well and burns slower. Resulting in a torquier bottom, but draggin ass on the top because it cant burn all the fuel.

[NMB2]

Rwilles, you're wasting your time racking your brain over pre cups being the cause of my low HP/TQ per CC, when I have the real answer.

The pump turned out to not be a 150cc pump, it is 120cc max output. This changes numbers quite a bit.

[rwilles]

Originally Posted by RacinNdrummin

Man, you guys go ahead and stress this issue, the chevy guys have been doing it for even longer, and still have nothing that says the pre-cups are a restriction.

Racin, Are we talking about how you think it is or what there is evidence for? The Greek study showed that when you double the fuel and keep the same precup, they went from 40% of max (I'll call stock) to 80% of max (Justin's) the fuel did flow into the cylinder but it takes 60 deg of crank rotation to burn. Heat not power. I'd propose that the charge was thrown to the outer walls of the cylinder.


A 90cc pump, injects roughly 90mm^3 into the Pre-chamber every power stroke, at Full Bore... If a pre-cup has a volume of 21cc's, its capacity is 233 times bigger than the volume of fuel being injected into the pre-cup in one injection stroke, and that doesnt even take into account the 40% that is burned to push the rest of the charge out of the channel. This idea that the pre-cup is a restriction, is something that seems like it would be obvious, but when it comes to practical application, works, and I think you guys dwell on the pre-cup premise too much. Id make the arguement that the shape of the outlet of the channel has more to do with the post pre-cup burn than does the channel itself.

My understanding is that the volume cc's are per every 1000 pumps. The DB2 maxes out at 90cc's, a turbo pump ~95. The liquid is transfered to a gas like state in the precup and then swirled into the cylinder. Our precups are not considered restriction type as we are at 1.5% of the piston area, max is/was 4%. It's getting the fuel into the engine in time to make power that is the issue. Detroit Diesel changed the precups from the factory with 5 or 6 (not sure if there is one or two military) revisions. Just trying to adapt their engineering.

If Anything, I would agree that a smaller pre-cup would be better in principle, as it means more fuel where it matters, however, it also means less volume to get an ideal spray pattern out of the injectors, so it very well could make things moot. I still stand by my comment that the spray pattern out of the injectors would serve the biggest gains over anything pre-cup related... You want to suspend bigger droplets in the air in the pre-cup, to be broken by turbulance post pre-cup and every bit of surface area exposed, ignited, and burned as fast as possible in the cylinder...

I agree, the smallest pre-cup, matched with a big port opening, offset with a bigger power divot on the piston will produce the best power. The '84 changes did this but also necked down the throat of the port. Ricardo, tested extensively and wrote 2 books about the 'comet' pre cup injection system. He tested all the spray patterns and a fine pattern was the worst for developing power. Just made things hotter as the charge from the pre cup couldn't mix in the cylinder. The liquid fuel hitting the red hot (comet) precup is what does that atomization.

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[NMB2]

Rwilles, he is talking about what there is evidence for. I don't care what your book says, we have real world experience.

There has been A LOT of IDI's dynoed.... they are always between 2.3-2.6rwhp/cc and 5-5.3rwtq/cc. Depending on charger, pump, injectors, displacement, d-train.... but that is a pretty consistent number.

You seemed convinced my pre-cups are a bottleneck in my system.... yet, my engine still made 2.4rwhp/cc and 5.1rwtq/cc. 292rwhp/614rwtq @ 120cc's With a charger that we know is too small, and a pump that defuels early-ish, and the highest parasitic drive train loss configuration......on top of that you talk about power being lost and transferred to heat.... my engine has zero EGT 'issues'....empty or towing.

I fail to see your logic.

[rwilles]

I think there is a point to this examination as Detroit Diesel manufactured either 5 or 6 (not sure if there is 1 or 2 military ports) different sizes of opening to get better power out of essentially the same motor. The hardest part will be matching real pumping capacity with the ports. A reduction from 150 cc's to 120 cc's (as Justin is dealing with now) would make the port under mix with the turbocharged air and that's worse (lean) than to much.

Justin, aren't the 6.5 military Tidi's in super heavy vehicles? I had read that an armored Hummer is over 6 tons and the big trucks are heaver. Lousy power to weight ratio, right?

So just have enough data for the NA 6.2 and International motors at this point. The more data we get the more accurate the ratios will be. Suspect the ratio will be dramatically different for turbo-NA motors.

*6.2 Square port .57x.2=.114 channel area. Divide area by torque to get ratio,
.114/240 ft/lbs=2105

*6.2 Circle port .625x.2=.125 channel area.
.125/257 ft/lbs=2056

Average for two different motors=2080/volume of 6.2=335.5 (it's just a ratio per liter)

If the ratio holds we can deduce the width of the ports in the 6.9 motors
NA 6.9 up to '83 'Big'. port depth-.270x port width-??= area/310 ft/lbs=(335.5x6.9=2315)
so we invert and divide, 310/2315= .134 port area. .134/.27=.496 (half an inch).
The math worked!

*NA 6.9 '83-87 'Small' port (not exact comparison as there were 4 changes-piston cup increased 25%- channel reduced 20%- compression increased 5%- swirl volume reduced by 20%)
Port depth-.245 x port width-??= port area/315 ft/lbs=2315 (estimate from above) ratio
Port area of .136/.245=.555" is what the math would suggest, but I suspect the other changes allowed them to keep the same width of .5". So width of .5 x.245 depth=.1225 area/315=2571/6.9=372.6 ratio (big difference, higher uncertainty of accuracy!)

Come on Justin, throw a mic on those ports you posted pics of over at TheTruckStop!

NA 7.3 Marked '88' on the face .245 depth x ??=port area/360=372.6x7.3=2720
so invert and divide 360/2720=.132 port area. .132/.245=.54

Sorry for all the math, it's super hard to do it justice in the format allowed on the site, it needs to be on a spread sheet.

But a couple of observations,
-The Detroit Diesel ports are more opened up in the worst configurations of 'circle' and 'square' than the International ports. The area per liter ratio on the Detroit's (power numbers from a NA 6.5 would make this more accurate) is 335 per liter, the International is 372. However you want to look at it the Detroit design is spinning the fuel charge 10% slower or the International is spinning 11% faster. Would agree with governor speed on each engine. Also explains how 500HP Salt Flats motor runs at 5000 rpm with 6.5 turbo head/port.
-If the head gaskets will hold (1/2 inch vs 7/16 might be the best reason for a 7.3 block with 6.9 sleeves), I'm not sure what is gained in decompressing these IDI motors.
-Flat-topping the pistons removes the power concentration area. The burn time is a function of the distance the flame front has to move through the fuel charge. Stacked up, or deeper on the piston, is shorter therefore you get bigger bang not a longer burning bang. Heat not power with a flat top. The '84 engine increased the area of the divot from 4 cc to over 6. Flat is the wrong direction. A

My ideal setup with the info we have now is a 50% smaller swirl port with a 300% increase in the channel would allow us to use a Cummins type piston with the power divot offset.

Justin, it's kind of funny to have you say stop trying when you wouldn't have the engine you have now if you had listened to others saying the same thing a year ago. Ahhh, irony.

[RacinNdrummin]

Originally Posted by rwilles

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90mm^3/stroke is the same as 90cc over 1000 strokes...

The idea that the fuel is thrown to the outer portions of the cylinder is flawed, and I can give you one big example of why...

If you look at the pics of when NMB2's piston was backwards (Not to bring this up again, but its a glaring example), you can see that on all the other pistons, the layer is even across the whole top, while on the backwards one, the carbon was a straight line all the way to the other side of the cylinder. The fuel was obviously not distributed by piston shape on that cylinder, but was completely even on the remaining 7. The burn coming out of his pre-cups was even, and that even more impressive being that his piston tops are .080" shallower than stock IDI pistons.

The reason you want lots of velocity coming out of the channel, because the more velocity, the more it busts the fuel droplets, and the more those droplets are exposed to the hot air in the cylinder, equating to a faster burn, than a comparatively larger channel that results in less velocity. The fuel droplets are blasted apart at the mouth of the channel, not further down stream.

As far as DD engineers and their experiments with PC's... There is a lot they experimented with... But getting the most power from the engine was probably the least considered factor in all of it... If that was the case, they would have ditched the IDI design all together...

Like I said, when the PC cant deal with the amount fo fuel that we are putting into the engine, that is when enlarging any part of them will be beneficial...We are not even close yet...

[NMB2]

Originally Posted by rwilles

Also explains how 500HP Salt Flats motor runs at 5000 rpm with 6.5 turbo head/port.

My engine would be 500hp too if I lived in ellensburg and refused to dyno it... give me a break. You cannot use Bill Heaths engine as proof of anything.


Justin, it's kind of funny to have you say stop trying when you wouldn't have the engine you have now if you had listened to others saying the same thing a year ago. Ahhh, irony.

Irony?..... I didn't tell you to stop trying, I told you that you were wasting your time. I want you to stop flapping your gums and build something. This conversation has crossed the line into annoying because your posts are loaded with logical fallacies and speculation.... it has no bottom to support it....

Its exactly like Bill Heath and his magical 6.5. On a piece of paper he can apparently manipulate the broken math to somehow get 500hp and 800tq out of 100cc's of fuel.... but he refuses to dyno it.

You seem to put a lot of faith in the research DD put into their pre cups. Maybe they should of put that research into the exploding crankshafts, splitting blocks, cooling systems.... need I go on? Those engines were a flop..... and until I start dumping so much fuel in that it is transferred into heat via extreme cyl head temps or EGT's, and low HP/cc numbers..... the pre-cups work just fine.

So here is what you're going to have to do.... you're going to have to fully commit to a build, and try your ideas.. and prove us wrong. Don't be scared.

EDIT:

here is the pic Justin was referring to:

[hairyboxnoogle]

One possibility that comes to mind no the detroit engines... is perhaps they werent exactly sure on how to build a pre-cup so they decided to build a bunch of different ones.

I will dyno mine with different pre-cups, that much i WILL do, to sate my own curiosity if nothing else comes from it.

As far as guys grinding ports and saying "it feels better down low" well... butt dynos are famously innacurate. Until i see "dyno'd XXXhp with precup 'A' and XXXhp with pre-cup 'B'" im riding the fence until i find out whatever there is for me to find out.

The way i look at it, there is NO proof that the pre-cups NEED changed.. however there is NO proof that we cannot gain from changing them. That is all ive been trying to say i guess, im open to trying it, and would love to see some proof either way.