Pop pressures and precups

[3500_6.5]

I've been thinking lately about ways to make more power efficiently. I saw some talks about raising pop pressures to upwards of 3500 psi (I guess this is the pop pressure John Deere uses with their db2s?) and increasing power and efficiency this way. And it seems everyone pretty much agrees that higher pop pressures make better power. I've also seen people work with precups where they open them up bigger to gain more power. It sounds like this can cause some excessive black smoke and high egts at lower rpms though, but still sounds like it has had some success. What I haven't seen is anyone doing both.



When GM went to a turbo, they increased the size of the precup openings and also increased pop pressure. So what I'm thinking is that if you can increase pop pressures to increase the ability to atomize the fuel better, couldn't you then be able to increase the precup opening to reduce heat loss into the heads and increase power? If you have a higher pop pressure, you wouldn't need as much of the swirling and pressures associated with the idi combustion process. If it's safe to run 3500 psi pop pressures, couldn't you open the precup up quite a bit and even drop compression some while still maintaining good cold start characteristics while reducing internal stress on the engine, lowering the heat loss and overheating issues with the 6.5, all while increasing power output? Now, I don't know what kind of stress 3500psi would put on the pump or how it affects the longevity of the pump, but is this a realistic theoretical scenario?


Sent from my iPhone using Tapatalk

 

[Will L.]

Flashback! I tried it a few times convinced from the same theory. My error was in trying to hand cut the precups. I know I did not get them (all 8) the same, and 1 that I did the worse on my closest set was obvious. I even pulled the head just to swap 2 precups and verified my error.

Problems with theory:
Higher pop pressure is more atomization, but less volume and theres a point when it gets harder to start.
Larger precup port also does better bigger, but gets harder to start.
When the 2 combine together, it got harder yet to start.

I did everything db2 a ds4 timing control might help that.

Yes higher pop pressures wear it out a little quicker, but not enough it should detour you. Power almost always comes at the expense of long life.

 

[JayTheCPA]

Have a reputable source where opening the pre-cups wider than the 'diamond' opening gets good power, no smoke (with the correct tune and an ATT), good economy, and sounds very close to a DI (much less clatter). Oh, and this is in one of the states that borders our neighbors to the North. I would have tried it had I known about it when I had to have the heads removed.

About the upper end of the pop pressure, from memory I have 2,500 on the mind where higher than that it messes with the IP's ability to refill the plungers fast enough. Naturally I am not the best expert, but that is what I recall. In terms of a better expert, am highly confident that Ferm can recite the exact number and issues with going past that.

 

[3500_6.5]

Have a reputable source where opening the pre-cups wider than the 'diamond' opening gets good power, no smoke (with the correct tune and an ATT), good economy, and sounds very close to a DI (much less clatter). Oh, and this is in one of the states that borders our neighbors to the North. I would have tried it had I known about it when I had to have the heads removed.

About the upper end of the pop pressure, from memory I have 2,500 on the mind where higher than that it messes with the IP's ability to refill the plungers fast enough. Naturally I am not the best expert, but that is what I recall. In terms of a better expert, am highly confident that Ferm can recite the exact number and issues with going past that.

That is the person I was referring to who had success with the precup machining. He told me he had some issues with smoke and high egts at a specific lower rpm but was able to fine tune his tune to fix the problem. As for the refill issue, I wonder if increasing fuel pressure to the ip (like Nate's Moose pump) could help with that issue. I am by no means an expert on either subject either, was just a thought I figured I could throw out and start a discussion on.


Sent from my iPhone using Tapatalk

 

[3500_6.5]

Flashback! I tried it a few times convinced from the same theory. My error was in trying to hand cut the precups. I know I did not get them (all 8) the same, and 1 that I did the worse on my closest set was obvious. I even pulled the head just to swap 2 precups and verified my error.

Problems with theory:
Higher pop pressure is more atomization, but less volume and theres a point when it gets harder to start.
Larger precup port also does better bigger, but gets harder to start.
When the 2 combine together, it got harder yet to start.

I did everything db2 a ds4 timing control might help that.

Yes higher pop pressures wear it out a little quicker, but not enough it should detour you. Power almost always comes at the expense of long life.

I wonder at what point does the pop pressure become too high and you lose more volume of fuel and power than what you gain from the better atomization.



Sent from my iPhone using Tapatalk

 

[WarWagon]

Smaller precups limit you on power for sure. Turns more fuel into smoke and higher EGT's. The fuel and air goes so fast with small precups high power reaches a point it will centrifugally separate the fuel and air. Yet lower power levels the swirl burns everything giving you high MPG low power engines. The Civilian NA precups I had in the 1995 with the ATT just smoked bad until we cut the fuel down. Timing made no difference.

Dennis did some work and noted a 'flat spot' in the power band with huge precups. If you haven't already check out the Mercedes fourms as they do some crazy stuff with the lost art of precups.

Just remind yourself the entire point of the precup design is swirl for fuel air mixing to burn everything on the primitave and cheap low pressure injection systems. Let alone get the low pressure huge droplet fuel to evaporate and burn - part of that is the extremely high 21:1 compression.

Higher pop pressure appears to somewhat affect timing on DB2 pumps. Yes it affects starting as I have higher pop pressure 2800 if I recall correctly and starting isn't pleasant even in our hot weather. How much is the pump I am not sure. The last pump with some head/rotor wear just wouldn't start anymore on the higher pop pressure.

 

[JayTheCPA]

Perhaps a modified IP can handle higher fuel line pressure and injector pop, but this out of my knowledge. In terms of trying to increase the fuel line pressure for a DS4, Stanadyne wants 5psi from idle to WOT, so am not sold that higher pressure is a benefit for a stock pump. Also had read that the DS4 does not like more than 10 psi.

And I can attest that with diamond precups and 2,300 pop (with marine injectors) his tune for the ATT produces nearly indistinguishable smoke. Although, sometimes if I stomp it while already moving it will briefly bellow until the RPM's come up a bit. Am about to get a revision to the tune, so will see if it still does that.

 

[Will L.]

There is a chart that Stanandyne made showing it. Bosch as well. Many, many moons ago when I used to rebuild injectors I had them and all my notes when I was playing hot rod. No clue where it all went.

If you look online I'm sure the chart are there somewhere. They show the relation between:
Pintle orifice size, pressure, volume, and timing event.

 

[3500_6.5]

You mean I have to search for it!? Geez....


Sent from my iPhone using Tapatalk

 

[Will L.]

Senior moment cleared up... Delphi injector info, not stanadyne. Before you search for wrong item.

BELIEVE ME I wish I knew where it was. That is the only reason I haven't put together my newest pop tester and rebuilt my spare set already. SO AGGRAVATING.

 

[JayTheCPA]

There is a chart that Stanandyne made showing it.

Senior moment cleared up... Delphi injector info, not stanadyne. Before you search for wrong item.

Good clarification as I was about to ask for the same reference to get a hold of it Finding Stanadyne docs on the web is a challenge as I would love to get my hands on a spec sheet and troubleshooting guide.

 

[WarWagon]

Good clarification as I was about to ask for the same reference to get a hold of it Finding Stanadyne docs on the web is a challenge as I would love to get my hands on a spec sheet and troubleshooting guide.

Try the methods outlined here to stumble across the dealerportal like I did.
http://www.thetruckstop.us/forum/th...-5-db2-5-7l-info-online-from-stanadyne.26581/

 

[JayTheCPA]

Good information, thank you!

Interesting how the site has password protection, but the underlying files are open to anybody with the URL . . .

 

[6.5L]

The increased pressure into the pump may or may not help. It all comes down to each individual pump. Depending on how many times the pump has been rebuilt, the pump overflow orifice may not be able to handle the extra pressure, in which case it won't do much. If the orifice is big enough in the pump, it can handle the extra pressure and help fill pumping chamber faster. If I recall, there are like 5 different orifice sizes that are used during pump calibrations. The more worn out the pump is, the larger the orifice if I recall. So on a old pump, you can only go so big. I turned my transfer pump pressure up and entire turn and it seemed to help a bit at the higher rpms, along with cranking my governor up to get my fuel curve higher at the top rpms so it didn't create a blind spot. The higher pop pressures are also created in the turbo motors to help overcome cylinder pressure during boost to create a better burn. Although creating higher pops also means the cam rollers have to spend a longer time on the cam ring raising pressure instead of injecting fuel. So at a point, it will be diminishing gains because of the lack of fuel delivered in the end. The turbo precups work fine it seems, even at higher fuel levels. Got to remember, the size of the orifice also determines the rate and speed at which the combustion can exit to the piston. Too slow, and still not good transfer to the piston. It's a balancing act between big and small.

 

[ak diesel driver]

so ideal on the nozzles would be to have a large orifice popping at a higher pressure. I would imagine a larger orifice would be harder to get good atomization too though

 

[6.5L]

Atomization isn't the biggest problem. Fuel delivery through the injector is the problem. You can't simply open up the orifice size. Doing so affects so many other things in the injector and can cause issues. Really the stock nozzles are fairly efficient at stock-fairly high modded fuel levels. The easiest way for more fuel/power is through the injection pump. The nozzles can handle it. Filling the plungers and increasing plunger travel would be the easiest way. Plunger travel is when things get interesting. Removing the leaf spring isn't the best idea since plunger travel is so great that it creates a fuel level that puts a lot of pressure on the cam pin, which controls the timing indirectly. At low rpm's the cam ring remains fairly stable. As fuel demand increases, the light load advance moves the internal pistons which moves the cam pin which rotates the cam ring so the shoes contact it later, thus retarding timing so you can spool and the IP and motor can "catch up". As rpm's increase, the transfer pump is spinning faster and faster, creating more internal pressure, which moves the pistons back away from the retard position, which retracts the cam pin, thus rotating the cam ring back to a more advance position so the shoes contact the cam ring sooner, which is what allows for the advance needed at higher rpm's to maintain steady good power with proper timing and fuel delivery. Pretty neat system. But as you can see, the more fuel you put into the chambers, the more pressure they put on the cam ring. As the cam ring is trying to push the plungers back together to create delivery pressure for the fuel, the cam ring is also being influenced by the cam pin. So the harder the plungers are to push in (from more fuel), the more pressure you put on the cam pin. After a while, things go pop. I have thought about drilling all components associated out for a larger cam pin, however the cam ring would crack if being drilled out. They are very hard materials and the larger hole wouldn't leave a lot of wiggle room to not crack. It's a interesting game of cat and mouse.

 

[ak diesel driver]

too bad stanadyne won't make a bigger pump

 

[6.5L]

Yeah. Kind of sucks. But necessity is the father of invention. Us 6.5L guys always seem to find a way lol

 

[Will L.]

Idk if any of the helps hut I'll throw it out just in case. I'll never get back into go fast 6.5 myself, maybe it'll help you all.

I've never been good inside the pump, I stumble through it, but I always had Scott (the S) from J&S Diesel in Vegas, and he was magic. He built 3pumps for my little fg 1/2 ton that was so fast. I remember shelling out $2500 for the parts he had custom made and that was 1993-1994. I know some was Teflon coated titanium, not all. And some AR plate he had pins machined out of. I would break the spring about every 125-150 miles. Also would Crack the ting in half, but never the pin. I know he made it bigger, but idk how big. So I definately agree with your line of thinking on those items, and your "break things" instinct is firing on all 8!

I was pretty good at swapping a pump on the side of the road. I always had a spare, and he always had 1 in his shop to fix.

He also ported the output to individual lines, and had a special fitting made the the lines attached to. The cups were made from a brass alloy, but I never got why on either of those. He explained a little, but it didn't make sense to me, I'd say I don't buy the theory, but he'd laugh and say "ya you paid for it, so you buy it!"

He had longer blades made and a new lining ring. The interior was more oblong. Only a tiny bit on the narrow side but a lot on the keyway side, and had a smaller keyway cut into it to accommodate. He removed the interior pressure spring and we used an exterior one in steel line set up- I never understood the pressure spring change either.

I know he did a lot of work to the housing, but it was beyond me. He was always worried the case would crack where he cut into them, but they never did on the ones that he completed.
He swore no one ever got as much fuel out of the pumps as those 3. He ruined 7 other pumps in the gutting. Gotta pay to play. haha.

When I tried injectors with that set up, there was no noticeable difference until over 2200psi. I ended up running 2875psi with that set up and it could drive very nice. But all my extra power was the home brew fuel getting in through the glow plug holes. (Sorry, don't think I'll ever share the secondary fuel mix). So I always took it that the injectors were kinda always was on the down side of the bell curve no matter the pump.

The only time I got good results above 3,000 psi pop was on propane, using moderately modded ip in my 1 ton. I had #6 or #7 orifice running the lpg at 2psi from 1200 rpm to 2000 rpm, then 4 psi up. When I didn't have enough lpg, it would struggle more to accelerate above 3100 rpm. (It would accelerate better than a stock engine, I mean hopped up comparison). I cant imagine trying to run that pop pressure for a DD that you don't want to fiddle with 1 a month.

The rebuild he did for my current db2 was the only 'stock' one he did for me. Weird it was the last one he did before passing away. Scott is a legend here.

 

[JayTheCPA]

Here is the basic question I have: what is the true end goal?

Point is that the motor can only handle so much power. Yes, I get it that some want to push power levels much further than OE, but for the most part we all share the same goal of getting more power without *intentionally* blowing-up the motor.

In terms of fuel delivery, I am currently on the hunt for a better regulated system as am getting more-and-more sold that we are throwing more fuel at the IP than it wants for idle to moderate power. But at heavy to WOT the IP is not getting enough fuel with the FRC10 or other common LP's. Agree that part of the equation also needs to focus on getting the IP the amount of fuel that it wants at WOT (which is more than GM tried to deliver and different than what we are currently doing).


So back to the question. We know that the DB2 and DS4 are capable of getting more power to the motor than OE. Modification of the pre-cup opening might help a get a tad more power. And increasing the injector pop helps in the total equation too. Currently I am getting ~245 hp / ~394 tq at the wheels with a nearly new ULSD rated DS4 and a slushbox. Am waiting on a tweak to the tune to see if I can get the torque up to 450 seeing as the motor has a rating of 500 (presumably at the flywheel) and the military is only getting around 450 with their DB4 and slushbox. If the next tune does get (or at least close to) the torque that I want, my vote is that the DB & DS are fine as-is and we just work on balancing the injectors to work within their limits (if there is any more room for adjustment).