• Welcome to The Truck Stop! We see you haven't REGISTERED yet.

    Your truck knowledge is missing!
    • Registration is FREE , all we need is your birthday and email. (We don't share ANY data with ANYONE)
    • We have tons of knowledge here for your diesel truck!
    • Post your own topics and reply to existing threads to help others out!
    • NO ADS! The site is fully functional and ad free!
    CLICK HERE TO REGISTER!

    Problems registering? Click here to contact us!

    Already registered, but need a PASSWORD RESET? CLICK HERE TO RESET YOUR PASSWORD!

Pop pressures and precups

JayTheCPA said:
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).
Click to expand...
As you know Gail Banks has done some nice mods on the center mounted version for the military the focus being 'air density' via CAC/IC ETC. add to this any good torque multiplication from larger turbo to custom torque converter I suspect you'll be right where you want to be w/tq output.
 
I was just going to suggest LPG also. I have a kit here but it will be a while before I get to that. LPG it seems would be good because it probably cost less than all the mods needed to do an IP, injectors, precups and tune like ya'll are talking about. Can turn off LPG when not needed. The bad is the dependance on LPG if you run out you lost your power. Don't see that being a major issue though. Also space for a tank can take up much needed room.

Also please show me where Stanadyne calls for 5psi. They call for 9psi. Most trucks are running much! better with a Walbro FRC10 than a stock pump. When you get into 240/50 + hp then I can see needing even a bigger LP like a Raptor 100.
I see what Jay is doing he wants to maintain 5psi all the time and that would work to, but I bet if you maintained 9psi it will do better as 5 is borderline low on high HP/TQ apps IMO. The rule has been "as long as you don't go to 0 psi" or worse a vac condition then you are OK. Thats why/how the Walbro is so good for our apps. Its not to high of PSI at low power demands but can maintain + PSI (4-5PSI) at WOT. Its a great pump for the money. So lets not start internet rumors that Walbro won't supply enough fuel without qualifying the statement of HP/TQ needs. For 99% its a perfect pump.
 
Apologies as the intent is not to state that the Walbro is anything less than a good pump and completely agree that it is far better than what the OE pump does.

Toward fuel pressure for the DS4, I E-mailed Stanadyne directly and stated that I had a new ULSD compliant DS4 as used in GM's 6.5 turbo diesel motor. Purpose for the reach-out was to reconcile a comment from my local Stanadyne dealer regarding my psi at idle (currently 12 - 13) and its negative effect on the IP (the local dealer stated the DS4 wanted 4 psi).

Response from Stanadyne was that the DS4 wanted 5 psi (+/- 0.5) at the IP inlet under all power loads (idle to WOT).

Granted this does not state the flow requirements at the various loads, but it does give us one of the design specs.

Naturally, if there is a better source document, I remain open to input as all I know is what I currently know :)
 
I have a feeling their responses are just standard answers (liability issue?) In the real world and according to docs I have seen (but now having trouble fining it) Stanadyne calls for 9PSI. Its just a fact these things run better with better LPs than stock. No argument there, 9-12 even 13 PSI is not over fueling.
Jay, I know what you are trying to do, its a good approach. I just want to nip in the bud for anyone else that may read this that the FRC10 LP does not under fuel under load and its not to much PSI at low load for 99% of users out there.
No hard feelings, just wanted to clarify my point.
 
I've never seen any docs from Stanandyne or GM on 5psi for the ds4, your call to them is the first. I've read many times 9 for ds4 and 5 for db2. Stock power numbers. I'd like to see any factory design LP that only produces 5 psi at idle, and all 5 psi at wot. Keep in mind no external regulator came stock- so how did they do it?

I would like to see the paper or link to page from unkle Stan saying 5 for ds4, I think he misread something. I believe you are repeating what he told you, and your intent is whole hearted. Keep the ip at 5psi will run perfectly good, stock. Just expect stock performance. Expect better performance at higher numbers.

My involvement on TDP ended over flame wars when I told people my over built db2 ran at 25psi with 3/8 plumbing on day 2.
When a Stanandyne rep was at our shop during SEMA week that came there with the Gm guys, I showed him that truck in the trailer.he swore it couldn't run 2 minutes & that he was one of the design engineers for it. Then I gave him a ride. I told him not to feel bad, the guy that invented the electric guitar hated rock and roll. He said something close to "Like a hemi gone drag huh? Not the original plan."

The factory ip can only be used at stock numbers is akin to factory boost only. You can run everything stock, or you can modify. Both work.
 
It's the DB2 vs. the DS4 with the DB2 requiring 5 PSI so it doesn't mess with the inlet referenced transfer pump regulator. The DB2 will have the timing messed with on high inlet pressure if you don't do something to it's transfer pump reference.

I have run 15 PSI on the DS4 and the only worry there is blowing the shaft seal as far as I know. I have run a serious Mallory drag pump rated for 110GPH on alcohol to the DS4 with only the pumps regulator that would peg my fuel pressure gauge north of 15 PSI.
 
I'm running the max positive modification to pulse width up to 4000 RPM (DS4) as of today with a FASS DRP-02 regulated at ~9 PSI and it only drops .5 PSI once I hit 3500 RPM. It likes where it's at right now and has never run better. This is all with 3/8 lines. I have 9.5 PSI at idle and 9 PSI while flogging it to death.

I've read some about running even more inlet pressure but it seems perfect where it's at and I feel raising the pressure spring might cause more bubbles in the fuel.
 
3/8 in only or return also? Idk about ds4, but the high pressure db2 it made a little difference.

In the fleets we ran 12-15 psi on ds4 and didn't loose seals, not for new pumps that we put high mileage on them in short time periods.

You can try doing .5 increases and see if you like results. If you aerate you'll know it quick and it wont hurt the pump.
 
Will L. said:
3/8 in only or return also? Idk about ds4, but the high pressure db2 it made a little difference.

In the fleets we ran 12-15 psi on ds4 and didn't loose seals, not for new pumps that we put high mileage on them in short time periods.

You can try doing .5 increases and see if you like results. If you aerate you'll know it quick and it wont hurt the pump.
Click to expand...

It's an all new 3/8 supply with the stock return line setup all the way back still. Would have to shim the pump spring for small increments and would probably annoy me so i'm leaving it as is. Trying to spend more time on PCM hacking right now that I have it running well.
 
Anyone try dropping pop pressure? I've heard mix thoughts on this. I saw on another forum a guy saying you couldn't run low pop pressures bc it would be too low and wouldn't be able to inject the fuel bc cylinder pressure would be too high. But at the same time, I saw (or read I should say) that a guys was running 17 or 1800 psi marine injectors and was pushing over 30 psi of boost and still couldn't burn all the fuel. But that tells me it was still injecting the fuel, but maybe it was still smoking bc it was too low of a pop pressure and wasn't burning well?

I know this is all probably useless and would make little to no difference in the long run (kind of like most things we all try in order to squeeze a little more power out), but it's just something I've always been kind of curious about but have never experimented with or seen others do much experimenting with.


Sent from my iPhone using Tapatalk
 
I tried some lower but not good results compared to raising pressures but that was many years ago. I dont remember doing it with really built up pumps. And I'm sure not the large port injectors (marine).

Even when I put my turbo on recently I had the lower n/a injectors. But maybe I swapped my injectors before turning the fuel screw. Hmm. My current db2 is nearly stock though.

Good thing about being a pump builder- you can play a lot on the bench...
 
On a DB2, the lower pop pressure acts like increasing injector pulse width. The rollers are spending more time injecting fuel instead of building injection pressure. The flip side of this, is it affects timing, and creates a lot smokier of a truck since it is a less efficient burn. Really, close to stock factory pop pressure (2100) or a tad higher actually yields the best results because it is creating a more efficient burn with less fuel. Timing plays a huge role.
 
You must log in or register to reply here.
Back
Top