Injector pop pressure and it's affect on mileage ???

[SASQCH]

Injector pop pressure and it's possible affect on mileage is a subject I have not seen discussed on the forum.Does the pop pressure of the injectors affect the atomization of the fuel enough to have a noticeable effect on fuel mileage?I suspect that it does.I'm on the third set of injectors in my truck trying to get a good balance between towing power and economy.I also realize that today's fuel is not as good as the fuel a few years ago.On the stock injectors in 2004 I was getting great mileage. Then I got a set of +80 injectors using the stock ones as exchange. Mileage went way down hill. I have since put in RV275 injectors and gained some of the mileage back but it still isn't anywhere near the original stock injectors.I still have the +80s and am thinking of taking them in and getting them set to the highest pop pressure I can to see if that helps the mileage any.Does anyone know what the pop pressure range for injectors on a vp44 is?

[guesswho512]

i don't know about the pop pressure, but the VP44 can produce up to 26100 PSI

[AH64ID]

26,100? That seems really high for a VP, that's more than my CP3 makes!

--- Update to the previous post...

Okay, dug out the service manual.

It says it may produce up to 17,405 psi, pop pressure is 4500 + or - 250.

I would say it would increase atomization and increase mileage and/or power.

[Mopar1973Man]

Lower the pop pressure more advancement of ther timing. Higher the pop pressure more retarded the timing. So its suggested to set the injectors properly and not alter the pop pressures...

[SASQCH]

Lower the pop pressure more advancement of ther timing. Higher the pop pressure more retarded the timing. So its suggested to set the injectors properly and not alter the pop pressures...

So what is the proper pop pressure? 4500 + or - 250 psi (310 bar)?

[guesswho512]

The VP-44 is a beefed up version of the original opposed plunger style pump with injection pressures of 1,800 Bar or 26,100 PSI and much more precise control over injection timing.

http://forum.mopar1973man.com/downloads.php?do=file&id=130 page 7, last paragraph. not trying to sling mud, but i don't want anyone to think i made that number up.

[SASQCH]

http://forum.mopar1973man.com/downloads.php?do=file&id=130 page 7, last paragraph. not trying to sling mud, but i don't want anyone to think i made that number up.

Good info in that doc. It also states the solenoid opening (triggered by the ECM and electronics in the vp44) controls the timing of the injection cycle. That would seem to say that the pop pressure don't have anything to do with the injection timing. So that brings me back to my question of whether the pop pressure (if set at 310 bar) helps with atomization of the fuel for more efficient burn and better mileage.

[AH64ID]

Timing is effected by pressure since it takes longer for the injector to open, and will probably close sooner too. So I would expect shorter duration as well. But the fuel will atomize better, and better atomization means sooner ignition, so that advances timing.. So the question is: Does the advance timing from higher pressure negate, exceed, or fall short of the retarded timing from the higher pop pressure?

[98whitelightnin]

Ive got a set of big sticks in right now but thinking about going back down to stock, would having them set to 310 bar help them or should I not mess with them? I also have a set of injectors that the truck came with and im not sure what they are but dont think they are stock, I think im gonna take'm apart and polish them up (thanks ISX) to see if I cant tell what I have.

[white01]

Injector pop pressure and it's possible affect on mileage is a subject I have not seen discussed on the forum. Does the pop pressure of the injectors affect the atomization of the fuel enough to have a noticeable effect on fuel mileage? I suspect that it does.I'm on the third set of injectors in my truck trying to get a good balance between towing power and economy. I also realize that today's fuel is not as good as the fuel a few years ago. On the stock injectors in 2004 I was getting great mileage. Then I got a set of +80 injectors using the stock ones as exchange. Mileage went way down hill. I have since put in RV275 injectors and gained some of the mileage back but it still isn't anywhere near the original stock injectors.I still have the +80s and am thinking of taking them in and getting them set to the highest pop pressure I can to see if that helps the mileage any. Does anyone know what the pop pressure range for injectors on a vp44 is?

i am thinking about getting some rv275's and sending the nozzles to gethoned.com

[AH64ID]

Something I thought of last night was what pressure does the VP run normally? We know max is 17K and pop is 4500, but say at WOT what pressure do you see? If its a long ways above pop then you will not see any benefit to increasing pop.

[JOHNFAK]

Hey jimWhat were the mileage results with the diff injectors ?Stock+80HPRV275Did you end up getting any of them pop tested.

[SASQCH]

Have not had any of the injectors pop tested.The factory injectors in 2007 gave me 20+ mpg on the highway running empty, and 12.5 pulling a 17K gooseneck living quarter horse trailer. That was with the factory 12cm2 turbo exhaust, factory exhaust pipe, and a K&N filter in the factory air box. Before I installed the +80 injectors I put on a 14cm2 turbo housing, BHAF, and 4" turbo back MBRP exhaust to lower the EGT.The +80 injectors in 2009 and last May gave me 13.5 pulling 8K enclosed trailer and 14.8 running empty (scan gauge II average numbers on long highway runs).Before the trip in May I put on a HX35/40 turbo with the 14cm2 housing and was not happy with it on the trip. I have now put the 12cm2 housing on the turbo and have been much happier with it. So that's one more factor that has changed. But I wouldn't think it would have much of an affect on mileage, just EGT and turbo spoolup.The RV275 injectors (also on the scan gauge II) are showing 16.2 average on the highway.I haven't pulled with the RV275 injectors yet but am leaving for Montana next week with another load of around 8K.Now I know that many things besides the injectors affect mileage and the intake and exhaust modifications also affect mileage, as well as the fuel blended for the time of year.However according to all accounts and claims I've read the intake and exhaust modifications I made should have affected mileage in a positive way increasing it not decreasing it.As I said before I'm thinking of pop testing the +80 injectors and getting them set to 310 bar to see how they perform for mileage then. I bought them but never had them tested as the vendor assured me they had tested them.I bought the RV275 injectors new also with no exchange but didn't have them tested either.If I test the +80 and install them I will test and set the RV275 injectors to 310 bar also.It just won't be in the immediate future as I've got more runs to Montana planned and need to keep the truck up and running.Jim

[JOHNFAK]

Yeah

My stock + BHAF I would get 17 on highway crusing, around 15 around town, around 10-12 towing 9000lbs.

That was wiith no VB/TC or chip.

Added chip and closer to 18.5 on highway. 16 around town. Not sure towing.

Now have TC/VB and edge and RV275's. Only have one measurement and that was 20MPG on 300 mile trip.

Will have to see on towing. Unsure how much due to injectors and how much due to chip.

--- Update to the previous post...

-- p.s - what did you find was best bang for buck for lower EGT's. I am about to put j-hook on my stock HY. Any other cheap mods to increase the compression and flange output - no way I can spend another $800-$1000 just for EGT.

[SASQCH]

The two items that lowered EGT the most was the 4" exhaust and the 14cm2 housing.You already have a 4"exhaust. but your HY turbo has a 9cm2 exhaust housing (can you say hot), other than that it is essentially the same turbo as a HX35 which has a 12cm2 housing. The HX will be a little slower spooling up than a HY but not much.You might try to find a good HX35 and put it on you can get them for under 300 if you look.You might PM TURBOLVR he may have a good one that he will sell you, not sure if he is on this forum but he is on the cummins forum.Anyway with the HX you can use the adjustable boost elbow to regulate your boost and at the same time get lower EGTs. It would also enable you to try a 14cm2 housing later if the 12 didn't lower the EGT enough. The 14 spools a little slower than the 12.