Injector Pop Off Pressures

[rattlnrench]

I was talking with the owner of a pump shop I use about building some injectors for my truck. I told him I had just about given up on 20 mpg. in my truck & might want to beef it up a little in the output area. He said they could increase the pop off pressure in my injectors 250 psi or so to atomize the fuel better. He said it works like a dream in 7. 3s & 6. 2s he has done it to & does this regularly. I ask him what the increased pressure would do to the injection pump & he said it could handle it without a problem. So I'm putting it up for review & discussion. Has anyone heard of this or done this to their injectors? Maybe a vendor in the performance injector business could chime in with their comments. Also would the increase in pressure cause alteration in timing or would it be negligible?

 

[Don M]

He will just shim the spring to do this. I would buy some ready made from a vendor.



As you increase the pressure you decrease the time the fuel can flow from the nozzle. This is sometimes done to performance injectors but it is not a fix all method to make more HP.

Generally speaking and I mean generally the pressure can be increased to help the atomization on injectors with larger holes or junk injectors that are built with lower qaulity trying to get them to atomize the fuel again or help the needle seal in its seat.



All in all if you want more power the nozzle holes are gonna need to be opened up or more holes made. That goes back to a vendor that builds a good product.



Junky injectors can dribble fuel and wash cylinder walls or even worse cause a meltdown. They do this buy not having a good seal in the seat area. Just blowing holes in the nozzles is not the answer either. This can wreck seats and many of the seats are two angle. Tough to get back.



Finally, in my opinion the higher pop off pressure you have the more long term damage you can have to the seat as well. The little needle is bangin on the seat close to 600 times a minute.

The harder it bangs the faster the seat/needle wears out.



Don~

 

[rattlnrench]

Don



Thanks for your reply. I was thinking about having this done to my injectors that are in the truck now. They are running fine but I am approaching 100k on them & thought a good cleaning, testing & having the pressures set a little higher wouldn't hurt if it was something that was commonly done. I'm not sure what the pop off pressure is on the injectors in my truck but I keep thinking of the figure of 1850 psi as kind of a ballpark on injectors. If you increase the pressure 250 psi that would be a 14% increase if I did the math right. Would I get injectors that would wear out 14% sooner or would they wear out on an exponential curve? I have a Mercedes with 245k on it & it runs better than ever. The injectors have never been rebuilt to my knowledge(If IT Ain't Broke... ). Also if the increased pressure would not hold the injector open as long would I be leaning the fuel charge to a certain degree & would that be offset by a finer atomization of the fuel? Maybe I'm trying "the cake & eat it too" syndrome(mileage & a power increase). Thanks again for your reply. I hope it's not the last one on this.







Curtis Haby

 

[Don M]

Your current pop-off is closer to 250-260 bar stock. About 3600 or so psi. I would not do it to stock nozzles. If I wanted more power from stockers I might even lower it a tad.



I have no data on wear out rates at all. I just know the harder you push something the less likely it is to last as long. With the stock nozzles and lowering pop pressure you would gain power, IMO. I feel the stock nozzle sizes are pretty close to good with the "pop" where it is, but the lower pop might be better. Too low and the things will get the dribbles. You dont want that. Somewhere close to about 285-300 psi lower than the designed pop is where they will generally begin to dribble if the are failing a leak test. If your pump guy can get them hold a 10 second or so test at that lower presure they are generally ok for use.





Try stuff and let us/me know what happens. I would like to see the results myself.



Don~

 

[rattlnrench]

Well I'm still mulling it over . The R & R is not what I'm concerned about but the pump shop would be a one day turn around & we have so much work I don't think I could tie up the bay that long @ this time. They're not open on Saturdays so I would have to do it through the week. I don't think I would see a big gain by running performance injectors without a fueling box to enhance flow(or not as much as I should). I will post if I do this. I might just try it to see what happens. I do have a transmission overhaul out here for next week. Maybe I'll run that one out while I've got the transmission on the bench & put my truck in there. I've also thought that after 100k that it's possible that the injectors could be a little off anyway & maybe that's why I'm not getting the economy I was hoping for when I bought the truck. It had 77k on it when I bought it with my best mpg @ 17. 8 on a trip. Don, I'm surprised you are the only one who's replied. I guess this is no mans land. I appreciate your time & comments. I'll let you know what results I get.



I noticed by your signature you've put injectors in yours. Are there any benefits to injectors alone or is it best to do them in tandem with a fueling box? Thanks & good luck to you.



Curtis Haby

 

[Archive]

Good thread......

It gets very lonely and quiet here when the topic concerns injector pop off pressures, nozzle orifice count, orifice sizes, spray angles, fuel atomization, cylinder wash down, plunger wear, and dribblers. Just try to find posted here what the flow specs are on any aftermarket injector. (CC/30 seconds @ 100 bar) FWIW, a 1999 Bosch automatic injector flows 600cc while the manual flows @ 640cc. Thats why the autos benefit more from an injector swap. I wish Bill K. would add his OWN in house brand of injectors to his product line up. I know he would be ready and willing to tell us how the "cow ate the cabbage". Good luck Don & Rattln.

(I will now hide my keyboard and return to silent mode. )

 

[FL70CAT]

250psi is not a huge increase, it WILL help the injector maintain it's atomization which can make the engine more responsive and will definetely clean up some smoke.



If I were you I'd just get some OEM 275hp RV injectors and set the pops up a little bit higher, I think you'll be VERY happy with this setup.

If you need to talk to someone about it you should give Dave Mitchell a call @ Enterprise engine performance



www.enterpriseengine.comOo.

 

[Don M]

Curtis,

Your 24 valve is kinda different than my 12. To be honest I have maybe seen close to 40 HP with my change. The stock 12 valve 215 HP injectors are pretty good already. So the increase is smaller than the 24's. There are drop-in 100HP injectors for 24 valves. Some guys make 'em even larger , but you need lotsa air upgrades i. e. turbo, exhaust, manifold, etc.



I liked FL70CAT's ideas of using the stock 275 RV injector. Good power increase and low price.



Don~

 

[rattlnrench]

O. K.

I think I could be standing @ the edge of the BOMBing black hole here. Is this how it starts out? I appreciate all comments & suggestions & I think I will get some 275's that are "adjusted". I also think that the hp & torque increase will not sound the death nell for the transmission. I replaced the converter with a stock unit about 10k miles ago & intend to get the DTT stuff when the transmission shells out. I just don't want to wipe it out prematurely. I agree about Bill K. . I met him in Kerville Tex. @ a transmission seminar there that was part of a rallye last September. A straight shooter is a definition that comes to mind. I guess the information is propriety to those in the business & I have read the vendors point of view thread in another forum. I can tell you this that because of Bills honesty & no bull approach with the willingness to help people first he's got my vote when the time comes to get the pieces upgrade the transmission or a customers for that matter. I've had an independent automotive repair shop for a long while now. I had a customer stop by last week who questioned me about an intermittent miss in his truck. I suggested wires(his were original-11 years old) & plugs. He is able to do some work himself. I could have told him I didn't have any idea what was wrong to get the job, but that would have been a lie. Honesty, helping others & sharing information doesn't hurt business, it helps. You develope a reputation that no advertising $$$ can buy. I know he will be back the next time he has a problem, he's been a great customer in the past. I'll post results after I can test the change. Thanks Again!!