92 cummins twin turbo 7x.0125 injectors, how much timing?

[dieselcowboy89]

hey guys, this is my first post here, I've spent the last several days looking up information from numerous sites on timing in relation to injector size. I still have a few questions or thoughts maybe you guys could shed some light on.

first I have some DAP 7x.0125 injectors (250 bar) and i'm told (and according to the numbers) they are supposed to be roughly inbetween 5x.014 and 5x.016. As far as flow, I'm not real sure. one would assume they would be similar. when you start running injectors that big you need to really start advancing the timing to compensate and to allow a longer and sooner burn,(if I understand correctly?) looking at what other people are running for timing with 5x.014 and larger injectors, I believe that I need to jump the gear one tooth.
with the pump to the head and the smallest coppers, I still have quiet a bit of white or lite gray smoke at idle and it only gets worse when I increase rpms. the smoke does get a tiny little bit darker when you increase the rpms, but it is still billowing out and I should have enough air to burn it all, especially since I don't have the fuel maxed out on the pump.
another thing, it idles smooth as glass(hazy and smells real rich) but as soon as you start increasing the rpms, it sounds and feels like it is missing and it shakes the whole truck violently. I've gone though and done a valve lash adjustment on it just to make sure they are good. there is a youtube video of it. type in 87 chevy cummins hx35/hx52 and it is the first one. it is kinda hard to tell because of the sky in the background, but it really is smoking a lot!
when you are looking to increase the timing, I realize there are a lot of factors that can change where it needs to be set, but are these injectors big enough to warrant jumping a tooth on the pump? maybe jump a tooth and retard the pump all the way back and go from there?
it brings up another question. when determining what to set timing at based on or in relation to injector size, does total volume/ area matter more or hole size and quantity matter more? ie- 5x.012 vs 7x.012, same hole size, however, there are two more holes in one injector than another, therefore more volume. would they require the same amount of timing (same engine, same truck same tune etc.) or would the 7x.012 require more timing because they have a greater amount of fuel being injected.
so basically, some people run 5x.016 with one tooth jumped and the pump anywhere from the head to all the way away from the head. if I run these 7x.0125's, would I run the pump one tooth advanced because they flow about the same. Or would I run the timing similar to what people with 5x.012 would run for timing? does that make sense? clear as mud?

if anybody needs more information about the truck, let me know and i'll write up some more, right now I gotta sleep because I need to get up at 4am. I just wanted to ask these questions so i'm not thinkin about it all night and maybe you guys can help me figure why my truck isn't running right.
thanks and have a good night.

[RCCUMMINS89]

Timing is more on how the fuel gets injected (how broken up it is)

Meaning you won't need as much timing with 7 hole per volume of fuel when compared to 5 hole.

It sounds to me like you need more timing........or you have an injector hanging up....are they noisy?

[dieselcowboy89]

They don't appear to be noisy, no loud ticks or weird things like that. I have been having a problem with one or two of the injectors leaking, either out of tge nut or the return line, (can't tell which) but when I crack each injector the idle drops like normal. I seems real smooth at idle too, even with the little leak.

[dieselcowboy89]

Timing is more on how the fuel gets injected (how broken up it is)

Meaning you won't need as much timing with 7 hole per volume of fuel when compared to 5 hole.

It sounds to me like you need more timing........or you have an injector hanging up....are they noisy?

So if I understand you right, these 7x.0125 flow about the same as a 5x.014 but require less timing?
I'm thinking that i'm going to jump one tooth and put the pump at the marks and see what it does. Maybe this weekend, hopefully.

[ellis93]

That's what they need,maybe a fuzz less than even with the marks. That's where my 7x10s ran best.....one tooth skipped and the pump mark just above the case mark.
I however had thick washers under the injectors to which may or may not have contributed to some serious hazing issues at 60° or less temps.

[RCCUMMINS89]

I know 7x10 injectors.....it is common for me to hear that they are hazy at idle. I found the same.....but they make up for it in driving around cleanliness.

I have yet to hear from one person with 7x12 or larger that doesn't have a SERIOUS, SERIOUS smoke issue. I'm not really sure why either. They shouldn't be that much worse than a 7x10.


Either way....... I was helping out another 1st genner with the same injectors you have. We skipped a tooth and it didn't do a thing except take away lots and lots of power.

However, I still stand by what I and Ellis think and suggest you MIGHT need more timing.


Lastly........stock gear marks and to the head is really close to the same as skipped a tooth and retarded about 1/8". Oh, and I'm running these "tester 7x10" sticks right now at skipped a tooth and close to the stock marks, maybe backed off 1/16" or so.

[dieselcowboy89]

thanks for the info. I have an m&h timing spacer on my pump as well. I noticed that the engine started to shake real bad and sound like it was missing and smoke once the rpms started to increase so I pulled the timing spacer and it seemed to help a lot. it still shakes some but a lot better.

I understand that the timing spacer increases the dynamic timing as rpms/case pressure increases, but could It increase it to much? how is it affected with bigger injectors? I think I remember reading somewhere(rccummins89 it think?) that the spacer was actual designed mainly with larger injectors in mind. how can one tell if their ksb even works haha? I have jumped 12v to it and no noticeable difference in idle sound or less smoke. it just doesn't seem to do anything. there is a little shim washer/spring/and another shim washer under the ksb solenoid. when I had the timing spacer in I did have the extra washer in as well and made sure to remove it when I pulled the spacer.

by the way, my pump is timed to the head as well. when I drive the truck around the neighborhood, I can't rev it all the way up before shifting, it just seems to lack any power or guts.

[RCCUMMINS89]

The problem you're seeing is the 7 hole injectors are rather short..........so they spray outside the bowl with very much timing......yet they are giving you enough fuel that you need more timing.

If your engine is shaking, back off the timing.

[dieselcowboy89]

The problem you're seeing is the 7 hole injectors are rather short..........so they spray outside the bowl with very much timing......yet they are giving you enough fuel that you need more timing.

If your engine is shaking, back off the timing.

I remember reading that about the 7 hole injectors, that they are shorter. before I took the timing spacer out, I retarded the timing as much as I could. didn't seem to change much. well, it seemed to smoke more, but it was getting darker out so I couldn't really tell. I tried it with the thinnest washers and the medium washers but couldn't find a setting that seemed to run even passably good

on a side note, my rebuilt pump, when it is on the stock timing marks it is on;y about an 1/8" from being timed to the head.

[dieselcowboy89]

update:

today I pulled the top of the pump off and changed the governor spring to the 366 spring, closed up the top, backed my idle off until it was just past the nut, bled her out and turned the fuel screw in until the idle was right. prior to changing the governor spring, I backed the timing off to what I would consider an 1/8" bump. (it really is on the stock marks but I think that the pump is marked wrong because from the mark to the head is barely an 1/8") anyway, I took it out for a drive and it acted exactly the same as before, ie; couldn't seem to get it past 1600, maybe 1700 rpms (tach not hooked up yet), couldn't build more than 10 psi overall, smoking pretty bad too. so, on the last leg home, it was a long straight shot, so I said "to he** with it!" and floored just to see what would happen. she belched black smoke, made some god awful weird noises, and then took off like a bat outta hell. at the end of the road was a cul-de-sac. as I turned around In it, the truck felt sluggish and died immediately when I stepped on the clutch pedal. pushed it the last 50 yds to my house and tried bleeding it out again. finally got it started and noticed an immediate difference in the idle and when you rev'ed it, it was smooth and felt "free", like it could finally breath. I went for another spin around the block. completely different animal now, 15 psi in first gear now and I felt like I could rev it easily without having to jump on the pedal. then about 3/4 mile from home, it died again, bleed it out, turned around, made it a hundred yds and it died. killed my battery trying to bleed it. I had to run home and get my other truck to jump this one, haha. she fired right up and I tried pulling into a church parking lot so it was off the road, didn't make it and had to have some people help me push it the rest of the way. one of the guys there works on these engines for ups and he looked at it, he was impressed with the work and saw that everything was new. he asked if the fuel lines were big enough, then asked about the tank, asked if there was fuel in the tank.
I shook the truck and couldn't hear anything sloshing around. stupid me didn't realize how quick 10 gallons can go though these enginge with as much idleing and testing I've done with it. anyway, went and got some fuel, got her running and drove her home. then I run back to my other truck and drove it home too.

I think that she sat so long that something inside was gummed up or blocking something, idk . now that she seems to be running right, tomorrow I play with the timing some and see what happens.