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Discussion Starter · #1 ·
Hi guys!

I'd like to hear personal experiences about advancing the injection pump timing? I've read a lot of threads on it and now have myself scratchng my head. Some say it IMPROVES bottom end power and just as many others imply that it hurts bottom end and makes better top end!??!

At this point the only thing I can figure is it might help both, bottom end and top end? For those who don't know, the idea is to loosen bolts at timing gear housing/pump mounting and rotate the entire injection pump towards the block, adding about 1/8" [25mm] at block & pump reference marks. If there are no existing reference marks use a prick punch to mark before you start. I'm going to do it regardless, but would like to get some feedback from others who have done it posted for myself and others that are interested. Thanks!
 

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It moved my usable power range upward in RPM's and decreased the lug ability of the engine right along with it. You just end up running the engine at a slightly higher RPM from where you are currently running which therefore requires you to shift to a lower gear a bit sooner.
 

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JimmieD I adjusted the timing on my Chevy diesel because on a cold start it put out white smoke, so I advanced the timing very slightly and started again still smoking but less, on the 3rd go on startup only a small whiff of smoke then clear. I know the timing was wrong (retarded?) when I got it as it always smoked like that but whether it was a stretched timing chain or just plain old wrong I don't know (thinking back when I accelerated from low revs I swear I could hear pinking, never heard it again after I adjusted timing) . I definitely lost a little bottom end and gained a little at the top but a chevy diesel makes max power at 3700rpm I think. Go careful and just a little at a time, the problem is you don't really know by how much you are adjusting it and too much could mean a new headgasket. If it increases bottom end for some then maybe there timing was really out before they advanced it a little and really just put it nearer what it should have been, who knows.

Gaza
 

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It would be one or the other, not both

Advancing timing reduces bottom end, to some degree, and adds some acceleration and power at top end. Exactly how much will follow your experiment, your seat-of pants observation or factual dyno result. Timing without fuel changes would provide questionale differences.

General concensus is mileage improves, albeit many will find mileage improvents with almost any change. How real are changes? Real improvement-do not know.

The real question is did Cummins get right and optimum at factory settings or did they retard engine timing just to meet EPA requirements. Likely, Cummins is real close to optimum, since EPA had little affect on 4BT.

All this advaincing, withing reason. Most cummins engines should not be advance more than one degree and two more more degree with added fuel may damage pistons.

In general, on natural diesel engines converted to turbos (added), timing is advanced. In general, some timing advance accompanies increased fuel and air delivery. Again all within reason.

Example. Go to the diesel truck and tractor drags. Those engines that require the driver to spool up the turbo, and quit pulling when they get below the turbo are good example (or bad example for on road). The engines have reduced bottom end, and some won't even idle because of advance timing. Talked to several truck and tractor pullers, who still had stock cam still, with only significant timing and fuel and air advances.

So, in general you don't get both with manual fuel injection. You want your bottom end to be there to idle and pull.

Be careful what you start. My old 4BT had the pump advance, fuel increased and the exhaust smoke particulates permanently tarnished the white letters on my new [email protected]!#$%^^&&! I back off fuel and reset timing, but the pump would not return to specs. Dam thing killed misquitos (oh, it ran good), but when compared to the 4BTA I have now, the Extra air and clean fuel settings of the 4BTA makes more power..

What you turn up, you must cool down.

My point, with diesels all fuel, boost, and timing advances follow the map the turbo can make, and how well your head is connected to the block. How far you can go, stay together and stand the noise is your experiment. My feeling is Cummins thought what was optim when they built it.

Wayne
 

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I mostly agree with Bobs description. I played with the timing some and in my opinion it is more of a fine tune for the rpm that you intend to cruise at. I advanced up to about 2mm but that seemed to run real good at 2100-2200 rpm, faster than the law will allow around here. Also definitely sacrificed bottom end power. Ended up just a hair over 1mm (1.25mm?), Runs really sweet 1850-1950rpm, still stout at low rpm. Better mileage- maybe so, maybe not, probably not a lot if so. I still would recommend mine runs smooth down the highway.
Carl
 

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Discussion Starter · #6 ·
Thanks very much for some great feedback everybody!

As mentioned before, I live in the mountains and 90% of my driving is real extreme. The small amount of flatland I do is only in town and I could easily handle that if it was only running on 2 cylinders. My engine runs fine and makes plenty of power but the blasted tranny ratios in the NV4500 just don't get it! 3rd and 4th are just too far apart. Because of the mountains and tight curves 4th gear is often max speed, plus lots of either revving 3rd or lugging 4th. The real problem isn't the hills but the screwy turns that force me to slow down. 3 or 4 hills are really tough but 10-15% more bottom end for 4th would do it!

Thanks again! I think I'll stick with the original plan: install my 3200 spring, swap compressors, and juice it up a little.
 

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How does the advance system in the VE pumps work?
I'm thinking it should advance enough with RPM to keep it in the happy spot for most of the usable rev range.

My Isuzu inline pump has an engineers dream inside the front timing cover, weights, ramps and springs to retard the timing for starting and advance as the rpm picks up.
You'd have to be unemployed to want to rejig it and alter the advance curve though.
 

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It doesn't advance with rpm does it? I'm afraid it's simply fixed. That would explain why altering it simply moves the engine's peak efficiency rpm.

Is it unaltered with rpm?
Inline pumps timing are certainly altered with RPM, some VE pumps are, but I don't know about the 4BT.
It sure sounds static listening to these guys.
 

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That's what I'm saying. Seems based on these reports that it just is what it is. You come into and out of it as you come up through the rpms. And a guy told me the other day that the P7100 is the same way. Static.
Could be a major factor in the 4BT's being governed to 2500rpm from the factory.
The Isuzu 4BD1 series has a 3600rpm limit, hence the timing device.

Here's a cutaway of the Zexel (Bosch) type A pump. You can see the flyweights inside the timing device inside the front drive gear.
 

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I cant remember the source, but I read that the VE pump did advance with rpm and the inline pumps were static. You fellers are a lot smarter on this stuff than I am but start rpm is only 150+, maybe it advances to a static position after starting. Even if the VE does advance, it may not be advancing far enough to get to your "happy" rpm depending on gear ratio's and tire size. In my opinion, advancing the timing seems to fine tune your cruise rpm, and when you get it right as I think I have, it doesnt take very much big toe pressure to make these rolling hills around here.
Note : Im advanced a tad over 1mm, cant tell any loss at low rpm, still plenty torquey. At 2mm there was definitely some low rpm power loss.
Note also that these power gains were measured with my well aged Hindend dyno and calculated with gray matter. (any performance gains are estimated, your performance will vary depending on :beer: intake. Individual testing is highly opinionated and likes to hear himself make noise. Proceed at your own risk.)
Carl
 

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Most Cummins engine are timed retarded , I have seem them at 14* way to much ,I like to set them at 16* - 17* .

It will change your low end and top end and will be harder to start ( above ) 18* when it's cold .

I will say this you drive a engine that has set stock timing and one that has been advanced is night and day difference.
 

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Discussion Starter · #14 ·
Well in a way this question is unfair to Cummins/Bosch, because I don't have an actual engine 'problem' as such. I suppose my timing is near ideal for the average installation, and there's the problem. The NV4500 with 4.1 axle ratio and 29.5" tires gives me 33-34 mph in 3rd gear. 4th gear isn't in the power range until 40 mph. It's that black hole of 5 mph that's killing me! Man, it's soooo close to right, but no cigar. Gotta stuff in that #366 spring. It's the combination of steep hills on a tight twisty road that drops the speed into that 3rd-4th gear hole several times in either direction driving to the nearest town.

One way to get dynamic advance from a VE pump is via the KSB wax motor cold start mechanism. It advances [? think so, or is it retards?] timing a few degrees under cold engine condition, then as engine warms the wax motor returns timing to normal operating range. Disconnecting the wire causes engine to run in that advanced mode all the time. I may try that to see if that works, having been told it can help in some cases.

I've got more info on that KSB somewhere in my files....
 

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Well in a way this question is unfair to Cummins/Bosch, because I don't have an actual engine 'problem' as such. I suppose my timing is near ideal for the average installation, and there's the problem. The NV4500 with 4.1 axle ratio and 29.5" tires gives me 33-34 mph in 3rd gear. 4th gear isn't in the power range until 40 mph. It's that black hole of 5 mph that's killing me! Man, it's soooo close to right, but no cigar. Gotta stuff in that #366 spring. It's the combination of steep hills on a tight twisty road that drops the speed into that 3rd-4th gear hole several times in either direction driving to the nearest town.
I had exactly the same problem with my truck. But between 3-4 on the Isuzu 5 sp box.
It annoyed me that much that right now I'm swapping in a different model gearbox with a smaller gap between those gears. But the delay in getting the adaptor shaft made is keeping my truck in pieces.:rasta:

Can more fuel help you? Or are you already in the smoke zone?
Smaller turbo housing to get 4th gear working earlier?
 

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The timing advance unit on the Isuzu 4BD1 inline pump (A series), is external of the pump and fits on the drive shaft, similar the cutaway diagram.

The timing advance specs for the non turbo 4BD1 are:
below 0.5* @ 1250 rpm
below 1.1* @ 1350 rpm
below 1.6* @ 1400 rpm
5 +0/-1* @ 1600 rpm

For the turbo engine 4BD1-T:
Start advance 0* @ 1200 - 1300 rpm
Finish advance 3.0 to 4.0* @ 1500 rpm

The timing advance in the VE pump is hydraulic and internal.

The VE pump has a vane pump in the front. This pressurises the fuel in the case. A control valve ensures the pressure is proportional to the pump speed.

The pressure acts on a hydralic piston located across the bottom of the pump, against a spring. As the piston moves against the spring, it turns the roller ring to advance the timing.

For those who don't know. The VE pump has a single injection plunger. A cam at the base of the plunger has lobes (one for each cylinder in the engine). As the plunger is rotated, the cam lobes run against radial rollers held in a ring (one roller for each lobe). The plunger oscillates as the lobes ride over the rollers.
 

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JimmieD you really should put that 366 spring in ASAP, I have heard people talk of the same problem your having and put the new Gov' spring in and couldn't be happier.

bush65, Have you heard of the modifications being done in the timing advance mechanism of the VE injection pump? Something to do with the shims and spring I believe. There was a link posted here not long ago, VW guy IIRC.
 

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Discussion Starter · #18 ·
Thanks, Dougal! I have the parts to tweak it some, a new 56 cm compressor housing with MWE slot and a new turbine wheel, takes it up to a HY35 spec, with 16cm exhaust housing. Also have the #366 governor srpring to install, then start twisting screws.

Right now waiting until I can afford to re-register a back-up truck for transportation while doing tweaks. I live far from civilization and can't do any major stuff on the Cummins without some kind of alternate transportation.

I got my tranny cheap but nowadays the price is ridiculous, all because guys want them for swaps ha ha! So it's what I've got or nothing.... :(
 

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Turn up the total power .... additional horsepower can shorten up even the tallest of gears IN A HURRY.
Could also add a little shot of propane to get things moving. Not the best, tho...
 
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