Fuel flow rate difference 6.2 - 6.5

[nev62]

I'm using a DB2 IP from a 6.2 na block on my 6.5 na block. At the moment there is only the slightest puff of smoke (look real hard and you might see it) when under heavy load and I'm left struggling up hills the 2.4lt na diesels leave me for dead on. I want to up the flow rate on the IP but unsure how much to go 1/16, 1/8 or 1/4 turn (etc). Is 1/8 of a turn a good starting point (I don't want to go through the hassel of may trial by errors - yeah lazy I know :-) )

[DmaxMaverick]

1/8th turn is a good increment for tuning by ear (or eye). You can fine tune with less, but w/o an EGT gage, your only measurement tool is the smoke and ECT's. I strongly recommend an EGT gage if you are tuning past a bench setting, which is where should be if it was new or rebuilt.

[JohnC]

IIRC the 6.5 injectors pop at a higher pressure than the 6.2's. The 6.2 pump may not be designed for that. Maybe this is part of your problem?

[nev62]

I cranked it up 1/8 of a turn on the weekend. Only real result was to push the idel speed up. There maybe some gain but so slight it is hard to tell.

[DmaxMaverick]

I cranked it up 1/8 of a turn on the weekend. Only real result was to push the idel speed up. There maybe some gain but so slight it is hard to tell.

If you turned a screw, and the idle went up.....wrong screw. The max fuel volume adjustment should only effect WOT. Did you notice any more black smoke at WOT?

[nev62]

nope, no smoke under load. How many allen key screws are there in the guide??? I only found the one after rotating the engine clockwise.

[gmctd]

Unfortunately, there is no max fuel volume screw - the fuel adj screw effects the ruel rate across the board - from idle to full out.

Externally, however, there is the idle adj screw and the full-throttle limit adj screw, both of which set the throttle arm travel limits.

To maintain correct idle rpm, the idle screw may require backing off when adjusting the fuel screw for increased fuel

[arveetek]

I, too, found that turning the fuel delivery screw up also increased idle speed. I cranked the pump up a 1/4 turn on my 6.2L years ago when it was n/a, and it produced good results. Eventually I turnd the screw as far as it would go. That led me on the quest for more power and that's when the turbo project came to fruition!

I'd turn the pump up some more and see what happens. Some pumps are calibrated to only give so much fuel no matter how far you turn the screw. That's the way mine was.

I saw EGT's above 1400 several times when towing with my 6.2L in n/a form. It never seemed to mind it at all. Not until I put the turbo on did the engine start to feel stressed. That's when watching EGT's becomes absolutely necessary.

Casey

[gmctd]

G'day, nev

If you're blowing a slight black haze under load, you have adequate fuel for the air you're moving - any denser haze, and you'll be wasting fuel.

And, forcing EGT's up, unecessarily.

Try opening up the air intake path, such as that which Dr Lee suggested awhile back - if that eliminates the haze, then turn up the fuel until you get equivalent haze with the additional air, for increased power.

You will also need adequate exhaust flow to effect the improvement - check out the Clevite Kid's exhaust modifications, also on this forum, for a proven scheme, to that end.

[93_Burrito]

DmaxMaverick has stated, at least twice recently that I've read, that turning up a DB2 only affects the pump's maximum fuel delivery at WOT.

GMCTD counters that turning up the DB2 pump increases fuel delivery across the board.

Who's in the right about this? Sorry if this is kinda off-topic to the parent post... this question is starting to nag me.


Andy

[gmctd]

The DB2 -831 rotor consists of a cross-drilled bore with two 0.310" plungers - pistons - one in each end of the bore, with a common center-discharge into the center of the rotor shaft, thence to the 8 timed distributor ports for the cylinders.

Each plunger is pushed into it's share of the bore by a pillow block cradling a ceramic roller, which rides up and down the ramps inside the camring - the camring is rotatable to advance\retard injection timing.

Housing fuel pressure @ 25-125psi forces the plungers out of their bores, against the pillow blocks and the rollers, which contact the camring ramps.

The pumping plungers are limited in stroke by a leaf spring placed across two fulcrums on the rotor, at 90deg to the bore, with an adjusting screw in the center between the fulcrums

The adjusted limit of the plunger stroke determines where the roller contacts the camring ramp - less ramp = less fuel, more ramp = more fuel.

Which, as you can see, also slightly alters injection timing.

Each outer end of the spring leaf presses against one of the two plunger pillow blocks, limiting it's outward movement.

Adjusting the screw changes the arch of the spring leaf across the two fulcrums, such that -

adjusting the screw out, increasing the arch, forces the plungers deeper into the rotor bores = less stroke = less fuel

adjusting the screw in, decreasing the arch, allows the plungers more travel = more stroke = more fuel

Adjusting the fuel rate screw changes the plunger stroke, which alters the fuel rate from idle to full throttle.

Hope that's helpful to ya, dudes and dudettes.

FYI - the DS4 plungers never alter stroke - fuel rate is controlled by varying the volume of fuel which is pumped by the 4 plungers - that's part of the FSD\PMD's task in driving the Fuel Solenoid - and releasing it.

The injectors set the actual injection pressure in both systems.

Yeah, yeah, I know - there's a show-off in every crowd......................;)