VE pump dynamic advance

[Dirty_Bill]

a little background:
chassis '76 280Z
freshly rebuilt LD28 .5mm over
SD28 STD pistons
RD28T pump w/ modified LD28 pump pulley and 10 or 11mm cant remember, exactly i do remember the RD pump having a 9mm head and the LD was a 10mm or 11mm also has the LD delivery valves in it, the RD delivery valves were too aggressive
L28ET exhaust mani slightly tweaked to fit
china special T3 .50 A/R hot side, nissan .63 AR compressor wheel, compressor housing bored out to fit nissan wheel (chinese wheel was about 6mm smaller on the inducer dia.)
runs 5psi cruising with very little throttle and peaks around 17 psi
21x7 core FMIC (needs to be bigger)
2.5" charge piping
3" SS straight pipe exhaust
factory gas 8mm fuel line, Carter 72GPH pump for a lift pump


i just bought a Sealey TL95 timing light adapter and new advance timing light to dial in my timing and figure out if the dynamic timing advance was working and to find out my total advance. dialed in the base timing to 15°advance on the gun to get the timing mark on the flywheel lines up with the notch in the inspection hole on the engine plate. proceeded to slowly increase the engine speed to get an idea of the advance curve and i was shocked to watch the timing retard by 5° around 1200 revs to 2000 revs. from what i have gathered from the RD28 diesel service manual there should be about 8 or 9 degrees additional advance, not the opposite as im getting.

at first i thought "oh duh this is pressure driven, the lift pump is off, must be that"... nope no change with the lift pump on.

any VE pump guru's on here that can help a guy out? im just baffled....

[Carimbo]

Seems like the highest population of passenger car VE IP for IDI engines are the VW Rabbits, Caddys, etc. Close second would be the Cummins engines in Dodge trucks. These have apparently done the most in terms of problem solving/ reverse engineering/ theory explainning. Anyway, from the first population, this may be of help to you if your RD IP is similar enough:

https://web.archive.org/web/20160420200 ... 9d3c04498d

[asavage]

The VE IPs, when new, develop significant internal hydraulic pressure as the RPM advances, and as you stated that pressure is required to operate the internal timing advance mechanism.

Problem is, when the internal pump's vanes get even just slightly worn, that internal pressure doesn't develop. It may be able to pull fuel from the tank, but can't make enough pressure to operate the advancer. The result is typically black smoke and lack of power. From my experience, I feel that most vehicles running VE IPs are not advancing the timing at all or almost not at all.

[Carimbo]

Also, in addition to that, the dynamic timing advance mechanism advances timing based on RPM and the pressure difference from before and after the IP internal vane "lift" pump.

It appears you are running quite an external lift pump ("Carter 72GPH pump for a lift pump") which would for sure overpower any pressure differential the VE IP dynamic timing advance mechanism needs to engage its advance operation.