?s for the VE guru's

[dragrdan]

When turning up the VE, what exactly does the fuel screw adjust? Volume, pressure or both?

[VEfreak]

it adjust injection pressure

[dragrdan]

I know some of the old gasser mechanical injection systems held pressure in the lines, and the IP added more to overcome the injectors pop off pressure. Does the VE operate the same way. I assume it would because there would still be pressure in the lines when the injectors spring pressure overcame fuel pressure in the lines. Unless the ve has a way to bleed that pressure back into the pump. When you turn up the screw, you turn up pressure, does it also increase the pressure held in the lines? or would this remain constant (based on the closing pressure of the injectors). Is the increase in pressure what causes runaway? If it is, could the pop pressure of the injectors be increased to get even more pressure(turns of the screw)? I know that the VE has a max pressure. does anyone know what it is? Has anyone ever experimented with pop pressures?

[dpuckett]

The fuel screw increases mass of fuel pumped, which based on the old physics equation of PV=nRT, by increasing the mass of fuel, will also increase the pressure when you keep the volume (in the lines) the same. So, it increases both, but primarily the volume (per stroke, but for purposes of plugging numbers into the equations, I called it mass)

Runaway is caused by characteristics of the governor system. IIRC, the gov return springs are overcome by the gov flywheights and the RPM cant come back down.

Daniel

[Begle1]

It pushes on the lever that controls the amount of fuel that gets into the injection plunger, so it gives more fuel into the plunger at all times, which creates higher injection pressures.

[dragrdan]

So basically when the screw is turned in it establishes a new baseline for pressure and volume. And runaway occurs when the P & V is increased to where it allows the engine to rev and the governor cant reduce it lower than the baseline? If this is the case, then pop pressure of the injectors has no effect on runaway, and just before runaway is the most P & V you can get from the VE

Pop pressure would still have an effect on atomization, and therefore efficiency and power. What is factory pop pressure, and has anyone experimented with it?

[VEfreak]

from what i have been told, you can't increase the injector pop pressure because ve's hate pushing high pressure.

[dragrdan]

The VEs dont like high pressures, such as pressures over what? At 10 bar over stock(still looking for the actual number to put here, lol), does the VE explode, or does it run worse? How about 20? I thought I read in a post somewhere that KTA had his injectors set higher than stock, but can't find it. I am looking for "real world" experience, rather than an injector tech saying "Nah, just stick with stock" (Having been an auto tech for 20yrs I understand perfectly why he would say that).

Not trying to be a PITA to everyone, but knowledge is power, and we're all in search of more

[fergavs]

A wise man once told me this:

"I set my injectors for 3400psi. I like to keep the pressure lower to help take some stress off the camplate and rollers. It also makes the length of injection longer since it starts sooner and ends later, that means more fuel delivered, all be it at a slower rate. It is kind of like how the common rails add duration to the injectors to make more power."

I set mine the same and my 14mm has stood up very well so far. I'm sure 28 psi of fuel pressure doesn't hurt either.

[KTA]

That quote looks familiar.

[Greenleaf]

The VEs dont like high pressures, such as pressures over what? At 10 bar over stock(still looking for the actual number to put here, lol), does the VE explode, or does it run worse? How about 20? I thought I read in a post somewhere that KTA had his injectors set higher than stock, but can't find it. I am looking for "real world" experience, rather than an injector tech saying "Nah, just stick with stock" (Having been an auto tech for 20yrs I understand perfectly why he would say that).

Not trying to be a PITA to everyone, but knowledge is power, and we're all in search of more

The OEM setting is 240 bar. Lots of us use POD's set to open at 260 bar. I know of no pumps exploding. I hope that covers your question........?

[VEfreak]

A wise man once told me this:

"I set my injectors for 3400psi. I like to keep the pressure lower to help take some stress off the camplate and rollers. It also makes the length of injection longer since it starts sooner and ends later, that means more fuel delivered, all be it at a slower rate. It is kind of like how the common rails add duration to the injectors to make more power."

I set mine the same and my 14mm has stood up very well so far. I'm sure 28 psi of fuel pressure doesn't hurt either.

i though stock pop pressure was 2600 psi.

[dragrdan]

OEM is 240bar=3480psi,Thanks GL for that part, fergavs (and I'm guessing KTA also) are running 230bar=3400psi, lots are using PODs at 260=3770psi. That is a pretty wide range. Who has experimented with pop pressures only(keeping all else the same to rule out as many variables as possible). Wondering effects on power and economy.

Fergavs and KTA, the slightly lower pressures, are they set to help the 14mm pump only, or as a result of trial and error tuning?

I've been into bracket racing for a while, and usually spent 100x more time optimizing what I had than changing parts. results, how about a 300hp gm crate motor with cast iron manifolds(intake and exhaust) runnin 11.9s

I'd be tinkerin with em, and posting the results, if i had a pressure tester, which is on my list and a warm place to work(not having a garage sux). but until it warms up, and I have the tools, I figured I'd ask and see if anyone else had results i could get a direction and compare with.

[cummins king]

Okay i would like to pick somebody's brain on this.

But how does lowering the pop pressure increase the time the injector is open?

As the rotor spins it pressurizes a certain amount of fuel which goes into the line. Now that quick bust of pressure pops the injector open, but once the pressure in the injector line is down below the pop pressure the injector closes. Now the only way that theory works is if the VE pump pressurizes the fuel way beyond the injector pop pressure, which i believe it does.

(Kind of answered my own question)

So if it reaches the pop pressure faster then it injects sooner. I just don't see how it "ends later," because your still getting the same amount of fuel, and that earlier injection used up anything extra.

So the way i see it advancing the timing would do the same thing, as lowering the pop pressure.

I thought that if the fuel went in at a higher pressure it would atomize better, with burns the fuel more cleanly, witch gives more power.
Sure it adds more stress on the pump, but if its power your after then a broken pump isn't a big deal.

[dragrdan]

As I understand it, the pump puts out a predetermined "shot" of fuel. The volume of each "shot" is constant based on pump settings and mods. Being that pressure is just resistance to flow, would't having a lower injector pop pressure actually decrease duration since you are removing some restriction? Sure the big pump guys(14mm&4mmcam) would get more duration over the 12mm due to the increased volume.