rockjeep73

Im talking about full throttle on a maxed out pump.

rockjeep73

Dave,
Have you got a chance to modify the advance piston in your pump yet, if so what were the results. And what side of the piston did you shave? Also, did you play with the spring or shims at all?

Bushy

Start thinking about 'fill time' as well guys.....that's all I'm gonna say on this one....

pb...

bgilbert

No secrets!

You pump guys ...

rockjeep73

Let the guessing begin

You must be refering to the time it takes to fill and pressurize the backside of the timing piston in order to move it. Hmmm...more volume to that area? If this is what you mean then you are saying that we not only need to modify how far the timing advance will travel, but how fast it will adjust.

I guess first I would need to know how the port is fed. I assume it comes through the upper opening in the piston where pin #4 (in diagram) comes through. Which would mean that the pressure on the timing piston is relative to the case pressure inside the pump. But I could be wrong.

rockjeep73

Pastor Bob,

If I may ask, what are your findings on the control collar during WOT with a maxed pump, does it completely cover the window port in the rotor and still have enough travel to return to idle without a runaway?

Or are we losing more than we think here.

Cory

wannadiesel

Never have messed with it, too nervous about leaking. I wanted to shim the KSB housing out for more travel, but after finding out how high the case pressure (80 psi) is I knew sealing it would be very difficult.

I think Bushy is talking about fill time on the pump plunger, not on the timing piston.

G1625S

''I think Bushy is talking about fill time on the pump plunger, not on the timing piston.''

That's what I was thinking! How does the saying go? Great minds think alike...no, that's not it...oh yeah, Fools seldom differ! J/K, Dave

I guess I'm not sure how plunger barrell fill time can be affected by timing...wouldn't it (barrell filling) be more sensitive to RPM?

Alec

Yes, which probably contributes to even more retarded timing at higher rpms -- if the plunger is not full of fuel, it will delay the point at which pop-pressure is reached. "pop-pressure" being a highly technical term . . .

rockjeep73

Well guess I was way out of line on this one.

But how is plunger fill time related to timing. The faster the rotor speed, higher RPM, the shorter the fill time.

G1625S

Alec, what you said makes sense, but my new question is, if the plunger barrell is not full of fuel, what is it filling with? It can't be air, obviously...

edit: maybe the pump just plain starves of fuel, decreasing the power, retarding the timing, and slowing the whole thing down till it can get back up to pressure? If that were the case, adjusting the spool and overflow valves to allow more volume to flow through the pump while maintaining the same pressure may be in order...

rockjeep73

Im assuming the spool and overflow valve control the amount of fuel that enter and exit the pump and maintain the pressure. As long as the pump is maintaining pressure at high RPM's then there is no reason to increase the volume that is pushed through the pump. Unless the pressure drops off which would call for a larger volume of fuel in order to maintain pressure.

G1625S

''Unless the pressure drops off which would call for a larger volume of fuel in order to maintain pressure.''

That's what I'm thinking. Maybe the stock spool and overflow valves can't support 3200 and 4200 rpm gov springs and thirsty injectors and ground afc levers etc etc

edit: ok, now who's gonna drill and tap their AFC housing and plumb a FP gauge into the cab AND videotape a WOT bonzai run?!

rockjeep73

If the pressure were dropping off in the case then it would affect the ability to comletely fill the rotor. Wouldnt it also affect the amount of dynamic timing, as in less case pressure means less dynamic timing?

G1625S

I'm thinking the rotor has to fill with fuel, since the pump is completely filled. Even if the pressure dropped to, say, 40psi, that's still 40psi, but I agree that this would make the dynamic advance almost nill, which would pull back top end horsepower. Come ON, Pastor, we're trying here--throw us a bone, eh?