Controlled Runaway (Kind of)

Smokin ACE

Smokin ACE

1st gen turbo tester
Joined
Aug 26, 2010
Messages
250
I woke up with a wild hair this morning. Can a truck make more power in a runaway situation rather than just full throttle? Or does anyone really know?

Now I know runaway is kinda scary but what exactly happens when a VE pump runs away? I've heard the governor just loses total control and just winds out til something gives, is this correct? Under a load will it still wind out to high heaven or will it find a balance?

Since VE pump runaway is so easy to reach I got to thinking. When you turn the power screw in so far the truck will "runaway", now the question is if you bring the screw back out real fast as it starts to runaway will it come back to normal? I've never personally tried it as I am usually panicking trying to get the board over the turbo as I'm sure many have been in the same boat. If it does work this way, then I thought about modifiying the power screw hole and rig up a strong actuator I can control in the cab. So in theory, in case of a sled pull or drag race (not street use of course) I could bump the actuator up to get the truck to runaway during the run then back it off as soon as the run is over with a safety button or switch on the brake pedal in case of a mishap. Thats if the theory worked and it would come from runaway back to normal. Of course I would have both fuel and air shut offs ready to be the backup plan.

Now I know this sounds kind of crazy but like I said I woke up this morning and thought "wonder if this would work" and so I thought I'd see what kind of answers I could come up with or if its a lost cause.
 
"but what exactly happens when a VE pump runs away"

For the sake of you question, let's ignore Run-Away situations brought about by an external source of fuel. ;)

In order to better understand what happens when the VE IP gets into a run-away situation, one needs to understand how the VE works, and more specifically, how it controls (or throttles) the fuel.

As you may know, the VE moves fuel to the injectors by way of its Head/Rotor assembly. It amounts to a single piston, moving in and out of a cylinder. Simply put, the piston moves out of the cylinder, drawing in fuel. The piston them moves back in the cylinder, raising the pressure within, and moves the fuel to a given injector.
So as to distribute the fuel to the appropriate injector, that same piston rotates as it moves in the cylinder, and by way of aligning with individual ports, the fuel is delivered to a given injector. One could liken it to an old-school ignition distributor on a gas engine.

See the following image . . .

fuel-delivery_zpsbd580eed.jpg




OK. :)


The way the fuel is throttled in the VE IP is by way of a passage in the piston itself that, goes to a Spill-port at the base of the piston. A sleeve or collar is mounted on the base of the piston (as shown in the above image (figure 3)) such that, by being positioned by the throttle linkage in the IP, that Collar covers the spill-port. Moving the collar so that it covers the port, results in more fuel being delivered to the injector, moving the collar the other way, results in less fuel being delivered to the injector.
Understand that the piston moves inside the collar as it strokes in and out of its cylinder. As the piston moves into the cylinder, it delivers fuel until the point that the spill-port is uncovered. With that, the pressurized fuel in the H/R is dumped back into the IP case. Moving the collar toward the head (pressing on the pedal), has the piston stroke deeper, delivering even more fuel to the injector before the spill-port is uncovered. Backing of the pedal, has the collar move away form the head thus, uncovering the spill-port earlier in the pistons stroke.

Clear as mud?


The typical Run-Away situation the VE owner usually sees, is when one tweaks the IPs internal linkage (by goofing the throttle levers indexing, or running the main fuel-screw in too deep) such that the collar doesn't uncover the spill-port enough that, enough pressure is relieved in the H/R to reduce the fuel delivered to the injector so as to reach a balance that, the engine stops accelerating.
The collar doesn't necessarily fully uncover the spill-port when defueling. Simply uncovering an edge of the spill-port is often enough to slow the engine.

But if you've got the thing whacked with the throttle assembly 9internal of the IP), then the collar may cover the spill-port enough that the engine will try to spin to the moon.


Will you make more power with the spill-port fully covered? No more than you would with simply flooring the thing and having it operate as it should. The only difference between the two things, is one is controlled and operating within an optimal (mechanically) engine speed and, the other is not.


Here's a better overall view of the internal gizmos of the VE including the throttle linkage in the Ip, and how it connects to the collar on the piston of the H/R assembly.

Fuel-Control_zps05cdef61.jpg




POP-Quiz in five minutes. :doh:
 
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Why not instead of an air shut off you plumb a fitting into the intake neck and connect it to a refillable CO2 paintball canister and either an electric valve or a manually opperated ball valve. You could flood the intake with CO2 and choke the engine out.
 
Lets suppose for a second that I had a 14mm VE that was running fantastically and doing things many people said would never happen. I'd be trying really hard to not chart new RPM waters where everyone else has seized them up. My day would be coming.

<Snap back into reality> Has this pump ever been on a bench? If it has, what does it theoretically put out at a theoretical (or known) runaway RPM? I'm not sure the effort and risk would be worth it for what could be a few more RPM and a few less cc of fuel.

Of course, just my $.02
 
I've had my truck runaway going down the road........didn't take off any faster than normal. EGTs or boost was not any different than a normal wot run.

In fact.......I've come to notice and realize that there is a balance between the power screw setting and the throttle indexing (gov spring length).

In the past I have successfully added a throttle stop at a specific point and/or backed off the power screw and GAINED fuel.
 
Smokin ACE said:
When you turn the power screw in so far the truck will "runaway", now the question is if you bring the screw back out real fast as it starts to runaway will it come back to normal?
Click to expand...

Yes it will come back to normal,
 
12vChapa said:
Yes it will come back to normal,
Click to expand...




Depends on how far you run it in. Keep in mind that if the above was completely correct....... one wouldn't get caught on runaway when they released the throttle. It also depends upon the load on the engine.......thus allowing the governor to work again as it should.
 
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No worries....I'm about the worse person to explain what goes on in my head.


The slide collar is both controlled by the power screw and the throttle. Which is why when the power screw is in too far it won't hit runaway at an idle.......it will only hit runaway when throttle is applied.

So, if once a runaway situation happens.......if one could back the power screw out to stop it....one could also just release the throttle to stop it (which doesn't work).



On a side note.....in many cases one can't hit runaway in the driveway, yet will hit it on the street. This is because the afc is doing it's job and not allowing full movement of the slide collar until full boost is achieved. So in short.....if one is hitting runaway in the driveway, they are a decent amount passed an on the street runaway situation.
 
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BC847 that answers my question and makes much more sense now. Thank you for your knowledge. I was wondering if it would be worth doing but didmt really want to risk my setup running it away all the time to find out. I will scratch that idea off the list as it makes more sense now
 
FWIW, every time I have ever adjusted for "full power", I backed the idle screw completely off and adjusted the fuel screw in until it idles like it normally would.

Never have needed a board, never have had a runaway.

The method above is as much as you're going to get without other adjustments or modifications, particularly to linkages.

Mark.
 
Mark Nixon said:
FWIW, every time I have ever adjusted for "full power", I backed the idle screw completely off and adjusted the fuel screw in until it idles like it normally would.

Never have needed a board, never have had a runaway.

The method above is as much as you're going to get without other adjustments or modifications, particularly to linkages.

Mark.
Click to expand...



^^^^^^^^ This^^^^^^^^^^

Every one I've ever been around, doing the above..... will put it within a 1/2 to 1 turn at absolute max from runaway. I've never gained any fuel passed the point of the above tuning and have never had one runaway on me doing the above.

Re indexing throttle shafts or messing with a governor spring length (different than stock length) has only taken away from drivability to gain basically almost nothing on top or down low.
 
oldestof11 said:
If you want technicality the full power screw is just a fulcrum.
Click to expand...
Actually, while accurate, it's not as simple as that.

The main fuel-screw moves a fulcrum which, has the pivot-point of a second fulcrum, that is influenced by the throttle's governor-spring. In that second fulcrum is a third fulcrums pivot-point that's influenced by the mechanical governor.

It's that third fulcrum that's actually directly, and exclusively connected to the collar.

One could safely say the main fuel-screw's fulcrum, puts the collar in the ballpark in terms of initially positioning the collar.


Like Mark mentions, I too set my idle by way of my main fuel-screw.
 
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