Torque screw

[Goofyexponent]

I decided I would try and play with my torque screw this morning. I also set my pump up another .5 of a flat as I had NO smoke, and I am hooking my pyro up this weekend.

I turned the screw all the way in, and it severly limited the fuel at lower RPMs (1800 and lower) but once it climbed to about 2000 RPM it was like someone turned a switch on. The truck took off like it was kicked in the ass for peeping in the girls locker room. I know the screw controls the fuel curve at a lower RPM to limit smoke.

The screw must have to be retracted to gain fuel at lower RPM's. I didn't wanna do any damage, so I returned the screw to where I found it and walked away.

How does this so called torque screw work? Is it supposed to deliver more fuel when retracted or threaded all the way in?

 

[f-two-fiddy]

It's NOT a torque screw. It's a low rpm fuel limit trim.

FWIW it' totally defeated by a certain RPM. IIRC 1100 RPM

I've experimented with it, and found no useful gains.

Why inject extra fuel down low? The engine can't burn it. It raises low rpm EGT's. So then when the boost finally comes on, Your EGT's are all ready elevated.

Your fighting a loosing battle by injecting to much fuel at low RPM's.

 

[Goofyexponent]

I didn't think it would give me anything, I am just playing with things like that, carefully of course, just to see what will happen.

the more I play with things, the more I would love to have that kit that converts a 7.3 PSD into a mechanically injected ingine

 

[Ironman03R]

You'll get more smoke. If you have a turbo the incresed fuel will help spool the turbo quicker. I backed mine out 3 turns but its been so long ago that I dont remember how much of a difference it made other than more smoke.

 

[Goofyexponent]

soyou have to back it out to make more fuel...good to know. I'll adjust mine to where I get maximum fuel with minimal smoke. The pyro will tell more this weekend.

Mostly what I wanted was the visual effect. We are going to "Sport Compact Weekend" this summer, and I want to enter the burnout competition....that extra black will look good while sitting still. I jsut don't wanna be one of those guys running around with a cloud chasing them all the time.

 

[Sycostang67]

This is good to know, I may be playing with my torque screw..if I have one, still haven't looked yet.

 

[Goofyexponent]

I played with it a little at the plant before I came home. I wouldn't take the truck on the highway at all with the difference in fuel input at lower RPM's.

I flattened it once to see what it would do and I litterally blacked out the right lane, smothered a couple of cars in a cloud of light stopping black smoke. And this was from a standing start. I tell ya, they ain't my new friends. I was NOT expecting this outcome at all! It did seem to give it a touch more pickup, but not anything significant.

It's a quick thing to adjust, and mine is turned back to factory (or as close as I could get to factory by memory only) I will be turning it up for the burnout competition this summer, but I would be a little scared to run it like this all the time....I don't want to ruin my engine!

 

[Sycostang67]

I'm getting more air at speed and want to to add another flat to the IP but I want to cut down the smoke I will get in the low gears. Just trying to balance everything out. I was gonna ask how the torque screw worked in my other thread, but you beat me to it.

 

[Goofyexponent]

If you thread it in, it will reduce fuel at lower RPM.

I want to turbo my truck now that I know how the delivery settings work on these pumps...I just have to be careful not to blow her up!

 

[82F100SWB]

The "torque screw" is there for exactly that purpose, so that you can add more fuel up high without turning the bottom end into a ridiculous smoke show.
Backing it out to help the bottom end isn't going to do all that much, I have found with my Cummins that there is a point of diminishing returns, much more than a light haze at wot at low rpm/boost actually softens turbo response and of course makes EGT's rise way too fast.

 

[LCAM-01XA]

Picture of said screw anyone? I don't recall seeing it on my IP...

 

[high psi]

Let me try and put some of this confusion to rest. The torque screw (which is only on some of the later pumps, thinking '93 and up but not positive) is there to create a torque rise effect. It basically starts cutting fuel slightly at the high end so that when you're cruising at max fuel and start getting a load on the truck (a hill for example), which in turn lowers the rpm you'll get into a higher fuel delivery to help with the extra load.

For example lets say the max loaded rpm is 3300, and the high idle unloaded is 3450 or so. Say your cruising with a decent load up a slight incline at full throttle around 3200rpm. The hill steepens and it starts to pull the engine down, 3150, 3100, 3050 keeps dropping rpm's, but by this point the fuel delivery is starting to climb towards the max delivery point at 3000. You'll notice as the rpm is dropping the smoke is increasing, that's because of the increase in fuel delivery. Obviously if the hill stays at the new incline or continues to steepen the rpm's will continue to drop, but if it's only for a short time or a slight increase that torque rise effect should help get the rpm's back up with the additional fuel and keep you happily trucking along. Possibly without ever even noticing the change occuring.

in the above example if you didn't have that torque rise, in theory the rpm's would continue to drop until the rpm's leveled out to a balance point where the fuel delivery could keep up with the new inclination of the road. In a perfect world this would be at a lower speed then the truck without the torque screw. However, in the real world most of us have tinkered with our pumps to some extent and some of this theory no longer applies.

All you really do when you back out the torque screw is get rid of the restriction to delivery above the preset torque rise point. I used examples at max rpm, but it comes into play throughout the rpm range depending on where the throttle is positioned. So essentially you are gaining a little more max fuel at the expense of having to push the pedal down a bit when higher load is encountered, rather then letting the pump do the work for you.

Sorry, started out trying to keep this simple...don't think I succeeded

 

[franklin2]

So the pump is tuned for a certain amount of fuel for a certain engine rpm and throttle position? And if the throttle position stays the same but the rpms start decreasing, it starts adding more fuel? The farther apart the rpms get away from the throttle position, the more fuel it will add? And all pumps work this way, but the later pumps have this feature adjustable?

Sort of like a power valve on a carb?

 

[high psi]

So the pump is tuned for a certain amount of fuel for a certain engine rpm and throttle position? And if the throttle position stays the same but the rpms start decreasing, it starts adding more fuel? The farther apart the rpms get away from the throttle position, the more fuel it will add? And all pumps work this way, but the later pumps have this feature adjustable?

Sort of like a power valve on a carb?

Actually on the non torque screw pumps you don't get the additional fuel as rpm decreases, only with the torque screw and only to a point. Once you've dropped a few hundred rpm you've limited out and won't gain any more. I'm oversimplifying it as the fuel curve isn't exactly linear, but as far as it concerns the torque screw that's how it works.

 

[f-two-fiddy]

I'm not trying to argue.

But, From everything I've read about the so called 'Torque Screw' (which it's NOT) is that is has no effect above 1100 RPM or so. It's simply there for emissions. It was added for the 93 IDIT in order for the truck to pass the 'Snap Test'

The Turbo will not spool/boost enough to burn the added fuel at low RPM's. It's there to trim the lower RPM fuel, and still allow max delivery at higher RPM.

The theory You've described goes against everything I've read.

Go Here and read the OPTIONS list at the bottom of the page. http://www.stanadyne.com/view.php?id=40

"•Low Speed Fuel Limiter (smoke and emissions reduction) "

The biggest problem with these rigs is they won't build boost until 1500 RPM's+
So there's no sense in trying to inject more fuel before the boost comes up.

Here's a common situation with the IDIT. Loaded with a good load You come to a hill. Your starting to loose some speed, so You hit the throttle a little. As the truck slows, RPM's drop. Once You get to 1300-1400 RPM's the coal is rolling and EGT's are climbing. Then it's time to downshift. (You've gotta be able to BURN that fuel. If You keep pouring fuel down 'er, She just keeps getting hotter)
Now that You've down shifted, the EGT's are still up there (from the over fueling at low RPM) The EGT's will come down, once the engine can BURN all of the fuel.

My theory is: Why fight the elevated EGT's, by over fueling at low RPM's?