Dyno Question

[krtillison]

I've got a chance to dyno my truck this week at school. The teahcer has never dynoed a diesel. I need to know where the engine's tach signal comes from, and how this is read by the dyno. Any help would be awesome since I have no experience with a chassis dyno.

[cleatus12r]

Optical pickup will be your best option if there's no way to calibrate the dyno roller speed to the engine RPM.

[Power Hungry]

On a Super Duty, you can also use the inductive coil pickup on one of the injector lines. The passenger side harness was usually the easiest to access. Look for any of the BROWN wires with a colored stripe. (See attached image) These are the injector power leads. The black ones on the end are the grounds. The big lead in the middle is the glow plug power. You may need to strip back a little of the loom and tape to get enough access to the leads, but this usually works quite well.

The OBS trucks are not too different, but they usually have a lower voltage output and often will not generate enough EMF for the inductive pickup to register a valid signal. You can try it, though.

Good luck! :D

[krtillison]

Thanks alot Bill and Cody. This was extremely helpful. Truck should be on the rollers tomorrow!

[krtillison]

‪Kyle's Powerstroke on the chasis dyno 3‬‏ - YouTube (http://www.youtube.com/watch?v=oPm3_Ad8v8s)

So here is one of the 5 pulls. As it says 275 hp 515tq with evolution on 100 hp setting. Is this about what everyone would expect to be, higher, or lower? Any input would be great. Thanks. Also we tried using the inductive clamp around the wire but RPM would not stay steady. It would read around 700 then jump to 2000. Any thoughts?
P.S. Outside temp was 95, humidity was 43%, elevation 974 feet

[Power Hungry]

DynoJets are really twitchy with the inductive pickups. Some trucks have no problem, others get all jittery like you were seeing. Our DynoJet at Edge was the same way. Not much you can do except switch to an optical sensor and run off the crank.

As for the run itself, 275/515 is a little lower than what I'd expect to see, but given the heat and humidity it's not all that bad. However, looking at the run itself (basically, the length of time the run took) I'd venture to say that the engine wasn't loaded enough to make peak boost and that probably cost you some horsepower. You were definitely making fuel but the turbo didn't seem to catch up. When we'd run on DynoJets, we would brake a little bit to give the turbo a chance to spool up and then let off the brake and start the run. This would give is the best numbers. Also, what gear was the run done in? The reason I ask is that the torque numbers seem a bit low for the HP. He should have been in 4th on a 5 speed or 5th on a 6 Speed. This gives a 1:1 ratio through the trans and helps reduce parasitic losses.

BTW - What was the HP on the stock setting?

Thanks.

[krtillison]

The truck was in 4th gear and on stock it made 222/403. Thanks for the feedback too, and for answering my questions.

[krtillison]

...and by 4th i guess it's technically 5th even though it's 4th on the knob. Im just bouncing ideas off of you, but I when i went to the track with it the attitude monitor would back down 20%. It never tried to back me down on the dyno, so I would think that would confirm your suspicions about the dyno not loading the engine fully.

[Power Hungry]

What did you happen to run at the track?

[krtillison]

16.7@87 mph

[Power Hungry]

At 87 MPH in a 7000 pound truck (approximate, incl. driver) you would be making an estimated 313 HP, which is about what I'd expect to see from a decent running Super Duty.

[krtillison]

Just to be sure, 313 at the wheels or flywheel?

[Power Hungry]

That would be at the wheels. Figuring an average 20% loss through the drivetrain, that would put you at around 390 HP at the flywheel.