ScanGauge horse power reading

Per the ScanGauge manual:

Displays the calculated Horsepower your vehicle is currently
making. This value can be adjusted for accuracy through the
Advanced Setup parameters (see page 17).

Page 17 says:
Set a Horsepower Adjustment
ScanGauge reports Horsepower (HP) as a built-in digital
gauge. This parameter allows you to make adjustments
to the HP reading ScanGauge reports.

Basically the way I read this is that the user has to adjust the Scangauge to read the HP that the owner expects from his vehicle. If you are at throttle that you feels is maximum HP, just set your Scangauge to read that HP. From then on, it should de-rate the HP as it gathers different readings from different sensors. This is in the advanced set-up portion of the owner's manual.

Tuners calculate this all the time so they know what size injectors to use and how much flow. The only inaccuracy comes from predicting the efficiency of the engine at different RPM. Since you know the fuel flow, you know how much power you are putting in.

Don't get too presumptuous about what can and what can not be calculated. I have a desktop Dyno software program to predict HP and Torque based on engine specs. Ran the numbers and it was dead on to what Edelbrock published on their dyno tests. (within 5 HP at any RPM). I then added in the modifications that I've put on and did acceleration tests. Those tests came within 20 HP of predicted HP.

While this in all very interesting, it really doesn't tell you anything useful, as it assumes the engine is in good operating condition. If the engine is having problems, the accuracy goes out the window, as it is based on known facts about how engines operate. HP reading won't tell you if there is something wrong, although if you loose power and the HP numbers are skyrocketing, you know you ran out of fuel.

As others mentioned, I'm fairly certain that all these monitors are just displaying 'guess-timates' for horsepower. I don't have a Scanguage so I don't know exactly how they are configured but I know that some similar devices make you enter things like vehicle weight and gearing and then provide horsepower estimates based on acceleration.

Another thing you often see is HP-at-the-crankshaft and HP-at-wheel. Depending on how they are coming up with the value, it's possible that it reflects the 'at-the-wheel' value which is always lower than the 'at-the-crank' value.

I believe the scan-gauge is simply providing the information given to it by the ECM on the engine. I have a CAT TECH program that was used for data reading by technicians on the cat engines. It does provide a computed HP reading. I don't think that it is accurate at all but does provide some number for a base line to measure decrease or increase in performance. The numbers on the scan-gauge appear to be the same that shows on the CAT TECH so it is not a scan-gauge computed number but rather from the ECM. I think you can adjust the reading on the scan-gauge to more accurately reflect the real HP output of the engine.

This is the OP.

I don't remember there being a place to program the weight in, but when I get to the MH, I'll read the manual again.

As for fuel milage, I only can wish I was getting the MPG that it was reporting.

Bill

I run the Silverleaf VMSpc program. It also gives HP and Torque readings. They're a guesstimate, but I have to believe that electronics now days can get pretty close. The Silverleaf program takes some fine tuning to get the fuel mileage and mpg information accurate, thus making the other readings more accurate.

On two occasions pulling grades in Oregon, I saw the Silverleaf show that I hit 400 HP and 1186 torque momentarily. My coach is rated at 400 HP and 1200 pounds torque. Since these are engine readings and not rear wheel, I suspect they're fairly accurate.

Side Note: I recently added the DIGI-CRTV computer chip and have only driven the coach three times on short jaunts. I got on it a couple of times and the HP went to 403-406 easily. It isn't the promised HP from the chip, but I was surprised t see it jump over 400HP. We'll take it out tomorrow for the Memorial weekend and have one large hill climb. I'm anxious to see what it does.

Do you program into the SG how much the rig weighs? If so then it could use that figure and input from an accelerometer or speed input from the vehicles computer to mathematically calculate HP - but it would still be a rough estimate.

You would have to be full-throttle at 2400 RPM for max horsepower with a 350 HP C7 CAT.

Torque and power curves on this spec sheet.

I have no idea how the Scan Gauge would calculate HP, since the engine doesn't have a way to measure BMEP or torque. Maybe calculating it from fuel consumption?

That's for the RV version of the C7, contemporary truck models requiring 100% duty cycles were rated 210 to 300 HP, most at the lower ratings also having lower torque ratings with much flatter curves.

And that is a significant part of your answer. HP is torque X RPM/52??. Anyway, RPM is a significant factor in achieving HP and you will not hit peak HP unless you are at peak RPM. Just to get some review, look at every HP graph, it is typically a fairly linear line that rises with RPM, until the torque drops off as the engine starves for air. Accuracy is going to be based on how efficient your engine is. The assumption is that you burn X amount of fuel, it will result in X amount of power output. The lack of efficiency is a result of if all the fuel burn all at once, or if some of it burns too late to do any good. It is somewhat predictable, so I would expect the scan gauge to be somewhat accurate.

This is the OP.

I don't remember what the RPMs were when I was looking at the HP reading. I'll get the MH out of storage in a couple of days, I'll take a look at the RPMs them.

Bill