I had, for the first time, a chassis dyno test done on my 400. I can't scan in the document, so here are a few point that give the general trend from the printout I was furnished:

2800 RPM 270 lbs/220 HP
3600 RPM 295 lbs/200 HP
4400 RPM 310 lbs/160 HP

The torque line was starting to flatten but was still tending upward at 4400. HP was supposedly max 222 at around 2800 and went nowhere but down.
Why is HP falling when torque and RPM are going up? The HP number seems crazy to me, this truck pulls, until it runs out of gas on the 600 cfm or valve floats (who, me?).
This was a "slam bam" dyno event. Mostly a bunch of Power-stroke dielsels. I was the only gasser there. Most vehicles were on the dyno about 10 min tops. Also, the operator, ran the truck up through the gears and did the test in 3rd. Does this make any sense, wouldn't it make sense to stick it in first and leave it there?
My print-out only shows 2800 RPM thru 4400 RPM.
I mainly wanted this test for the A/F data from idle to WOT, obviously I didn't get it and didn't know enough to question it right then. My truck was unhooked before I even got the paper.
I guess what I am asking does any of this sound believable or did I get ripped off?

The particulars on this engine are as follows:

600 Edlebrock, performer intake, 2V heads fitted with 4V S/S valves, moderate porting, long tube headers into 2.25 duals. Stock pistons, .030 over. 351M block w/ 400 crank. Crane "Energizer" (266 advertised/210 @ .050/.508 lift) Stock ign w/ 100:1 coil. About 6K on build. C6 and a 3.00(pretty sure) diff. Runs good on regular gas, nice throttle response.

Thanks in advance for your time on this. I need some advice before I write a hasty letter to this shop that will remain unnamed for now.

 

The formula for calculating horsepower is very straightforward:

hp = torque * rpm / 5252

So, assuming the torque and rpm numbers that you gave are correct (maybe a big assumption?), the hp numbers should be:

2800 = 144hp
3600 = 202hp
4400 = 260hp

If you figure the C6/drivetrain is sucking about 25% off the top, your net flywheel numbers are something like this:

2800 = 192hp
3600 = 269hp
4400 = 346hp

That's not too shabby for a 400 with a single-pattern cam.

If the dyno guys were taking just one run each on a bunch of trucks for a club event, they were probably trying to make the most expedient, snap decisions about how to get the best one-time pull on each truck. With an automatic transmission, third gear is the most efficient, and it produces the least parasitic drag with the most direct torque (what they really measure). First gear produces much more parasitic drag, and torque multiplication through the converter, so it's nearly impossible to get any real numbers.

 

The numbers given are a direct transcription of the print out, whether they are correct or not is the $64 question. There were two pulls registered and they were extremely coincident. I guess what I am getting at is that it seems to me that I can believe the torque graph, but that the HP plot is nonsense? From what you are confirming for me, the HP plot is a joke and this makes me suspect of the entire test. What I was expecting to see were three plots over RPM from idle to say 5K for torque, HP, and A/F. Is this a reasonable expectation? (For $60.00 American money, paid in advance. And, I did by the way, express that this data was why I was there. The Hp and Torque don't really concern me much as I allready know the truck in quick, I was much more interested in getting data to calibrate the carb properly.) Thanks, and BTW, I read a writeup you did that is posted on the net and found it to be first rate.

 

Some general guestimates. See,
http://www.amotion.com/fcm.html#10

MILD STREET PERFORMANCE (1400 rpm to 4400 rpm, max. HP @ 5400 rpm)
Fair idle, moderate fuel economy, improved mid-range performance
and enough torque for medium/heavy towing. 4 barrel carb recommended.
ENGINE CAM RANGE* CARB CFM RANGE HORSEPOWER
351 C 2V 20400 to 21200 581 to 719 cfm Max. 316 HP
351 C 4V 20300 to 21100 581 to 719 cfm Max. 316 HP
351 M 20400 to 21200 581 to 719 cfm Max. 316 HP
400 20800 to 21600 662 to 819 cfm Max. 360 HP
400 w/4V heads 20700 to 21500 662 to 819 cfm Max. 360 HP
*The cam range refers to the 2nd half of
the Accelerated Motion part number.
Compression: Gasoline 8.5:1 to 10.0:1, Propane 10.0:1 to 11.5:1
Exhaust: Stock dual exhaust or small tube headers
Gear Ratio: 3.1:1 to 4.1:1
Idle: 900 rpm or less, slight lope
Ignition: Recurved distributor and electronic ignition

---------------------------------------------------------------------------------

What is Horsepower? Part 1: The Equation

Contributed By: Bucky EdwardsEverywhere you turn, people and manufacturers are making horsepower claims for their cars or products. Unfortunately, most people do not really understand the theory and history behind the horsepower rating system. In this short article, I would like to explain a little of the history, and use analogies to help the reader to better visualize the concepts. Understanding how the formula for horsepower works may help you sort through the jungle of performance information out there. The math behind calculating horsepower is extremely simple, but let’s start with a brief history.
In the middle 1800’s, America and the rest of the world for that matter, was going through a period called the Industrial Revolution. Because of the growing use of the steam engine, industry no longer needed to be located next to a river for power and horses were no longer the only means for transporting goods and people. However, no one had a "ruler" for measuring the power of a steam engine or any power-producing device. If you needed a power supply to run your sugar cane press, what size steam engine would you need? Experience may tell you that a team of 4 horses would probably drive the press, but what size steam engine would suffice?

Without doubt, you have heard of a unit of electrical power called a Watt. Named after James Watt, he also defined a system for rating power producing devices.
Watt started with the definition of WORK, which is FORCE multiplied by DISTANCE. If you pushed a 100-pound box a distance of 1 foot, you have done 100 pound-feet of work. If you pick up that same box 1 foot off the floor, you have done the same amount of work. What James Watt really wanted to define though, was the POWER that an engine could produce. POWER is defined as WORK / TIME. If it took you one minute to push that 100 pound box one foot then the power you expended was 100 pound feet per minute. If it took you two minutes then you did 50 pound-feet per minute of work. Get it?
In our example of the sugar cane press, you may have come to the conclusion that the obvious answer is a four horsepower engine. This must have been obvious to James Watt also; because what he did was to try and define how much power a horse could produce. We don’t know if the horse he had in mind was a Shetland pony or a mighty Clydesdale, but nevertheless, the number he came up with for one HORSEPOWER is 33000 pound-feet per minute or 550 pound-feet per second. So what James Watt figured was that a typical horse could pull or lift 550 pounds one foot in one second.
We now have a definition for horsepower. Just like we know that 12 inches equals one foot, we know that 33000 pound-feet per minute equals one horsepower. Horsepower would be hard to measure on an engine directly, so we must use a little math to find some quantity that we can measure and convert it to horsepower. That quantity is TORQUE. TORQUE is defined as a twisting about a point caused by a force on a lever arm. For example, a one-pound weight at the end of a 1-foot long wrench applies a torque of 1 foot-pound on a bolt or nut. Note that WORK and TORQUE have the same units and foot-pound equals pound-foot.

Now, let’s imagine that you get an exercise bicycle. You know, one of those with the big wheel in front and a strap running around the outside of that wheel that can be tightened to make it harder to pedal. Now let’s say that you adjust the strap tension so that the wheel is difficult to turn. Now get a wrench and a spring scale. Attach one end of the wrench to the center of the bicycle wheel and attach the scale to the other end of the wrench. Suppose that it takes a 50-pound pull at the end of the wrench to turn the wheel. If the wrench is one foot long, it requires 50 foot-pounds of torque. Now start turning the wheel with the wrench as fast as you can. Suppose you can turn the wheel 55 times in one minute. (I’ll bet you can’t!) How much horsepower are you producing?
This is actually pretty easy. To figure horsepower, we need to know work per unit time. Earlier, we established work as:
Work=Force x Distanceand Distance for our example = 2 x Pi x wrench length
Since we are moving in a circle, 2xPi x radius (wrench length) is the distance around a circle. (Remember that Pi = about 3.1416) We have already pointed out that power is
Power=Work/Time So our equation looks like this:
2 x Pi x wrench length x Force x rpm= power we expended.
Since this will give us foot-pound per minute, we can divide the answer by 33000 foot-pounds per minute and get the horsepower. But before we start plugging in numbers, note that
wrench length x Force = Torque.
Replacing that into the equation has:
2xPi x Torque x rpm/ 33000= horsepower. (Pi= 3.1416)
Simplifying the equation yields:
Torque x rpm/5252= HorsepowerThis equation is the one that most people recognize. Plugging in the numbers from our exercise bicycle example:
Torque = 50 foot-pounds
Rpm = 55 rev/minute
50x55/5252=0.524 hp!!!
To turn that bicycle wheel 55 times in one minute, you produced over 1/2 horsepower. Most trained athletes can only produce a little more than 1/4 horsepower for any extended length of time. So my example might not have been the most realistic, but you get the picture.
A dynamometer can only measure torque and rpm, but can use this formula to calculate horsepower. Also note, that by definition, at 5252 rpm horsepower equals torque. So be very skeptical of someone’s horsepower and torque chart if the curves don’t cross at or very close to 5252 rpm.

In the next article, we will play around with this formula some more and use it to compare different engines. The results might surprise you! F/M

HOW MUCH HORSEPOWER DO I NEED?
HORSEPOWER TO ET CONVERSION CHART
The following chart shows how much total engine horsepower (i.e. "at the flyhweel") is need to run a particular ET at a given weight. Keep in mind this is under optimal conditions (traction, shifting, etc.) and assumes that your are utilizing every bit of power.

In reality very few cars run 100% of their optimum. Wheelspin, slow shifting, clutch slippage, and other factors "bleed off" the usable horsepower. Figure on adding as much as 10% to the power numbers below (or add a few tenths to the ET) to get a real world estimate.
ET (seconds) VEHICLE WEIGHT *(pounds)
2600 2800 3000 3200 3400 3600 3800 4000
15.0 152 164 176 187 199 211 223 234
14.5 169 182 194 207 220 233 246 259
14.0 187 202 216 230 245 259 274 288
13.5 209 225 241 257 273 289 305 321
13.0 234 252 270 288 306 324 342 360
12.5 263 283 304 324 344 364 385 405
12.0 297 320 343 366 389 412 435 458
11.5 338 364 390 416 442 468 494 520
11.0 386 416 445 475 505 535 564 594
10.5 444 478 512 546 580 615 649 683
10.0 514 553 593 632 672 712 751 791
9.5 599 645 692 738 784 830 876 922
9.0 705 759 813 868 922 976 1,030 1,084
8.5 837 901 965 1,030 1,094 1,159 1,223 1,287
8.0 1,004 1,081 1,158 1,235 1,312 1,390 1,467 1,544
*fully loaded with driver, fuel, etc. © 2002 CAPublishing


Calculators: www.fordmuscle.com

· Compression Calculator
http://www.fordmuscle.com/calculator/compression.shtml
· Horsepower Calculator
http://www.fordmuscle.com/calculator/horsepower.shtml
· Engine RPM Calculator
http://www.fordmuscle.com/calculator/rpm.shtml

 

Thanks for the responses, but the question remains... what kind of profile does one normally get when one pays for a dyno run? A limited band or a full band? Could some folks who have been through this tell me how it worked for them?

(I am satisfied that the torque curve is reasonable, and, therefore, accurate. So this is no longer an issue.)

 

I've worked with a few dyno guys, and I don't know of any who would even hook you up for less than $400.

For $60, I'd say you got your money's worth. Maybe the guys organizing the event mislead you about what to expect, or maybe they really didn't know what to expect themselves.

The rpm range that you can test depends on the vehicle and the dyno setup. If the guys who were testing you were set up for diesels that maxed out at 3000 rpm with 500+ lb ft of torque, their system might not have been easily adaptable to your vehicle.

When you pay (a lot more) for your own dyno time, part of what you get is more individual attention, including the time spent adjusting and recalibrating the dyno equipment for your specific vehicle parameters, and then tuning and re-tuning your vehicle to get its optimum performance.

 

Thanks, that's exactly what I needed to know. I will chalk it up to experience.

 

here in jax its about 85-100 an hour including tuning. so a dyno run for 60 is usually a club pull, and has limited tuning at best.

 

My $60.00 got me about 12 min. with no tuning or even a "Thanks, glad you stopped by." I am feeling fairly put out by the whole experience. I would have gladly paid another $40.00 to get useful info. as it was, I might have well taken the $60.00 and thrown it out the window. Heck, I didn't even get a 'reach-around".

 

well id say save up your money and schedule some time on the dyno for tuning