Dyno calibration

[rodneym]

I have a question:

In my business, we are ISO certified, GMP, BQM and a myriad of others quality standards. Even our steel rules are 'calibrated' every 6 mos.

This is not meant to be provocative in a negative way. Just wondering...

Are engine dynos officially certified by a governing body of any sorts?

rodneym

[ERA Chas]

Not to my knowledge. But dyno owners can have them re-calibrated. I've seen DTS do that annually.

[RestoCreations]

And a lot of dynos can be adjusted to make the numbers more favorable.

[ERA Chas]

Originally Posted by RestoCreations

And a lot of dynos can be adjusted to make the numbers more favorable.

That's known by disreputable operators. The legitimate differences depend on how much load is dialed into the water brake.

[Barry_R]

Dynos in the OEM universe are calibrated to an SAE defined set of specifications.

Dynos in the performance aftermarket are calibrated to the integrity of the owner.

Both are subject to legitimate variances due to outside environmental issues - temperature, humidity etc. These issues are addressed with software derived correction factors which are deemed reasonable but still not perfect.

[RestoCreations]

When i see someone post up monstrous numbers from a Naturally Aspirated Small Block, i usually take it with a grain of salt.
There are two specific shops in my area that are known for fudging the numbers to make the clients think they are getting more bang for their buck.

[Danr55]

Well, the proof is always where the rubber meets the road. Numbers on paper don't stand for much outside of discussion.

[redmt]

First liar never has a chance, and you always have to look around before you tell the story. The guy that knows the truth may be listening.

[Keithc8]

Dyno's can be calibrated and should be checked if you want to keep the machine accurate. You need it to be accurate if you are building race engine to make sure you are getting repeatable numbers. When you are looking for 5 to 10 HP on an engine that is making 800 to 1200 HP already this is very important.
This is done by hanging the same weight on the strain gauge and checking the readings. You also need to make sure that all of your sensors are reading right from temp to borrometer.
Like I have said here several times my Super Stock and Stock NHRA guys know how fast their car should go down to the hundreth and you can not blow bogus numbers up their but. With all of this said you can jack with some things to change the numbers but that does not tell you anything in the end. The dyno is a tool to be used like the flow bench and any fudging will show up at the track.

Good luck, Keith Craft

[rodneym]

Thanks to Barry and Keith for their responses.

[blykins]

Originally Posted by redmt

First liar never has a chance, and you always have to look around before you tell the story. The guy that knows the truth may be listening.

Sometimes that's not the case....

The first liar sometimes sets the standards.

Like Keith said, guys that drive their cars to the grocery store and back don't know if their engine only has 400hp when it's supposed to dyno 600.

The guys that run the race tracks definitely know...

I'd rather have a conservative dyno any day.

[Barry_R]

Every dyno owner I have ever met says his is "tight".
Same for flow benches.

You will for sure know if you have a 200 horsepower liar. The 20 horsepower liar is harder to find.

[blykins]

I tend to hear that as well. "My dyno is pretty conservative..."

I know for a fact that there are two dynos within 50 miles of me that read 100hp different from each other.

Dyno numbers sell engines, plain and simple. The majority of engine customers don't know if their engine is 500 hp or 550hp....and if they have never been behind the wheel of something stout, then they may not know the difference between 400 and 500.

It should be pretty simple to spot if you look at the components. A guy brought me a 482ci BBC on Saturday evening that had spun a couple of rod bearings. It had a GM Performance crank, factory truck rods, Procomp heads, and a solid roller cam. The builder told him that it was a 750hp engine.

[vector1]

i think it would be difficult for someone selling engines, the fudge factor could be appetizing.

used to shoot trap and clubs although supposed to set all their targets to the same distance would fudge to keep the scores up, and the shooters knew where to go. some of that has probably been aleviated with the use of radar guns.

[RestoCreations]

Originally Posted by vector1

i think it would be difficult for someone selling engines, the fudge factor could be appetizing.

used to shoot trap and clubs although supposed to set all their targets to the same distance would fudge to keep the scores up, and the shooters knew where to go. some of that has probably been aleviated with the use of radar guns.

I dont know, there are a lot of people out there that are a bit clueless when it comes to engines and are desperate for a number to brag about. I was one of those people about a decade ago. I had a 327 SBC built by a local shop and they gave me a dyno sheet that said it put out 360hp at the rear wheels. This was a stock motor, with stock iron heads, 600cfm holley, stock crappy flowing aluminum intake, etc. I believed them and bragged to everyone about the motor until i was corrected by educating myself. Not to get further off topic, but my favorite dyno sessions to watch are the ones with stock sixties muscle cars. The owners tend to think that the factory flywheel hp ratings that were done 40 plus years ago with zero accessories attached and long tube headers installed are accurate. Then when their small block rated at almost 400hp from the factory puts out a 160-200 at the wheels they are scratching their heads.

[undy]

and another thing....


Most builders have optimal flowing headers, very free flowing air cleaner (or none at all) and zip point squat accessories when it's on the engine dyno. Now take that same engine, add the average Cobra side pipes, 1 7/8" tall air cleaner and the remaining accessories and your legit 600 hp engine now is 525 HP, engine builder's integrety still intact (somewhat).

The OEMs ( and a few such as Katech, etc) are really the only people who dyno an engine "as installed". This is not a zinger to the engine builders here as there's an infinate amont of installation variables that just can't be accouted for in every dyno instance. That's why a bone stock Z06 typically chassis dynos around 450 RWHP, providing a nominal 11.5% drivetrain power loos and the average "600" HP Cobra loses 20%+ on the chassis dyno.

[jaybnve]

The torque measuring sensor on a dyno is just a test instrument, and it needs to be calibrated like any other test instrument. It will have a perfect value +/- some tolerance for acceptable results. Since it is measuring torque, all you need to calibrate it is a lever to act against the sensor, and a known weight to hang on the lever. Length of lever in feet X weight in pounds will give you the correct torque in lb-ft, and this can be compared to what the torque sensor is reading on the dyno's display to determine if it is accurately calibrated.

On my Superflow 901, Superflow provides a bar that bolts onto the absorber and acts against the torque sensor. The bar has a notch exactly three feet from the center of the absorber where you can hang additional weight. The weight of the bar itself should cause the torque reading on the dyno console to be 17.5 lb-ft of torque. To calibrate my dyno, I built a steel frame that hangs on the notch in the bar, and that can hold weights from a Sears barbell set. I took the steel frame and weights to a certified scale, and weighed them all to an accuracy of 0.05 pounds. Now when I hang the steel frame and the weights on the bar, I know exactly how much weight is on there, and can multiply this weight by 3 feet to get lb-ft of torque on the torque sensor. Over the last five years I've regularly calibrated my dyno, and it is typically accurate to within 0.5% of the total torque on the torque sensor.

I think that intentionally mis-calibrated dynos are much more common than a lot of people realize. I've seen plenty of dyno data sheets where the numbers just don't pass the smell test. For example, one shop operated by a VERY well respected NHRA racer gave a friend of mine obviously bogus dyno results. Anyone familiar with dyno operation could tell, because the barometer reading on the dyno printout indicated that the shop was located at around 5500 feet of altitude, when in fact it was probably only at 1000 feet or so. Changing the barometer reading built into the dyno is only one way to fudge the numbers; there are other hardware and software tricks that can be easily employed to make the dyno read however you want.

In order to protect yourself when taking your engine to a dyno, you can always ask the operator to calibrate it for you while you watch. This will take about 15 minutes, and will involve having the operator attach the bar and his calibration weights to the torque sensor, to show you that the reading is accurate. Any reputable dyno operator will do this, especially since you are paying for his time to do it. Of course, if his calibration weights are labeled incorrectly you could still get snookered on this, but it is more likely that the dyno operator will give you some lame excuse why you should trust him, and he doesn't need to perform the calibration. Buyer beware at that point. You can also do a quick check of the dyno's barometer reading to see if it is accurate, along with the other weather conditions monitored by the dyno. These are usually available from the printout, and should be a good match to the day's ambient weather conditions.

There's more detail to this, but none of it is particularly complicated, and anyone should be able to go to the dyno and be confident in the accuracy of the results by checking a few simple things. My book has all this information in excruciating detail, for anyone who is interested. FWIW, when I hear a dyno operator say his dyno is conservative, I consider it a big red flag. What you want is a dyno that is accurate. Then you've got useful data that can be used for comparison purposes.

Jay Brown
FE Power - Dedicated to Building and Racing the Ford FE Engine, 390, 427, 428, SOHC