Is your dyno lying?
 

Since the topic comes up often, I thought others might gain something from an article I read in Car and Driver.

http://www.caranddriver.com/article.asp?section_id=4&article_id=8020&page_numb er=1

If you can't sense the difference in the horsepower when operating the car (under your actual driving conditions and operating habits) what's the point of doing a dyno run? The point of bragging rights about flywheel horsepower is lost on me; what reaches the pavement is what matters. The story's point about losing 10% of the car's horsepower because the car wasn't getting cooling air equivalent to going 150 mph (and the engine's computer was protecting the engine) was interesting but almost irrelevant to any real driving. The concern of the tuning shop about the missing 40 to 50 hp seemed misplaced unless they were worried about justifing the costs of their upgrades. I guess if you put all that aftermarket stuff on and can't do better than the manufacturer's oem output one looks pretty foolish. Jim

The discussion of HP is almost always rife with inaccuracies and folklore. Two cars may have the same HP, but may have significantly different performance:

- differences in weight
- differences in where that HP actually exists (high band / low band)
- differences in transmission gearing
- losses due to aerodynamics (OFTEN overlooked)
- losses due to drivetrain
- differences in driver's ability
- temperature / altitude differences

The list goes on and on. One thing is certain - this will be debated forever...

-Wayne

It will NOT :)! Seriously, thanks for the link...interesting article.

Yes, It's getting ridiculous. I see people posting #s from home built specials that are missing half the factory parts(Important things like valves, cams, pistons etc) and claiming significantly more than the factory ever saw They are in a dream world and unfortunately many are gullible enough to believe.

A dyno that we have access to is not a precision instrument. Never will be, believe in the tooth fairy Santa Claus, Dyno #S or whatever you want. It's all the same.;) and it' still a free country

JMPO;)

Good article,

Different day, different ambients=different HP #'s

3 dyno pulls performed with no changes to any setting or parameters will give you 3 different HP numbers...

BTDT

Chassis dynos are still VERY useful tools

Usefull, yes, gospel NO

0 - 100 timed runs are as usefull but more likely to involve official notice:(

Lap times are best

One thing to remember

An engine produces different HP values off the dyno also.....

Cold damp days (dense air) turbos and well all other engines make more power...Lap times prove this

We use the dyno to run the car "against" something. Dial in load and see how the advance/egt/o2 etc react... listen with a chassis ear for knock and dial advance till we reach the threshold..


I have base maps that can get most EMS up and running Motec, Haltech, Tec etc....the dyno refines it even more, then real world and fine tuning further...

Im sure an engine on a test stand will make different outputs when ambients are differnt.... havent done a hands on yet though

Keep in mind Porsche states minimum horse power numbers. Most other car makers state average. Anybody remember a couple years ago the mustangs, Was it the GT, or the Cobra, not getting the claimed 325hp. This article reminded me of an article in a national mag on a Ferrari Bob Norwood modified. On the day of the testing, they ran the car and came up with numbers slower then what Ferrari claimed. Then again, he blew up several engines for a friend of mine by leaning them out to much. He was trying to get more HP, claimmed it was R&D. (wReck & destroy?) Am I getting to far off topic.............

Not to mention the differences in Dyno mfg. brands. On some products that we test on the Dynojet 248C we get slightly higher readings than on a Mustang dyno (slightly lower readings). Both machines located near sea level. Go figure.
I say take your mods to a drag strip (if a road course is n/a) and study your 0-60' times and 1/8 mile , besides the 1320' mark.

I'm going to make MILLION$
 

Here's my product that will end the eternal debate:

"The Calibrated Butt Dyno"

It has sensors that attach to your A$$ to provide a relative assessment of HP. The sensors accurately measure Pucker Of Orifice (or POO).

(1) Begin by taking a reference reading in a static/controlled environment (like while sitting at your computer debating HP #'s).

(2) Take another reading while driving as hard as you can in stressfull scenarios (speeding up to make the light you shouldn't have pushed, passing another car on a two lane with an 18 wheeler bearing down on you, sitting at a light next to a hopped up ricer wondering if you should just blow it off).

Now compare the measurements. If the relative POO of step #1 is lower than #2, your investments have paid off and you can claim you have POO'd out #2.

Just have to figure out how to compensate for the "Taco Bell Factor" and I will have it all worked out.


Gordo

BTW, Thanks for the good article.

cold days yes damp or not , not much of a differnce

using a load bearing dyno you load the car at a ceriain break point and then look at real time tourqe and tune the timing till no more tourqe is made. this is at the edge of detonation,no real need to listen for knock since knock is just a result of the flamefront completely buning before your 4deg atdc, and remember one thing the only thing you are doing with fuel is controlling the temps in the cylinder.


yes after you get off the dyno you still need to street tune for your accel decell ovverrun idle situations

an engine on a test stand is the best and most accurate meter of tourqe, no calculating drivetrain loss,additions cause remember even though transmissions and driveline use up power a transmission is nothing but a tourqe multiplier,

Sophisticated dyno setup variables allows the operator to virtually "cheat" almost as much as they want.

Just look at some of these inputs:

Drag coefficient
Drivetrain loss Percentage ( I'll set that at zero.... Muhahaha!!!)
Vehicle Weight
Frontal Area in Sq Ft.

Muhahahahaha!!!!

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