Question about dynos

BlckOnBlckBrd

Registered User
OK here's the deal, tonight, my brother took his truck to a chassis dyno. It puts out an estimated 400 crank hp. The dyno he took it to was Midwest Dynamo LLC in Topeka KS. This dyno seems to have notably lower readings than everyone else. The guy said other dynos rig their dyno to show more hp. I didn't fully believe this, but also, he does the run in second gear, I thought all dynos run in the 1:1 gear ratio which would be third gear on his TH-350. Anyway his readings were showing 205RWHP and 215RWTQ. Anyone have any comments on this?
Also the 5000lb truck runs high 13's in the 1/4.
 
A little more data is needed to accurately identify the discrepancies.

1. Does the truck really weigh 5000lbs? Has it been weighed? Don't rely on somebody's word or some published numbers. Get it weighed at a track or a truck stop.

2. Where did the 400hp estimate come from? Most automatic drivelines lose about 20-25%. This equates to about 300-325hp at the wheels if it really makes 400hp.

3. What kind of dyno is it? Is it a Dynojet or a Mustang Dyno?

4. Yes, 2nd gear is not good for measuring HP. You could easily lose another 10% or so this way.

5. In second gear it is possible for the tires to spin on the dyno. Not likely, but possible. Look at the graph, does it have any strange dips in it?

6. You say it runs "high 13's". Be more specific. What is the best it has run? Mph is more important than ET.


Having said all of that, the comment about dyno's skewing numbers on purpose is most likely directed at a shop which uses a Dynojet. The Dynojet uses a standard load of *I believe* 2000lbs for all vehicles. This allows heavier vehicles to accelerate much faster than they would in real life, thereby skewing the numbers a certain percentage. The Mustang dyno allows the operator to specify the load placed against the vehicle. This lowers the readings (usually about 20% I think). It raises the question also of just how much load did the operator put into the machine for the testing if it is one of these types of dyno's.

One thing you need to remember about dyno testing is that it should ALWAYS be used for comparison purposes only. The actual numbers are not to be totally relied on. A dyno should only be used for evaluating the effectiveness of parts and for tuning (well, and bragging if you get good numbers. :p ).

That being said, if it really weighs 5000lbs and runs high 13's, then the HP calculator that I believe IS real world accurate puts the motor at somewhere near 340rwhp which would put it over 400hp at the motor. But this is only as accurate as the #'s you gave us which I think you really need to verify before you put much stock in these numbers either.

Bottom line, I think the dyno guy is out to lunch. :)
 
I'll try to answer your questions as good as possible.

1. Does the truck really weigh 5000lbs? Has it been weighed? Don't rely on somebody's word or some published numbers. Get it weighed at a track or a truck stop.

It was weighed at a scrap yard to measure the amount of scrap with the truck then just the truck and minused the numbers (understand?) and that showed it to be about 4800lbs

2. Where did the 400hp estimate come from? Most automatic drivelines lose about 20-25%. This equates to about 300-325hp at the wheels if it really makes 400hp.

The Dyno2000 Program estimated the engine to make about 421hp at the crank.

3. What kind of dyno is it? Is it a Dynojet or a Mustang Dyno?

I believe that it's a Dynojet, The exact brand is Dyno Dynamics Dynamometer

5. In second gear it is possible for the tires to spin on the dyno. Not likely, but possible. Look at the graph, does it have any strange dips in it?

It doesn't really have a strange dip, but it does have a dip. It did not appear to have any wheelspin.

6. You say it runs "high 13's". Be more specific. What is the best it has run? Mph is more important than ET.

It has ran a best of 13.92 at 98mph.
 
No 2 dyno's even of the same brand come up with the same #'s for the same car, ask the mfg. I've had lenghty talks with there reps and they will admit this.
Dyno's are a fine tool if used properly, problem is 98% of the time there not used properly. The only way you are gonna get #'s that mean anything is to use the same machine for all your tests and even then the oporator of the dyno must do everything properly and many do not.
All those adds you see from performance parts co's listing dyno sheets to prove there claims mean nothing. You do not know how the test was done, period!!
The marketing whores of the speed shop industy have discovered that if they publish dyno charts for there parts that people will flock to the store in groves to buy those parts.
You can put a VW Beetle on a dyno and make it look like the most powerfull car on the planet if you want to, but that does'nt make it so.
 
Ok, I would say 330rwhp or about 400-410 at the flywheel. That dyno is wacked. 205rwhp is ridiculous no matter how you look at it.

That also means that Dyno2000 is pretty accurate, at least for a naturally aspirated motor, and it also means that the motor is tuned pretty well and running at or near it's potential.

:)
 
I don't think that the dyno is wacked, I think that its the operator. He seems to put excessive load on it. My brother told me that he controls how much load is on it. He also stated that his truck barely had enough power to turn it in second gear.
The guy has dynoed a lot of Lightnings here and said most of them dyno at about 250rwhp which I thought was also ridiculously low. And also they had a heavily modified 528 Hemi Cuda before them on the dyno that was only putting out 502rwhp. This could also just be lack of experience on his part because he has only had the dyno running for a couple of weeks.

Thanks for your input guys.
 
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