Different dynos = different numbers?
 

A programmer thread had people comparing dynoe'd HP numbers.

I saw a stock 06 put out 268 HP on a Mustang dyno, someone else's 06 truck got 305 HP on a DynoJet.
I got 443 HP with BDTD and CL on the Mustang, someone else got 510 on a DynoJet with an 07 running CL on a BD PMT, that's quite a difference. The DJ was said to be the most accurate cuz it doesn't load the engine, that seems a little odd to me, how can the dyno measure HP without loading the engine?



Can someone explain how the different dynos work, how they come up with their numbers and why there's so much difference between the different types of dynos?

Mods, please move this to 5.9 hiperf and access?

The DJ is not a load control dyno so therefore it is pretty much the same as putting your truck on jack stands and putting your foot to the floor which is why their numbers are high. Sure the guys that go looking for the high number want their trucks run on DJ's but in reality people much like myself want to know what the truck makes on the street so the load control mustangs simulate how your truck would run on the street and produces that load. Sure everyone will have their oppinion but you can call mustang and they will explain the same as well..i have been working with dynos for 5 years now and when first introduced to them i asked the same question.

The way I understand it the DJ measures rate and calculates from that.

Measures the rate of what?

You have to look at all of the parameters measured when comparing dyno runs. The most obvious are the atmospheric conditions. A lot of people let you go out the door with a correction factor being used which is not right because our trucks have forced aspiration using a turbo. So, if one dyno operator is using a correction factor and another isn't then the one that isn't will not show as much power because they are using actual horsepower figures and not corrected horsepower to perfect conditions. Dynojet is the industry leader and those who don't have access to one or own one will always bash them, its' the way it is when you're at the top. Dynojet measures rate of acceleration using Newton's second law, FORCE = MASS x ACCELERATION. Basically it's time, distance and weight. So, it's the weight of the drums (weight) and the circumference (distance) of the drums and the time is provided by the vehicle. From this they measure HP and calculate TQ using engine RPM. The old way (other/load dynos) was to measure TQ using a load cell of sorts and calculate HP using RPM. Each way works but with an inertia style dyno like a Dynojet, the load never changes nor does it ever need calibrated once it leaves the factory. Load cells need constant maintenance and calibrating and can easily be cheated on. People always bring up the load problems on a Dynojet. I've never had a problem so I guess my truck just runs the way it's supposed to. I hit 38 PSI on the Dynojet I run on and I have never ran any more boost on the road empty or towing my hauler. The conclusion is when comparing dyno numbers always ask for the graphs of said runs and compare the atmospheric conditions as they are just as, if not more, important as the run itself.

Hope that helps a little.

So how could it measure more power if no boost is present?

Yeah, I just put mine on another dyno jet today....got 366hp and 679#tq. Torque seemed a little low, they put some sort of tape on a wheel at the front of the engine and used a camera that tuned to that and measured the torque partly by that. The other dyno jet, put the brake to a certain level to put load on it. Both dynos I ran in 5th gear....tried 6th also today, just to see....there was no dif. in power at all...picked up actually 4#tq. in 6th lol. Im kinda new to this dyno stuff so I don't have too much room to talk. The only thing is I think my torque seems low to most I've heard with same hp.

why wouldnt boost be present..boost is relevant to load so it will boost but not apply the load equivalent to what your vehicle see on the street so you may miss out on a few lbs.

If your dyno does NOT use a strain guage it isn't as acurate as it could be.

Wow, OK, here are some basics...
Mustang dynos typically require the operator to input certain parameters to calculate the numbers. Weight of the vehicle, tire size, gearing, etc....If the operator is lazy or inaccurate...the numbers are bad.

Dynojets will be the most consistent from machine to machine as they do all of the calculation based on the acceleration of the drum. As far as load is concerned, the drum weighs between 4 and 6 thousand pounds, so it does apply some load on its own. It is definitely NOT like putting your truck on jackstands.. We also have an eddy current brake or "Load Cell" that applies up to an additional 1500lb/ft of retardation to the drum. This is critical for trucks with big singles or twins that need load to spool up. We will apply a consistent load when testing different setups on a truck to determine if the tuning is working or not. We want to get the boost up to a certain #, 15-20lbs normally before the run starts. This allows us to achieve full boost on the dyno, just like on the street.
Hopefully that helps!

And, sorry, to clarify for the OP..Dynos are tools for tuning, and they are all going to have some variance. The point of using them is to see if you are making progress with tuning. For that reason, its generally pretty important to use the same dyno--and more importantly--the same operator to test/tune your rig.
Also, FYI "uncorrected" dyno numbers are what the vehicle ACTUALLY put down that day, under those weather conditions, etc. SAE Correction is the standard for comparing dyno #'s, and it takes into account the altitude, air temp, humidity, etc and corrects up or down to a standard set. In theory, using SAE corrected numbers, your rig should make close to the same numbers on my dyno (sea level) and at one a mile high in Colorado.

It is definitely NOT like putting your truck on jackstands.. that was a figure of speech implying that there is very little load to get my point across.

I don't think 4000lbs is "very little load" its fine for pretty much any car. Spooling a turbo and simulating load for a 7500lb truck makes it a different story, but you can still get good numbers by foot braking on a non-load dynojet. That's pretty much what is used at dyno competitions around the country, and our record setting VP truck made 1060hp on one with just footbraking.

Because you said it was the same as putting your truck on jack stands. If you did that then I doubt you would see anything over 10 lbs. at best. Just wondering why you said they show more power with less boost. I thought maybe it was some kind of magic trick or something.