Dyno methodology

[djza2u1]

Some good info that i found at P&L Motorsports website and wanted to share. I cannot stand people compaire there dyno numbers to someone else. I have always wanted to saw this but ctrl+C i / ctrl+V is alot easier.

"First off, you can never, EVER, compare numbers on a dyno. Not even across the same dyno on
different days. On top of that, I try hard to tell people that it’s actually possible to make a lateral
move on a tune, not even making any more power. That being said, there are only 2 things I can
promise them, and that is a safer and more consistent tune.
Secondly, I tell people all the time that a dyno is a tool, curves and trends are what matter. If it so
happens to produce a hard-on inducing number, so be it!"

 

[Saskatchewan17]

What about the same dyno on the same day. Within an hour of each other.

 

[Design]

Some good info that i found at P&L Motorsports website and wanted to share. I cannot stand people compaire there dyno numbers to someone else. I have always wanted to saw this but ctrl+C i / ctrl+V is alot easier.

"First off, you can never, EVER, compare numbers on a dyno. Not even across the same dyno on
different days. On top of that, I try hard to tell people that it’s actually possible to make a lateral
move on a tune, not even making any more power. That being said, there are only 2 things I can
promise them, and that is a safer and more consistent tune.
Secondly, I tell people all the time that a dyno is a tool, curves and trends are what matter. If it so
happens to produce a hard-on inducing number, so be it!"

That comment is a bit misleading. It is possible to dyno in "similar" testing conditions on the same day in order to measure the effect of a performance change, such as a bolt-on part, tune, etc. Numbers by themselves mean very little, but % gains (if any) are fairly relevant. For example, your tuner could claim to give you a very flat and predictable power curve, but what's the overall change above/below baseline? We assume it'll increase, but you still need a few dyno pulls for comparison.

He is right that a dyno is meant to be a tool and not for bragging rights. I am constantly being scrutinized on my MS3 "numbers," despite telling people over & over that the my sole purpose in utilizing a dyno is to evaluate conditional changes of the overall power curve.

 

[8.5MS3]

+1 same here. dynos can give you the difference in power before and after a mod, provided the swap is done quickly and that the dyno calibrations are the same.

 

[Design]

+1 same here. dynos can give you the difference in power before and after a mod, provided the swap is done quickly and that the dyno calibrations are the same.

Even then, going back to the same dyno on a different day is just as important. I would imagine most people slowly build their mods over a period of time. Humidity, air temps and testing variances will only account for so much...

 

[dmention7]

The most critical thing in that quote is that trends and the shape of the curves are what matter. So many people fixate on the peak number, but completely ignore where that peak happens, or the shape of the curve--both of which are at least as critical to how fast the car is and how it feels to drive.

 

[8.5MS3]

agree 100% if i make 500 hp at 1 spot and 50 everywhere else, the car sucks balls. the more area under the curve the better. I'd rather have 250hp from 3.5k to redline than 350hp at 1 spot and under 200 everywhere else

 

[MSMS3]

Great observations. Dynomometer readings are a tool for comparison on the same vehicle under the closest conditions that can be replicated.

Even dynoing before and after making a mod change on the same car and on the same dyno can be fraught with reliability issues because the ECU must be reset and must be allowed time to "relearn" from the changes.

You just hope that the changes keeping moving you in the direction of your target power goals based on multiple pulls under the closest conditions you can get.

And indeed, peak numbers are far less important that how broad and fat the power curve turns out to be.

Finally, dyno pulls can be terribly misleading because there are certain aspects of real world performance that they simply do not recreate, such as actual air flow into the closed engine bay in actual street driving and also the effect of aerodynamic drag on acceleration at higher speeds.

I've never really understood the wisdom of popping the hood and letting the fans blow into the engine bay, rather than through the front grill, like we actually drive our cars. Popped hood makes better numbers, but is totally unrealistic regarding actual power while driving.

And I think we all understand that chassis dynos do not take into account the effect of aerodynamic drag. A dyno pull in the gear closest to 1:1 gearing is not the same as the amount of power available for acceleration after overcoming air resistance if the car were going that same speed out on the open highway. For instance, even with a very aerodynamic body shape, there is a 50 hp difference at 90 mph and a 75 hp difference at 120 mph and it gets worse as speed climbs.

Great tuning tool, though, used prudently.

 

[oaklandopen]

agree 100% if i make 500 hp at 1 spot and 50 everywhere else, the car sucks balls. the more area under the curve the better. I'd rather have 250hp from 3.5k to redline than 350hp at 1 spot and under 200 everywhere else

i can agree with that, but there are some areas where it works better as a peak and not so much a steady horizontalish curve

take, for instance, a NASCAR engine. they have peak hp that arrives at a very acute angle on the dyno graph, and a few hundred rpms can mean a huge difference in hp numbers. without getting into too much detail on the design on the engine i will just say it has to do with the peak velocity of the air coming in (since they're all NA and depend on velocity), and it's only within a few hundred rpms that it reaches this peak, and the intake plenum and valves and whatever are specifically designed for max performance at a specific rpm to get to it's highest volumetric efficiency

and i think, to an extent, super street motorcycles are kinda the same way. i remember my gixxer 600 only felt like it had power in the upper few thousand rpms, and not really anywhere else. im sure it's dyno must have looked like an upside down checkmark

but as for a normal daily driver on the road, a lot of area under the line is best

 

[8.5MS3]

tru but in nascar they have the tachs pinned between 7 & 9 grand for hours at a time. so yes ideally for nascar or any constant high speed, max power at a point would be ideal. for the street....not so much, same with race ready street bikes

 

[oaklandopen]

^^^yea...i just posted for the sake of arguement that sometimes it is better to have a short amount of high hp as opposed to a long steady amount of decent hp


in addition, everyone i've ever personally known has always been die hard "my dyno numbers are..." type ppl, who totally rely on those numbers to not only put other ppl with the same car down, but to prove that their penis size is in direct opposite proportion to how spectacular their car sounds

btw, my ms3 got 473 whp the other day on the dyno

 

[8.5MS3]

(lol)

hahahaha nice

 

[Design]

I've never really understood the wisdom of popping the hood and letting the fans blow into the engine bay, rather than through the front grill, like we actually drive our cars. Popped hood makes better numbers, but is totally unrealistic regarding actual power while driving.

Ironically, a closed hood produces better numbers on the MS3/MS6. A couple members have reported 3-4% gains by simply closing the hood and running a 25 mph shop fan to the grill, which is more synonymous with the real world environment. Apparently the RAI is fairly efficient at sealing off the TMIC from excess heat around the engine bay.

 

[8.5MS3]

not sure which would be more accurate. either case cant simulate road conditions. no fan placed in front of, or on top of the car/engine can simulate the amount of air movement across the car. if your fans are all placed in front of the car, then closed hood would seem better, whereas if you can suspend a shop fan from a chainblock, an open hood scenario may be more baneficial. this is sometimes the reason when, while tuned for a specific boost target on a dyno, you can sometimes see higher boost when driving around in the real world. the cooling effects are much more dramatic

 

[destrux]

I agree completely that you can't compare two dyno runs on two different dynos (even if they are the same model dyno).... but....

I disagree that you can't compare runs from the same dyno.

While I was working out computer problems (vista hates my dyno software, long story) I ran my speed3 on my dyno over a dozen times over the span of 2 months. Each run was within 4hp (peak) and the curves were always nearly identical (a few small spikes and dips at the RPM extremes were different). The weather varied from 60 degrees with rain to 90 degrees with low humidity (although, the dyno has a weather station built in and compensates according to current conditions).

However... I did get big variations everytime I cleared my ECU. Also, if I pulled the car in with the engine hot vs cold it made a difference on the first two runs (till temps stabilized). Once the engine temps and IC temps stabilized the runs were all nearly identical. I also time between runs, 10 minutes, with the dyno fans running and the car's engine idling to keep things consistent between runs. No bags of ice, no running for numbers with a cold engine. It may not be the best way to get peak numbers that will win chat room arguments with muscle car guys.... but it's the best way to get consistent numbers and know how much power your car is actually making when it's up to temp driving on the street.

 

[oaklandopen]

the old way to test out the correct timing was to take your car to the track, run it, and at the peak rpms shut the engine off. that way when you coast to wherever you take the spark plugs out and see where the mark is on the ground electrode. if it's right near the elbow the timing is good, can't remember which one is too advanced or too retarded but you would be able to see marks on the end or beginning of the ground electrode if the timing was off. somehting like a discoloration

not to say that this has anything to do with dyno, just thought i'd add