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      11-11-2008, 07:42 PM   #12
Got Track!!!!!!
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Drives: 08 M3 coupe
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Originally Posted by PencilGeek View Post
They certainly read as if they were stated as fact. You even went on to recommended other dynos and said they produced numbers that you believed in (which implies accuracy). But let's move on and possibly look into the numbers you got from the dyno.

The most accurate way to measure is using steady-state. But steady-state testing will put a lot of continuous load on your motor, and might be rather hard on it. So most people do ramp testing. If the ramp is too low (like 1 second per 1000 RPMs) then the numbers will read too LOW (not high) because the wheels are somewhat free-running. I've found that 2.5 seconds per 1000 RPMs is a good compromise. It seems to produce numbers that are very close to steady-state numbers, only a few percentage points off. How does the dyna take into account the wheels rotational mass?? Is this data inputed to correct for the missing wheels and tires?


You also want to look at the correction factors. The Dynapack will allow you to select one of 4 or 5 correction formulas (all based on standards-bodies such as SAE). I typically use the SAE 1349 correction because it's meant to correct for temperature, humidity, altitude, etc. But if the ambient temperature sensor is placed in the motor intake (as many dyno operators will do), then this causes the sensor to read very hot,<--- 100% true I seen this multiple times, or some time it's place near something hot.. and produces VERY HIGH corrected results. I've had this problem myself at one operator. I had to go back and use the national weather service to get the temperature, humidity, and barometric pressure for that time and area and plug them into the SAE 1349 correction formulas and "re-correct" my own results because the operator had placed the sensor in the wrong location.

If you still have your Dynapack dyno files, I could look at them and give you an idea if anything looks wrong. I will see if I have them.

I've heard this before, but I find it impossible to believe. In fact at SEMA I asked this exact question to a professional drag racer, and he said it was utter nonsense. He even laughed and said "where did you hear that...on some forum on the internet?"

So if you are correct, then the following would be true.

I could accelerate as fast as possible in 1st gear. Coast for two seconds before shifting into second gear. Accelerate as fast as I can in 2nd gear. Coast for FOUR seconds before shifting into third gear. Then accelerate as fast as possible in 3rd gear to achieve the same exact trap speed as if I hadn't coasted for six seconds in between gear shifts. Dude come on!! Your killing me!
I am taking into account a average driver that will take a second to make a shift..

I'm sorry, but I do not even remotely believe that is true. And if it isn't true, then obviously driver ability plays a role in final trap speed.<-- it absolutely does play a role, giving he is consistent
Sorry for the thread Jack
PG PM me with your reply so we dont thread jack..