What is a better dyno-Dyno Dynamics or Mustang?

[niterydr]

You really ought to get your facts straight before spouting a whole heap of BS! Shoot out will inflate or deflate as conditions dictate. It is not an automatic inflation!




Other dyno's use weather station readings too not just dd's.

André

In my old shop and the shops around here they typically show higher due to the dyno room conditions and the correction factors that get applied. Being around 950 elevation with crazy temperature and humidity swings can really account for some favorable corrections. I never said higher or implied that they are higher, just that usually in shootout mode the numbers show up "higher". In the end, WHO CARES? They are numbers and it is a tuning tool.

[Permanent grin]

In my old shop and the shops around here they typically show higher due to the dyno room conditions and the correction factors that get applied. Being around 950 elevation with crazy temperature and humidity swings

Maybe I was a bit harsh in my previous post, for which I apologise Niterydr. I do think that needed to be clarified though as obviously I wasn't the only one who mistook what you were saying.

Ray Pampena
the shootout mode reads higher than the standard with no "x" factor? that i didnt know.

The shoot out mode is there to allow comparative figures so that results at higher altitude or in a hotter climate can be compared with results at sea level, in colder climatic conditions and / or in different seasons. In other words, it creates a level playing field be it inflating or deflating figures to equate to test results that would be produced according to SAE correction J1349.

Like you say though, the dyno is a tuning tool to measure gains rather than absolute numbers. The best proof is at the track.

André

[BaadVR4]

Ummmmm..........let me see..................my car had a difference of 9.5 mph (123 vs 132.5 mph) in trap speeds due to different weather conditions. You ran 128 on day one and BETWEEN 122 and 125 on day two. I would be much more concerned about what caused a 3 mph difference on the same day. Unless the weather changed a good deal on day two, there was something else that caused the difference between 122 and 125 on day two. Usually, what causes differences other than weather is shifting at different rpm or some change in engine tune (i.e., change in ignition timing). I would say your engine made less power on day two, probably due to weather condition differences. Tyre pressure will affect traction and thus Elapsed Time, but not trap speed; wheelspin has virtually zero effect on trap speed.

To a degree yes. Then you get into atmospheric conditions, tyre pressures etc. My car ran 128 mph terminal on day 1 and terminals between 122 and 125 mph on day 2 after it had rained on the afternoon of day 1. The car never left site as we camped there and had no modifications to it. A worse case scenario of 6 mph difference!

What I am trying to say is terminal velocity can be used as a guide but is not an absolute definitive.

André

[niterydr]

Maybe I was a bit harsh in my previous post, for which I apologise Niterydr. I do think that needed to be clarified though as obviously I wasn't the only one who mistook what you were saying.



The shoot out mode is there to allow comparative figures so that results at higher altitude or in a hotter climate can be compared with results at sea level, in colder climatic conditions and / or in different seasons. In other words, it creates a level playing field be it inflating or deflating figures to equate to test results that would be produced according to SAE correction J1349.

Like you say though, the dyno is a tuning tool to measure gains rather than absolute numbers. The best proof is at the track.

André

No worries Andre, you came off sharp, as so did my first post. You don't know me from Adam, and sometimes I won't post a fully detailed explanation. Ray and Jeremy know that and will ask me probing questions if I need more detail.

What I was saying that in my experience, locally in the MN area, the shootout mode tends to raise the values for the cars. This is because of the dyno room setup, and typically weather conditions when tuning. The only time I've ever seen shootout drop is when I was tuning my car mid winter with the shop doors open, and it was cold. Weather correction offset was .8xx or a very low .9xx something, it was very favorable to tune. Granted, this was 5 years ago now, so memory could be a bit foggy, I just remember the negative correction factor was impressive.

I've got a few graphs to post up to show the discrepancy, need to validate it with my friend first as it is his car using that local shops dyno.

[Sin'sVr4]

i post on both because alot of people stay away from the other site and some dont come over here.

[Permanent grin]

I would be much more concerned about what caused a 3 mph difference on the same day

Yes there were some differences between the runs as this was only my 2nd ever 1/4 mile!

Tyre pressures that are lower do have a greater rolling resistance.....fact. Mine were lower on day 2 to try to reduce wheelspin.
I had difficulties with the launch where the clutch would just bite and bog therefore covering distance with far from optimal acceleration.
Most of the runs yielded 124 mph with 1 at 122, 1 at 123 and 1 at 125 mph and yes there was some experimentation with different shifting points. I ended up shifting at 6500 rpm to get my best times.

I think you are trying to find fault here there is none.

Perhaps something else that I misunderstood was that this thread was about dynos??????

André

[BaadVR4]

Not trying to find fault at all. I agree lower tyre pressure would tend to offer more rolling resistance, but IMHO not enough to have much of an effect on trap speeds unless you lower the pressure to where the tyre is nearly flat. My comment was in response to your statement that on two different days your car had 6 mph difference in trap speeds and that was an indication that trap speed was an unreliable measure of HP. But, as you now post, there were differences in driving methods/etc which affected the trap speed. What I'm saying is the most accurate indicator of how much HP a car is producing is 1/4 mile trap speed. That's what you use to tell you what rpm to shift/what driving methods produce the best result. Just as you did on day two at the track.

I readily admit to electronic incompetence. That means I don't have the knowledge or skills to tune my AEM car myself. But I DO have nearly 50 years of drag strip experience and a more than a little knowledge of drag racing. And, IMHO, the drag strip is the most accurate dyno of them all. If you make back to back runs and the trap speed changes dramatically (without dramatic temp/press changes), then the HP output of the car has changed. We use dynos to tune our cars. We use the drag strip to tell us how well we have done and how we should drive the car to optimize the car's performance.

Yes there were some differences between the runs as this was only my 2nd ever 1/4 mile!

Tyre pressures that are lower do have a greater rolling resistance.....fact. Mine were lower on day 2 to try to reduce wheelspin.
I had difficulties with the launch where the clutch would just bite and bog therefore covering distance with far from optimal acceleration.
Most of the runs yielded 124 mph with 1 at 122, 1 at 123 and 1 at 125 mph and yes there was some experimentation with different shifting points. I ended up shifting at 6500 rpm to get my best times.

I think you are trying to find fault here there is none.

Perhaps something else that I misunderstood was that this thread was about dynos??????

André