Why is almost everyone dyno-ing their 5AT in 3rd?
 

My understanding is the gear which produces and overall ration of 1:1 is 4th gear with the 5AT. This is the only gear ratio which will provide reasonably accurate HP and torque values.

Third gear runs will produce numbers that look good because they are inflated. While I can understand wanting high numbers, what good are they if they are false?

Why not run all dyno tests on the 5AT in fourth gear? I know it is possible because I did it.

Re: Why is almost everyone dyno-ing their 5AT in 3rd?
 

Some dyno operators aren't too comfortable with the cars going 130 MPH, even though the manual transmission would be going about that speed in 5th. I've always requested my dynos to be run in 4th though (5at).

A lot of people say that it shouldn't make a difference, but looking at the results of past dyno events, there's about 7 HP gain by dynoing in 3rd on a 5AT

Re: Why is almost everyone dyno-ing their 5AT in 3
 

how do you get the car to dyno in fourt in an AT
is it like a rolling start and then the machine is activated when your in 4th? me and my freind were trying to dyno my car with a digimoto and a laptop and I got like 216hp and 189 tq in second gear as close to a dead stop as possible so I never actually got great numbers with it though. I did get a 15.5 second 1/4 mile with two of my friends in the car lol it was fun doing all that with a laptop. kinda ghetto but fun.

2004 Skyline 350GT 5AT DG/G Clears,Bats, Now wit Bumps in da back! [img]/w3timages/icons/shocked.gif[/img]
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Re: Why is almost everyone dyno-ing their 5AT in 3rd?
 

I've heard that concern before, but I didn't run onto any conflicts. I would think that could be addressed well before a dyno was scheduled and if one operator didn't want to do it, just go to another shop. I ran two dynos at two different shops, both in 4th gear. Neither operator said a word about top speed. I just told them what gear I wanted the test run in, and that was it.

In one test, the operator drove the car, and in the other one, I did. I preferred to drive because I was familiar with the shift-down points of the tranny and knew I could get a 4th gear run without a downshift.

The test started, I manually shifted through gears to make sure it was in 4th, increased rpms slowly to around 3800 and then applied WOT.

It might have even been possible to apply WOT at 3500 or so, but this should be tried only if you have time for repeated tests and cool down - just in case that undesired down-shift occurs. Because the load is different, the car/tranny behaves a little different on the dyno than on the road and it seemed somewhat less inclined to down-shift on the dyno.

In any event, the question remains - why run dynos in a gear that is known to produce inflated results, and then publish those results as representing output - when they don't?

Re: Why is almost everyone dyno-ing their 5AT in 3rd?
 

Here's my opinion...

Wheel speed a valid concern. IMO, however, the AT 3rd gear dyno practice started because the AT Sedan's transmission's would often "kick down" from 4th to 3rd during the pull and skew the dyno results. It happened once during last Saturdays dyno day. While this is no longer a problem with the later AT car's TCM, it remains a challenge for the earlier ones like mine. This is why my car's dyno plots start around 3700 to 4000 rpm. This high starting point is required to keep the car from downshifting during the pull.

Powerwise, my data and personal experience are exactly the opposite of E_K's... lower gear = lower numbers.

Over the years I have talked to several dyno "experts". A few said dynoing in a lower gear doesn't matter that much (within dyno error). The majority saying the lower gear numbers will produce lower (< 3%) results.

To support my position I have provided E_K a two G35 AT Coupe dyno charts for his review. The first pull in second gear produced 215.5 HP, the third gear pull produced 237.5 HP. Same car, same dyno, same day, within 5 minutes of each other. And no, I don't know why they selected second and third gears. I wish they'd done these pulls in third and fourth.

By the way, I've always wanted to dyno in the gear that provides the best numbers while maintaining a safe condition for man and machine.


DaveO
03 G35 AT Sedan / DP / Willow / Premium / Sport / Aero / Mods / 262.0 & 260.7

Re: Why is almost everyone dyno-ing their 5AT in 3rd?
 

At the CFL dyno day, the automatics were initially going to be dynoed in 4th gear. After my car (5th gear 6MT) slipped on the drum, the operator didn't like 130 mph all of a sudden. I talked the operator into dynoing Dabomb's car in 4th gear (5AT) and then in 3rd to see the difference. 4th gear read 3-4 rwhp lower than 3rd on a dynojet at peak hp. I was not thinking quick enough to have him print out the comparison charts over the operating range.

My guess is, by lowering the gear, the gear ratios are different, thus giving a slightly higher reading. That part's just a guess however...

<font color=blue>The above statements are only my take on the issue. If you disagree with anything I typed then you are 100% right!</font color=blue>

Re: Why is almost everyone dyno-ing their 5AT in 3rd?
 

I dyno mine all the time, only in 4th gear. I cruise through the gears in MM mode, then at about 35-40 mph in 4th, I slam the gas and off we go. Ford Mustang Dyno only for me....... Just do not like Dyno Jets.

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Re: Why is almost everyone dyno-ing their 5AT in 3rd?
 

I did mine in both 3rd and 4th. There was only a 3 HP difference in peak values. I was able to get 2 runs in 4th with no downshift. Brought it to redline in 4th and topped 140 MPH. Yikes!