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Discussion Starter · #1 ·
Most know that a dyno has to be completed in a 1:1 gear, (many use 4th) however many has used 3rd when dynoing our cars problem is the numbers come out high. and too low in 4th. if 4th is a .89 gear woulded that take away 11% of the power? like mine dynoed 217hp in 3rd and like 189 in 4th

189 x 1.11 = 209.79hp

seems like a more logical number and i think the 4th gear with a 11 percent fudge factor should be the baseline. just for a more accurate reading, does this make sense?

or is anything over a 1:1 ratio give the same hp, because on the SRT forums many are saying they dont see a difference between their 3rd gear and 4th pulls. being 3rd is 1.38 and 4th is .98. maybe a lower than 1:1 affects the dyno but a pull in 1, 2 or 3 will produce the same numbers. this I really dont know but I just want to know how we can get a number to compair against other cars.
 

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Superd00d
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To the best of my knowledge, the dyno needs to be corrected for a gear ratio of 1:1 for an accurate reading.
 

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Discussion Starter · #3 ·
but how to shops correct? i know mine did not ask the ratio of the gear they was pulling in. is there something in the software that can do this? im asking because im going back sometime this week for a pull with a rpm reading,

also does anyone know the wire coming off a individual coil pack to get a rpm reading?
 

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Not sure, perhaps they're just leaving it for you to calculate?

And in your case, look at how close the numbers are...
 

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BlackLine said:
but how to shops correct? i know mine did not ask the ratio of the gear they was pulling in. is there something in the software that can do this? im asking because im going back sometime this week for a pull with a rpm reading,

also does anyone know the wire coming off a individual coil pack to get a rpm reading?
It's the dark green wire with the white stripe.

Also, I pulled a 216 whp and 191 tq on a 4th gear pull.
 

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Yeah basically you gotta figure out what the gear's ratio is and if they are not doing correction at the dyno, then you want to do it yourself just like you are. For instance you could dyno 1st but it would give you such torque multiplication you'd have like 500 whp :p

With the proper math you could figure out what it was REALLY supposed to be. In my experience most dynojets do not do this. They get in the closest gear that's not an overdrive (i.e. 3rd for us) and do the run.

216whp in 4th is pretty sick though :)
 

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garland said:
They get in the closest gear that's not an overdrive (i.e. 3rd for us) and do the run.

216whp in 4th is pretty sick though :)
I know!!! And that was before I installed the header I just got. I can't wait to get back to the dyno and see where she's at now.

Actually, I think 4th gear is the closest to 1:1 ratio for us.
 

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i thought 4th was .98?
 

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Most dynos automatically adjust for gear ratio by comparing MPH to RPM. I did a pull in both 3rd and 4th gear and the difference was less than 2%.

Also, horsepower readings will vary from dyno to dyno by a small percentage, even if they are the same equipment (ie one DynoJet vs another DynoJet). There's an even bigger difference between DynoJet, Mustang, and Land & Sea dyno systems, simply because of the methods used to determine power.
 

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Then why are some of the people doing 4th gear pulls getting such low numbers sometimes?

Some have reported numbers in the 170-180 hp range. I think it was Vita that dynoed low like that.
 

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JPK said:
Then why are some of the people doing 4th gear pulls getting such low numbers sometimes?

Some have reported numbers in the 170-180 hp range. I think it was Vita that dynoed low like that.
Hmm...I'm messing around with the dyno software now, trying to show the difference, and something weird is happening. Maybe I'm wrong on the whole thing.
 

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Discussion Starter · #13 ·
ahhh well next time i go ill have them upload the info, and yes 4th is .89 and 3rd is 1.18 pretty strange havent seen a car with that ratio.
 

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well i pulled some low numbers in 4th, it was something like 178 stock, 189 with airbox removed, both in 4th, but you can't really compare numbers to other cars that were not on the same dyno.

when i had my car dyno'd for the 3rd or 4th time, there was this SRT there with a BUNCH of mods like big intercooler, the intake kit and hardpipes, new sparkplugs, and boost controller, basically too much for me to remember, andhe pulled 220whp when i was pulling 189 with only the airbox removed. i've got pictures of the SRT if you don't want to believe it.

basically what i'm saying is, you should only use dyno #'s to see where you are at from stock, and should always go to the same dyno, not to compare with other cars, to do that, take it to the track and get some times
 

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I have been kind of wondering about this myself. I was guessing that alot of the really high dyno numbers were coming in from uncorrected 3rd gear pulls. I'm not 100% sure if thats the case but it had me wondering. BTW I made 189 whp on a 4th gear dyno pull.
 

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Vita said:
well i pulled some low numbers in 4th, it was something like 178 stock, 189 with airbox removed, both in 4th, but you can't really compare numbers to other cars that were not on the same dyno.

when i had my car dyno'd for the 3rd or 4th time, there was this SRT there with a BUNCH of mods like big intercooler, the intake kit and hardpipes, new sparkplugs, and boost controller, basically too much for me to remember, andhe pulled 220whp when i was pulling 189 with only the airbox removed. i've got pictures of the SRT if you don't want to believe it.

basically what i'm saying is, you should only use dyno #'s to see where you are at from stock, and should always go to the same dyno, not to compare with other cars, to do that, take it to the track and get some times
What kind of dyno were you using? Mustang dynos almost always read lower than DynoJet.
 

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it was a 4 wheel drive mustang dyno

edit: and the intercooler water pump wires were crossed. bet it'd have been higher than that...
 

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Sp00ner said:
To the best of my knowledge, the dyno needs to be corrected for a gear ratio of 1:1 for an accurate reading.
Just dyno'd the Red Line last Sat and that is NOT what the dyno guy said (as far as has to be corrected for a 1:1 ratio). His experience is the graphs on a 3rd & 4th gear pull will almost exactly overlay on each other. Mine were 214.7 in 4th and a 216.2 in 3rd, thats only a 0.69% difference(less than 3/4s of 1 percent, not bad). Mine was on a Dynojet, and he stated that the Dynojet uses a Known dia. drum of a known mass to figure out the HP while the Mustang Dynos use an electric motor and heat of the motor can and does vary from pull to pull and day to day. The dynojet remains constant from event to event and is more reliable when comparing dyno pulls done under diferent conditions (different days).

The thing that most impressed them at the dyno was our torque band. We are at 150 or so lb/ft of torque at 2500 rpm and remain flat all the way to redline with the averaage peak of 187 lb/ft. That is 80 - 100% useable max torque through out the entire RPM band. They have not seen anything quite like that and commented that the GM performance guys had their shit together on the tuning of our engine. And if you look at all of the posted graphs, they mimic each other as far as the profiles of the curves, only the numbers change by a wee bit.
 

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Vita said:
it was a 4 wheel drive mustang dyno

edit: and the intercooler water pump wires were crossed. bet it'd have been higher than that...
Well, then the numbers sound just about right for a Mustang dyno. Just for example, a Camaro putting down 360+hp on a DynoJet only registers about 325-330 on a Mustang dyno.

It's all in the method used to measure horsepower.

Don't worry, your car isn't a wuss. :)
 

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the biggest problem is that you care about what your numbers say. I know it sounds crazy, but trying to compare dyno numbers to others isnt very accurate. Not all cars are going to dyno the same and that is because of dynos themselves, weather conditions, what you had for breakfast...etc. Im pretty adament about this, but the ONLY thing good about a dyno is to compare YOUR OWN progress. Dynos are good for tuning (street is actually better, but) but thats about it. Numbers can also be scewed drastically by the data that the operator puts in. For example, the dyno here is set on SAE correction for N/a cars....should be different for FI. This leads to higher than normal dyno numbers, but does it matter? not really. Thats because everyone here has the same dyno correction so the field becomes level, but if we compare numebrs to elsewhere in the US, it seems like we have a bunch of freaks here!

hopefully i added something worthwhile, but if you want to tune your car and compare your car to your own car, use a dyno. If you want to know how fast it is.....race it.
 
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