Can someone explain this too me please. I watched my buddies charger get dynoed the other day on a dynojet in 4th gear and he told me his numbers would have been higher if they did they dyno pulls in 3rd gear. He mention that he got his car dyno'ed two other time on different dynojet in 3rd gear and his numbers were at least 15 horsepower more. Im confused because i thought everyone did dyno runs in the same gear, but i guess not. So my question are, Why do shops use different gears to do dyno runs and why is their a power difference between 3rd and 4th gear?
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I recently had my ride Dyno Tuned by AJ and just as Charger4Life had his car Dyno Tuned by AJ they both were tuned in 4th gear. The only time AJ ran the car in 3rd gear was to chase down a Cat-over-Temp-Protect that was causing the car run rich at the top end of a 4th gear pull. The reason for this is that it took longer for the car to reach top RPM in 4th than in 3rd. So he re-mapped the tables and that was the end of that.
6.4 Apache Heads, 6.1 SB, SRT-MAxx Cam, 6.1 Intake, 87mm TB Ported by MM, TTi Long Tubes and Mid pipes, Dyno-Max Ultra-Flow 3" Exhaust, LMI 4" CAI, Predator, BC Racing Suspension, Magnum front w/69 Cuda Grill inserts, Trufiber SRT8 hood, SLP 25% Under Drive Pulley, Zeitronix Wideband, Hotchkis Sway Bars, SPC Front/Rear Camber Kits, 3.06 GETRAG, Builder Bill Billet Stator 3200 TC, Flex-Plate & Valve Body, MTCM, Brembo brake set and Dyno Tuned by AJ Hemituner.
All else being equal mine dyno'd higher in 4th than 3rd.
(Mine also dyno'd lower with the 3.23s than the stockers)...go figure
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2006 Inferno Red Charger SRT8
SHR trans|Wavetrac&3.23s|DSS shafts
Built by Cam
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4th gear is MANDATORY
unless... your shop has a Superflow type load dyno.
a lot of shops dont want to do 4th gear dynos because wheel speed is VERY high (160s or so???) and it can be dangerous to the tires if the car owner has cheap tires.
ive heard of a couple tire blow out stories on the dyno and its scary.
same goes for the dyno. its more stress on the dyno
tell em to suck it up or take your business elsewhere
you can dyno in 3rd with simulated load and still get an accurate tune.
i dont know the ifs ands whys or buts about it..
but i have seen a few local cars get tuned in 3rd (on a dynojet.. not loaded)
then they hit the street and the tune is off in every gear except 3rd.
we started pulling 4th gear and tuning in 4th.
the tune stays consistent thru all gears.
some one else can try to explain the hows and whys... but ive seen it with my own eyes.
since then, we only dyno in 4th (on a dynojet)
Johan and his boys at DS have a superflow, a loaded dyno, and do their pulls in third to keep the wheel speeds down,
but they cam simulate true load of the street, so its consistent thru all the gears.
in regards to horsepower readings?
who cares. its a freakin dyno. its a tuning tool, not a hp calculator.
the two dynos youve used are just differently calibrated and done read the same anyway regardless of gear.
ive heard the same as what kingsavage suggested.
shorter gear ratios in the rear end give LOWER numbers
and shorter gear ratios in the transmission give LOWER numbers.
not sure why, it seems backwards to me, but thats what ive heard.
Last edited by dudeiwin86; 05-18-2010 at 02:31 PM.
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I was at SVS a few months ago...from their web site: "Superflow SF 840 autodyn chassis dynamometer"
We were checking out an oddity with how my transmission/tc were acting in 3rd gear.
I wasn't too concerned about the top number but I noticed a couple of interesting things:
Call the base 3rd gear dyno number X. Dyno'ing in 4th gear yielded X+~15 and this was recreatable.
The next day we swapped gears from 3.06 to 3.23 and dyno'd again just for the heck of it. X-~20.
Nothing else changed and the torque curves were identical except for being up or down on the chart.
I had heard changing gears would affect the numbers but was a little surprised that it actually seemed to do just that.
Dynoing in 4th gear will give a higher number as more power is going to the rollers, less to internal inertia of accelerating the components.
As for rear gear changes, try it again in a couple months when the gears have meshed and the new bearings seated and you will have your power back.
I have a post in the knowledge base that answers the details of this question if you need more info.