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Re: 3.55 vs 3.91 track time differences? [Re: FurryStump] #3148365
06/03/23 10:17 AM
06/03/23 10:17 AM
Joined: Jan 2003
Posts: 2,916
A shed in England
Tig Offline
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Tig  Offline
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Joined: Jan 2003
Posts: 2,916
A shed in England
Originally Posted by FurryStump

Flash rpm yes, stall no. Rear gear has no effect on stall and it really only changes flash rpm because of how flash rpm is defined, not a “real” change to the actual flash rpm. The change is the car just moves easier/sooner. So yes the rpm will be lower when the car first moves, but you can still get to the power band quicker during the run. (The reason we play with flash in the first place)I went with a low gear set 904 which would “lower” my flash rpm, but because the car is moving, I would get to peak torque .5 second quicker in the run, even with the “reduced” flash rpm.


Just for info, rear gear changes did have an effect on stall speed on my combo, verified by the racepak.


'74 Challenger..9.46 @ 145.9 1/4, 6.001 @ 118 1/8 so far. 4023lb !!! # N/A, Marsh performance 655ci, Indy Maxx, T/R, Indy 600-13 X's, Street legal, pump gas, full interior, Cal-Tracs, mufflers, 3:73's and real 10.5 radials.
9.51 @ 142.4 1/4, 6.003 @ 114 1/8 with our old mule KB, 572-13, 580 wedge.
RHD '68 Barracuda Fastback 323ci street/strip. Best ET 13.88 @ 99.03
Re: 3.55 vs 3.91 track time differences? [Re: Jeff_383] #3151471
06/14/23 12:30 PM
06/14/23 12:30 PM
Joined: May 2008
Posts: 5,399
Aurora, Colorado
451Mopar Offline
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451Mopar  Offline
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Posts: 5,399
Aurora, Colorado
Likely not much change, and its mostly going to be in the first 60' times. Think it will depend on how hard you can launch the car.

Re: 3.55 vs 3.91 track time differences? [Re: 451Mopar] #3151822
06/15/23 04:21 PM
06/15/23 04:21 PM
Joined: Oct 2004
Posts: 2,820
Connecticut
FurryStump Offline
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FurryStump  Offline
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Joined: Oct 2004
Posts: 2,820
Connecticut
It will definitely show a change, but from the car moving sooner. When I heard that with the low gear set 904 I would “lose” flash rpm I got nervous. In reality you lose flash rpm, but you actually get to power band quicker during the run and while moving faster. I reach peak torque 1/2 sec quicker. Flash being stomp on the pedal off idle and how high the rpm’s climb BEFORE the car moves. Not really the same as if you actually took some flash rpm out of the converter.


best of 11.39 at 117 mph 1.60 60’. 68 340 S Barracuda Fastback F.A.S.T [IMG]http://i67.tinypic.com/2mnnnnt.jpg[/IMG]
Re: 3.55 vs 3.91 track time differences? [Re: FurryStump] #3152075
06/16/23 03:19 PM
06/16/23 03:19 PM
Joined: Jan 2004
Posts: 877
Pittsburgh, Pa
J
Jeff_383 Offline OP
super stock
Jeff_383  Offline OP
super stock
J

Joined: Jan 2004
Posts: 877
Pittsburgh, Pa
Thanks guys. If I can find a decent price on a 3.55 member, I'll probably get one. Otherwise I'll stick with the 3.91's. Drove 130 mile round trip on the highway last week. And at 65-70 it wasn't that bad

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