Do I need 4.88s?!
#1319738
10/13/12 03:05 PM
10/13/12 03:05 PM
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Joined: May 2004
Posts: 617 Corvallis,OR
540CUDA
OP
super street
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OP
super street
Joined: May 2004
Posts: 617
Corvallis,OR
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Current set up goes through the lights at 7000 rpm with 4.56 gears at 145mph with 33" Goodyears. Engine made peak HP at 7300 on the dyno and I shift at 7500. I need new slicks for next season and was thinking of some wide 14x32's but I dont think there will be enough difference in rollout to change what it traps at. My converter is an ATI 9" that flashes at 5800. My inner voice tells me to try the slicks and go from there, but I was looking for some opinions. I also plan on installing a hood scoop before next season so I know I'll have some retuning also. I just have a hard time believing a 540 needs 4.88's to get down the track optimally. Thanks, Tony
Last edited by 540CUDA; 10/13/12 03:08 PM.
PRH 540,T-ram,-1's tagged and insured. 9.24et 146.13mph 1.30 60'3300#s
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Re: Do I need 4.88s?!
[Re: 540CUDA]
#1319739
10/13/12 03:20 PM
10/13/12 03:20 PM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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Basically you are wasting the last 600 rpm's of your power.... you make peak power at 7300 and in MOST cases you want to cross the line at 10% above peak HP but you also need to look at the drop back RPM on the shifts.. so if its falling down past peak torque its most likely hurting the ET
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Re: Do I need 4.88s?!
[Re: Cab_Burge]
#1319742
10/13/12 05:34 PM
10/13/12 05:34 PM
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Joined: Jan 2004
Posts: 903 Saskatchewan, Canada
cudabin
super stock
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super stock
Joined: Jan 2004
Posts: 903
Saskatchewan, Canada
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I have 4.56's and 10.5W-31's w/ 727 auto.
I shift such that it goes into second at 7,300 rpm and into 3rd at 7,600 rpm and it traps as high as 8,100 rpm.
Peak power on Dyno was at 7,200 rpm.
If i wind it higher in first say to 7,800 rpm before the shift actually happens, I lose .05 easy...
I would keep the bigger tire and go with the 4.88's first. All the ET has happened by 1,000 feet IMO.
Good luck with it!
67 Cuda 8.48@ 158.7 mph 1.18 60' 2,600 DA(so far...)
70 Super Bee 440 Six Pack 4-speed. 13.2 @ 104 Stock exhaust/Street tires.
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Re: Do I need 4.88s?!
[Re: jim sciortino]
#1319745
10/14/12 10:27 PM
10/14/12 10:27 PM
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Joined: Jan 2003
Posts: 17,918 Akron, Ohio
ProSport
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 17,918
Akron, Ohio
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All the testing I've done over the years, my cars have always liked to trap 300 RPM's over the best shift point. I shifted my 340 Scamp at 6700, trapped at 7000. Shifted my 451 DartSport at 6300, trapped at 6600. 69 Dart 500" shifted at 6600, trapped at 6900.
1970 Challenger, all aluminum 528 Hemi, HDK suspension, Tremec 5 speed manual
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Re: Do I need 4.88s?!
[Re: 540CUDA]
#1319746
10/15/12 05:14 AM
10/15/12 05:14 AM
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Joined: Jan 2003
Posts: 10,006 Frostbitefalls MN (Rocky&Bullw...
gregsdart
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 10,006
Frostbitefalls MN (Rocky&Bullw...
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I would try the shorter tire which should pick you up about 300 rpm. With the overly aggressive first gear in a 540/Torqueflite combo (assuming you run one!) you might lose on the bottom what you pick up at the stripe. What was peak torque on the dyno sheet? 5800 rpm might be a tad low, and a converter loosened up to gain 400 stall may put you up around 7600 rpm with a 102 roll out and 4.56 gears. Mine gained 300 rpm on top when loosened up.
8..603 156 mph best, 2905 lbs 549, indy 572-13, alky
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Re: Do I need 4.88s?!
[Re: gregsdart]
#1319747
10/15/12 01:47 PM
10/15/12 01:47 PM
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Joined: May 2004
Posts: 617 Corvallis,OR
540CUDA
OP
super street
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OP
super street
Joined: May 2004
Posts: 617
Corvallis,OR
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I would try the shorter tire which should pick you up about 300 rpm. With the overly aggressive first gear in a 540/Torqueflite combo (assuming you run one!) you might lose on the bottom what you pick up at the stripe. What was peak torque on the dyno sheet? 5800 rpm might be a tad low, and a converter loosened up to gain 400 stall may put you up around 7600 rpm with a 102 roll out and 4.56 gears. Mine gained 300 rpm on top when loosened up. This was in the back of my mind too Greg and yes its a 727.Peak torque was 5800rpm. The ATI conv is very tight 4% if I figured it correctly?
Last edited by 540CUDA; 10/15/12 01:47 PM.
PRH 540,T-ram,-1's tagged and insured. 9.24et 146.13mph 1.30 60'3300#s
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