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do i have enough gear or not enough?

2K views 6 replies 2 participants last post by  xoliex 
#1 ·
currently i have a mild 466 with 28 inch tall slicks and running a tko600 5spd with a 2.87 first gear and 3.7 gears. i trap at about 108-110mph and barely use 4th gear and i'm crossing at 5000rpms in fourth.

i'm going to be getting back my 521 from scotty j with about 640ish HP. with the 28x10.5 slick i have now, i went to the track with it last time and i was all over the place until i made the calvert as stiff as they recommend.

before that motor is going in, the car is in the fab shop to get the mods needed to fit a minimum of 29.5x10.5W slicks. that is 30 inches tall and was possibly thinking about going with 31x13 slicks if i absolutely have to relocate leaf springs. i'm going to be limited with a 15x12 with a 7.5 or 8.5BS.

this is a 73 mustang.

so if i go with a 30 to a 31 inch slicks, do i have enough gear or not enough? i'm trying to nail down a consistant 11.0'ish ET for the brackets and something that will handle the 125hp shot of nitrous of course.

any input would be perfect guys, thanks!
 
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#2 ·
It's really gonna depend on where the HP peak is gonna be with the new engine. Figure out your mph using your car weight and horsepower then calculate the gear ratio using that. My best et's have come when I could go through the traps about 300 RPMs above my peak HP.
 
#3 ·
the iron motor made max power at 5900rpms, with the higher breathing SCJ's, scotty to expect around a 6300rpms peak.

to be able to cross 4th at 6600rpms, it'll take somewhere around a 4.10 gear. by that time, my 2.87 first gear and a clutch might be useless.
 
#5 ·
the car in stock trim weighs 3800lbs. but i have gutted interior, alumium seats and the added weight of the 460. i'm at least in the range of 3500-3600lbs.

i will know for sure today because my fabricator is scaling the car today to know the exact weight.

he looked under my car and is suggest we hold off on the tires and work more on suspension. but regardless if i don't go huge with the tires, i need to know if i decide to just go with teh same width tire, if i am going to kill the motor with going with a 30 inch tall tire instead of staying with a 28.
 
#6 ·
I wouldn't change tires our gears until you get the new engine on there and take it to the track to see where you are at first. The added torque may pull the gears you have now, I am thinking 3.89 may be the cats meow.
 
#7 ·
my fabricator agrees, he wants me to address the source of the problem first before tires. he wants me to do suspension before he takes my money on doing a mini tube which will only bandaid the problem.

so i am doing a poly bushing ladder bar suspension.
 
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