fiat 48 and merit to this?

[Blown 472]

Theory #1 says go with deeper gears to improve traction, because if (when) the tires start to spin, they won't blow away as fast, and slight backpedaling will recover quicker. There may be other points on the deeper gear theory too.
Theory #2 says use taller gears so there is less torque at the wheels and more MPH is achieved before the 2nd gear shift. At a higher MPH, the tires are less likely to break loose.

[Floored]

#1 no the gears multiply tq and can make you traction limited, depending on,vehicle weight, hp, trans, converter, flywheel weight, suspension, tire size and type, strip or street, launch rpm, N2O, blower, turbo. set gearing for 2-500 rpm past hp peak at end of 1/4 mile and start tuning to track and atmospheric conditions. #2 why they use powerglides. taller first gear reduces tq to tires which helps in light cars with big hp to hook and leave hard. puts serious load on engine internals and makes use of race gas critical for high cylinder pressures encountered on a pass.

[Fiat48]

I guess this is applies to a drag car. In which I'd have to say Theory 1 is closer. But not the whole story.
Most guys overtire the car. Biggest tire they can fit or pull. They gear the car to run the RPM where they make the most HP at the finish line. The lower the gear (either differential or trans low gear), the easier it is to get the car up on the tire. Some guys opt for a real low ratio low gear in the trans which supports theory #1 to get the car launched and improve 60 ft. times. Too high a gear can cause tire "shake", meaning the tire tries to run over itself and wads up, shaking the Hell out of the car and driver.
Lots of variables here in suspensions vs soild mount cars, weight etc. But you get the idea.
"At a higher MPH, the tires are less likely to break loose" theory is somewhat correct I guess. But tire shake on the gear change put me in a guard rail at 145mph.
More gear doesn't always mean more MPH. You gotta be able to pull that gear at the rpm where your motor makes the power.

[Blown 472]

I found that on the moparts site, a guy running the FAST series and limited to street tires. I am trying to go as fast as I can on street tires too, and once the tires break loose it takes a bit for them to stop spining, I have a 2.76 rear gear and going to a 3.91 with a 28 inch tall tire.
I would like to see low 11's on a street tire before I go to slicks, going to see what I can mph in the lights with 3%, 9% and 13% over.

[Fiat48]

Are you allowed to use the DOT approved street "slicks"?

[Blown 472]

Originally posted by Fiat48
Are you allowed to use the DOT approved street "slicks"?
I can use what ever I want, and I will be going to a full slick soon just want to see what I can do with a street tire, kinda bragging rights thing. Some buddies that think they have fast pontiacs.;)

[Fiat48]

Need to know:
Desired or rpm max
Car weight with driver
Trans speeds ( gear ratio's help)
The can give you some calcs.

[Blown 472]

Trying to find the gear ratios on the 727, car weighs 4360, wet.
looking for 6300/6500 rpm in the lights. My buddy has a small block with a 28 inch tall tire and 3.91 that run 10.59 and turns that rpm in the lights.
Ok, first 2.45 to 1, second 1.45 to 1, and 1 to 1 in third.

[Fiat48]

Well, you need about 600 hp to do 11 seconds. Speed of 120 mph. And a 28 inch tire with a 3.91 gear at 120 would be about 5900 rpm. a 4.10 would get you about 6300. A 4.56 get you to about 6900. I have added 400 RPM converter slip and no real tire growth.
The 3.90 gear may put you into the lights just shifting into 3rd. Big heavy car. With a 3.90..you may want to fisnish in 2nd. You need a trail run first. Just kinda what to expect.
You're buddy's car should be running about 125 mph if his application is correct. Am I close?

[Blown 472]

Originally posted by Fiat48
Well, you need about 600 hp to do 11 seconds. Speed of 120 mph. And a 28 inch tire with a 3.91 gear at 120 would be about 5900 rpm. a 4.10 would get you about 6300. A 4.56 get you to about 6900. I have added 400 RPM converter slip and no real tire growth.
The 3.90 gear may put you into the lights just shifting into 3rd. Big heavy car. With a 3.90..you may want to fisnish in 2nd. You need a trail run first. Just kinda what to expect.
You're buddy's car should be running about 125 mph if his application is correct. Am I close?
Going by the weight and the mph I am pulling right now I am in the 600 to 650 range, last time out 117 in the lights.
I am just pulling third about 50 feet before the lights and going thru a 4000 rpm.
I think it runs 123/124.

[396_Z]

Seeing as I forgot how to figure out he HP from time slips and such can one of you be so kind to give a guy a hand?
14.05 @ 99.7, 3450 lbs
and
13.7 @ 101, 3400 lbs (this car dyno'd at 260 hp to the wheels 4 months later)

[Fiat48]

Originally posted by 396_Z
Seeing as I forgot how to figure out he HP from time slips and such can one of you be so kind to give a guy a hand?
14.05 @ 99.7, 3450 lbs
and
13.7 @ 101, 3400 lbs (this car dyno'd at 260 hp to the wheels 4 months later)
99.7 mph @14.05 et for 3450 lbs = 230.69 BHP
101 mph @ 13.7 et for 3400 lbs = 237.37 BHP. 14.32 Lb/HP , 60 ft should be 1.558, 1/4 et should be 13.17, 1/8 et should be 8.56, 1/8 mph should be 82.82 mph.
Application (ET) is 1/2 sec shy of what it should run with that HP.

[396_Z]

Thank you Fiat, I owe you a beer if ever we meet.
(or I can ship if you prefer)

[Blown 472]

me too, fiat you rock, thanks for all the info.