killer305

iTrader: (1)

right now i have a stock 2.73 non-posi(i think) and am waiting to put 1000 mile on my engine so i can go drag-racing. i currently have a 3.23 posi in my basement that i am grinding down and re-painting, and i was wondering how much that would effect my time, i know that you should go through the traps at redline, and if these gears dont do the trick i'll try some 3.43's or 3.73's thanks

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90 RS 305 tbi, 4 3/4" cowl Hood, Edelbrock TES headers, Flowmaster exhaust, Crane roller cam, comp roller rockers, vortec heads/intake, ported tbi, w/new injectors, MSD probillet Distributer/ coil, 1 inch tbi spacer, air foil, 14x4 k&n flat base air cleaner, Rebuilt 700r4 w/ B&M shift kit, B&M Megashifter, 3.23 posi, 2 12 RF's with mtx amp, top of line alpine cd player, soon to have 90-91 gfx, z-28 wing, new paintjob, rims, and all new lowered suspension.

F-BIRD'88

Going from 2.73 to 3.23 won't be worth the effort, but going to posi track will.
Why not trade the 3.23's for a set of 3.73's or 4.10's. remember 4th is overdrive and will still give you a nice low rpm at hiway cruise. You can make a good guestimate of the required gear for best street performance.
by making a few 1/4 mile passes and noting the speed and rpm (in Drive) at the end of the quarter just when u cross the finishline.
Do more than one pass and take the highest mph and RPM acheived. Divide this rpm by your gear ratio and then multiply by the new gear ratio till you get an rpm equal to
that which peak horsepower happens. (in Drive) {3rd} .not 2nd or OD. This will be the correct Gear/tire combo for your car/motor for 1/4 mile.Your ET should improve
because you will be using all your motors power to get down the track. If you switch the tires, adjust your gear the same way.
Taller than stock tires require more gear Shorter need less gear for the same speed/RPM
PS... Ignore the ET when doing these tests.
It will vary too much to be an accurate indicator, but the MPH will be real close.
A set of sticky tires (don't have to be any bigger than stock, just sticky) will really set you in your seat with your new gears.
By the way your motor with your combination will reach peak horsepower, right around 5500 RPM so this is the rpm you should finish the quarter mile at.
http://photos.yahoo.com/russ_q




[This message has been edited by F-BIRD'88 (edited November 03, 2001).]

killer305

iTrader: (1)

thanks, i knew their was some type of a formula somewhere.

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90 RS 305 tbi, 4 3/4" cowl Hood, Edelbrock TES headers, Flowmaster exhaust, Crane roller cam, comp roller rockers, vortec heads/intake, ported tbi, w/new injectors, MSD probillet Distributer/ coil, 1 inch tbi spacer, air foil, 14x4 k&n flat base air cleaner, Rebuilt 700r4 w/ B&M shift kit, B&M Megashifter, 3.23 posi, 2 12 RF's with mtx amp, top of line alpine cd player, soon to have 90-91 gfx, z-28 wing, new paintjob, rims, and all new lowered suspension.

AlkyIROC

Gearing affects torque multiplication. Too little and the car is slow off the line. Too much and the wheels just spin.

Finding the best gearing also depends on tire size. 3.73 gears react differently with 26" tall tires than they do with 28" tall tires.

Tall tires usually need deeper gearing. While a street car with 26" tall tires may only need 3.73 gears, going to 28" tall tires may require 4.10 gears to get the same results.

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and check out the race car

87 IROC-Z SuperPro ET Bracket Race Car
461 naturally aspirated Big Block (times are for the current engine)

Best ET on a time slip: 11.447 altitude corrected to 10.99
Best MPH on a time slip: 119.42 altitude corrected to 124.86
Altitude corrected rear wheel HP: 493
Best 60 foot: 1.586

Racing at 3500 feet elevation with a typical race day over 5000 feet density altitude!
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87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley