MattW

iTrader: (1)

right now i have a one wheel peel 3.73 rear end and im thinking about swapping out for a posi...but i was thinking maybe i should change the gears to 3.42 so i dont run out of rpm in the 1/4 mile......right now im running 13.5's @101mph and i never pay attention to what rpm im at but im afraid that IF i do some more mods and get my car into the 12's then i will be running out of rpm....and i definately dont want that to happen

any comments or suggestions would be greatly appreciated...

1989GTATransAm

iTrader: (3)

Well going by what SLP used to advertise when they sold the gears I would say around .1 second.

89IrocZ350TPI

It should be easy to get a better launch with the 3.42s. The 3.73's must burn those tires pretty easy huh?

Trevor86TA

You are likely not even close to running out of gear. For example, I use tiny 26" tires with 3.73 gears and go through at 114mph between 5600-5900 depending on which converter I have in there. Even if you pick up to 110mph, you should be fine unless your converter is slipping outrageously.

BTW - are you running slicks?

MattW

iTrader: (1)

yah since i have a peg-legged 3.73 rear it is VERY easy to spin off the tire.....and i dont run slicks....i wanna get some DR's soon....either BFG or MT ET steets.....right now my best 60' time was a 1.945...which is why i really wanna get a posi and DRs

i will really have to look at my rpms next time, because it seems like it is reving up pretty high.....but yah if im under the 5500 range then i will keep 3.73's when i swap to a posi......and if im over i will just keep the gears and then go with a taller tire for the drag strip.....

Trevor86TA

There is a link to an RPM calculator on the main TGO page. Enter your tire size, gears and MPH and it will do the math for you. Try it wit the current MPH and desired MPH. Also remember that the calculator doesn't consider TC slipage and that trap MPH is an average of the last 60' while you actual peak MPH (and therefor RPM) is a little bit higher.

MattW

iTrader: (1)

yah well the tc slippage is what i am afraid of....when i swapped the motor i needed a torque converter for a cheap price because i wasnt planning on buying one when i did the motor swap....so i think that this tc is a cheap crappy one so it probably slips a little more than the better ones.....

itsjustabird

iTrader: (1)

personally i say stay with the 3.73s and spend the money on tires. if in the future the rpms become a prob then swap a set of 28" drag radials on it and youll be fine. besides the taller tire looks good on these cars. just my $.02

Dialed_In

iTrader: (3)

I'll trade you some 3.42's for your 3.73's

You'll lose around a tenth but you'll pick up some in the 60 and gas mileage.

Orr89RocZ

iTrader: (20)

hell you might not loose at all....

i have yet to get solid evidence yet but i went slower going to 3.27's from 2.77s. so it all depends on ur power band and such.

i would think u might trap abit higher with the 3.42's, but not too much more.. maybe just 1-2 mph. and the ET should be about the same

but it depends on what rpm ur at now when u cross the line

smoktire

Last year my setup was somewhat like yours stock vortec - manley race flow valve - xe268 cam - 1.6 roller rockers -Air gap rpm intake - holley 600 hp -1 5/8 shorties with 2.750" single exhaust - th700 with shift kit... with MT ET drag 28X9X15 sliks and locker rear with....

-3.42 I went 13.35@103

I change for a

-4.10 and i went to 13.17@104

So the gain is about .18s

87TPI350KID

You also have a stall, which helps the guys with lower gears tremendously and compliments the weak power-band of the TPI. The 3.27 gears are nice for guys without a stall.

I doubt you would loose any time. If you spin of the line now, those will help you hook better and give you a better trap spd.