effective gear ratio

Falco

Falco

Donating Member
Howdy,



I'm just wondering on tire sizes and gear ratios. Since I couldn't find here the original tire size for a reasonable price I put on 245/45R16's last year. This put down my tire diamter from 25.65" to 24.68" which makes my effective diff ratio to 3.55 opposed to 3.42 if I'm right.



My question is the following. How much could this slow me down on the 1/4th beside the disadvantage at the launch? I just wanna know how much tenths costs me to be a poor ass. :oops:

TIA,
 
dgoodhue

dgoodhue

BuSTeD 4.3
Re: effective gear ratio

Falco said:
My question is the following. How much could this slow me down on the 1/4th beside the disadvantage at the launch? I just wanna know how much tenths costs me to be a poor ass.
Click to expand...

I don't think it will make that much of a difference. You may notice that you need to use OD at the end of the 1/4 mile, which you might notice a small drop in MPH. I doubt you would see a .1 loss.
 
Falco

Falco

Donating Member
Thanks...

Thanks...

Thanks guys. Then it must be something else which makes me slow. :wink:
 
xcaliber

xcaliber

New member
OK, this confuses me,, all my life I have raced cars, along with more friends than I can name, and in all but 1 case (tirespin), deeper gears help your E.T.
I am considering putting 4.11 gears in my sy,, is there something I dont know??
I realise more gears kill your stall, so a bigger converter is in order, a converters stall is decided by engine torque, gears and vehicle weight.
deeper gears multiply your torque,
gets you into the torque range sooner,
with a built motor, better rods, pistons etc, you could turn more rpm, to stay in drive through the quarter at least to 115 mph or so, depending on what rpm that puts you at.
however for two years I havent heard anything possitive about deeper gears, whats the scoop???


Jamie Sanders
sy 0252
heber springs AR
 
T

turboj91

New member
Remember, changes in actual engine output of horsepower or torque are made only by making changes to the engine. If you change your gears, you do not make additional horsepower or torque. It will change the way the vehicle responds to the h.p. available (yes the rpm's will come up quicker). The gear change should not effect your stall speed. If you power brake the stall, your not moving and the drivetrain has no idea what gear ratio you have. Different torque outputs will effect your stall speed. Example, a generic 2800 stall converter may stall to 3000+ rpms with a healthy big block but only to 2500 or less with a weak 283 inch small block. You can have a converter custom made to your vehicles engine output, cam profile, vehicle weight ect... Higher numerical gear ratio's will run higher rpm's at the same vehicle speed. If you were to install 4:11's, with everything else remaining the same, you would need to shift into 4th gear (O.D.) to cross the finish line (or run at max rpm in third and stop accelerating). If I have read correctly, shifting into 4th under high boost conditions is not a good idea for a stock trans. You would prob. need a Brian Hartman built unit. If you wanted the higher rpm range to run the 4:11's, you need to build another motor. Our stock rpm limit is low as the cam is small, the heads do not flow high cfm's. Can get your higher rpm's from a bigger cam, but make the combo work. Change the heads to flow what the cam is capable of (make them a matched set - its actually factored the other way around), and build a bottom end to take the additional h.p.. It all equates to another motor. How fast you want to go depends on the size of your wallet as there is nothing faster than the cubic dollar.
 
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