Hi Guys,

Unfortunately I had a little problem with my current 4.27 gear and I will need change them. So I'm running with a 904 Trans, 4200 stall, Hoosiers 28x10.5 and the car has 3300lbs with me.

I'm having some doubts about how to choose. Keep 4.27, or change for a 4.09 / 4.56? Just for information here in Brazil we run 1/8.

follow below an image the I recorded from my datalogger and two more images with dyno informations.

Are you happy with the way the car ran with the old gear ratio? If not, swap it Now comes the hard part, which way
If you choose the 4.10 it will stay in low and second gear a little longer but run in third gear less
If you go to the 4.56 it will get into high gear sooner and maybe be quicker and maybe not
If it leaves the starting line fine now, no tire spin, then the 4.56 might be a better choice, if it spins now it would not a better choice
IHTHs

Thanks Man...

With 4.27 I Haven't tire spin. This is the main reason that I'm thinking to change from 4.27 to 4.56. No tire spin and heavy car.

Maybe 4.56 will be car faster at 1/8.

Before you try anything get that 4200 stall converter out of there and get the stall up to "at least 5200" if not more. My Sons 360 and went from 11.0's to 10.50's by doing this and picked up even more going from a 4.56 gear to a 4.10 gear at 3200 pounds. his converter foot braking stalls at 5400-5600 rpm and shifts at 6400 rpm.

I'd try the 4.56 in the 1/8.

if you have to change gears go ahead with the 56s if not id leave the 27s in and do the stall increase like pittsburg said.....5200+.its not worth it $$ wise for a small gear change like that unless your current gears are broke.

Thanks for your advices... So, about the converter this is supposedly be 4200, on footbrake I got around 2800 and when I leaved the brake the flash stall goes to 5200 as you can see in the image below:

Do you think that I need more stall?

If you are trying to go faster, gear it to finish a little above the horsepower peak, if you think it will still have traction. If you are bracket racing and looking for the best consistency, a gear that will let you shift later, like the 4.09 will do two things. It will increase your consistency in the 60 ft if you have much inconsistancy, and it will increase consistency of your shifts, which in some cases can mean a lot. If I didn't have an airshifter to shift perfectly on time, my car would not be as consistant. Things happen too fast at the 1 to 2 shift to be dead on all the time.