how do i figure out trap rpm with my diff gear?

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mshred

mshred

The Green Manalishi
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Hey guys,

I was wondering how can i calculate what gear, speed and rpm i will ge going through the traps at in the 1/4 mile with the gears i have? I have a 3.91 gear right now and will be running a 28 or 29 inch tall tire and my tranny first gear is 3.35 and fourth is 1:1...I want to know what gear i will be in going through the traps with this setup and what rpm as id like to be maxing out fourth around 6k...I also want to try to figure out how this setup would fare with a 4.56 and 4.88 gears- do you guys think that those last two ratios are way too big combined with my first gear ratio and will be me traction problems at the line? (overall first gear will be 15.1 and higher with these but im thinking they will put me at a more desirable trap rpm)...cruising speed is not a problem here, i have an OD..curious to know about off the line with these gear combos and trap speed/rpm...if this seems unclear i will try to explain it more please let me know

thanks
matthew
 
thanks for the link...it asks for speed, but i dont know what my speed will be when im crossing through the traps so i cant really use the calculator accurately....here are the ratios of the tranny im using
T-5- 3.35, 1.99, 1.33, 1.00, 0.68
 
You cant figure out rpm without having a trap speed. What do you expect it to run?
 
I know low 13's are in her indefinatly, but im shooting for high 12's with some seat time and good consistency
 
tried it again with a 4.89 ratio and seems id be better off with that ratio...at 6000rpm i would be going 105mph...that sounds more realistic to me...dont know how well i would fare having a 3.35 first gear though with that rearend gear (overall first gear ratio of 16.3)
 
105 is probably pretty reasonable. A lot of guys are surprised when they start doing the math to find just how much gear a slower car needs for optimum drag strip perf. The od is a big plus on the street
 
george said:
105 is probably pretty reasonable. A lot of guys are surprised when they start doing the math to find just how much gear a slower car needs for optimum drag strip perf. The od is a big plus on the street
Click to expand...

that was with a 4.89 gear ratio...do you think that 4.89 combined with a 3.35 first gear will be too much tire spin off the line and impossible to control?
 
more than likely the bias ply M/T sportsman tread in 29x13 inch size...im worried im going to have a hard time hooking with this much gear on a street tire...gonna have slant 6 t bars up front and trying to get my hands on a set of 002/003 ss springs for the rear; i also have an adjustable snubber for it
 
why don't you run a 26 or 27" tall tire and keep the 3.91s. the if you drive it on the street with a 27 or 28" tire it will be a lot more livable, and it will work better with your 1st gear launch.
 
im only going to run one tire for both street and strip..dont have the money for two...plus, i want the bigger footprint of a 29 inch...thats why i minitubbed my car afterall...will the 4.89s be too much?
 
Honestly, if you cant get it to hook with 4.89s, it probably wont hook with 4.10s or 4.5s either. Especially with the OD, I would go for the 4.89s. Hope you can shift good, cause that thing is gonna eat up first gear in a hurry.
 
cool thanks for the info george...im actually excited to get a huge gear under her man because acceleration will be awesome and i can still cruise real nice!
 
im hoping late july...i really dont know to be honest with you. we'll see how things go
 
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