How much will 3.73 help me?

[timfoster405]

I am running my 07 GT at 12 psi right now... which made around 540 rwhp at JDM.

With this set up, I just ran 11.05 at 122 mph w/ 1.60 60 ft. today at cecil county

The weather was pretty good today... about 65 deg.

I am running a stock rear w/ 3.31 gears.... with that, the car is shifting 4th very late and running through the traps at around 5000 rpm.

Anyway, I am thinking its time to switch to a lower gear ratio in the rear.

What will I see from an improvement in ET, mph, and 60 ft. time going to 3.73's. 4.10's won't work, I will be switching to to my 16 psi pulley soon...where my mph may jump up to around 126 to 128...

 

[Rob72]

I'm surprised that you're shifting in 4th with 3.31s.

 

[skwerl]

What size tires are you using? Maybe try going to a slightly shorter or taller tire for the track. Either adjust it to stay in third or else shift into 4th earlier and get in the powerband. I had the same issue when I first started drag racing. My first set of drag radials were 28" tall and I was having to shift into 4th almost at the 1000' mark. Staying in 3rd bouncing off the limiter killed my trap speed but I wasn't in the peak powerband if I went into 4th. Went to a 26" tire and it was perfect. Now I'm crossing the line in 4th at around 5800 rpm.

 

[marcspaz]

I have an RPM vs. Speed calc. It looks like if you borrow tires from someone that are 2 - 2.5 inches shorter than yours (regardless of the size you currently have) and you'll see the same affect. That will let you know if you want to change gears or just get some tires..

 

[timfoster405]

I am shifting into 4th since I am going 122 mph !!!


There is no way I can keep it in 3rd gear and rev it out... at 122 mph my rpm would be 7800 rpm w/ my current tires...MT 325 50 15 Drag radials (revs/mile is 747 w/ these tires - or equivalent diameter is 26.98" even though the tires are 28" OD w/ no load on them).

3.31's shift@6500 rpms 3.73's
1st gear 0 to 49 mph 0 to 44 mph
2nd gear 49 to 69 mph 44 to 61 mph
3rd gear 69 to 102 mph 61 to 90 mph
4th gear 102 to 122 mph(5030 rpm) 90 to 122 mph(5700rpm )