Quick question for all you hardcore guys.

I'm gonna be making enough power here shortly to be trapping low 120's. It will be on N20.

Currently have Nitto 275/40/17's and 3.73 gears. Car is an A4 with a TCI 4000 converter. Tires would be 25.7" tall.

Gonna build my axle to race this season. Was wondering if I needed to step down a ratio to 3.42's so that I don't hit the rev limiter when I'm crossing the traps.

Gear calculator says that in 3rd with the 3.73's 6000 rpm would be 123mph.
In 3rd with 3.42's would be 142mph. Of course that's not taking converter slip or tire growth into account.

I have future plans with the car to go even faster within the next year or two, into the 130-135 range. Would it be worth it to me to change ratios? Would it change how hard the car launches or how it does off the spray?

Oh, and before anyone asks, I don't have tuning software currently, but it's on the short list, so I would have my tuner change the gear ratio, but I wouldn't be able to change tire sizes quickly, so I couldn't run the Nittos on the street, and then a 27" or 28" at the track.

Any advice would be welcome.

 

Rewire your speedo sendor to your front ABS wires. I did this for my th350 swap and I can swap rear tires no matter what size difference.

Also if you are going to run a 28" tall tire for the track, do just that, use it ONLY at the track. It won't mess with anything but your speedometer, and you shouldn't even have your eyes on it going down the track. (That is if you don't rewire your speedo)

 

But wouldn't it throw off my shifts? The car wouldn't know that there's a taller tire back there. Car is tuned for a 25.7" tire.

 

Bump for opinions.

 

i went to the track last night to make a few passes with my new 4000 stall. I also have 3.73's and i was crossing the traps at 109mph at 6100 rpm. On a that same tire size also. Im confused.

 

I've gone 114.5 @ 6000 before. I swear I've hit the limiter at 113 due to converter slip before in the warm weather.

 

my converter is brand new. that was the first pass on it. I wouldnt figure it would be slipping.

 

Check into a high growth tire. We did that years ago on our dragster and changed from a 3.90 gear and went to a 4.10 with a high growth tire. That helped all thru the quarter mile.
I'm just not sure if they make them for your application though. It would be worth checking into though.

Here is a pic of my car.

 

High stall converters aren't as efficient as stockers. There is some degree of slip involved.

 

be careful that is not true for all lines of converters...

when i went from a stock stall to a ss3600 i gained 1mph at the track with all conditions and everything taken into account...you should gain or stay the same with a good aftermarket converter...

now with a cheaply made converter or a fuddle type you are not going to be as efficient...and will lose mph...this is the exact reason i went with yank

 

What ratio are you running man? You're probably running what I need to be.

EDIT: Duh, look at your sig. I'll probably step down to 3:42's now.

 

yeah depends on what you are shifting at if you are staying stock internal, i am not sure what gear would work for you...

i am shifting around 6600-6700 and am leaving some on the table being 3.23 gears but i am not going to make the 10 bolt any weaker with 3.73s, when i get a 12 bolt i will definitely be getting some 3.73s...4.10s if i go with a 28" tall tires...

i used to shift my SI at 6300...

i think right now i am going through at 4900ish i believe......

if you got 3.73s in now i would just keep them you should be fine