FSUNole17

iTrader: (18)

I am still a little confused, why is it better to pick a milder set of gears (3.73) for a blower? what makes it different than a N/A engine (i know what makes it different, but why would u want your gear selection different) thanks!

Slowhawk

iTrader: (12)

Most people do it so they don't hit the rev limiter before the end of the track. The second reason is that FI boosts up the midrange,so you will be a faster car if you can use that midrange.Shifting slow's you down.

FSUNole17

iTrader: (18)

would a 3.89 be too much gear?

Pro Stock John

iTrader: (34)

Depends on tire size, shift point, and power level.

I ran:
144mph
28x10.5 slick
shifted at 7000
3.50 gear
T400 trans

I was doing 6700-7000 rpms thru the traps. Calc's had suggested a 3.65 gear, but there is no such thing. I'd rather go a little under. I had 4.10's at one point, and they ran me thru the gears too fast. I was in 3rd too quickly.

So it depends. Some say less gear will load the blower more, but I have not done any reading on that so my comment is at this point purely anecdotal about that.

WAHUSKER

iTrader: (4)

Mostly it's to allow all that power you get from boost in the mid-range to do you some good. Like others said, you blow thru the gears pretty fast. I have 4.10s & I shift into 2nd just past the 60' mark. And I'm into 3rd not long after that. So my rear end is in the shop now getting 3.40s installed.

There are other reasons for me making the change. 1 - I was shifting into 4th gear at about 1100' (BAD juju for an A4). 2 - extending the shift points high enough to stay in 3rd could over-drive the S/C (60K max). 3 - 4.10s + >500rwhp = 0 traction!

PS and if memory serves me right, taller gears are 3.23s, deeper gears are 4.10s

engineermike

My power peak is at 5800 and I have a 25.5" tall tire. Do the math and the top speed is around 150 mph at 6200 rpm with my 2.73 gears. Plus, they make the TH350 real livable on the highway.

FSUNole17

iTrader: (18)

wow guys thanks for the insight, i ALMOST bought a rear end for my procharger with 4.11's on an M6 and after reading these threads, im GLAD i didnt, thanks again!!

Drewstein

The goal would be to keep in your power band as long as possible. A blower's power band is nice and fat, so you want it to last as long as possible without needing to shift. Shorter gears help n/a cars more because they need to rev to 7k way faster than we want to be there.

Pro Stock John

iTrader: (34)

On the dyno, my car was seeing like 138mph with 4.10's, but after I went to 3.50's and turned up a bit, it was seeing 162mph LOL.

Richiec77

iTrader: (3)

Oh man. Here's the Dyno again. LOL

Sound advice and something I know that I guess I took for granted. I need to think over what I'm doing more and come up with some Q's like this.

SuperZ

iTrader: (2)

Once you start getting more power you will need less gear.You will be in the gear actually moving instead of shifting the whole time.

Pro Stock John

iTrader: (34)

This is all for the 1/4, maybe some folks might advocate a 4.10 for a 1/8 mile track. Veteran racers have strong opinions on how they pick a gear, and some folks pick gears that are a little too short (IE a 4.10 not a 3.73) because they would rather be overgeared.

I think that might be more the case for NA. With a power adder setup, maybe more so for turbo, if you are overgeared you might see a big drop in power. If you keep going through the power band, and then beyond, you might be at like 6500, and you're making a lot less power than you made at peak. You can tell because the car starts to nose over.

I think with the Speed Inc. project Camaro, they were overgeared for a little while, and the car ran great but the mph was a little low... They might have regeared that car twice.