Ford 9" rear ratio discussion
 

67 camaro , ls3 447rwhp, t56 magnum 2.66 , 315/30/18 rear tire (25.44") Ford 9inch

4 or 5 times a year autocross, weekend fun car

Currently have 4.11s and I was thinking about switching to a 3.70 or 3.90 gear. 4.11 are a blast but I would like to lower the highway rpms down slightly but don't want to lose to much of my 2nd and 3rd gear around town pulls. Not alot yoy can do in 1st and 2nd gear goes by quick .

What do you suggest? Will I notice a difference with going to a 3.90 or should I drop down to 3.70s?

What is the engine and powerband?

I think you're in the right range - 3.70 or 3.89

Ls3 447 rwhp

I would go with the 3.70.

Here's what the different ratios will yield in 6th gear with that trans.

3.70 3.89 4.10

8000 RPM 259.75 MPH 247.06 MPH 234.41 MPH
7500 RPM 243.51 MPH 231.62 MPH 219.76 MPH
7000 RPM 227.28 MPH 216.18 MPH 205.11 MPH
6500 RPM 211.05 MPH 200.74 MPH 190.46 MPH
6000 RPM 194.81 MPH 185.30 MPH 175.80 MPH
5500 RPM 178.58 MPH 169.85 MPH 161.15 MPH
5000 RPM 162.34 MPH 154.41 MPH 146.50 MPH
4500 RPM 146.11 MPH 138.97 MPH 131.85 MPH
4000 RPM 129.87 MPH 123.53 MPH 117.20 MPH
3500 RPM 113.64 MPH 108.09 MPH 102.55 MPH
3000 RPM 97.41 MPH 92.65 MPH 87.90 MPH
2500 RPM 81.17 MPH 77.21 MPH 73.25 MPH
2000 RPM 64.94 MPH 61.77 MPH 58.60 MPH
1500 RPM 48.70 MPH 46.32 MPH 43.95 MPH
1000 RPM 32.47 MPH 30.88 MPH 29.30 MPH

You can go to the Wallace Calculator and play with ratios http://www.wallaceracing.com/gear-speed.php

Can you view this?

https://m.facebook.com/story.php?sto...06&id=48502792

Agree with these guys, 3.70.

3.70s is what im leaning towards. Maybe 1st and 2nd will be more useful. Now after i swap the gears out i guess im going to need to add more power.

I had a 440rwhp/385rwtq heads/cam LS1 with an Fbody T56 in a 2950lbs car (includes driver) running 3:90's and MichPSCup 285/30/18 square. I felt that gear ratio was perfect for the power and always put it down anywhere on track aside from slow 2nd gear corners where I actually really stabbed it. One could easily modulate the pedal and apply the power. I daily drove the car.

If you are not caring about the last few tenths when racing get the 3:70 gear ratio for overall better fuel economy. An LS3 isn't very far away from making 500rwhp with a better cam and long tube headers :)

I already have lonftube and a cam. While it's only the hotcam it's nice and safe. Now if ( when) I decide to upgrade the heads I'll swap out the cam as well. That's why I was leaning towards a intake to compliment my future mods. Fast lsxr 102 with the stock throttle body should gain some power and be more than enough for future upgrades.

Most autocross tracks run 60 mph or so at the fastest part of the track for the faster stock cars (SCCA rule/suggestion/insurance limitation).

Gear the car to run between 60 to 70 mph at redline in 2nd gear