Ford 9" rear ratio discussion

[randy]

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?

[Flash68]

What is the engine and powerband?

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

[randy]

Ls3 447 rwhp

[71RS/SS396]

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

[randy]

Can you view this?

https://m.facebook.com/story.php?story_fbid=10101410507319306&id=48502792

[Vegas69]

Agree with these guys, 3.70.

[randy]

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.

[gnx7]

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 :)

[randy]

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.

[markrieb]

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

[Vegas69]

That would probably mean about a 4.88. :lol:

[randy]

The 3.70s are perfect. Cruising 70 plus mph at 2200 rpms helps on gas and noise. 5th gear is more usuanle around town. 2nd, 3rd, and 4th is still a blast. Only bad thing is my gears make some noise while decelerating above 40 mph to 60 mph

[TheJDMan]

I realize we are splitting hairs now but I'm running a surplus NASCAR center section with a 3.89 and I think it is perfect with my 26" tire. I recommend that you take a look at the Tremec gear ratio calculator and play with different gearing to see what suits you.

http://tremec.com/calculadora.php

[randy]

I just wish moser would have built it right in the first place. Made noise while accelerating before and after a new gear swap it makes a slight noise during deceleration but acceleration if quite as can be. Buddies moser made a real bad noise and after new gears it's dead quite all the time.

Not worth pulling the 3rd member on the ground again. Total pita

[simon455]

I purchased ex nascar 9" cooled center section with g force locker (run sutton has tuning springs for them) Its equipped with pretty odd 3.80 ratio rem polished gear set.
Would of gone with 373s but came across this center section and decided to give it a try. Price was really right consider nascar team pays over 5k for one of these. Car still in progress, lsa/tr6060 335 30 18s

[carbuff]

I'm curious where you purchased the center section from. Is there a particular good site to shop for these parts? As I recall, there are several vendors of these types of parts...

Thanx.

[Flash68]

I'm curious where you purchased the center section from. Is there a particular good site to shop for these parts? As I recall, there are several vendors of these types of parts...

Thanx.

If you're talking about the guy who posted above you, any of the Nascar resellers in NC and surrounding areas generally have those 9" lockers, REM polished gears, internal pump, in a wide variety of common and in between gear ratios (I got 3.64). I got mine from Roush Yates for $900 I think a few years back. Added the Sutton 40# locker springs as well. Will have to test it out one of these years.... :D

[simon455]

I'm curious where you purchased the center section from. Is there a particular good site to shop for these parts? As I recall, there are several vendors of these types of parts...

Thanx.

Mine was from the guy from Knoxville Tn. Area
Found him on racingjunk also he's on eBay. Got his number still somewhere in my phone. Contacted him, he had his son I believe text me close up pictures and details About given section. Though to find one with a ratio close to 3.73
Seen 3.60, 4.00. I also bought the 4.00 section for a for a friend
Both came with R.E.M. Treated gears, cooling pump, arp hardware, g force locker, billet caps, bilet yoke, n case, all safety wired. Not all of them come like
that...basically you want to verify that before you get it, they usually have a lot of those "pigs" but again, desiresble ratios, gota catch em fast

[TheJDMan]

I'm curious where you purchased the center section from. Is there a particular good site to shop for these parts? As I recall, there are several vendors of these types of parts...

Thanx.

I purchased my 9" center section direct from Hendrick Motorsports. They have what they call their "Raced Parts" dept. I know Roush Racing also used to have a used parts dept but I heard they have spun that off to a separate company now. There is also a company called "2nd Chance Race Parts" which is just down the street from Roush.

http://2ndchanceraceparts.com/