Rear Axle Gearing Suggestions. What should I start with?

[Iamtheonlyreal1]

My Volvo X project is in its final stages of getting road worthy, and I am ordering the rear end gears this week. Normally this is a fairly obvious choice, but this car is just a bit differnt..

Here is what we have... A 2500-2700 pound 1967 Volvo Amazon, with a 540 Horsepower LS6, Tremec TKO600 5-speed with a 2.87 first gear (.82 5th) I am running a B.F. Goodrich G-Force Tire (265/35/18), which gives the overall tire diameter to be 25.3in. I am also running a Speedway Engineering Full Floater Mod-light 9in rear end, 14in Wilwood front brakes, and 13in Wilwood rear brakes with the full Wilwood pedal and hydraulic pedal assembly, ect.

With the gearing, I am looking for a happy medium of Daily Driving, along with being to have a very respectable track car. I am running QA1 coil over suspension, along with the bolt in front and rear end suspension kits I have designed for these cars.

I know there are some experience track/road course people on here, and any experienece input would be greatly appreciated.. I can look at all the calculators I want, and that will give me some idea of a starting point, but I would like to see if I can get some idea's from experience.

Here are Two Gear Ranges I have been looking at, and some figures for those ranges.

3:08 gears

Gear__________RPF*__________RPM__________Speed____ ______RPM__________Speed
1st___________1.33__________3000__________26______ _______6500__________55
2nd___________0.88__________4280__________55______ ______6500___________84
3rd___________0.60__________4402__________84______ _______6500__________124
4th___________0.47__________5078__________124_____ _______6500__________159
5th___________0.38__________5330__________159_____ _______6500__________194
Your RPM at 70 MPH is 2348 (5th gear)


3:50 gears

Gear__________ RPF*__________ RPM__________ Speed__________ RPM__________ Speed
1st___________1.52___________3000___________22____ _________6500___________49
2nd___________1.00___________4280___________49____ _________6500__________74
3rd___________0.68___________4402___________74____ _________6500__________109
4th___________0.53___________5078___________109___ _________6500__________140
5th___________0.43___________5330___________140___ _________6500__________170
Your RPM at 70 MPH is 2669 (5th gear)

Here are some pics of the setup I am running.. These pictures are with the mock up motor, so things are quite cleaned up yet.. LOL

[Flash68]

With a TKO trans, 3.50 for sure. IMO

[GregWeld]

I'd look at one other criteria.... your torque curve of the cam you're using...

Are you at the bottom, middle or end of the curve at your shift points. Look at it as a "system".

For the track -- I don't think there's any question about using the 3:50's... You probably don't need the 190+ top speed of the 3:08's unless you're running Nurburgring...

[Iamtheonlyreal1]

Originally Posted by GregWeld

I'd look at one other criteria.... your torque curve of the cam you're using...

Are you at the bottom, middle or end of the curve at your shift points. Look at it as a "system".

For the track -- I don't think there's any question about using the 3:50's... You probably don't need the 190+ top speed of the 3:08's unless you're running Nurburgring...

I do believe the Torque curve is somewhere in the Mid RPM, but I will double check that with my builder for sure..

[GregWeld]

If you were just going on the street it wouldn't make much difference... but on the track -- then that whole combination needs to work together... and that has to do with gear spacing etc. It was more critical back in the day when we ran 4 speeds... probably -- but as long as you have time to ask the questions and get into it... nows the time, before you commit.

[Flash68]

Agreed, Greg. And taking what you said and applying it we have a very wide ratio trans here (2.87. 1.89. 1.28. 1.00) and a LS motor probably not making a ton of torque (assuming it is not stroked here). With those big gear spreads I certainly would not want the 3.08 ratio with all that performance oriented setup in there. Lots of people run 3.70 or even 3.89 ratios with the TKO.

[GregWeld]

Yeah ---- I like the 3:70 over the 3:50

[FETorino]

Originally Posted by Flash68

Agreed, Greg. And taking what you said and applying it we have a very wide ratio trans here (2.87. 1.89. 1.28. 1.00) and a LS motor probably not making a ton of torque (assuming it is not stroked here). With those big gear spreads I certainly would not want the 3.08 ratio with all that performance oriented setup in there. Lots of people run 3.70 or even 3.89 ratios with the TKO.

Remember his car only weighs 2700lbs so he can get away with big gear spreads and less torque.

I'd plan it around the 2nd thru 5th for track use. 1.89 1.28 1.00 .82
With a 3.89 it looks like below. I figured 5500 rpm for peak power and around 3000 for peak torque.

First will let you take off from a light in idle and great for parking lots.


Gear RPF* RPM Speed RPM Speed
1st 1.11 3000 31 5500 56
2nd 0.75 3725 56 5500 83
3rd 0.59 4297 83 5500 106
4th 0.48 4510 106 5500 130
Your RPM at 70 MPH is 2966 (4th gear)

Below is some food for thought from a racer with a heavier car.

Originally Posted by 73CPCAMARO

I got the transmision back from Competition Transmissions and Gears in North Carolina this week. I changed the gearing to a better setup for the road courses. I ended up with 2.24, 1.73, 1.30, 1.0 gears.

Originally Posted by 73CPCAMARO

I have 3.70 rear ratio. We will see how it is. I may go to a 3.89 if 2nd gear is a bit too tall. I like to run 2nd gear on most autocross courses. 1st gear will be good for the peanut Goodguys courses or slow portions of other autocross courses. The beauty of this transmission is that it is so easy to shift up and down (no clutch).

[Flash68]

Originally Posted by FETorino

I figured 5500 rpm for peak power and around 3000 for peak torque.



Below is some food for thought from a racer with a heavy car.

If that is a stock displacement LS6 at 540 hp, that is a higher peak than 5500. I'd bet 6000+. And torque peak is not at 3000. I'll bet it's at 4500+. Remember, this is LS land. I don't have one, but I am forced to be familiar with them as they represent the majority of the competition.

If this was a 3000rpm torque peak motor with a lower power range, I would tend to agree with you.

You're calling Hobaugh's car heavy? Compared to 2700 lbs every car is heavy I guess! His is only 2900 before he adds ballast.

https://lateral-g.net/forums/show...&postcount=765

[FETorino]

Originally Posted by Flash68

If that is a stock displacement LS6 at 540 hp, that is a higher peak than 5500. I'd bet 6000+. And torque peak is not at 3000. I'll bet it's at 4500+. Remember, this is LS land. I don't have one, but I am forced to be familiar with them as they represent the majority of the competition.

If this was a 3000rpm torque peak motor with a lower power range, I would tend to agree with you.

You're calling Hobaugh's car heavy? Compared to 2700 lbs every car is heavy I guess! His is only 2900 before he adds ballast.

https://lateral-g.net/forums/show...&postcount=765

Meant heavier car not heavy.

I don't know s t about LS motors, and don't care too, just making some assumptions based on their OEM sataus and design parameters for drivability. But from a quick google on the LS tech forum somebody posted this.

"The T1 racing corvettes with stock LS6 motors, and stock air intake and stock headers and cats, then straight pipes are dyno tuned to 385-387 wrhp, 375-380 wrtq with peak HP at 6300 and red line of 6700. and a flat tq curve from 1500 right up to 4800"

I'll give you I was almost 1k off on peak hp rpm but 3000 rpm is about dead center of the torque curve flat spot so maybe my assumption is good or the guy on the LS forum shouldn't be posting.

If this is true the LS makes near peak torque right off idle so he could pull tall gearing but then what is 5th for and the gap between 1st and second is like the grand canyon so I wouldn't want to be rowing between those gears on an autocross.