Rear Gear HELP

[Repsol58]

Educate me please. I'm trying to figure out which rear gear to run 3.33 or 3.73? I have an LS3 crate motor and plan on marring up to a t56 6 speed. My goal is to beat the hell out of it on the auto cross track but also enjoy putting in long mileage trips with the wife. Which gear would you suggest and why?



Thanks,

[lbluecamaro69]

If possible I'd suggest something in between like 3.50 or 3.55:1 .Mark stielows 67 camaro has a 3.25:1 I believe but he's pushing almost 900 horse.it depends on what you'd prefer though.with the t56 you'd probably be fine with the 3.73s

[Schwartz Performance]

Which T56 do you have? I'd go for 3.73 if its the Fbody style.. And 3.33 for a close ratio t56 magnum

[Repsol58]

I haven't purchased the Transmission yet. Trying to figure out which would be better, although I was leaning towards the magnum as I am planning on supercharging the motor down the road.

[Schwartz Performance]

Gotcha. Yeah I'd go for the close ratio magnum and a 3.33 if that's what's available for your rear end. That way in the Goodguys autocrosses you may not even need to shift into second ;)
Shoot me a pm or email if you get close to ordering a magnum, I can help you out a bit

-Dale

[badazz81z28]

If you have a crap load of torque, you don't want a lot of gear. With a T56, I would opt for a 3.73-3.90

[Repsol58]

Thanks for all the replies guys and Dale, thanks for offering to help. You'll be hearing from me in the near future.

Wade

[Todd in Vancouver]

Check out a gear calculator and do the math so you are making an informed decision. Check out the driveline forum and you'll see lots of help there.

[Motorcitydak]

May want to consider something else. I have a t56 with a 0.50 6th gear and will be running a 4.56 gear

[Sean Cooke]

The less you have to shift the better - the longer you can stay in one gear the more time you have to focus on actually driving the car - just my opinion- I have a GM 12 bolt w/3:73 behind a 4l80e could have gone with a lower gear - I like smooth & fast some people prefer a harder hit though - figure out what kind of driving you want to do & what's comfortable for you

[Scott Parkhurst]

If you run too high of a gear (low, numerically) the 6th gear in a T56 will be useless. PLEASE do the math before making a purchase! I did, and I have a 3.89:1 gear behind my RS Gear T56. It turns only 1,400-1,600 rpm at freeway speeds. If I had 3.55s, 6th would be useles, as the engine would lug below 1,000 rpm at freeway speeds.

Consider how much time you'll spend autocrossing vs. how much time you'll spend driving on the freeway, and also how important freeway MPG numbers are to you. That LS engine will pull you down the freeway at 1,400 or so...you'll need enough rear gear to put it there.

[Zachalanche]

I built a sweet spreadsheet for this. I gan get you cruise speeds, and optimal shift points for a few different rear gear ratios, if you can provide rear tire size, transmission ratios, and a dynograph from a similar engine. with vehicle weght, drag coefficient, and some vehicle dimensions, I can take it a step further.
here's a sample:

[Schwartz Performance]

Tire size is obviously a big factor. As well as the t56 you go with. The close ratio is only .62 6th gear so with a 26-27" tire 6th is still useable. Whereas the .5 wide ratio will need at least a 3.73.

-Dale

[Todd in Vancouver]

I built a sweet spreadsheet for this. I gan get you cruise speeds, and optimal shift points for a few different rear gear ratios, if you can provide rear tire size, transmission ratios, and a dynograph from a similar engine. with vehicle weght, drag coefficient, and some vehicle dimensions, I can take it a step further.
here's a sample:

This is cool! Can I send you my imformation and a couple variables I'm looking at?

[Zachalanche]

This is cool! Can I send you my imformation and a couple variables I'm looking at?

sure. just need the following:
-transmission ratos
-HP curve (I can make some estimates and assumptions if all you have is peak HP and Torque numbers, and thier corresponding RPMs, but the outcome is only as good as the data you put into it. this is used to determine where the optimal shift point is - where the higher gear torque exceeds the lower gear torque)
-Tire size
-elevation that you will be driving the car at unless HP numbers you provide are measured at that altitude.

[Motorcitydak]

Something to add is that I plan on having a 7000rpm limit and will be hitting it often. My 2nd gear will top out at 60 and with the 0.50 6th gear I will be just under 2000rpm at freeway speed. Post up your tire sizes, rear gear choices and the ratio's available for the trans. How do you plan on using the car? Are you willing to thrash it a bit or do you want to keep it under 3000rpm just about all the time?

[XLexusTech]

i went with 3:70.. closs ration t56 on a 26 inch tire.

[Todd in Vancouver]

Perfect, as I am starting on the rear suspension soon and I'm going to need to make some decisions. I'm looking at using a 4.11:1 or a 3.91:1 rear gears and a 26" or a 27" tall rear tire. If you can show me this combination of these 4 options than I can get an idea what will work best for Autocross and also for cruising at highway speed because I've got to be able to drive this car to the races and then back again and in most cases thats going to be a long drive.

The information you need is below in red;

sure. just need the following:
-transmission ratos -TKO600 #5009
First Gear Ratio:2.87:1
Second Gear Ratio:1.89:1
Third Gear Ratio:1.28:1
Fourth Gear Ratio:1.00:1
Fifth Gear Ratio:0.64:1
-HP curve (I can make some estimates and assumptions if all you have is peak HP and Torque numbers, and thier corresponding RPMs, but the outcome is only as good as the data you put into it. this is used to determine where the optimal shift point is - where the higher gear torque exceeds the lower gear torque)

-Tire size
Using an 18"rim @26" or a 19"rim @27"
-elevation that you will be driving the car at unless HP numbers you provide are measured at that altitude.

Dyno was done at local shop and will be raced at seal level same as dyno sheet shows
*please note that the dyno sheet stops at 6,800 and that I should be slightly higher with a fine tune and a bit more RPM, closer to 500+hp @7,500

[Zachalanche]

Perfect, as I am starting on the rear suspension soon and I'm going to need to make some decisions. I'm looking at using a 4.11:1 or a 3.91:1 rear gears and a 26" or a 27" tall rear tire. If you can show me this combination of these 4 options than I can get an idea what will work best for Autocross and also for cruising at highway speed because I've got to be able to drive this car to the races and then back again and in most cases thats going to be a long drive.

The information you need is below in red;

Dyno was done at local shop and will be raced at seal level same as dyno sheet shows
*please note that the dyno sheet stops at 6,800 and that I should be slightly higher with a fine tune and a bit more RPM, closer to 500+hp @7,500

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