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Rear gear Ratio Recommendations

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What diameter tires? What rev limit? 3.7 works well with 25" and 6700 rpm but not so much with smaller diameter. At least for most all the road courses I've raced. You'll never use first and likely not second either on a road course. Im currently switching to 3.54 to better match 23" race tires. For fun runs it really doesnt matter though.

 

Cameron

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What diameter tires? What rev limit? 3.7 works well with 25" and 6700 rpm but not so much with smaller diameter. At least for most all the road courses I've raced. You'll never use first and likely not second either on a road course. Im currently switching to 3.54 to better match 23" race tires. For fun runs it really doesnt matter though.

 

Cameron

Since I am installing a big disk brake I will probably use 16" wheels, not sure on tire diameter maybe 25" The LS3 peaks around 6000 rpm so maybe 6500 rpm limiter

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You can use that thing by you right knee with the knob on it to make minor adjustments in gear ratio when needed. All ya gotta do to make your diff ratio all wrong is to change tracks or events. And forget about using 6th gear, unless you get a 4.38 diff, in which case, you can forget about using 1st.

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You can use that thing by you right knee with the knob on it to make minor adjustments in gear ratio when needed. All ya gotta do to make your diff ratio all wrong is to change tracks or events. And forget about using 6th gear, unless you get a 4.38 diff, in which case, you can forget about using 1st.

I guess when you put it that way. There are three tracks within an hour or so, all quite different. The heck with it, I'm leaving the 3.54's in. Thanks

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Yeah, that's what most of us run.  Its just a great all-purpose ratio.  If you find a LSD, it will most likely be in a 3.70 ratio.  I don't know that it is really worth the time it takes (not a lot) to swap it into a 3.54.  I actually have every factory ratio on my shelf: 3.90, 3.70, 3.54, and 3.36.  I will be buying a 3.18 likely next month.  I run the 3.54 for just about everything.  Once I come up with, and prove, a quick-change front diff mount, I hope to change ratios often.  But, that front diff mount is just such a pain to deal with(!), and that is what keeps me from making as many changes as I'd like.  For example:  for the 1/8-mile, I love the 3.54 with a 27" slick.  But guess what - Mickey Thompson just discontinued their 27" slick, leaving only a 26" or 28".  So, that 3.70 that I've been hating on might become relevant again.   Perhaps after you start with a 3.54, you will find that there is an awkward shift on your favorite track-then you can figure out how to change around that by changing ratios.

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I have the the 3.70:1 LSD in mine with a T56 and 24.9" diameter 225/50-16 tires.  That being said:

at 60 MPH in 6th (.50:1) the engine turns 1,500 RPM

                  in 5th (.75:1)                            2,250 RPM

                  in 4th (1:1)                               3,000 RPM

 

A 4L60E with the 3.70:1 would essentially cruise at 2,250 RPM at 60 MPH

A set-up with the same size tires but a 3.54:1 R200 would see:

at 60 MPH in 6th (.50:1) the engine turns 1,435 RPM

                  in 5th (.75:1)                            2,152 RPM

                  in 4th (.50:1)                            2,870 RPM

 

Bottom line.  No matter what tire or transmission you're using the 3.54 will reduce RPM at any given speed by 4.3% over a 3.70.  You can accomplish the same thing by upping your tire diameter by 1", as long as it will fit in your fender. 

Edited by Phantom

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