Hot Rods Quick Change Ratios

I am running a Tremec 5 speed behind a Scot blown 286 cu. in. 8BA flatty in a 29Tudor.
The trans has radical .63 overdrive. The differential is a Winters V8 currently running a 4.11 ratio gear. Rear tires are 29 1/2 in. diameter. I would like to be able to use the over drive at the current 55mph Wisconsin speed limit. ( I would also like to be able to run 70 on the interstate ) Would some one please be kind enough to help me with the math I need so that I can order an appropriate gear set.

 

I get asked this question all the time when I sell a T5 kit or Quick Change. For most installations I recommend a 3.78 gear set. Most of my sales are to guys building highboys or other cars with tall rear tires (31 inches tall) There's all kind of opinions and I'm sure they'll be voiced here. I think with your tire size and OD ratio the 3.78 gears would work just fine. I have used this gear ration in a number of cars and pickups with results. JMO

 

Simple math, with a 4.11 gear, and a .63 overdrive you have around a 2.58 gear in 5th. With a 29.5" tire @ 2000 rpms, at 55, you will need a 1.28 spur ratio. That is a set #6, 21-27 teeth. These are the numbers I came up with. It all depends on what rpm you want to turn at 55 mph. Let's see what others think.

 

I’m guessing guys today are different Marty. When I ran a quick I had at least 15 sets of gears for all occasions. They want just to one set and it needs to be perfect for all driving.. you and know that isn’t going to happen with a .63 OD. Too me that was a poor choice.

 

First use this calculator

https://www.strangeengineering.net/gear-ratio-calculator/

And look up gear sets on a chart like this.

Speedway has a good one as well



That OD ratio is what is going to make it a hard compromise. QCs are there for a reason, you will probably end up swapping a couple different gearsets

 

Your right JD, I have buckets of gears, wired together per set, that way you can fine tune, what you want or need. It can be tough to select the right gear, first time out of the box.

 

I don't get it either. It's equal to a woman needing a ring on her finger. It's all for show. I think I read some time ago here on the HAMB that the Quick Change is the new Jag rear end.

 

I had an old Craftsman tote type tool box with all my gears (it was heavy). It also had a speed handle with the correct flex socket, a small bucket and a suction gun. The lid had a Speedway gear chart with the ratios in the box underlined. I remember for sure we had a #1&#07A, #5&#6 , #7&#8 , #3&#4 (only 3 gears needed for these pairs) and various ratios suited for certain track and tire combinations. We did most of our chassis adjustment with gears and tires. I don't know why you would buy a quick change and then have only one gear set; even on the street.

 

For me it was the only rear end that I could easily modify and get parts for to run backwards.

 

I’d bet the car was built with a certain look in mind, not one that needs 10+ sets of gears for any occasion.
Like putting a mild hood scoop on for a look, not necessarily a need.
I mean if he built it with a 9inch, you wouldn’t expect him to have 6 or 7 drop ins set up and ready to go.

 

Drive the car in 4th gear (1:1, easier for math, and not as fast).

If possible, don't pay strict attention to speed. Figure out where the "sweet spot" is in RPM, where it is neither lugging, or over-revving.

That's the RPM you want for your top cruising MPH. Do the math to figure out what QC gears you need to get there in 5th.

0.63:1 is not that radical. My top gear is 0.50:1.