Ratio

[cal.cheesehead]

Can someone tell me what the rear end ratio is on a Unique 427? Thanks

[TurnpikeBoy]

Whatever you want it to be :).

Seriously, that's set by the owner when you buy the kit. If you can get up under the rear of the car, there's a small (3/4" x 1+") metal tag that the rebuilder sets under one of the rear cover bolts - and the ratio is stamped into that tag, along with some other cryptic info.

[eliminator]

For awhile most 427 cars with the FE series of engines had 3:31 gears. The buyer can specify what he wants. Butch Capps at Mid-South Gear in Knoxville does the differentals for Unique. He got a hold of several 3:42 gear sets and used them until they were depleated (not made anymore). The 3:54 gear sets are popular and now there has been a move by some folks to the 3:73. I ordered a 3:31 with my 427 side oiler 427 and a Top Loader close ratio. Was never happy with it so when I changed I went to the 3:73, wow you better have it pointed straight and both hands on the wheel, what a difference, that big block loves it. :3g:

[Jeff 427]

Rick
I've though about doing the same thing.
What RPM are you turning in high gear at 70 MPH?

[eliminator]

I can answer that after this week-end....I have learned with the use of my GPS that my speedometer is 5.5 MPH fast with this gear. At 60MPH with the GPS I was showing nearly 66 MPH on the speedometer.

[Jim Harding]

I can answer that after this week-end....I have learned with the use of my GPS that my speedometer is 5.5 MPH fast with this gear. At 60MPH with the GPS I was showing nearly 66 MPH on the speedometer.

Well at least this works to your favor... not going faster than the speedo. Mine is the other way, at 60 MPH indicated, the GPS says 65.

[eliminator]

Nice evening yesterday so I did a nice little 60 mile loop through the back raods of Bourbon Country (Jim Beam, Makers Mark).

With the GPS showing true speed this is what I discovered;
Approximate

2900 RPM 60 MPH
3400 RPM 70 MPH

My engine likes the new gear, one thing I noticed to my suprise fuel consumption was pretty much equal to the 3:31 rear gear. The reason is probably because I wasn't moving back and forth from 3rd to 4th all the time.

At 70 MPH you can nail it in 4th and it walks the dog!!!:3g:

[Brent]

Calculate RPM for given Speed(MPH), Rear Gear Ratio and Trans Gear Ratio
Enter MPH: 70
Enter Tire Diameter: 26.5
Enter Rear Gear Ratio: :3.73
Enter Trans Gear Ratio: :1

Result -- RPM: 3310


http://golenengineservice.com/calc/calcrpm.htm

[cal.cheesehead]

Thanks for your time and assistance.

[Justin Upchurch]

I really like the 3:31 gear in my car (FIA). I had ordered a 3:54, but they were out of stock at the time Butch did the rear-end. Although the cam doesn't really smooth out until a little North of 2100 RPM, I have no problems running along in 4th or 5th gear.

Lighter cars don't seem to need as much gear as the heavier cars and with the taller rear ratio, I can use 1st gear when most can't. Even at the track I have found that the quicker cars are running anywhere from a 3:27 to 3:55 rear end ratios. Originally I would have thought it was the other way around and would have never known any different.

Justin