Sure grip 489 rear end with a 4.1 ratio

[dan73challenger]

Looking for some honest opinions I have been up grading my 73 Challenger which has a 360 with a 727 that has a shift kit in it. I recently bought a lot of 73 Challenger parts in it included a sure grip 489 4.1 ratio rear end My current rear end is a 489 also but not a sure grip. I've been hearing a lot that the 4.1 ratio really isn't all that practical for a daily driven car, as mostly my RPMs on my engine are going to be very high going down the highway. Any feedback would be great he appreciated before I put this rear end in my car. There's nothing wrong with what's in my car it was is factory. Thank you in advance

 

[Challenger RTA]

isn't all that practical for a daily driven car, as mostly my RPMs on my engine are going to be very high going down the highway.

That would be correct. Calculate RPM for Given Speed(MPH), Rear Gear Ratio, and Trans Gear Ratio

 

[gzig5]

Do you need a Sure-Grip? A large percentage of these cars were built with open rear diffs and driven every day. The SG comes in during performance driving or drag racing. If you aren't going to be using the car that way, there is no reason to change the diff. If you still want the SG but are happy with your current gear ratio, you can simply resell the 4.10 unit and use the funds to add a SG unit to your current setup. Dr. Diff has several options for SG units including upgraded helical units.

 

[pschlosser]

For a few years, I drove a 440-6 car with 4.10 sure grip in the rear as a daily driver.

I could go to and from work without any freeway driving, just city driving, and some farm roads. That worked out great for those 4.10 gears.

On the occasion I was on the freeway, it did feel a bit unkind to be zipping along at 3800 RPM for extended periods.

So, is 4.10 impractical? Not at all, but it does impact highway driving, some. If you ARE on a road trip, you cannot be in a hurry, as you won't like hitting those high RPMs at 65-80 MPH for extended periods.

The sure grip was essential on the 440-6 car, especially with 4.10s. But maybe less so, for small blocks. That said, the sure grip is a pretty transparent upgrade, but introduces one small issue a driver must be prepared for, that is when both wheels break loose under hard acceleration on a curve.

 

[dan73challenger]

That would be correct. Calculate RPM for Given Speed(MPH), Rear Gear Ratio, and Trans Gear Ratio

How wood I be able to calculate it out the transmission gear ratio