Rear end gear question

[D-CEL]

Ummmm excuse me girly men!!
4.10s (or 4.30s) would be a hell of a lot more fun and are the only possible choice for that motor/trans!

Jason

[1985 CCX]

My $0.02

3:31 is overall best.................

3:54 tachs too high on freeway with a 4spd. If you have a 5 spd probably good eitrher way.

[michel schryer]

[That's true,5th gear is suppose to be boring, I should have said that it sounds like I'm idling almost, the RPM is that low. I just have to keep it in
4th at 60 mph If I want to get good sound. The main reason I want to change gears is to get the torque easier without having to punch it too much, I have to admit, I like to do small burnouts and drift a little, just for myself and also I found that sometimes in town at lower speed I was in between gears, wouldn't mind trying something different.

[Mr Jody]

To give you a quick calculation of the change in RPM you will see:

3.55/3.08 = 1.15…….so for a given speed, your RPM will be 1.15 times what it is now.

3.73/3.08 = 1.21…….so for a given speed, your RPM will be 1.21 times what it is now.

For example, if your engine is currently turning 1500 RPM at 60 MPH, if you change to a 3.55, you will be turning about 1729 RPM at 60 MPH after the change. If you change to a 3.73, you will be turning about 1817 RPM at 60 MPH after the change. Using the above calculations, try running in fourth gear at what the calculated RPM is, based on your current cruising speed RPM in fifth, to see if you like the sound or not.

It is also worth noting that if you do change the rear end ratio, you will also need to change the speedometer gear, or your indicated speed will be off by the above multipliers as well (ie., you will be going slower than indicated by 15% or 21% respectively). The speedometer is measuring the speed of the output shaft of the transmission and not the axle or wheel speed.

[xb-60]

Gearing really is subject to personal preference, yes?
I'd go with a 3.08 rear with a Toploader, so I would still be in 1st gear at 60mph when the guys with a 4.3 ( ) are already changing into third
Cheers,
Glen

[joyridin']

Originally Posted by D-CEL

Ummmm excuse me girly men!!
4.10s (or 4.30s) would be a hell of a lot more fun and are the only possible choice for that motor/trans!

Jason

I had 4.56 rear gears with a T56 and it pulled about 2100 at 70mph. Unfortunately, 1st gear topped out at about 20 mph. I'm down to 3.73's now.

[mpanten]

Originally Posted by D-CEL

Ummmm excuse me girly men!!
4.10s (or 4.30s) would be a hell of a lot more fun and are the only possible choice for that motor/trans!

Jason

Agreed, I went from 3.27 to a 3.73 and wish I would have went 4.10. If your going to change make it worth while

[mdross1]

Originally Posted by D-CEL

Ummmm excuse me girly men!!
4.10s (or 4.30s) would be a hell of a lot more fun and are the only possible choice for that motor/trans!

Jason

Good one D-Cel, had a set of 4;11's in a big block Chevelle when most driving was around town and only lived 3 miles from work.Loved it then,now it's almost 40 miles to work and this big block Ford is very happy with the grunt 1st gear of the Tremec and 3:70 cog.Row this thing out of 5th back into 4th and hang on.Gave the gear change in this car a lot of thought.

[D-CEL]

Remember this is not a 9 inch or a Jag, it’s an 8.8 and God loves them! They are strong, efficient and ridiculously cheap! I bought another complete 8.8 center section for under $100 and a used set of 4.10s off of eBay (I think they were $60 shipped!) and having it set-up was about $175? (Out of the car) R&R it in a couple of hours and you’re good to go. And you will have your orig. center section as a spare or sell it off to recoup some of the cost.
When you have an over driven 5th, 4.10 + gears are perfect. Mine has a .68 and spins about 2400@70-75. Puts the motor into the power band and makes 5th more useable.
Once you go 4.10, you’ll never go back! Lol


Jason

[joyridin']

Here, this site will give you the various speeds for different ratios.

Speed Potential Calculator For Ring Gear And Pinion Changes

[chomama1]

I, too, have a 3:08 rear gear in my FFR 302 and I end up driving most of the time in 4th gear, only going to 5th gear when on the 4-lane. The sound of a revving 302 thru the sidepipes is intoxicating and I love it. I would go to a 3:73 or lower, but why when I can just motor around most of the time in 4th?

[xb-60]

Originally Posted by D-CEL

When you have an over driven 5th, 4.10 + gears are perfect. Mine has a .68 and spins about 2400@70-75. Puts the motor into the power band and makes 5th more useable.
Once you go 4.10, you’ll never go back! Lol


Jason

With a rear end that low, do you always start from rest in first gear, or do you use second?
Cheers,
Glen

[G-Pete]

Originally Posted by D-CEL

Ummmm excuse me girly men!!
4.10s (or 4.30s) would be a hell of a lot more fun and are the only possible choice for that motor/trans!

Jason

Jason,
still grinning about that commend hahaha.

Yes, 4.10 are great gears to wake up small blocks. If I like to cruise with 70mph and 1500rpm ---- I take the Suburban

[D-CEL]

I laughed when I read “gears that low”. I’ve been running (and recommending to friends) 4.10s in Mustangs for years. Most had the same view point, until they drive with them. I would say “low” gears starts at 4.88 and go up from there.( I once saw a set of 7.33s for a 9”)
Actually 4.10s are much easier to live with everyday. The added toque multiplication makes coming out of the hole a snap. You can just about dump the clutch without adding throttle and it won’t stall. No need to slide the clutch to get it rolling. They naturally idle thru parking lots at idle rpm. It’s just an all around good deal. They make the car snappy and ferocious….just like a Cobra should be.
The “4.10 is too much gear”myth was born in the days of 1-1 top gears, 5000 rpm max, hydraulic lifter motors and E-70-14 tires (25” tall).
That combo with 4.10s @ 65mph would have the motor was buzzing along at about 3600 rpm (73% of max)and a blinding top speed of 90mph. Dropping the gear all the way down to a 2.73 would put the 65 mph rpm @ about 2400, you could live with that every day. But at the expense of 35% less available torque (give or take) that is a huge number in a “torque challenged” small block car.
Times have changed.
The simple swap to an over driven 5spd makes all the difference. A .64 high gear and 4.10s puts the 65 mph rpm @ 2300. Add a set of 295-50-15s and it drops to 2195.

Jason

[michel schryer]

That's awesome reading guys,so now I'm debating between 3.73 or 4.10, I'll keep reading until I decide with what gear to put in. I have to go to bed, I'm leaving for Mexico tomorrow,cheers guys !

[mdross1]

The only way you will ever know for certain is try each of the two gears 3:70,4:10 and decide which works the best for you.Our car has a 9" Ford back when we raced the car a lot always kept another third member with a different gear on hand,actually still have it under a bench.Having the big block with our setup Tremec TKO and 3;70 cog is ideal for the street,lack of torque is not an issue traction is at times.

[michel schryer]

Originally Posted by mdross1

The only way you will ever know for certain is try each of the two gears 3:70,4:10 and decide which works the best for you.Our car has a 9" Ford back when we raced the car a lot always kept another third member with a different gear on hand,actually still have it under a bench.Having the big block with our setup Tremec TKO and 3;70 cog is ideal for the street,lack of torque is not an issue traction is at times.

That a big job, not sure i can swap gears like that, plus the cost of the part, I will most likely go with 3.73 .Should I pay somebody to do it or I can do it myself,never done it before, I put the car together by myself, but not sure about the rear end, do I need special tooling to do that job ??

[RET_COP]

No one is wrong here.
All great posts [nice to hear from our more experienced guys too] and worthy of thought and talk.
It's all about your driving style, tire size, engine combination and Location {location intrigued me} [we all have a light car].
Drag racing and road racing get into trans gear spacing which is not really the top of our discussion but can be added for specific reasons.
With that said, read and choose, this thread is worthy of a sticky.
Merry Christmas all
Lou