Input on rear gear ratio decision

I'm having trouble deciding which gears I want to put into my car.
The Grand National 8.5" rear end that I'm putting in has 3.42's in it right now. I currently have 255/60's on for rear tires. From the online calculators I've used I've figured that my highway RPM would be virtually the same (within 1mph) if I went with a 3.73 gear and a 275/60 tire.
The cam will work with either according to the designer of the grind (the guy who designed the Lunati Voodoo series). My converter is a B&M 2400 Holeshot.

The car is built mainly for street fun with an occasional trip to the track. Either choice will only run around 2500rpm on the highway at 55.

Which set-up would you choose with the info I've given? Any input to try and decide this would be greatly appreciated! I have a little while to decide yet.

[MR.hp]

I'm having trouble deciding which gears I want to put into my car.
The Grand National 8.5" rear end that I'm putting in has 3.42's in it right now. I currently have 255/60's on for rear tires. From the online calculators I've used I've figured that my highway RPM would be virtually the same (within 1mph) if I went with a 3.73 gear and a 275/60 tire.
The cam will work with either according to the designer of the grind (the guy who designed the Lunati Voodoo series). My converter is a B&M 2400 Holeshot.

The car is built mainly for street fun with an occasional trip to the track. Either choice will only run around 2500rpm on the highway at 55.

Which set-up would you choose with the info I've given? Any input to try and decide this would be greatly appreciated! I have a little while to decide yet.

You are right the 3.73 gear and taller tire will be better as the car will rpm faster through the gears and will have good top end due to the taller tires.
I currently run 3.55 gears in my street car with a tall tire.

[ReRod]

Another thing that I like about the 275/60 and 3.73 combo is that there are more choices for drag radials in that size in comparison to the 255/60's.

and will have good top end due to the taller tires.

Do you mean good top end power or good top end speed? Because when I input the two combos the mph drops a few with the 3.73's (using the same engine rpm).

[MR.hp]

Another thing that I like about the 275/60 and 3.73 combo is that there are more choices for drag radials in that size in comparison to the 255/60's.


Do you mean good top end power or good top end speed? Because when I input the two combos the mph drops a few with the 3.73's (using the same engine rpm).

Top speed but you will get the mph back I think when you change the tune
after the gears.

[speedo]

Depends on your gearing in your Trans also, your going to have to talk to fastkeen on that but I think the 3.73 would be a nice all around gear for your goals with the car. Can still drive it and get down the track without leaving to much on the table with RPM.

Or you could go 410's and try to squeek by with a 26" tire and see what she does for a max effort gear. If you need a bit more just jump to a 28" tire.

Did you ever find out if they are narrowing them rears to get a bigger tire in with the correct offset wheel?

[ReRod]

Depends on your gearing in your Trans also, your going to have to talk to fastkeen on that but I think the 3.73 would be a nice all around gear for your goals with the car. Can still drive it and get down the track without leaving to much on the table with RPM.

Or you could go 410's and try to squeek by with a 26" tire and see what she does for a max effort gear. If you need a bit more just jump to a 28" tire.

Did you ever find out if they are narrowing them rears to get a bigger tire in with the correct offset wheel?

From what I've seen, lots of the G-body guys will notch the frame and trim or roll the fender lips to get nice meaty tires under. I'll probably roll with it the way it is for this summer and see how it goes. Hopefully it'll hook okay with some DR's! If not, maybe I'll have to consider some further changes.

[mustangmike]

I'm having trouble deciding which gears I want to put into my car.
The Grand National 8.5" rear end that I'm putting in has 3.42's in it right now. I currently have 255/60's on for rear tires. From the online calculators I've used I've figured that my highway RPM would be virtually the same (within 1mph) if I went with a 3.73 gear and a 275/60 tire.
The cam will work with either according to the designer of the grind (the guy who designed the Lunati Voodoo series). My converter is a B&M 2400 Holeshot.

The car is built mainly for street fun with an occasional trip to the track. Either choice will only run around 2500rpm on the highway at 55.

Which set-up would you choose with the info I've given? Any input to try and decide this would be greatly appreciated! I have a little while to decide yet.

You should go with 3.73

[mustangpauly]

I think you should you go with 5.13 you sissy.

[ReRod]

I think you should you go with 5.13 you sissy.

:rotfl:I like driving on the highway too much for that

[KrisR]

I'd leave the 3.42s in it, unless they need replacing anyway. Are you going to use a non-l/u converter? If so, definitely keep the 3.42s. IMO, anything more would become a pain on the street without a lockup converter.

[ReRod]

I'd leave the 3.42s in it, unless they need replacing anyway. Are you going to use a non-l/u converter? If so, definitely keep the 3.42s. IMO, anything more would become a pain on the street without a lockup converter.

I'm running a non-l/u converter (B&M Holeshot 2400). Still can't make up my mind though about the gears. I think it will come down to the condition of the stock 3.42's. If they're good yet I think they'll stay in there. Gears are too easy to change later on if I'm not happy with 'em...

[ramairws6]

I'd stick with the 3:73, it's an all around good gear for street and strip. You can allways change your stall to acomadate. Traver

[ReRod]

I'd stick with the 3:73, it's an all around good gear for street and strip. You can allways change your stall to acomadate. Traver

I think I'll take the easiest route. Check conditon of stock 3.42's. and run them if they're in good condition. If I'm not happy with the performance, swap in 3.73's. Later down the road would be the hydraulic roller cam and a different converter

[ramairws6]

I thought you had the 3:73's in there already. If that's the case then ya, keep the 3:42's in there and see how it goes. You might even like them with that stall. You should have a fun car there Rerod!! Traver

[Red Rocket]

I think I'll take the easiest route. Check conditon of stock 3.42's. and run them if they're in good condition. If I'm not happy with the performance, swap in 3.73's. Later down the road would be the hydraulic roller cam and a different converter

Good plan. Also, when converter time comes again spend the extra coin for a custom built unit. Properly spec'd they will all around out perform a shelf converter.