Sure Grip Gear Ratio

[Glow Worm]

My 73 Cuda has a 3.55 sure grip. I am upgrading the 340 to at least 400 horsepower. I plan to drive it quite a bit so I am going to change the rear end to a 3.23.

Do any of you know of anyone running a 2:93?

I'm thinking it wouldn't be able to get out of its own way out of the hole, but highway driving would be awesome.

Pros - Cons?

Thank you.

 

[challenger6pak]

I would leave the 3:55. My 340 loved it.

 

[moparleo]

Ditto. 340's love RPM's.

 

[Glow Worm]

Ditto. 340's love RPM's.

Not for driving 400 miles . . . one way . . .

 

[moparleo]

Drive something else. Again, 340's need RPM's to make power. Or money up for a overdrive. Then you can do both.

 

[Glow Worm]

I don't want to sound argumentative, but why would I want to run the high RPMs at 75 MPH for a 6 hour trip? At 60 it already sounds like it wants to fly apart, and yes I know about the "high revving 340" history.
I'm not going to be racing. I'm just an old man who want to go places in my Cuda. I had a 3:23 in my 390 horsepower 318 (Built by Mike Liston @ MRL Performance) and it was just fine. I was mainly interested in hearing if anyone knew anything about the 2:93. I suppose I'll just go with the 3:23 and if I don't like it I can switch it back.

 

[moparleo]

It is just that a high horse power engine and 6 hour drives usually don't go together. Over drive is the best solution. You can run low ( high numerically) gears for good low speed acceleration and on the hiway the overdrive will act like a low (numerically) rear gear. There are add-ons like Gearvendors or there are the GM 4 speed overdrives with a Mopar bellhousing bolt pattern.

 

[ramenth]

I've had several AHB M-bodies with 2.76's and I can tell you, those cars screamed for 3.23's at the very least. Even with highway driving (my cars have been known to cruise all up and down the East Coast). While the RPM's may drop with the longer legs you're actually cheating yourself in the need to put your foot in it and go, especially in heavy traffic when discretion might call for you being able to pull in the passing lane in 80 mph traffic. Might not be as big of a deal with a worked 340, but still, it's a nice advantage to have.

Personally, I like 3.23 as an all around gear. Long enough legs for the RPM drop you're looking for while still allowing the engine to get into the power band quickly.

 

[DetMatt1]

I get where you're coming from, I like road trips in my classics too. I think 2.9 to 1 would be a mistake but the 3.23 to 1 was a very common gear and I think would be fine for the way you want to drive it. You could also go with taller tires to alter the final ratio and might even find a plug in calculator on the net to calculate the ratio.

 

[challenger6pak]

Ok. You originally said drive it a lot but did not mention the 6 hour trips part. I've had the 2:93. Like Robert said it isn't enough gear to move the car in passing gear. Use the 3:23 or a taller tire to cut the 3:55 ratio down.

 

[340challconvert]

A lot of good feedback here. You would kill your 340's acceleration with gears taller then the 3;23s.
Hard to set up the engine for "400" HP and look for lo RPM,s. They do not go together.
I used to keep an extra set of rally rims with taller tires for my 340 / 3:55 Challenger when I was taking a long road trip.
I would put on the taller tires and it would effectively reduce the 3:55's on the highway. You could feel the difference in the seat of the pants acceleration though.
What tire size are you currently running 14", 15"?
By going from a 235/60-15 (26.1in) to a 235/70-15 (28in) you gain almost 2 inches of height. You could also achieve this with a taller 14" tire if needed.
Find a tire height chart and make some comparisons. Good luck!

 

[moparleo]

This should keep you guys busy for a while. Good links
Wallace Racing - Calculate Rear Tire Diameter needed
Interactive RPM and MPH Computator Program
Mopar Overdrive Transmission Swap - How To - Hot Rod Magazine
Tire Height Calculator - Wallace Racing

 

[340challconvert]

Some cool information here Thank you

This should keep you guys busy for a while. Good links
Wallace Racing - Calculate Rear Tire Diameter needed
Interactive RPM and MPH Computator Program
Mopar Overdrive Transmission Swap - How To - Hot Rod Magazine
Tire Height Calculator - Wallace Racing

 

[moparleo]

I have many links in my favorites folder. Great reference material.

 

[Glow Worm]

A lot of good feedback here. You would kill your 340's acceleration with gears taller then the 3;23s.
Hard to set up the engine for "400" HP and look for lo RPM,s. They do not go together.
I used to keep an extra set of rally rims with taller tires for my 340 / 3:55 Challenger when I was taking a long road trip.
I would put on the taller tires and it would effectively reduce the 3:55's on the highway. You could feel the difference in the seat of the pants acceleration though.
What tire size are you currently running 14", 15"?
By going from a 235/60-15 (26.1in) to a 235/70-15 (28in) you gain almost 2 inches of height. You could also achieve this with a taller 14" tire if needed.
Find a tire height chart and make some comparisons. Good luck!
View attachment 25709

I'm thinking of going from 14 inch to a taller 15 inch on the rear. That might be the best/cheapest route.

 

[340challconvert]

Glow Worm, don't forget to plug in the tire sizes for the 14in tires into the links that Moparleo provided.
Check the overall tire height. You could go to a 15in tire and it might not be taller than the 14in tire you replaced.

 

[challenger6pak]

Your car will accelerate faster with a lower gear ratio and a taller tire, due to roll out, when compared to a high gear ratio and a shorter tire. I have always run a 3:91 with a 31 inch tall tire on my 383 4 speed RT.

 

[moparleo]

14" or 15" is just the diameter of the hole in the tire. What you are trying to do, is to get the engine speed up into the peak torque/horsepower range with the tire/wheel speed slower to prevent wheel spin which increases maximum starting line traction. A perfect example is the different pulley diameters on the engine accessories like the water pump, alternator, power steering pump, a/c and so on. To increase accessory speed you go with an larger drive pulley diameter on the crankshaft and smaller accessory pulleys. This is one way to help with low alternator out put at idle. A smaller pulley acts like an increase in engine speed.

 

[Glow Worm]

Thanks to all. I am in the process of "borrowing" aset of 15 inch wheels/tires that are taller than what I have. We'll see what happens.