Advice on street car rear/ tire size

[Bad B-rad]

I had a 66 Charger 383 auto with a 3.23 rear, and 25 inch tall (14 inch) tires.
It was a great all around street car, for me, good power, ok on fuel (15MPG ish) I could go anywhere with it.
I changed the 3.23, for 3.91's and it was a great change until I tried to take it on the highway.
The rpm at 60/65MPH was just to much for my liking for any long highway trips, and I was forced to stick to backroads, it was just the wrong rear for my combo.

That was 18 years ago, with my current 69 Charger, I have a 383 auto with 3.23 rear gear, but I have 15 inch tires, 28 inch tall.
I need it to cruise on the highway, at 70MPH for hrs, as I will be using it as transportation.

So with the taller tires of the 69 Charger(28) vs the 1966's 25 inch tall, will the 1969 turn a lower rpm at 60mph then the 1966 did, when it had the same 3.23 rear gear?

Or is the 2 inch tire height change just too small of a change to affect rpm much?

 

[Longknife]

http://wallaceracing.com/calc-gear-tire-rpm-mph.php

 

[Bad B-rad]

Thanks!
What is the avg. stock convertor slip% I should be using for 727?

Using the 5% that is on the screen, it looks like the 14 to 15 inch tire is worth about 317rpm at 65mph.

 

[33 IMP]

I think 3.55s and 28/29 tire is the same as 3.23s with 25/26 tire, maybe a few rpm either way. 3.23 with 29 is 3.08 with a short tire.

 

[Bad B-rad]

Is there a calculator, or formula for how gear ratio swaps will affect acceleration?
Like how much going from 3.55 to 3.91, will change the 0-60mph time, something along that line?

 

[Longknife]

http://wallaceracing.com/calc-gear-tire-rpm-mph.php

 

[Bad B-rad]

I

http://wallaceracing.com/calc-gear-tire-rpm-mph.php

I don t see how any of those calculate time. Like if a car dose 0-60 in 5 seconds with 3.91's how quick will it do it with 2.94.
The first time you posted it it works great for figuring out the rpm for tire size, and gear ratio.
I was wondering if they have one for time, or like a rule of thumb?

 

[33 IMP]

Is there a calculator, or formula for how gear ratio swaps will affect acceleration?
Like how much going from 3.55 to 3.91, will change the 0-60mph time, something along that line?

I don't think so, and if there was, I don't think I would believe it.
My personal experience only ,so take with a grain of salt. Applied to my drag cars, I have changed from very low gears (high numerically) to more moderate gears, several times in two different cars, and not slowed down yet. With enough torque, and a good converter, it just doesn't seem to matter.

 

[forphorty]

Yep, converter has a greater effect on acceleration than gear ratio.

 

[BSB67]

I don't think so, and if there was, I don't think I would believe it.
My personal experience only ,so take with a grain of salt. Applied to my drag cars, I have changed from very low gears (high numerically) to more moderate gears, several times in two different cars, and not slowed down yet. With enough torque, and a good converter, it just doesn't seem to matter.

My experiance, this is generally true for 440 cars, and even more true for 440 street cars. I think that the small block motors will be more sentative to a gear ratio change.

 

[Bad B-rad]

The gear change having more of an effect on small blocks makes a ton of sense,(as its just torque multiplication)


So if building a car to highway cruise, and using a 440, what type of convertor,(make and stall?) should be used with a 3.23 rear?

My only time changing out convertors was a 440 with 3.91's (14 inch tires)and 3500 stall, it would take off like a rocket, but again too much gear for high speed prolonged cruising, for me at least.

 

[Bad B-rad]

I have a Mopar performance 166K stall(2250-2350rpm) convertor on the shelf, would that be a better choice then the stock 1969 383's?
(the claimed factory stall speed in the 69/383 convertor is close to the Mopar 166K) I also have a stock 1973 440 truck convertor, again with the goal being a finding the balance between fun acceleration, and lowest highway rpm, I am entering new to me territory, so I am just looking for as much good advice as possible.

 

[BSB67]

Use the stock converter. A different converter is not going to help it "feel" snappier down low around town. A converter really helps 60 ft time at the track if you have a sticky tire when you drop the hammer.

 

[hunt2elk]

I have 2 B-bodies, both with 275/60/15 rear tires on them. 28" tall. 3.23's in one and 3.55's in the other. The car with 3.55's I consider a 60 mph cruising car and the one with 3.23's a 70+mph car. I like to keep the rpm's around 3000. If you do a lot of freeway cruising I believe you will prefer the 3.23's.

 

[Bad B-rad]

I have 2 B-bodies, both with 275/60/15 rear tires on them. 28" tall. 3.23's in one and 3.55's in the other. The car with 3.55's I consider a 60 mph cruising car and the one with 3.23's a 70+mph car. I like to keep the rpm's around 3000. If you do a lot of freeway cruising I believe you will prefer the 3.23's.

Thanks!!!
I am a HUGE 3.23 fan, they always seamed to be a great balance of off the line power and highway cruising rpm.(being limited to a non OD trans)

I will know more after hitting the road in my car, and getting seat time, but I have even toyed around with the idea of doing a 440 up for max torque and even doing a 2.94/2.76, but we will see, it may be a pipe dream, the 383 will most likely be fine
Once I start building an engine, I will slowly go off track, and start building it as if I am running it on the strip!

 

[BSB67]

I put a 2.94's in my 12 second - stockish 440. I really could not tell any real difference between it and the 3.23s.

 

[33 IMP]

This is an anecdotal story, but true.
One of the most impressive rides i had as a kid was in a 68 or 69 gtx with 2.94 gears.
I was a chevy guy at the time, and was driving a lt-1 powered 57 chevy, with a muncie and 4.56s. I dont even remember why we went somewhere in this gtx but memory says there were four of us. The driver said this was his street setup while he redid his race gears, that was the reason for putting in the 2.94s. Well, that car was not impressive at all , off a dead stop, how could it be with no gear, 3700 lbs of car and probably another 800 pounds of people, BUT! when it kicked down into first again at about 30mph and didnt shift out of second till above a hundred, well.....
I was never a friend of the owner, tho a couple friends of mine did end up with a car he built and i can still remember his name. My buddy traded a 454 chevy (they were hard to get at the timel) for this guys 440,727,d60 duster, that ran elevens with a carb, cam headers and tires. I still have the custom Marco headers from the duster hanging on my wall. A person would need a lot of engine to use them, they were 2 1/4 pipe into a four inch collector.

 

[Bad B-rad]

BSB67, thanks, that is making me think more about that 440 swap!!!

33 IMP, good story,
I know with some combos, and mostly it happens with big torque engines, swapping rear gears, wont make it much quicker off the line, then it was before the change, unless you added a ton of weight, or were towing something.
Meaning at a certain point you would have to put that torque multiplication to use.
Hard to explain, but its very easy to see or feel in a big rig.
For example,
The low boy driver at work had a 379 Peterbuilt, and a worked 500 HP CAT, he got 3.5 MPG, bobtailing or trailer empty or pulling, and the truck would accelerate at the same rate empty or with a load, up to about 65,000 lbs.(I am estimating with the weight, as up until a machine larger then a 270 LC's wt, it made almost no difference to the truck)


BSB67, what is your stockish 440 combo?

 

[hunt2elk]

Thanks!!!
I am a HUGE 3.23 fan, they always seamed to be a great balance of off the line power and highway cruising rpm.(being limited to a non OD trans)

I will know more after hitting the road in my car, and getting seat time, but I have even toyed around with the idea of doing a 440 up for max torque and even doing a 2.94/2.76, but we will see, it may be a pipe dream, the 383 will most likely be fine
Once I start building an engine, I will slowly go off track, and start building it as if I am running it on the strip!

I should add that both these cars have 400 based striker motors, so the torque curve is down low. Plenty of torque down low even with the 3.23's.

 

[Bad B-rad]

I should add that both these cars have 400 based striker motors, so the torque curve is down low. Plenty of torque down low even with the 3.23's.

Ok thanks for the heads up, so your engines are making at least 440' style torque, if not more.
But they are defiantly making more torque then my stock 383.