How streetable is a 4.10?
 

I seem to be able to find more 4.10s than 3.91s available for a posi pumpkin.

How streetable are the 4.10s?

I have a buddy who keeps telling me I don't want one since I'll be doing like 5000 rpms at 60 mph or something like that. My RR will be driven more on the street than raced and taken on occasional highway trips. It's a 3 speed slapshift.

I had one in my '71 Sebring auto for a while. It wasn't all that bad. I don't remember what the rpms were. This was back in the mid '70s. I went back to the 3.55 after a summer. It won't be 5,000 rpms anyway. I think my 4.56 in the AMX is 4,000 at 60. Been 2 or 3 years since I had those in.

Taller tires will help. With a 4.10 stock height tires will run the engine to about 4000rpm at 60 or so. It will be kind of loud. Also, at those rpms any minor imbalance in the driveshaft will show up larger than life. Over extended cruises that could end up wearing out tranny mounts or even crack the tail housing. Just things to consider...........

My first car (a 70 Challenger) had unknown gears in the back would hit 3500 rpm's at 50-55. I had an out of balance drive shaft, and boy did it drive me nuts!:guns:

I think some magazine had an issue on balancing driveshafts and getting the angles right.

It really all depends on the tire size. Find an online RPM/gear/MPH calculator and punch in different values to see what changes, and if you can live with it or not.;)

Good street gear - with a 27" dia. tire @ 60mph you will be reving ±3150rpm

Thanks!
 

Thanks all for the info! I think I'll try to find a 3.91 first.

I have taller tires, but I don't think they are 27" tall.

Try this:

RPM = (MPH x Gear Ratio x K) divided by Tire Diameter (in)
The K value = 336 for stick cars and lock up converters
and = about 355 for non lock up converters.
For a 26" tire and 4.10 gears, (K=355) you get about 3600 RPM at 60 MPH.
You said that this is primarily a street car. I'm an old fart, but I'd be running 3.55's. I couldn't bear to listen to 3600 rpm at 60 all day long.

Thanks for the info
 

Thanks! :)

Hmmm...
 

I thought I had a 3.23 rear, but it looks a little lower than that...unless my tach is off...

(60*3.23*355)/25 = 2751.96 rpm

at 60, I'm cruising at 2500 rpm.

I really doubt that you have 25" tires. I've got 26" tires (close to factory size) on my '69 Coronet and they look too small. From your avatar, I would guess that you are running a 27" or a 28" tire.

A 27" diameter tire will give you 2548 RPM, according to the presented math. A 25" with 2.94 gears will give you 2504 RPM with the same math.

What is your actual metric tire size? With tht, I can give you a closer ballpark on the diameter.

Believe it or not, they are 24.5" in diameter to be exact (so I rounded up a little). I measured them with a tape for Don a while ago when I got a carb for my 413 (since departed) since he wanted that info for the carb spec.

Maybe it looks taller cause I have SS springs? The springs kind of jack up the rear end a little.

With the 2.94 plugged into the equation, it looks dead on with what I was seeing on the tach at 60 mph. Whatever is in the 8 3/4 rear right now is not original. The owner before me, who is neighbor, had the original rear give out on him while he was on the road. That one was a posi too. :(

Thanks a lot for your help!

Based on my experience, the 4.10 ratio is great on the strip and around town, but on the highway they are an absolute PITA. Even the 3.91 ratio is pushing it on the highway, in my opinion.
The 3.54 or 3.55 gearing is pretty hard to beat if you want good acceleration and also want to stretch your cars legs on the highway.

As an example, my Charger came with the Super Trac Pack which meant 4.10 gears in the rear, and they were great with the Six Pack around town and at the strip, but not on the highway!
Finally bit the bullet a few years ago and went to 3.54 gears. It was a compromise, but one that I can live with.
No more driving in the slow lane on the freeway.

I run 3.91's in my car. I also run 275/60's so they help some. I drive to and from the track on the interstate around 65 mph at around 3200-3300 rpm's. I switch at the track to a set of 28x 10.5 Goodyear drag slicks which also kills my gear even more. I have run a 4.30 gear on the street before, all i can sayis its liveable in and around town, down 2 lane country roads around were i live, most people dont see 50 mph anyway. I will be replacing my gears for a set of 4.30's or 4.56's soon.

4:10's for highway......never, I had 3.91's and I couldn't stand it. I now have 3.21 and love it. And guess what, my driveline vibration is almost completely gone and I can top out the 120 mph speedo and more. Great for passing on the highway!

Was the wife with you, Doug?.....120 mph on the 401 that is...:D

Don't they run you off the 401 if your going any slower than that??LOL:eek:

Thanks!
 

Thanks a lot for the replies all!

From what everyone has said I'm definately sold on not going to 4.10. I think I'll go with the 3.91 unless a really good bargain comes around on the 3.55.

I'm in the process of a tire switch (I have no traction with the current tires, they are too hard), so I'll make sure I get taller tires if I go with the 3.91 route.

Thanks again! :)

That means the 401 would only have Mopars on it, Dave?.....Of course....says the "white rabbit"...(Jefferson Airplane):D

well, i would say to get the 4.10 gears, but i run a 28 inch tall tire on all my vehicles.
and personally, imho, the short, wide tires don't look as good as tires that will fit inside the wheelwell, and actually fill it. just my opinion. a taller tire also has a larger footprint, for better traction.

the 3.55 gears would be like a set of 3.91's anyways. i ran 4.88's in my satellite on the street for a while, and wow are those crazy for the first two blocks. however, i didn't find any of the vibrations you guys were talking about, even with 4000 rpm at 55 mph. my motor (440) is pretty quiet, if your not on it, anywhere below 5000.

I have 3.54 and recently got some BFG drag radials 325 50 15s. 27.9 in. Im thinking 4.10 iis the way to go now.
fastmopars iis right, they really fill up the well. Those 295 50s just dont do it.
Anybody interested in a set of 295 50s?

I just did a quick calculation with the 28 inchers and the rpms looks much better too. Around 3100+ at 60 mph.

Not too bad....I'm waffling around. :rolleyes:

I guess the 4.10s are tempting since I seem to be able to find a bunch of them around and I'll probably be driving this more on the street than on the highway. I have plenty of room in the wheelwell for taller tires too. I'll keep trolling Ebay and some misc Mopar parts listings for now...

Is this car a toy or transportation? That 3000 + rpm gets real old if your going back & forth to work like that. I used to have a '56 Chevy with a 383 Chrysler engine back in the 60's. It had 4.88 gears but I had 29" Casler cheater slicks on it. I would sit in the right lane at 3500 rpm and watch the gas gauge go down (and all of the other cars go by) between exits on the parkway on the way to school. It's a good thing that gas was only 33 cents/gallon for premium. I got about 7 MPG.

If you decide on the 4.11s I have a set of richmonds for a 742 case that i am pulling out. They have under 1000 miles and 3 passes on the track. Put them in over a year ago then whent to a supercharger... more power means less gear , going to a 3.55.
Set up buy a local shop that has been raceing mopars for a long time so I am sure they are in exalent con. 112mph with a 27in tire, crossing on the rev box @ 6400 w/ 5lbs of boost for a 12.2et. The 3.55 and 10 lbs should put it at 130mph and a low 11.00

Gary, dave, I just had to pass a Semi truck and he was only doing about 50 mph, by the time I went by him my speedo was reading 85 so I figured what the heck lets wind 'er up, didn't take long for the needle to disappear past the 120. I was alone, I would never do anything that foolish with someone else with me. Although she has been with me on a few 100 mph runs and I promptly get THE LOOK and the elbow to the ribs to "slow down dammit". LOL
At the time it seems alright, but hurts a bit later.

I know the look you speak of Doug:)

It's more of a toy and a learning tool. I'm new to Mopar so you can say I'm taking a crash course in it and sponging knowledge from all you more experienced folks. :)

I have two other cars for daily drivers - they are much better on MPG so I don't really worry about this one that much, I'm sure right now it's in the single digits. It guzzles gas really good, especially after I changed out the engine.

I'm part of a Mopar club in Indy where I have to take the highway to get to the meets, about 20 minutes or so...so that and when I go to shows will be the extent of the highway driving for now. Maybe a once a week drive for 10-20 minutes on the highway. During the Winter depending on the snow, the RR gets put in dry dock until the Spring.

What the hell, you might as well go for the 3.91's if that's the case.

I'm keeping my eye on some Ebay auctions, but I would be interested. If you want to sell email me at MasterProject2002@hotmail.com

Thanks. :)

well, with an 8 3/4, once you do it enough times, it only takes about an hour to change gearsets. i drive my car to the three hills car show and cruise which is 3 hours away every year and i throw in a set of 2.94's in the satellite. 3000 rpm is just around 85 mph.
im pretty sure its doing almost 150 mph at around 5500.

but you could use the 4.10's for all your street cruising, and if your far away trips are limited, keep another open rearend around with a set of 3.23's or whatever. open 8 3/4 are everywhere at the junkyards.