how much difference between 3.91 and 4.10

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mshred

mshred

The Green Manalishi
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Hey guys,

I am building my scamp with a 340 as a daily driver...it will have a 727 behind it with something along the lines of 3000-3500 stall....I know its not practical for the road, but its the way im going to go...my question is for gear sizes....i plan on running a 325/50/15 MT street radial and i want to run either a 3.91 or 4.10 gear... i know neither will be pretty on the higway, but i dont take the highway that much anyways...i hear there is only a 5% difference between the two ratios, so my question is how big of a difference will i see between the two? how much higher would my rpms at cruising be with 4.10's compared to 3.91's?
 
My Dart Sport Has 4.10 Gear 255 60. 15. 65mph=3000rpm.so I Would Think 3.91 Would Be Somewhere Around 2700.hope This Helps.
 
not enough to worry about.

Going from 4.10 to 3.91 is about a 4.6% reduction. About 150 rpm if you are basing on 3000 RPM with a 4.10, will run 2850 RPM with 3.91.
 
pettybludart said:
My Dart Sport Has 4.10 Gear 255 60. 15. 65mph=3000rpm.so I Would Think 3.91 Would Be Somewhere Around 2700.hope This Helps.
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My 69 dart 3.91 is at 3600 rpm at 65 with a 245/60/15 i must have a looser converter 2800
 
There are a few calculators on line to help you figure RPMS.
I used the one on SMR transmissions overdrive info page.
According to the calculator a 325/50/15 tire (BFGoodriches are 27.9 tall), running 60 mph would give you 2825RPM with 3.91 and 2960RPM with 4.10.
 
so would 4.10's really kill me that much more than 3.91's on the highway?
 
Mshred,I have driven my Dart Sport with 4.10 from Oakville to CayUGA SPEED WAY.i TOOK THE Q.E.W to hwy 20.On the hwy revs were 3000 in slow lane at about 60mph,so i would think 3.91 would rev. a little lower.How much hwy.driving are you planning on driVing?I have 3.23 gears for both 8 1/4 and 8 3/4 if you want to step down to a lower GEAR.
 
well i have 3.23's now and i definatly want as much gear as i can without being massive overkill on the highway...i dont drive the highway that much, and usually if i do its for a half an hour at total maximum....however, i do envision wanting to take my scamp to my aunts place in wasaga which is about 1 and half hours away all highway from where i am...does the fourspeed in your dart sport make a difference rpm wise on the highway?
 
i TRAILOR MY CAR TO THE TRACK NOW,INCASE OF BREAKAGE.I,LL BE SWAPPING CHUNK TO 3.55 TO GO TO MOPARFEST,IT,S ABOUT HOUR AND 20 MINS. I JUST DON,T LIKE TO REV FOR TO LONG.MY TEMP GAUGE NEVER GOES PAST 180.BUT IF I PLAN ON GOING TO THE BIG SHOW I DON,T WANNA BE LAST.DON,T KNOW IF 4 SPEED IS DIFFERENT THAN AUTO,never had auto in my car.If I were you I,d stick with the 3.23 unless your taking to the track
 
my car is minitubbed and it will see the track...plan on running a 325/50/15 tire
 
mshred said:
...does the fourspeed in your dart sport make a difference rpm wise on the highway?
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Not if its a standard A-833, the 4th and final gear ratio is still 1:1 just like 3rd gear in a TorqueFlite.

If you went with the latter 75-87 OD A-833, you would basically have a 3 speed with an Overdrive 4th gear. 3rd gear is 1:1 and 4th I believe is 0.73:1 which would make your 3:91 or 4:10's very driveable on the freeway.

Check out this link below, I screw with this calculator a lot and hope it helps you.

http://www.bigblockdart.com/techpages/speedtire.shtml
 
mshred said:
well i have 3.23's now and i definatly want as much gear as i can without being massive overkill on the highway...i dont drive the highway that much, and usually if i do its for a half an hour at total maximum....however, i do envision wanting to take my scamp to my aunts place in wasaga which is about 1 and half hours away all highway from where i am...does the fourspeed in your dart sport make a difference rpm wise on the highway?
Click to expand...

All automatics have some slippage,and it can be better or worse depending on how the stall was built,usually a auto will run a couple hundred more to run the same speed as a manual trans car.There are calculators that can tell you how much slippage you have but you need to have the mph and the corresponding rpm to calculate it,Ive seen as much as 15% on a 12 sec car with a b&m convertor.
 
hey guys thanks for the tips...i want to go 4 speed, and i think the 4.10's will be fine for what im doing...i dont mind spinning 3000 grand on the highway, but anything more and i think i will go 3.91's
 
3.91 at 60 mph = 2900 rpm
4.10 at 60 mph = 3000 rpm



had 3.91's in my dart with a 28" tire and hated it. allot of fun around town but once it got on the highway it sucked screaming and having people cruise past me. the 8 mpg really sucked too...lol have 2.94's in it now and love them.
 
2.94 is definatly way out of my range..atleast 3.91's for me...im still young so i like putting up with what you guys call nonsense lol
 
i'm sure not old. just into getting on the freeway and actually cruising hours away. i couldn't do that so well with the 91's. :)
 
mshred said:
2.94 is definatly way out of my range..atleast 3.91's for me...im still young so i like putting up with what you guys call nonsense lol
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I've said that myself (I'm 21) However I've found a combination of spirited driving, and too many highway miles have taken it's toll on my engine. For only about 15,000miles on it. Oil pressure is about 40-45psi at 6000rpm with 15w-50 synthetic. Also, "nonsense" is best cured with an overdrive setup. Which is a move I plan on making with my car in the somewhat near future.

Just my 2cents. Being young doesn't have much to do with screaming down the highway, but you're engine may take it differently....
 
Abodyjoe,what rpms are you turNING ON THE HIGHWAY?YOUR CAR MUST WANTA KEEP GOING AND GOING..AS IN TOP SPEED.I HAD 3.23,4TH GEAR WAS AT VERY LOW RPM=GREAT GAS MILEAGE.
 
318/349 stroker, 3.91s, 27" tyre, 2950 rpm at 65 mph

Have a 3000-3200 stall (Continental), and have driven the car to a big show 3.5 hours away with two fuel stops.

Ive done this twice and the car is happy sitting on this speed all day.

The secret is a decent converter and not trying to keep up with hwy geared 6 speed ZF auto trans family cars that can do 70 mph at half the revs.....
 
abodyjoe said:
i'm sure not old. just into getting on the freeway and actually cruising hours away. i couldn't do that so well with the 91's. :)
Click to expand...

I meant it more in the sense that im too young to care right now, gotta learn for myself, ya know teenagers right? lol i just want power and speed, and until i learn my lesson i guess thats all i'll want

Moparmal said:
318/349 stroker, 3.91s, 27" tyre, 2950 rpm at 65 mph

Have a 3000-3200 stall (Continental), and have driven the car to a big show 3.5 hours away with two fuel stops.

Ive done this twice and the car is happy sitting on this speed all day.

The secret is a decent converter and not trying to keep up with hwy geared 6 speed ZF auto trans family cars that can do 70 mph at half the revs.....
Click to expand...

This is what im talkin about...i dont do lots of highway miles, but i dont mind going 60mph and being passed cuz really like you say those cars passing have 6 speeds so i could care less....im willing to make a little sacrifice for the highway (not too much) to have more fun in town
 
The 3:23 is the way to go and they are spirited enough around town. They won't help you keep your license longer but you get to make your motor last longer!
 
Allow me to chime in!! I had a 3:23 suregrip in my bone stock 67 GTX 440 auto, and my best time down the 1/4 was 14.06. OK for a bone stocker but I wanted more so I swapped in a set of 3:91's. Guess what!! Except for the time I had to pedal it and might have broke into the 13's, the 3:91's did little to no good for my E.T. I'm with the guys on this one, unless big smoky burnouts are your goal, stick with the 3:23. There is a reason Chrysler referred to that gear as their "Maximum Performance" ratio!! Party on, Geof
 
I think a 3.91 is as deep as any street/strip car should go. I have run 2.8, 3.23 4.30, 4.56, and 4.89 on the street.
Anything lower than a 3.9 should be avoided on the street. I loved the 3.23 for normal performance. The 4.30 was testy. The 4.56 was a ball from red light to red light but when I tried to drive it 5 miles on the interstate, I almost got ran over with the engine screaming.
We use to have a 3/16 mile drag strip here. Launched at 3000 with the 4.56. Shifted at 6000 and went thru the trapps at 5000 with street tires about 26" tall tires.
It really depends what you expect from your car.
 
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