Which to install 391 rearend gear or lower?

-

plumdart69

Well-Known Member
Joined
Feb 26, 2005
Messages
265
Reaction score
6
Location
Ontario,Canada
I need to get the readend fix in my dart but i am not sure wether to go with 391 gears or lower.It will mainly be driven on the highway,maybe on an rare occasion,a run down the dragstrip.Thanks for any replies.
Mike
 
I like 3.55s. 3.91s and higher, numerically, are a PITA to live with every day.
 
If this helps, 3.91 gears on my car equals 3000 RPM at 60 MPH. I'd go 3.55 for the highway/occasional strip.

Terry
 
I'd recommend 3:23's, they worked good for me, even @ the track, with the four speed I didn't need the fourth. Mind you it won't get you into the 11's, but mid to high 12's.

3:91's max. for highway driving regularly.
 
I think it really depends on how your engine is built and what size tire you have. 3:91's aren't enough for my car but for some 3:55's are still way to steep. 3:91's will be pushing it for hwy use though unless you have tall tires.
 
I think it really depends on how your engine is built and what size tire you have. 3:91's aren't enough for my car but for some 3:55's are still way to steep. 3:91's will be pushing it for hwy use though unless you have tall tires.
Engine bored 30 over
Cam 501 lift
Tire size P245 60 R14
 
P245/60R14 would be a hair shorter than a 26" tire, 25.6" by my math. 3.91 gears would be a bit low if you plan on extensive highway use. I would go 3.55. If you stay mostly on back roads or take it to the track more than once or twice a year, 3.91 would be my choice.

I'm running 4.30:1 gears in mine with a 28" tire "275/60R15". Great around town, back roads and on the track, but I won't take the car more than a few exits on the highway. Further than that, it goes on the trailer.
 
I have 4.10,s in aa 4 speed car and 391,s in my auto car,both cars have tall 15,s on the rear.I don,t do alot of hwy driving,but I would suggest 3.55,s for abit of performance on the street/track.If 75% of hwy driving?go with the 3.23.s.
 
Another vote for 3.55's. Starting to get tired of the 3.91's in my car, so I'm going to 3.55's sometime in the next month or so. 3000 RPM at 60 mph with 27 inch tall tires with the 3.91's. Great for driving around town, but for trips longer than 15 miles, that 3000 RPM sound starts to get to you.
 
3:55 is the lowest I'd go with those short tires since you say it's mostly a hwy cruiser. I had 3:73's in my Cuda with 27" tires and it was revving over 3000 at 65. I put in 3:55's and taller 28" tires and I like it alot better. It's not as quick but not a tremendous diff and the hwy cruising is sure alot more enjoyable. Gained about 3 mpg too.

BTW: What cubic inch is the engine. Bored .030 over means nothing in the realm of things.
 
With your tire size, 3.91 will be a bad idea for lots of highway driving. Like many said 3.55 is best of both world, but it might still be too low.
 
I have to agree with the other posts for the 3.55s (best of both worlds), but I also like the 3.23s on the highway. They run nice on the highway and still have a little bit of pep to them.
 
3:55 is the lowest I'd go with those short tires since you say it's mostly a hwy cruiser. I had 3:73's in my Cuda with 27" tires and it was revving over 3000 at 65. I put in 3:55's and taller 28" tires and I like it alot better. It's not as quick but not a tremendous diff and the hwy cruising is sure alot more enjoyable. Gained about 3 mpg too.

BTW: What cubic inch is the engine. Bored .030 over means nothing in the realm of things.

Oops!! it's a 340
 
3.23 gears in the dart works good for me had 3.91 gears just to much gear
 
If highway is what you drive most of the time, I'd run 3.23 or the 2.76s but that cam is too large for those and will feel soft driving around. I think 3.91s will get very tiring fast but the cam determines it more than anything else.
 
Thanks for all the replies.This info will help me in deciding which gears to go with.I might go with 3.55 but i will think about it.Thanks again for the help.
Mike
 
if it's going to be mostly highway i'd definatly go with a 3.55, if it were a mainly track or street machine or something then i'd consider 3.91
 
-
Back
Top