Dakota Durango Forum banner

1 - 9 of 9 Posts

·
Registered
Joined
·
114 Posts
Discussion Starter #1
from most of the reading here everone likes 456 rear gear. Im new to fuel injection hot rodding but on carbed motors a low gear makes up for weak motor, just wondering what everones thoughts is on this?:huh:
 

·
.:.:.:.:.:.:.:.
Joined
·
10,424 Posts
Factory gearing (3.55) put my truck right about 1500 at 60mph. Entirely too low...especially if you want to tow anything.

I run 4.56 now and I turn a tick over 2000 at 60. That's not bad...at all. My wife's VW Jetta turns more RPM bone stock.

Back in the days of carbs, you were lucky to have overdrive. Most were straight 1:1 in top gear. Couple that with small car tires and you turned about the same RPM we are now using much taller rear gear.
 

·
Don't be "That Guy"
Joined
·
7,400 Posts
from most of the reading here everone likes 456 rear gear. Im new to fuel injection hot rodding but on carbed motors a low gear makes up for weak motor, just wondering what everones thoughts is on this?:huh:

even in carb'd hot rods, low gear does not "make up" for "weak motor" your parts have to match each other. high rpm HP race type cam? it's not going to have any "off idle grunt" so you need a loose torque converter and high numerical gears to make it all work...but that's ok, because you'll be turning your motor to 7,000 rpm anyway.

vs a torque cam that has lots of off idle torque and grunt, but is all used up by 5,000 rpm. in such case, you want a tighter torque converter and lower numerical gears.

it's not a matter of "weak engine vs strong engine"

and the 4.7s are rev happy motors. the factory shift point is 5500 rpm at WOT. the older 5.2s and 5.9s were around 4800 with the rev limiter at 5200rpm.

anyway, the reason so many guys like the 4.56 is because of tall truck tires and the OD gear in the automatic trans. most of these trucks came with factory 29-31" tall tires. a 3.55 in these trucks is like a 3.21 in a car, because the car will have at most, a 26" tire (typically)

throw in body/suspension lifts, tires taller than 31s, and suddenly that 4.56 behaves like a 3.70 gear in a car...or 3.55 once OD kicks in.
 

·
Resident Craigslist Whore
Joined
·
3,230 Posts
from most of the reading here everone likes 456 rear gear. Im new to fuel injection hot rodding but on carbed motors a low gear makes up for weak motor, just wondering what everones thoughts is on this?:huh:
lower gear ratio in the axles = slower wheel rotation at higher engine RPM which translates to more low speed power for rock crawling, mud bogging, towing... pretty much anything that requires the engine power but you dont want to be going 85mph to achieve the HP you need. take two identical trucks, one with 3.55's and one with 4.56's and chain them hitch to hitch. the one with 4.56's will pull the other backwards all day long. and lower gears in the axle also compensates for larger diameter tires. i cant remember the exact formula, but its out there. put 38's on a truck with stock gearing... horrible low end power loss because the engine has to work way harder to get them moving. put in lower gears to compensate for the tires, and you're back to the same general characteristics of a stock truck.
 

·
Registered
Joined
·
140 Posts
4.56's put my cruisiing RPM right on the sweet spot (approx 2000) and when you put your foot in the water pump it hunkers down and SCOOTS. Also the OD does not hunt in/out since the gear change. Aint too shabby coming off a light either. edit: back in 1970 my Chally had 3.55 rear and the tach said it cruised at 3200 rpm (65-70 MPH) with the OD tranny the Dak if really flying at that rpm
 

·
Registered
Joined
·
333 Posts
i got 3.55 with 33" tires and i see about 10-12 mpg avg with a sc tune. If i went to a 4.11 or a 4.56 id most likely see a big increase right? maybe up to 16 mpg avg
 

·
Registered
Joined
·
1,649 Posts
from most of the reading here everone likes 456 rear gear. Im new to fuel injection hot rodding but on carbed motors a low gear makes up for weak motor, just wondering what everones thoughts is on this?:huh:
Guess that why all the 1500 horsepower cars run 2.55's or lower.......LOL
 

·
.:.:.:.:.:.:.:.
Joined
·
10,424 Posts
i got 3.55 with 33" tires and i see about 10-12 mpg avg with a sc tune. If i went to a 4.11 or a 4.56 id most likely see a big increase right? maybe up to 16 mpg avg
City and low speed driving (50 and lower) will likely get a fair increase. Highway might go up a bit, but likely not much, especially on flat ground.

Don't do a gear swap for fuel savings...it'll take forever to recoup the money, if you even can.
 

·
Resident Craigslist Whore
Joined
·
3,230 Posts
Don't do a gear swap for fuel savings...it'll take forever to recoup the money, if you even can.
+1 to that. by the time you get gears and the setup kit for an axle, your lookin at $300-$500, and double that if its a 4x4. and thats if you do it yourself. the shop here in NY gets $500 per axle just for install! i built differentials for Caterpillar when i worked there in Tennessee and i always hated doin them cause it involved assemble, measure, disassemble.... assemble, measure, disassemble, and over and over again until it was perfect. and you NEED gears to be done right the first time or you'll be pullin chunks of teeth out of your diff after a few thousand miles.
 
1 - 9 of 9 Posts
Top