2.76 vs 3.23 vs 3.55

-
7

74 dart sport

Kameron
Joined
Jul 7, 2015
Messages
171
Reaction score
1
Location
Southern California
As of now, I have a 8 1/4 peg leg rear axle with 2.76 gears. I am thinking of upgrading to 3.23s or 3.55s. I drive mostly around town and a fair amount of time on the freeway. I occasionally make 300 mile trips out to lake Havasu. I have a few questions regarding the new gears.
1) difference in gas mileage between 2.76 and 3.23s AND 3.55s
2) off the line speed between 2.76s (horribly slow lol) and 3.23/3.55s
3) if 3.23s or 3.55s would be more suitable in driving conditions described above.

I drive a 74 dart sport with a 67 318 and a 727.
 
IDK but I use 4.56's in my DD. 3.55 would be as tall as I could go. I also don't care if the engine turns 3600 or so down the road. I ain't driving a Prius or prelude.
 
Define "fair amount" of time on the freeway?

3.55 is generally seen as the best "compromise" gearset for highway/city driving. 4.10 can be as well. Can't speak as to RPM until we know your rear tire height. 2.76 - 3.55 is gunna make a huge difference. Your 318 will feel a lot bigger!
 
yellow rose said:
IDK but I use 4.56's in my DD. 3.55 would be as tall as I could go. I also don't care if the engine turns 3600 or so down the road. I ain't driving a Prius or prelude.
Click to expand...

Hahaha.. I wish I could not worry about MPG as much but I'm only a sophomore in high school. I have to worry about mpg because every job only want to pay minimum wage :( lol
 
What has been done to the 318,modification wise? Any time freeway rpm goes up, gas mileage depends on the "sweet spot", or where the current combination start making good torque.
(And do you have an expectation, for such modifications,gear wise.?)
 
With 3.55 you'll be turning 3300 rpm at 65 mph. As for fuel consumption. Can't say. Really depends on your setup. Depending on cam/engine that might be high or low to you. If you're spending that much time on the highway. And really concerned about fuel/power etc. I would sit down. Calculate each one. Drive at that rpm for an extended period (your average highway trip). See what kind of power you have. And see if the noise is too much for you. With your tiny tires and the 3.55, you'll definitely move off the line. Might become a problem in terms of grip depending on how wide your tire is.
 
Modifications: RV cam , zero decked, 4 bbl, headers, true dual exhaust (no cross pipe)
Expectations: at least squeak the tires lol

And I think I should be good with grip. I have Kuhmo KU 27's 15 inch rims
 
74 dart sport said:
Modifications: RV cam , zero decked, 4 bbl, headers, true dual exhaust (no cross pipe)
Expectations: at least squeak the tires lol

And I think I should be good with grip. I have Kuhmo KU 27's 15 inch rims
Click to expand...

Getting close....you by chance ,have camshaft specs?
 
No, sorry. The guy before us put it in. It's right inbetween stock and mild .. I'll put in a video so your can hear the idle and get an idea for yourself. [ame]https://m.youtube.com/watch?v=P94HO27JbwE[/ame]
 
It's got some camshaft...If you are unhappy with the 2:76's, 3:23 'S will bump up the 60-70 standard Cali speeds up,300-400 freeway rpms... That should be a 1_to 2_mpg difference, could go either way.I like the 3:23's ,on experience. Realize that's a lot of torque multiplication, you are adding. You may see difference in subtle Street manners....
 
I run 3.55's in my Duster at the moment, and have put about 40k miles on the 3.23's in my Challenger. I ran 2.76's in the Challenger for probably 20k miles or so, and 2.94's for a bit in the Duster but it's got too much cam for those.

The Challenger lost about 2 mpg going from the 2.76's to the 3.23's with no other changes. It's a stock/mild 318, cam is stock or close to it, has a 600cfm 4 barrel and headers, nothing fancy. It was built by a previous owner so I don't know a ton about the internals, safe to assume it's just a fairly low compression 318. I was getting 17-18 mpg on the highway with the 2.76's, about the best I do now is 15-16. I would guess you'd probably lose another couple mpg's or so going to 3.55's. I can't use the Duster as a comparison though as I've never run 3.23's in it and it makes a good 150 hp more than the Challenger, so I try not to keep track of my mpg's in the Duster.

I wouldn't go higher than 3.55 for the freeways out here. You have to be able to pull a consistent 70 mph on the freeways in California otherwise you get run over, even that's marginal for SoCal. With my 26" rear tires and 3.55's I turn about 3,300 rpm at 70. It's manageable on longer trips, but it would be nice to keep it at 3k or a little less. At 80 it's closing in on 3,700 rpm, and that definitely starts to get old after awhile. With your 23.4" tall tires and a 3.55 rear gear you'd be turning just under 3,600 at 70, and almost 4,100 at 80. You will not like that for 300 miles, not at all. And holy cow are those short tires!!!

If you're on the freeways in SoCal with any regularity, you don't want anything more than 3.55's, and 3.23's would be easier at the pump. You will miss rolling down the freeway at close to 80 mph turning 3k rpm with the 2.76's on those 300 mile trips out to Havasu.

This is a neat little calculator tool that lets you play with your gearing, tire heights etc and will tell you what kind of rpm's you'd be turning with each set up.

http://vexer.com/automotive-tools/speed-rpm-calculator
 
............U will notice a small increase off the line........u will most likely loose mpg.........cause spirited driving will take its toll............kim..........
 
Abodybomber said:
My choice,without converter change,3:23 gears should tickle your fancy..
Click to expand...

8 1/4 will be 3.21. Add a sure grip while you are at it. With your tires, that would be what I would choose. I doubt you'll notice any big acceleration gains going to 3.55 but it will cost you more mpg.
 
I have 3.21's with 28" tall tire I turn about 2700 at 65 mph, last time I checked I got around 14 mpg on a 4 hour road trip running 70+ mph.
 
I couldn't stand 3:55 gears in my car. Fun around town but I also like to actually take my car places. The highway sucked with 3:55 gears.

I ended up with 2:94 gears and was still wishing for OD on the highway.

And that was with a 28" tire.
 
First of all, IF your "dead" out of the hole, can't spin a pebble, then you have other issues. Your not going to go from 2.5 60ft. time to a 1.9 60 ft. time because you installed 3.55's. Not happening. I've done this lots of times. It will make a difference, but it won't be like you dropped a 408 stroker in there. 2nd of all, if you can listen to the motor sound like it's in 2nd gear at 60 mph, then install your 3.55's, cause that's what it will seem like to you. If your dead out of the hole, again, something isn't right with your current combo. Laying black marks shouldn't be a problem with a 318 "one-legger" turning a normal radial tire.
 
I've got 3.23 with 245 60r15's and a 904 with low gear planeary with stock converter for now. 2600 at 65 mph and get beween 16-17 mpg in my 318. Not bad off the line but won't win any street races. Not obscene on the highway either. For a non overdrive it's not a bad compromise.
 
Ok , cool thanks guys. And I haven't tried any butouts yet. We just recently got the car running and we are trying to fix the steering and brakes before we do anything too crazy! I think I will go with the 3.21s ( someone said 3.21s were for 8 1/4) / 3.23s .
 
2.94 is also a nice gear set. I run those behind a 904 with the low first gear and it's really nice off the line and doesn't howl on the highway.
 
You must log in or register to reply here.
-

Back
Top