Modded Mustang Forums banner

1 - 20 of 23 Posts

·
Registered
Joined
·
129 Posts
Discussion Starter #1
According to my calculations, my 1/4 mile will be exactly the same.. but the 3.73 will have a faster 0-60... assuming my tires are planted I suppose lol. I hear the 3.73 will give better city milage? I find myself at around 18MPG largely due to idling, but I suppose I spend most of my time in the city going between 0-60MPH.

So, will going to 3.73 from 3.31 be worth the cost? (I wont be doing the labor) I DD the car, autocross occationally, and eventually plan to drag it and see how it does (with street tires for now..yes I know)

The plan is to maybe swap the driveshaft out, change the gear, and do a tranny/diff fluid change all at the same time. Assuming changing the gear is even a good idea

The reason I don't consider 4.10 is because I figure street tires cannot handle it much, plus I fear killing higher MPG too much, and the 1/4 mile time will be worse...and lower gears = worse dyno numbers apparently
 

·
Registered
Joined
·
5,648 Posts
I did it, its not a crazy difference, but it is noticeable. As long as you shift at low rpms your mpg will be very similar in the city, but lower in the highway.

I did it because it was hard for me to hold 3rd gear drifts with stock gears, but it became a lot easier with the 3.73
 

·
Registered
Joined
·
129 Posts
Discussion Starter #4
Do it. I did, it's a great gear for an N/A car. Now that I have a TVS blower, I want to switch back lol.
I have a V6 with a procharger, but the care is most awake after 2.5k RPM and the exaust note is its nicest around 2k RPM so I figure the slight higher cruising RPM the 3.73 will give may make for nicer harmonics too lol. Its a borla s-type so rather tame when cruising near 1k rpm, absolutely gets loud when you demand it though.

---------- Post added at 01:29 PM ---------- Previous post was at 01:27 PM ----------

I did it, its not a crazy difference, but it is noticeable. As long as you shift at low rpms your mpg will be very similar in the city, but lower in the highway.

I did it because it was hard for me to hold 3rd gear drifts with stock gears, but it became a lot easier with the 3.73
I hear some claim the city will actually improve, just you wont notice, and the combined will be around the same, the only time you notice is on a majority highway situation. Do you know how the "ideal cruise speed" is affected? I assume the car will prefer to cruise at closer to 50MPH instead of 60MPH with the 3.31's. I usually go 70-80 anyways because some of the limits are high enough anyhow..

---------- Post added at 01:34 PM ---------- Previous post was at 01:29 PM ----------

I should mention that part of why I'm thinking of doing this, is sometimes I'll shift from 1st to 2second too early, then I'll be at say 20MPH, I can't go back down to 1st at that speed, then if I want to accelerate, theres a bit of a lag before I'm in the best part of my power curve. Similar situation arises in autocross where if I take a bad curve and slow down too much, my RPM's are lower than I want and I'm in 2nd gear. Highway is no issue, if I need to haul ass, I can always downshift, get instantly higher RPMS and I'm happy flying down.
 

·
Registered
Joined
·
5,648 Posts
Well, basically how it affects the car is the car will be going 10 mph slower at the same rpms, so think of it this way:

Consider there is no wind resistance/tire drag... Stock gears you are on the highway going 70mph at 2.5k rpms (I dont think this is exact), you travel for 2 hours, and you have covered 140 miles at 2.5k rpms.

With the 3.73 gears you will be at 60mph at 2.5k (again, this is not exact, but the mph difference at the same rpms is exact), again, you travel for 2 hours at 2.5 rpms. You will use the same amount of gas since in both cases the engine is spinning at 2.5 rpms, although when you are going 70mph there is more wind resistance and tire drag which does decrease fuel millage by a small amount.
Now in those two hours with the 3.73 gears you covered 120 miles, compared to the 140miles with the stock gears, and you would have used almost the same amount of gas.

Thats a 15% decrease in fuel mileage when going 70mph. Which means that if you were getting 18 mpg before, you will now get about 15.3 mpg.

Its 300 miles from Weston to Gainesville, before the gears I could do the whole trip with one tank of gas exactly, after the gears It took me almost an additional 1/4 tank to complete the same trip.
 

·
SlowFiveOh
Joined
·
2,370 Posts
Do it. I did, it's a great gear for an N/A car. Now that I have a TVS blower, I want to switch back lol.
Same. My 3.73s are way too much gear now
 

·
Registered
Joined
·
129 Posts
Discussion Starter #9
Hmmmm maybe my compromise should be, stick with the 3.31's unless I ever get wheels that end up increasing the total wheel diameter.
 

·
Registered
Joined
·
52 Posts
i have factory 3.73 and average 16.8 city. i plan to supercharge in a couple of years and now you guys are making me regret i searched for a factory 3.73 car.
 

·
Biz Jet Fixer
Joined
·
4,985 Posts
Not worth it. Plus you're increasing the chances of gear whine tenfold.

THIS!

I have a factory 3.73 car. It's had 3 or 4 sets of 3.73's put in under warranty and the whine is still horrid.

I'm eventually going with 3.55's.
 

·
Registered
Joined
·
1,099 Posts
ive got a build date of march 2010 and no gear whine in my factory 3.73 lol. I love em, great for auto x and daily driving. if you pussy foot it youll get 18mpg. and about 22 on interstate. I cruise all the time at about 70 and my rpms are around 2800, not so bad.
 

·
Registered
Joined
·
709 Posts
70mph is 2k for me? I have 3.73s
 

·
Registered
Joined
·
52 Posts
ive got a build date of march 2010 and no gear whine in my factory 3.73 lol. I love em, great for auto x and daily driving. if you pussy foot it youll get 18mpg. and about 22 on interstate. I cruise all the time at about 70 and my rpms are around 2800, not so bad.
I really need to work on my foot.
 

·
Biz Jet Fixer
Joined
·
4,985 Posts
ive got a build date of march 2010 and no gear whine in my factory 3.73 lol. I love em, great for auto x and daily driving. if you pussy foot it youll get 18mpg. and about 22 on interstate. I cruise all the time at about 70 and my rpms are around 2800, not so bad.
Mines a 07/10 date IIRC. I love them but the whine. Jesus. It's deafening at certain speeds. I get 20mpg around town and an easy 24-26 on the interstate.
70mph is 2k for me? I have 3.73s
That's what it is for me.
 

·
Registered
Joined
·
1,099 Posts
Mines a 07/10 date IIRC. I love them but the whine. Jesus. It's deafening at certain speeds. I get 20mpg around town and an easy 24-26 on the interstate.


That's what it is for me.
thats crazy man, i have heard no whine at all... my brothers old 2012 with 331s howled like a mofo lol. i think its just realitive
 

·
SlowFiveOh
Joined
·
2,370 Posts
My 3.73's whine bad.
 
1 - 20 of 23 Posts
Top