Rear gears

[Cainsable]

So I am debating what gear to go with in my 73, looking a pro street gear thinking a 389 or 411 what experience have you guys had. Good or bad with these gears

 

[Don C]

The good, a real kick in the pants when you stand on it, the bad 3,000+ RPM at 60 on the highway. I won't mention gas mileage, because if a person is worried about that, better go buy a Prius.

What transmission are you running? Planning any upgrades?

Play around with the spreadsheet in this thread, to see the affects of tire sizes and gearing.

https://www.7173mustangs.com/thread-tire-sizes--5980?pid=56388#pid56388

 

[Cainsable]

Don't plan on much highway, chart is great. I have a c6 and running 275/40/18 rear. Motor is a stroked 351 c, I really don't know what was done to the c6 before me but it does have a small stall and shifts like it has a kit or transpac

 

[turtle5353]

I have a 408C stroker. C-4 and 3.73 gears. I am running around 3,000 rpm at 60-65mph. If you get into steeper gears like 411's and that c-6 you are going to be very gearbound on the highway even for short trips. Fast as hell telephone pole to telephone pole. But done after that. I can smoke my back tires rolling down the road at 40-45 MPH with a simple stomp of the throttle. I wouldn't go much steeper gear unless I was getting an OD trans. Which I am planning on if this damn c4 ever dies!

 

[Jeff73Mach1]

Like my 3.89 but I have 28" tall rear tires and I'm not driving on the highway often or far. 150 mile trip stretches the range of the gas tank and the tolerance of my ear drums.

I had a 5 speed with overdrive and it was really awesome until my engine shredded it and I threw the toploader back in.

 

[Tnfastbk]

I run a 410 gear with a 408 Stoker and a Tremec TKO 600 and can run 70 mph at about 2300/2400 rpm range in 5th gear. Below is an article I ran across. Sorry for the size it would not let me resize it.

MUSTANG REAR GEAR RATIOS OVERVIEW





WHAT IS A REAR GEAR RATIO AND HOW DOES IT WORK?


When you get to the point in your Mustang build where you’ve already hit the basics like an intake, tune and exhaust, it may be a good idea to examine your rear gear ratio and see if it’s worth swapping gears to something more or less aggressive. In simple terms, the rear gear ratio dictates how quickly your car accelerates and its top speed from a mechanical standpoint.


With that said, there are various factors that go into choosing which gear ratio is best for your Mustang build, so keep reading for a brief overview of how and why rear gears are important to any Mustang build.

SHORTER VS TALLER REAR GEAR RATIOS

The higher (or shorter) the gear ratio is – 4.10, 4.30, etc. – the quicker your car will accelerate through the gears but will sacrifice some top speed. The lower (or taller) the gear ratio is – 2.73, 3.15, etc. – the slower your car will accelerate but will have a higher top speed and lower cruising RPM for better gas mileage.

Where do these numbers come from? Well, if you’re in your transmission’s 1:1 gear, such as 5th gear in a manual 2011 Mustang GT with 3.31 gears, it means that for every revolution of the rear wheels at 60 MPH, the driveshaft will rotate 3.31 times. So, this means that the engine does not have to work as hard to spin the rear wheels and at cruising speed you will be at a lower RPM to obtain better gas mileage.

On the other hand, if you have that same Mustang and transmission combination but with aftermarket Ford Racing 4.10 Gears, your driveshaft will have to spin 4.10 times to get the same exact revolution out of your rear wheels. Meaning that your engine is putting 23.8% more effort over 3.31 gears into one wheel revolution equating to noticeably quicker acceleration. However, RPM will be higher on the highway, thus sacrificing a little top speed and gas mileage for quicker acceleration.


We know it can be a lot to grasp, so here are a couple bullet points to make things easier to understand:

• The higher the number or shorter the gear, like 4.10 or 4.30, the quicker your car will accelerate, but sacrifice some top speed and cruise at a higher RPM.
  
• The lower the number or taller the gear, like 2.73 or 3.31, the slower your car will accelerate, but will obtain better MPG on the highway due to a lower cruising RPM.
  
• Keep in mind, going with too short of a rear gear ratio can result in reduced traction, bad gas mileage, and unnecessary wear and tear on your engine at highway speeds.
  

WHICH REAR GEAR RATIO IS RIGHT FOR ME?

 


That is a loaded question. It all depends on what you plan on doing with your Mustang and what other modifications you plan on adding. Yes, that means there are different ideal rear gears for a car that is strictly a street car versus one that runs solely on a 1/4 mile dragstrip. Another factor can include whether or not you plan on adding a forced induction setup (supercharger or turbo) in the future. On top of that, the engine, transmission and tire combination can also dictate what type of rear gears you should put in your car. All of these various factors go into choosing the correct rear axle gear ratio on your Mustang.

Street Car With Occasional Dragstrip Use - Most of the Mustang enthusiasts out there probably fall into this category. With this particular combination, you’re going to want to find a set of rear gears that will take into account not only acceleration at the dragstrip, but also RPM when you’re cruising down the highway. There are outliers, but more times than not the ideal gear ratio for this combination is 3.73 on most naturally aspirated Mustangs.

Dragstrip Only Use - There are probably a few of you out there who plan to build up your Mustang as a drag-only car. That’s awesome – but it’s important that you find the right gear ratio for getting your Pony down the quarter mile the quickest. With a drag setup, there are many other factors that go into figuring out what will make your car the fastest at the strip including size of your rear tires and transmission specifically.

Road Course Only Use - Some of you may not be into the straight-line racing scene and prefer to carve corners. That's great - but that means there is a different ideal rear gear ratio for your Mustang as well. Most road course cars tend to have longer rear gears due to the fact that means less shifting time. And less time spent shifting, means quicker lap times. A track car may use something like a 3.55 rear gear ratio, whereas a drag car may have 4.10 or 4.30 rear gears. It all depends on the build.

A NOTE ABOUT YOUR SPEEDOMETER

After replacing the rear gears in your Mustang, you will more than likely notice a difference in your speedometer reading. This is because your Mustang’s computer thinks that you still have your factory gears installed and will output the speed using that gear ratio.

There are a couple ways you can go about having this corrected:

• If you have a tuner such as the SCT X4, COBB Accessport or nGauge Tuner, have your tuner fix the gear ratio in your tune so your speedometer reads correctly.
  
• If you do not have a tune on your Mustang, you can have the Ford dealer reflash your ECU and correct it that way.
  
• For those who have Mustangs older than 1999, you can pick up a speedometer gear to correct the issue.
  

 

[Hemikiller]

Really depends on what you're doing with the car. If it's cruising around town, a 3.50 or 3.70 will get the job done nicely, especially since you're running a shorter tire.

 

[barnett468]

So I am debating what gear to go with in my 73, looking a pro street gear thinking a 389 or 411 what experience have you guys had. Good or bad with these gears

I wouldn't use 4.11 under ant condition unless your engine revs to at least 6000 rpm.

 

[jbojo]

Running a 3.89 TruTrac with Gear Vendor on a C6 and I do around 2750 RPM at 70 mph. Mostly do in town driving and 45mph which is about 1600 rpm in OD. I am happy with this setup.

 

[Mikes73]

Just finishing up my 4.11 install today. I will post a follow up later

Our local dragstrip is reopening soon so I yanked the 3.50 gears out for a while in favor of the 4.11's. Our stang sees almost no highway miles so this was also a factor for us.

 

[johnwanzel]

Like most people have already stated, it really depends on your setup. If you are running a 3 speed automatic, you are confined to gears of no more than 3.50, 3.55, or 3.73 if you want to cruise at a decent speed down the road. If you are using a 5 or 6 speed, you can afford to go 4.11 or 4.30 without sacrificing cruisability. Also keep in mind that you need to keep the rpms in the power band of the engine while cruising. If you don’t and you are below your power band, the engine will feel like it’s “lugging” while cruising.

 

[Cainsable]

Let me know how it works out for you

 

[Mikes73]

Will do, I should have the swap wrapped up soon.

 

[Mikes73]

Cainsable. I finished up my 4.11 gear install last night and got to drive it around the block a few times, so far I am very impressed with them. The car feels like it lost 300 lbs. and gets up nicely now. When I get more seat time I will post more thoughts on them.

 

[Jeff73Mach1]

a 3.70 gear might be worth a try-should be relatively obnoxious and loud without being unusable

 

[Heavy Metal]

My old 71' Mach 1 had 3:91 track lock with 4 speed.

And a 351C 2V making 400HP camed to max, It was a ripping good time.

I think 4:11's are too much for a driver and 70 mph on the freeway.

Just my opinion.

 

[red351]

Made a trip cross country with 3.50, no over drive. Sounded like a nascar race 4 days out 4 back.

 

[Mikes73]

I went with the 4.11's on my ride because 95 percent of our driving is below 60 mph and the other 5 percent will be at the 1/8 mile drag strip. I love this setup, the car will chirp the tires shifting into 3rd and feels fast now not just quick like it was before. I was under the impression that the original poster was building a somewhat drag car not a daily driver that is why I threw my experience out there.

 

[Cainsable]

Yes you are right I will rarely go over 55 in the area I drive. I am leaning towards the 411