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Found this article on some mustang forums. Thought it might be useful to some members here. I still think I am going with the 3.73 but this does make me think about the 4.10. I think there are some facts that could be added/removed to/from this article and then maybe thrown into the tech articles?


Gearing, What minimum gear to get, and the benefits.

"Probably the most frequently asked question on every mustang message board, gears are not debatable. 4.10s minimum on a daily driven 4.6L N/A mustang. I’ll get to why in a minute but to realize why there is no debate, we must first look at what gears do. Gears live in the rearend, bolted to the pumpkin and driven by the driveshaft. The job of gears is to multiply the engine’s torque. So with a 250 TQ engine with 4.10 gears, your multiplied torque will be 1025. You might be thinking, “Why the hell do we need that much torque?” Well, the truth is, without a multiplication of torque, our cars will not move. For some visual information about gears and differentials, go here. Most stock mustangs have 3.27 gears from the factory. I have no idea why Ford put these gears in our cars because they’re awful.

Despite what some “experts” might tell you, gears will not decrease your top speed in a mustang; in fact, they’ll probably increase it. If you were to top out your car with 3.27 gears, you’ll notice that the power just stops when you shift to 5th gear. This is because you are not in the car’s powerband to pull the car up to higher speeds. Not only will steeper gears allow you to pull quicker but also they’ll keep you in your powerband which will, in turn, enable you to pull in 5th gear; something you could NOT do before. Other experts claim that you will lose gas mileage due to the higher RPMs that your car will now be traveling at on the highway. In reality, you’ll lose maybe 1-2 MPG at best. By far, the biggest misconception out there is that 4.10s are “too much gear” for a car. These people that tell you this are morons. Those people are stuck in the pushrod days where the cars can’t rev past 5500 RPMs. Our cars rev to 6000 RPMs for a SOHC and 7000 RPMs for a DOHC. Our torque comes on later than the pushrods, hence the need for the steeper gears. Sure, there are instances where you might want to get a different gear ratio if you have a poweradder or are a drag only car, but be it Auto-Xer, Open Tracker or Drag Racer, do NOT get less than 4.10 gears for a daily driven N/A mustang. For those who want to play around with gear ratios, go here.

The recommended brands for gears are FMS, FRPP. FMS and FRPP are the same gears however. Ford has two markets for the same rearend; one is the SUV market and one is the Mustang market. The SUV market isn’t as high performance and not as willing to spend the big bucks for items like the Mustang market is, so they take the gears they make and label one FMS and one FRPP even though they’re the exact same thing. In the end, just get whatever is the cheapest. I recommend getting a shop to do the install as this is a pretty complex thing to do. The install kit depends on how many miles you have on your car. If you have more than 35k miles, I recommend stage 2. If you have more than 75k miles, I recommend stage 3."
 

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Link to the original article?
 

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I have no idea what the stages mean, but there are other things to think about. If you are going to drive it a lot on the highway (like me) why would you go with one so high? I ask because in the olden days, you did not want to run a 4.10 gear with anything less than a 33" tire becasue if you were on the highway a lot, you could warp the gear. I am sure there is SOME possibility of that, but I think of the other stuff I have to worry about.

One more thing, for those who have a dyno for their cars, anything 3.73 and higher will knock about 15 hp/tq off of the peak numbers.

SWS
 

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Discussion Starter #4
Link - http://www.mustangspecialties.net/mustang-gear-selection.html

Gears warping? sounds like a bad ring and pinion gear more than anything else. When you say a 33" tire then I assume your talking about lowering the rpms at the various speeds but I am not sure why that would have any effect on the ring and pinion gear.

BTW - Love your sig I think its great
 

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The reason at the time was the amount of speed of the gear. The do get hotter because they spend mort time in contact and spin faster. The taller tire slows the gears down...because one trip around of the tire is a longer distance than a shorter tire. Kind of like the way you want to add a tail shaft cooling mod if you go 3.73s or higher.


SWS
 

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This is not a political forum. If you want to talk politics take it elsewhere.
 

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Thought process was that they would warp in the car and stay warped causing a howling after only a short while. I can totally see that happening back when metals were different. Like the all aluminum 427 GM had back in the day. When it was warm, it would start to leak because the aluminum was not a good alloy. When it would cool down, it would seal back up. I know of a few people who run 4.10s in the street cars and as far as I know there is not a problem. The more and more I think about it, the more I think I am going to do it....maybe.

I will probably put a cooler on mine that pumps like a mechanical fuel pump as the suspension cycles.

No save, just missed one of the rules. TM did the trimming to keep this thread open and on track.

SWS
 

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GM
i've been wondering...what's your rev-limit/goal gonna be once you get this bad boy together 7000-7500?
it all depends where the HP peak rpm ends up being at. From talking to the makers of the intake manifold, taking into account the cams I'm gonna use, its gonna peak at somewhere in the 7000-range (the runners are tweaked and shorter than a "stocker" lol). So the 1-2 shift will have to be significantly higher than the peak given the wide-ratio between 1st and 2nd.

I have no idea what the stages mean, but there are other things to think about. If you are going to drive it a lot on the highway (like me) why would you go with one so high?
If fuel economy is your primary concern, then don't get shorter gear ratios; they are strictly for multiplying wheel torque and thus acceleration potential--something you won't need.
 

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Cars come from the factory with 4.10's.
Ex. 4cyl. mustangs.
4.10's are for street cars.
 

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I would have to say 3.73s would be as steep as I would recommend for any of these cars you plan on taking on the highway for more than a few miles at a time. I never saw a decrease in mileage in the city (sub-40 MPH areas) after the switch, but I did see about 20% lost on the highway (60-70 MPH, went from 26-27 average to 21-22).
 

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GM, When your engine hits it's powerband, people are going to think that its turbo just came online, lol.

Extra points if you shatter all your opponents glass on launch... :headbang:
 

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GM, When your engine hits it's powerband, people are going to think that its TURBO just came online, lol.

Extra points if you shatter all your opponents glass on launch... :headbang:
dont give him any ideas :D
 

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Discussion Starter #18
I would have to say 3.73s would be as steep as I would recommend for any of these cars you plan on taking on the highway for more than a few miles at a time. I never saw a decrease in mileage in the city (sub-40 MPH areas) after the switch, but I did see about 20% lost on the highway (60-70 MPH, went from 26-27 average to 21-22).
Wow that much? I've never heard of that much a drop in gas mileage. I am still thinking 373 too because I drive to Nashville every day for work during the summer. But I have driven my friends 04 mustang with 4.10 gears and if your not concerned about gas mileage 4.10s is the way to go, it flys. We seem to have similar mods tho Brandon how do you like your 3.73s? best mod so far?
 

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The gears are most definitely the most noticeable mod I've done thus far, aside from the grip and handling offered by the tires and the J-mod. I was able to get an assembled pumpkin ready to bolt in for 250, so it was a good deal.

Before I started playing with the car the economy was 26-30 on the highway. Now that I think a little, before I put the pumpkin in (with all other mods), I was averaging the 25-27 range. On my first highway trip with the 3.73s, I was surprised that the highway economy was as low as it was, it was just under 20. The last times I've made that highway trip though it was more like I mentioned above - 22ish. But like I said, city economy remains high teens (A/C on all the time) or low 20s (A/C off).
 

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Discussion Starter #20
Wow 250 for an assembled pumkin thats great. Yes I am kinda worried about doing the gear without bigger tires. Currently I am running a tire slightly bigger than stock in the rear and its not a huge problem because I normally race from a roll but I would like some grip if I hit it from a stop.
 
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