Gear Question
 

So will i lose or gain hp by getting 4.10 gears. will i lose top end speed or how does that work? im really not sure and i would like to understand before i get them!

you will lose hp by a small amount. Your top speed will reduce.

You're going to be magnifying the torque multiplication, and increasing the number of engine revolutions per wheel revolution. I think 4.10's are too steep for the street but I'll be shouted down in a minute. I prefer 3.73's for street cars .

4.10's in my DD and very happy. Not too sure why people complain about 4.10's on street cars? On 4v's I wouldnt go with anything less then 4.30's.

maybe for the highways? and gas mileage. thats why ive heard bad news about em only reasons

I just hate the super duper short 1st gear with the stock 5speed tranny. On auto's no problem... hell autos should come with 4.10's but for manuals, 3.73 (and I think those should be factory options anyway).

I just like to get across the intersection before I have to shift.

How can you say you lose HP with gears? Horse poweer is made way before the rearend gets involved. When I put the 4:10 gears in, it changed my 5th gear RPM's by 500 Rev's at a given speed, so the gas thing is almost a moot point. The only effect it will have on top end speed is you'll be reving higher. I may be wrong on some of what I said, so please, everyone jump in and set me straight.

Since putting in 4.10 my gas mileage hasn't changed at all even when getting on it pretty hard. It's a daily driver and I wouldn't change a thing. The performance gain you get is awsome. Top speed in 3rd gear (High gear) is only about 110MPH but that's plenty fast. It will just about top out in high gear through the 1/4.

My MPG went up by one with my 4.10 gears:breakdancesmilie: . They really arent that bad for highways either. I turn like 2350 rpm at 70 which really isnt that bad. I guess if you cruise at 80 it wouldn't be the best, but I have no complaints.

2350 at 70? Mine is sitting on 2600 at 70.

He has a 5-speed, you have an automatic. The OD gear is a little bit shorter on the manual.

The manuals may have taller 5th gear than an auto's OD and lock up converter but that just seems to be a large difference. I remember reading an article that showed the same RPM's at cruising speed (70) for both auto's and manuals with the stock gears. Auto's came with 3.27 and I thought the manuals came with the same for the GT's.

so 4.10s would be best for autos?

I don't think u actually lose hp. But on the dyno u will show less not to sure how to explain that it's just my experince. but when I build my rear I think I will go with the 4.10's.

No question, go with the 4.10.

horsepower is a measure of work done. If you reduce the total distance traveled (with bigger gears like 4.10's) then you've increased the amount of engine rotations required to do any amount of work. Thus, you've LOST hp. Math is math and the math says if you go a shorter distance then you've done less work.

Torque is a measure of force and is what most enthusiasts confuse with horsepower. Torque is what gives you the shove in the back and is multiplied a bit by bigger gears.

The best example of this is the RX7 rotary motor. It can make stupendous amounts of hp for the size of motor it is but it makes almost zero tq. They go fast but they don't "feel" fast. That's the difference.

This is not to say that hp is not important... those same RX7's making no torque can still smoke you in the 1/4 when properly set up and tuned. It just means that hp is not the be all end all and peak power is meaningless... average power under the curve is what really matters.

Not necessarily, since you have to factor in the fact it is rotational work, which is different. In this case, you would used (torqueX5252)/rpm=power. So, horsepower will be the same with the 4.10 gears since you are increasing the torque from the driveshaft by that much but also are decreasing the rpms by that much so in the end, you net no gain or loss in power.

FACT #1: Stock gear ratios suck.

FACT #2: 3.73's, 4.10's....ANYTHING is better then stock!!!

FACT #3: 95% of the people (according to a Harris Poll) say hat after getting 3.73's they should have gone with 4.10's.

FACT #4: 3.90's are for people who can't make up their mind. Anyone with 3.90's should be made fun of for not having the balls to get 4.10's in the first place.

FACT #5: Your top speed with either 3.73's or 4.10's should be lower, HOWEVER, this is not true! Why? You may actually find the top speed to be higher because the car will be higher in the power band at higher speeds and make a better time overcomming wind resistance. (I know of no actual test done to show this).

FACT #6: Only girls who drive Mustangs should ask about gas mileage. If you drive a Mustang, are a dude, and ask about 4.10's costing you fuel, then you should have your car taken away and donated to charity.

FACT #7: Mustangs with gear swaps, always show less hp on a dyno. You will loose about 9 hp because of dyno error. It is a mathematical error because when doing the 4th gear pull, you will no longer be at a 1:1 ratio. There is no added friction loss, otherwise your dam pumpkin would melt from all the added heat.

but you don't see a giant increase in tq readings when you bump the gear ratio up. it doesn't all work that way when you get to the wheels.

there is no difference in rotational work than there is in dragging uphill... It's still represented as something like lbs/ft per second. 1 Horsepower if I remember correctly is equal to work done by lifting ~500lbs 1ft vertically in 1 second. While the formula is correct the application isn't. Unless toruqe and power are related on a 1:1 basis your statement can't be correct. The correction factor of 5252 makes the equation get more and more unbalanced as you tinker with either side of it.

Aside from the math of it all, every dyno run for gear swaps I've seen and all of them pals of mine have seen show the same thing. Single digit percentage loss to hp.

No fair. I got 3.90s and it wasnt because I couldnt make up my mind. Its because youll be seeing 10 psi at 2300 rpm.
:salook: :kekekegay:

Manuals have 3.27's stock.

From what I heard, rear wheel dynos calculate torque and using that formula, horsepower is calculated. Also, rear wheel torque does increase with taller gears since that's what a higher ratio does, it multiplies torque by that much. Just curious, when doing dyno runs, are you asked what your rear gear ratio is? http://www.fordmuscle.com/archives/2001/05/horsepower/ here's an article that shows you how that formula is derived.

so if i get 4:10s approx. how many MPH will i shift into 5th at after redlining 4th gear?

I know exactly where the formula comes from but you're not understanding a big part of the application of it. Torque and hp are related but NOT DIRECTLY. if that were the case you'd see cars making 28% more tq after a swap to 4.10s... doesn't happen. They are related and a change in 1 affects the other but not on a 1:1 basis. I don't want to get off the subject much more but trust me...your math is incorrect.

No, you are not asked what gears you're using because nobody is trying to establish bhp using a chassis dyno. There are frictional losses that are about impossible to calculate which prevent the numbers from coming out accurately.

I'm just trying to understand this, that's all since to me, it seems very odd that horsepower is reduced after a gear swap.

that's cool... see if I can splain what's going on so it's easy to understand because it is really very very complicated. First off, there are several variables in the mix that are important to the equation. The equation you quoted earlier is valid but it is painfully simple which allows it to be incorrectly applied without obvious sign that that is the case.

When you reduce the number of wheel revolutions per engine revolution (this is important since in 4th gear we're at 1:1 in the tranny and the rear is now the only gearing variable so we don't have to compute for gearing interactions) you've reduced the distance that the car has "traveled" while increasing the force it used to do so. The distance is reduced because you've increased the RPM at which any given wheel speed will occur and since there's a RPM limit which can't be exceeded you end up with a shorter distance traveled by the time redline is reached (that's the critical detail). This means you've moved the wheels over a shorter distance. Smaller distance=smaller work. Horsepower=work. Smaller distance=smaller hp.

Now... keep that concept apart from force... force is not power. Force is energy which is being used to perform work. If you up the force then the work will happen in a shorter time and/or over a longer distance. Unfortunately on a dyno we're limited on distance to that which it takes to reach redline in 4th gear...not long on most v8 cars. If we could even out the time or the distance then the numbers would be about the same as they were... minus changes for frictional losses. So, with sufficiently giant wheels and 4.10's you'd have evened out the distance. If in that case the time to reach the end of the distance were the same, power would be up.

This really is in the realm of a physics class. If you're truly interested in understanding the fundamentals of power delivery, force, energy, and such, I suggest taking a class. I have a natural predilection toward math and physics... they just make sense to me but not everyone thinks like a calculator which is the source of my suggestion to take the class. Once you learn some of the fundamentals, then the whole arena is opened up to you and it's really quite interesting when you can understand complex concepts and take action based on knowledge of math rather than mnemonics.

Let me know if I typo'd anything... I'd hate to confuse an already confusing subject.

OK, now that makes sense to me. In fact, I'm at school to be a mechanical engineer just right now, I'm a freshman and I'm only going by from what I've heard on the internet/TV and what I learned in my high school physics class. Unfortunately for me, I have to wait until my next semester until I take physics...

cool. Mechanical eng was a career path I explored a long time ago but there was too much time in unrelated classwork to get a degree and without a degree in it there's no point in trying to get into the field.

Work hard and you'll be able to invent machines to fix any problem. That's pretty cool all by itself.

The sad part is that you are right. You spend about 4 years in school and in total, if you are lucky, only two years worth is related to your major. And even then, like in mechanical, your major may still be too broad for what you want to do.

that's pretty much why I went into computers. I figured if I can't do something that interests me then I'll at least be paid like royalty for having no degree. Of course the downside is now I'm basically a janitor on the information super-highway (sysadmin).

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