4.77's
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From: Miami, FL
Originally Posted by Swimshady,Jun 21 2007, 09:33 PM
I see alot of misinformation here... lets see where to start...
Your acceleration is determined by the actual TQ produced by the wheels. This is the engine TQ x transmission ratio x rear end ratio minus friction. If you take that torque rating (which is not the same as RWTQ and is typically in the ballpark of 3k+ lbf-ft for 1st gear) and divide by the diameter of your tire (in feet), then you will get a force in pounds. If that force equals the weight of your car, then you will accelerate at 1g or 9.81 m/s^2... and it can of course go up and down from there as well.
By adding steeper rear end gears, you effectively increase that wheel torque by 16% in your first gear. The effects die off fast after that point.
One way to look at gearing is to think of a race from 0-100 (or whatever speed)... if you have your gears set up so that your top gear maxes out at 100 and your oponent has much lower gears, then you will get to shift more times and keep your RPMs up.
An extreme example of this is to say that you have a car with a 2 speed racing a car with a 6 speed (all else equal), then the 6 speed will win because it can utilize its powerband more effectively.
Now lets take the example of 2 cars, one with steep gears 5.xx+ and one with low gears 3.xx, and they are both cruising at the same RPM and the same speed. If the cars both made the same power, then they would both accelerate at EXACTLY the same speed, regardless of the fact that they have different gears.
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On the topic of HP gained or lost on a dyno with gears... in my experience, steeper gears tend to have a higher drivetrain loss than lower gears and are always weaker due to the nature of ring and pinions. In order to make a higher ratio, you have to sacrafice tooth contact. The question is really where the weak point is. I am not very familiar with the S2K rear ends enough to say if the weak points are in the ring gear, posi unit, output shafts, or simply the casing itself. But I can tell you that 2 equal quality ring gears, the higher the ratio, the weaker the ring gear.
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This whole "16% power gain" is not the propper way to look at it. Just think that it will accelerate 16% faster in 1st gear, but you also lose 16% speed in that gear. You need to understand the basics of horsepower...
Acceleration can be determined by TQ and gearing (but that requires you to know your individual gears) or by HP and Speed.
Acceleration is directly related to HP produced at a given time (in whatever gear, all that is important is the HP at that RPM) and the speed (the faster you go, the more horsepower it takes to accelerate).
If you double your speed, you need to double your horsepower to obtain the same rate of acceleration due to the fact that horsepower and speed are both rates of time, whereas TQ is not.
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Horsepower is often hard for most people to understand, but I hope that helps.
Your acceleration is determined by the actual TQ produced by the wheels. This is the engine TQ x transmission ratio x rear end ratio minus friction. If you take that torque rating (which is not the same as RWTQ and is typically in the ballpark of 3k+ lbf-ft for 1st gear) and divide by the diameter of your tire (in feet), then you will get a force in pounds. If that force equals the weight of your car, then you will accelerate at 1g or 9.81 m/s^2... and it can of course go up and down from there as well.
By adding steeper rear end gears, you effectively increase that wheel torque by 16% in your first gear. The effects die off fast after that point.
One way to look at gearing is to think of a race from 0-100 (or whatever speed)... if you have your gears set up so that your top gear maxes out at 100 and your oponent has much lower gears, then you will get to shift more times and keep your RPMs up.
An extreme example of this is to say that you have a car with a 2 speed racing a car with a 6 speed (all else equal), then the 6 speed will win because it can utilize its powerband more effectively.
Now lets take the example of 2 cars, one with steep gears 5.xx+ and one with low gears 3.xx, and they are both cruising at the same RPM and the same speed. If the cars both made the same power, then they would both accelerate at EXACTLY the same speed, regardless of the fact that they have different gears.
-------------
On the topic of HP gained or lost on a dyno with gears... in my experience, steeper gears tend to have a higher drivetrain loss than lower gears and are always weaker due to the nature of ring and pinions. In order to make a higher ratio, you have to sacrafice tooth contact. The question is really where the weak point is. I am not very familiar with the S2K rear ends enough to say if the weak points are in the ring gear, posi unit, output shafts, or simply the casing itself. But I can tell you that 2 equal quality ring gears, the higher the ratio, the weaker the ring gear.
--------------
This whole "16% power gain" is not the propper way to look at it. Just think that it will accelerate 16% faster in 1st gear, but you also lose 16% speed in that gear. You need to understand the basics of horsepower...
Acceleration can be determined by TQ and gearing (but that requires you to know your individual gears) or by HP and Speed.
Acceleration is directly related to HP produced at a given time (in whatever gear, all that is important is the HP at that RPM) and the speed (the faster you go, the more horsepower it takes to accelerate).
If you double your speed, you need to double your horsepower to obtain the same rate of acceleration due to the fact that horsepower and speed are both rates of time, whereas TQ is not.
----------
Horsepower is often hard for most people to understand, but I hope that helps.
Registered User
Joined: May 2006
Posts: 364
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From: Melbourne
For those concerned about MPH vs RPM this should help
Gear calculator
I also recomend 4.77's. The fact that they're OEM and give awesome results are really all the selling points u need..... my 2c
Gear calculator
I also recomend 4.77's. The fact that they're OEM and give awesome results are really all the selling points u need..... my 2c
Joined: Oct 2005
Posts: 2,932
Likes: 58
From: Ohio
Sorry to bring a topic back from the dead... just had a question on engine stress/engine life with gears. Is it going to be harder on your engine and possibly decrease the life span of your motor or cause other issues because you are traveling at higher RPMs more often than not? I'm interested in the 4.77 gears but not at the expense of my motor. Thanks for any input.
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Joined: Aug 2005
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From: No va
not if you drive the speed limit 55-65 your only running about 500rpm higher than normal. Through the city if you shift earlier into a higher gear you'll be at the same rpms as if you were shifting normal. Highway is where it makes the biggest difference.
Joined: Jan 2006
Posts: 4,953
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From: 17 ft below sea level.
500 rpm extra won't do damage to your engine.
Everthing "upstream" from the diff will have a slightly easier life with gears.
More mechanical leverage.
But..it IS a lot of fun going through the revs & gears (transmission) with the higher final drive ratio, again and again and again
.. and THAT will make the whole drive train & engine wear a little more I guess.
Hardly though.
Everthing "upstream" from the diff will have a slightly easier life with gears.
More mechanical leverage.
But..it IS a lot of fun going through the revs & gears (transmission) with the higher final drive ratio, again and again and again
.. and THAT will make the whole drive train & engine wear a little more I guess.Hardly though.
Joined: Oct 2005
Posts: 2,932
Likes: 58
From: Ohio
Thanks guys, so it sounds like there would be minimal, if any wear from what I'm hearing. I do travel highway quite a bit and usually stay anywhere between 75-80mph... I just want to make sure the gears won't cause extra stress on my car because that is the speed the car sees a lot.
Joined: Aug 2005
Posts: 8,908
Likes: 2
From: Ventura Co, CA
Originally Posted by freshs2k,Feb 15 2007, 08:46 PM
its still cold here in n. va but i think the first track day is gonna be march 3rd but im going to get dynoed and hopefully tuned that day so i won't be going to the 1/4 until the next weekend. i think its gonna take quite a bit to break that 12 second mark with street tires we'll see. i heard with gears alone it takes something like .5 off your 1/4 if drivin properly. i never lower my tire pressure which i am definately doing this season.
Getting into the 13 is feasible with the S but going down into the 12's takes a lot more hp to get there. I dont think 4.77's and a good intake n exhaust will do it.
13's for a NA S isnt easy but it can be done.
I have a 4.44's and I ran up against the same year car as mine, '07, with 4.77 and he got me by 3/4 of a car in first gear and we stayed the same through 4 gears. We have similar set ups, i/h/single ex.
The only diff was the gearing. 4.44 vs 4.77.
Hope this helps a bit. This is just one tale so take this as ONE source only. I understand there are diff variables like drivers, tires, psi, etc.
Only reason I chose 4.44 is cause I do take the car past the 4.77 mph cut off.
Either gear is good it just depends what you want but you wont get an S on steroids.
My co-workers STI still leaves me standing. The funny thing is im trying to run past him
