3.73 & 4.10 gear topspeed
09-23-2006, 11:45 AM
#2
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RE: 3.73 & 4.10 gear topspeed
The only way to know is if someone has gone to Bonneville or somewhere they can do some actual testing.
Changing gears and then calculating top speed brings in many variables. In many cases, lower gears can INCREASE top speed due to the multiplied torque allowing the engine to spin up tighter.
Changing gears and then calculating top speed brings in many variables. In many cases, lower gears can INCREASE top speed due to the multiplied torque allowing the engine to spin up tighter.
09-23-2006, 04:20 PM
#4
09-23-2006, 11:08 PM
#5
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RE: 3.73 & 4.10 gear topspeed
Gear Calculator will tell you how fast you will be going for any given RPM. The question here is how many RPM will the engine be able to pull at high speed. If it were as simple as doing the RPM/speed calculation, we could all gear our cars for about 250MPH top speed.
09-24-2006, 01:40 AM
#6
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RE: 3.73 & 4.10 gear topspeed
http://www.type2.com/library/misc/calcspd.htm (He says the source is Road and Track. Someone else will have to check, but I got very believable numbers using the formula.)
mph = (rpm * cir) / (gear * final * 88)
where rpm = engine rpm = 6,250
cir = tire cicumference, in feet = 7.11 ft (stock tires)
gear = gear ratio of your car =.68
final = final drive ratio of your car
88 = combines several conversion factors
I think the answer is not all. By all accounts the new Mustang has poor aerodynamics. Wind resistance would probably stop you long before you hit the theoretical top speed at least, it seems to me. I have never gone anywhere near this fast in mine, just looking at the math. Ok here's the right answer I think, all calculations for a manual:
First, let's check the model by relating it to engine RPM at a speed most of us see all the time around 1800 rpm is about 60 mph, right? Well...
3.55 gears @ 1800 RPM = 60 mph
Ok, now for your question:
3.55 gears = 209 mph @ 6,250 rpm
3.73 gears = 199 mph @ 6,250 rpm
4.10 gears = 181 mph @ 6,250 rpm
I think top speed is usually given in the low 140's, right? It seems to me that you'd need a pretty radical gear in order to limit your top speed.
mph = (rpm * cir) / (gear * final * 88)
where rpm = engine rpm = 6,250
cir = tire cicumference, in feet = 7.11 ft (stock tires)
gear = gear ratio of your car =.68
final = final drive ratio of your car
88 = combines several conversion factors
I think the answer is not all. By all accounts the new Mustang has poor aerodynamics. Wind resistance would probably stop you long before you hit the theoretical top speed at least, it seems to me. I have never gone anywhere near this fast in mine, just looking at the math. Ok here's the right answer I think, all calculations for a manual:
First, let's check the model by relating it to engine RPM at a speed most of us see all the time around 1800 rpm is about 60 mph, right? Well...
3.55 gears @ 1800 RPM = 60 mph
Ok, now for your question:
3.55 gears = 209 mph @ 6,250 rpm
3.73 gears = 199 mph @ 6,250 rpm
4.10 gears = 181 mph @ 6,250 rpm
I think top speed is usually given in the low 140's, right? It seems to me that you'd need a pretty radical gear in order to limit your top speed.
09-24-2006, 10:38 AM
#8
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RE: 3.73 & 4.10 gear topspeed
You're missing the point fella's!
Sure, you can calculate the speed vs RPM with formulas and charts no problem. The question is whether or not the engine will have enough power to overcome wind resistance, weight, friction, etc., to spin the engine up to that RPM while under load. In many cases going to a lower gear (higher numerically) will actually INCREASE top speed due to the multiplied torque allowing the engine to provide enough power to spin faster, propelling the car faster.
I think some of you might have missed high school physics.
Sure, you can calculate the speed vs RPM with formulas and charts no problem. The question is whether or not the engine will have enough power to overcome wind resistance, weight, friction, etc., to spin the engine up to that RPM while under load. In many cases going to a lower gear (higher numerically) will actually INCREASE top speed due to the multiplied torque allowing the engine to provide enough power to spin faster, propelling the car faster.
I think some of you might have missed high school physics.
09-26-2006, 11:21 PM
#9
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RE: 3.73 & 4.10 gear topspeed
Well, I've had plenty of college level physics, although it has been awhile. There are way to many numbers that I don't know and can't find. I'm going to estimate.
Fdrag = 1/2 (drag coefficient * air density * surface area * Velocity Squared)
The gears are 4.10 vs. 3.55. That means torque would be multipled by about 14 or 15% at the rear wheels.
I suppose the force exerted would there would be about 15% greater...that means we need to calculate the speed that exerts 15% more on the object to reach terminal velocity. Assuming that 143 mph is the correct top speed stock (as quoted all over the internet). The V^2 term is killing you if the car goes 155 mph, then you've increased drag by 15% already. I'm not convinced that gears would make much of a difference.
These new Mustang have terrible drag coefficients, the GT500's drag coefficient is a sad 0.38, note that top speed is limited to 155 mph (electronically, but I wonder how well it handles at it's true top speed?).
http://www.autozine.org/html/Ford_USA/Mustang.html
A new Corvette Coupe has a drag coefficient of 0.286! My last peformance car was a 1971 Corvette, I sold it last year, it had a drag coefficient of 0.325. Heck, I did a little searching and found that a 2001 Honda Accord has a drag coefficient of 0.295. A 2004 Dodge Darango has a drag coefficient of 0.39...
The 2005+ Mustang body style is for looks, not for speed.
http://en.wikipedia.org/wiki/Drag_coefficient
Fdrag = 1/2 (drag coefficient * air density * surface area * Velocity Squared)
The gears are 4.10 vs. 3.55. That means torque would be multipled by about 14 or 15% at the rear wheels.
I suppose the force exerted would there would be about 15% greater...that means we need to calculate the speed that exerts 15% more on the object to reach terminal velocity. Assuming that 143 mph is the correct top speed stock (as quoted all over the internet). The V^2 term is killing you if the car goes 155 mph, then you've increased drag by 15% already. I'm not convinced that gears would make much of a difference.
These new Mustang have terrible drag coefficients, the GT500's drag coefficient is a sad 0.38, note that top speed is limited to 155 mph (electronically, but I wonder how well it handles at it's true top speed?).
http://www.autozine.org/html/Ford_USA/Mustang.html
A new Corvette Coupe has a drag coefficient of 0.286! My last peformance car was a 1971 Corvette, I sold it last year, it had a drag coefficient of 0.325. Heck, I did a little searching and found that a 2001 Honda Accord has a drag coefficient of 0.295. A 2004 Dodge Darango has a drag coefficient of 0.39...
The 2005+ Mustang body style is for looks, not for speed.
http://en.wikipedia.org/wiki/Drag_coefficient
09-27-2006, 10:45 AM
#10
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Join Date: Aug 2006
Location: North East Texas on the Red River
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RE: 3.73 & 4.10 gear topspeed
wmtheflash,
Thank you! You understand most of the issues here. The only significant one that you left out was the fact that by changing gear ratio, you may very well be allowing the engine to get into an RPM range that provides more torque, allowing more top speed. That is why lowering the gear(numerically higher) can possibly give you MORE top speed. That is also why some cars, our Mustangs might be included, can go faster in fourth gear than they can in fifth. I know my 85 5.0 GT was in this category.
This is one of those many areas of engineering where you can calculate until you're blue in the face, but you don't really know without some testing. So, what do you say we ship one of our cars to Germany along with a few different sets of gears and do some testing on the Autobahn?
Thank you! You understand most of the issues here. The only significant one that you left out was the fact that by changing gear ratio, you may very well be allowing the engine to get into an RPM range that provides more torque, allowing more top speed. That is why lowering the gear(numerically higher) can possibly give you MORE top speed. That is also why some cars, our Mustangs might be included, can go faster in fourth gear than they can in fifth. I know my 85 5.0 GT was in this category.
This is one of those many areas of engineering where you can calculate until you're blue in the face, but you don't really know without some testing. So, what do you say we ship one of our cars to Germany along with a few different sets of gears and do some testing on the Autobahn?