Different gears
06-05-2006, 12:58 AM
#1
5th Gear Member
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Location: Florida
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Different gears
Ok, Im back.. lol back to ask about something else. Sorry I know Im being the annoying "car noob" but hey, gotta learn sometime right? So here goes.. whats the difference between the stock GT auto gears and these 3.75 or 4.1 that everybody talks about.. I really have no idea what any of that means... all I know is people say upgrading them makes our car better so here I am..
06-05-2006, 02:12 AM
#3
2nd Gear Member
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RE: Different gears
With a 3.55 gearset, the pinion turns 3.55 times to 1 revolution of the ring gear. With 4.10 gears, the pinion turns 4.1 times to each revolution of the ring gear, and so on. To oversimplify it, you can almost think of it in terms of leverage that the driveshaft has on the axle .
06-05-2006, 02:13 AM
#4
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RE: Different gears
A stock GT has a final drive ratio of 3.55 if it has manual or a 3.31 if it is an automatic. The final drive ratio determines how many times the drive shaft (output of your transmission) needs to turn on order to have the axle turn once. So a final drive ratio of 3.55 means that with the transmission in 4th gear (not overdrive) the drive shaft turns 3.55 times to make the axle turn once.
Therefore a final drive ratio that is numerically higher, for example a 4.11, means that the drive shaft must turn 4.11 times to have the axle turn once.
This is giving the engine a higher mechanical advantage in all gears. Switching to a numerically higher final drive ratio will give you better acceleration but a lower top speed.
This does not however take into consideration aerodynamics and other friction generating forces.
For example many vehicles that were originally equipped with a 2.73 final drive ratio actually showed an increased top speed after a change to a 3.73 ratio. This is because with a 2.73 final drive ratio, the engine could not achieve enough RPM at higher speeds to overcome wind resistance.
Also consider the fact that different engines have drastically different power characteristics. For example, a large V8 may work fairly well with a final drive ration of 3.00 - 1 but this would be a disaster for most 4 cylinder engines because the 4 cylinder engine does not have enough torque to overcome wind resistance at lower RPM.s Therefore you will find final drive ratios of 4.11, 4.56, ect much more common in 4 cylinder vehicles.
Basically the final drive ratio as well and the transmission ratios need to be matched to the engine characteristics and intended use.
Therefore a final drive ratio that is numerically higher, for example a 4.11, means that the drive shaft must turn 4.11 times to have the axle turn once.
This is giving the engine a higher mechanical advantage in all gears. Switching to a numerically higher final drive ratio will give you better acceleration but a lower top speed.
This does not however take into consideration aerodynamics and other friction generating forces.
For example many vehicles that were originally equipped with a 2.73 final drive ratio actually showed an increased top speed after a change to a 3.73 ratio. This is because with a 2.73 final drive ratio, the engine could not achieve enough RPM at higher speeds to overcome wind resistance.
Also consider the fact that different engines have drastically different power characteristics. For example, a large V8 may work fairly well with a final drive ration of 3.00 - 1 but this would be a disaster for most 4 cylinder engines because the 4 cylinder engine does not have enough torque to overcome wind resistance at lower RPM.s Therefore you will find final drive ratios of 4.11, 4.56, ect much more common in 4 cylinder vehicles.
Basically the final drive ratio as well and the transmission ratios need to be matched to the engine characteristics and intended use.
06-05-2006, 02:23 AM
#5
2nd Gear Member
Join Date: Apr 2005
Location: Chicago, IL
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RE: Different gears
Dear Bl1nkage,
Think of yourself riding a 10 speed bicycle...
In the lowest gear, you pedal faster but the bike accelerates faster too...
Then when you have your speed, you shift into a higher gear in order to pedal slower and conserve energy but you remain at the same speed..
2005 GT automatics have a rear ratio of 3.31 and manuals have 3.55...
If you increase the rear gear in an automatic to 3.73 (as I did) or 4.10, you will gain speed faster from a dead stop...
Dave
Think of yourself riding a 10 speed bicycle...
In the lowest gear, you pedal faster but the bike accelerates faster too...
Then when you have your speed, you shift into a higher gear in order to pedal slower and conserve energy but you remain at the same speed..
2005 GT automatics have a rear ratio of 3.31 and manuals have 3.55...
If you increase the rear gear in an automatic to 3.73 (as I did) or 4.10, you will gain speed faster from a dead stop...
Dave
06-05-2006, 02:36 AM
#6
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RE: Different gears
...soo let me get this straight, you either have to pick what you want, a higher top end or a faster acceleration... low numbered gears (3.35) provide lower top end but faster acceleration.. and higher numbered gears (4.1) provide faster acceleration but lower top end?? right?
06-05-2006, 02:43 AM
#7
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RE: Different gears
That is basically correct. A change to 4.11 gears will do wonders for acceleration. Keep in mind that your car has an overdrive so even with 4.11's your higway driveability will still be very good. In the days of the old Muscle cars there were no overdrives. Lots of them had 4.11's but they were not good on the highway because with no overdrive their engines were spinning way too fast at speeds above 60 mph. This is not as issue with the newer cars with overdrive. As far as top speed goes you will will loose very little. I took the speed limiter off my GT with the stock 3.55's and it will exceed 240 kph. Do I really need to go that fast? Nope. I don't think you do either. On the street it's a good way to die. I would go for the acceleration that you will get from the 4.11 gears. You will loose a little bit of your highway fuel economy but it's a small price to pay for a huge gain in performance.
06-05-2006, 02:59 AM
#9
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RE: Different gears
ORIGINAL: bl1nkage
how much top speed are we talking? like i meant the speedo goes to 140, i havent been able to get it that high yet but... are our stock gt's capable of more than 140?
how much top speed are we talking? like i meant the speedo goes to 140, i havent been able to get it that high yet but... are our stock gt's capable of more than 140?
No......
With a final drive gear selection such as 3.73 or 4.10, you car will accelerate faster and you will probably get the same top end speed...
You and I know that you will never it 145 MPH unless you are on a race track...
But if you junk those 3.31 gears that are in your automatic, your life will be much better...
TRUST ME!!!
06-05-2006, 03:08 AM
#10
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Join Date: May 2006
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RE: Different gears
well... i havent gotten 140 yet... but ive gotten damn close.. fastest i have been able to go so far is 129.. im sure i could max it out but i always slow down because less than 1/4 mile after i start hitting the brake theres about.. a 40 degree curve and i dont feel like dying... of course i dont do this in traffic.. only late late at night when there are no cars around..