Increasing top speed
01-25-2007, 08:29 PM
#41
3rd Gear Member
Join Date: Feb 2006
Location:
Posts: 740
RE: Increasing top speed
^if you have really high horse power then 2.73's would help, if you have stock or even less then 500 id say, your going to severely hirt your speed with these gears....think about chugging along at sixty in fifth....floor it...nothing much happens...thats what would happen,just at more like 90...it would take forever to accelerate, and you would have less torque tot he ground to push you against th drag, so you would slow your top speed unless you have tot power (big power) to make up for it.
with 4.30's your rpms would increase ~500-700? rpms from the 3.31's meaning you would hit your limiter that much faster. you WOULD get to your top speed faster,but your top speed would be lower
with 4.30's your rpms would increase ~500-700? rpms from the 3.31's meaning you would hit your limiter that much faster. you WOULD get to your top speed faster,but your top speed would be lower
01-25-2007, 08:35 PM
#43
Join Date: Jan 2007
Posts: 2
RE: Increasing top speed
ok I really dont see what the problem is, I'm not one of those people that talk crap about my car is so much faster but, I have hit 140 or 145 in 4th gear and slammed it in to 5th and had more room to play... I have a 07 GT with Small mods $600.00 total.... and im happy with what i've got. I would like to someday break into the 11s 1/4 but thats along way from now.....
01-25-2007, 08:47 PM
#44
RE: Increasing top speed
ORIGINAL: kopfjager
4.30s would run out of RPM before reaching speeds over 150 no doubt.
I have hit 160 + with 3.73 gear and forced induction - had power left too.
4.30s would run out of RPM before reaching speeds over 150 no doubt.
I have hit 160 + with 3.73 gear and forced induction - had power left too.
if you have very little power, shorter gears will help you pull even thought your actual top speed will be higher, your hypothentical will be lower, but were not driving on the moon
01-25-2007, 08:54 PM
#45
2nd Gear Member
Join Date: Oct 2006
Location: SoCal
Posts: 229
RE: Increasing top speed
or in a vacume... I get that part... thanks for that...
buthow is the higher gears going toincrease your "top speed"??!! [&:]Forget it...I'm not getting it and I don't want to be told where I'm not driving any more...
Cheers!
buthow is the higher gears going toincrease your "top speed"??!! [&:]Forget it...I'm not getting it and I don't want to be told where I'm not driving any more...
Cheers!
01-25-2007, 09:02 PM
#48
2nd Gear Member
Join Date: Oct 2006
Location: SoCal
Posts: 229
RE: Increasing top speed
ORIGINAL: sonicblue05
^if you have really high horse power then 2.73's would help, if you have stock or even less then 500 id say, your going to severely hirt your speed with these gears....think about chugging along at sixty in fifth....floor it...nothing much happens...thats what would happen,just at more like 90...it would take forever to accelerate, and you would have less torque tot he ground to push you against th drag, so you would slow your top speed unless you have tot power (big power) to make up for it.
with 4.30's your rpms would increase ~500-700? rpms from the 3.31's meaning you would hit your limiter that much faster. you WOULD get to your top speed faster,but your top speed would be lower
^if you have really high horse power then 2.73's would help, if you have stock or even less then 500 id say, your going to severely hirt your speed with these gears....think about chugging along at sixty in fifth....floor it...nothing much happens...thats what would happen,just at more like 90...it would take forever to accelerate, and you would have less torque tot he ground to push you against th drag, so you would slow your top speed unless you have tot power (big power) to make up for it.
with 4.30's your rpms would increase ~500-700? rpms from the 3.31's meaning you would hit your limiter that much faster. you WOULD get to your top speed faster,but your top speed would be lower
You can't increase your top speed with a simple gear adjustment, basically your top speed stays the same you simply change how fast or how slow you get there with gears...correct???
01-25-2007, 09:26 PM
#49
RE: Increasing top speed
ORIGINAL: sonicblue05
if you wanna run your car at yes doubt, at 6500 rpms yand 175 mphbe my guest.....ill not....limiter is about 6100 stock
if you wanna run your car at yes doubt, at 6500 rpms yand 175 mphbe my guest.....ill not....limiter is about 6100 stock
01-25-2007, 09:56 PM
#50
3rd Gear Member
Join Date: Mar 2006
Location: New Hampshire
Posts: 854
RE: Increasing top speed
Ohhh boy, I wasn't going to post, but...I'm going to try my hand as explaining what I *think* the gear point is, so here goes...
As I am sure I'll be ripped up one side and down the other for posting numbers that no one will agree with, here's a little explanation. I used the following data with the help of a spreadsheet that was posted in the forums months ago, entitled RPM_vs_SPEED.xls. Obviously different tire sizes would yield different results:
Tire Diameter: 27.18 inches
Ratios: 1st = 3.38, 2nd = 2.00, 3rd = 1.32, 4th = 1.00, 5th = 0.675
Lets take a stock GT. It has a theoretical top speed of, say, 200MPH. This is based on the stock 5th gear @ redline. I think everyone has agreed on the theoretical part (even if it's not exactly 200MPH). The "real world" top speed is less, due to air, friction, etc. Lets say "real world" top speed is 140MPH, just as an example.
This would be a lot easier if I knew right off hand the HP curve for these cars, but generally speaking we see our max HP at, what, between 5K and 6K? The point is we make most of our HP in the high RPMs.
With 3.55 gears we get to 141MPH at 4200RPMs. With a set of 4.10s we are getting there at 4800RPMs. With 4.30s we are at a little over 5000RPMs. The goal for using 4.30s is to get into the sweet spot in the RPMs (where the engine is making it's max HP) by the time you approach your target speed. Since even with 4.30s the theoretical top speed would be about 167MPH, the car would not be limited by gears to if your target speed was160MPH.
The trick (I think) is to choose a gear ratio that puts you in the power band before the air/friction drag stops your acceleration. This way your car is working with the maximum amount of HP it can generate, to hopefully push just a little bit further. It doesn't appear that the stock gears quite get you to the power band at 140MPH, but obviously choosing a gear which is going to limit your theoretical top speed to less than your target speed also doesn't make sense.
On the other hand, you could make the argument for 2.73s and try for 140MPH in 4th @ a bit over 4700MPH, but you may actually be running into the same non-power band problem you'd have with the stock gears in 5th!
As I am sure I'll be ripped up one side and down the other for posting numbers that no one will agree with, here's a little explanation. I used the following data with the help of a spreadsheet that was posted in the forums months ago, entitled RPM_vs_SPEED.xls. Obviously different tire sizes would yield different results:
Tire Diameter: 27.18 inches
Ratios: 1st = 3.38, 2nd = 2.00, 3rd = 1.32, 4th = 1.00, 5th = 0.675
Lets take a stock GT. It has a theoretical top speed of, say, 200MPH. This is based on the stock 5th gear @ redline. I think everyone has agreed on the theoretical part (even if it's not exactly 200MPH). The "real world" top speed is less, due to air, friction, etc. Lets say "real world" top speed is 140MPH, just as an example.
This would be a lot easier if I knew right off hand the HP curve for these cars, but generally speaking we see our max HP at, what, between 5K and 6K? The point is we make most of our HP in the high RPMs.
With 3.55 gears we get to 141MPH at 4200RPMs. With a set of 4.10s we are getting there at 4800RPMs. With 4.30s we are at a little over 5000RPMs. The goal for using 4.30s is to get into the sweet spot in the RPMs (where the engine is making it's max HP) by the time you approach your target speed. Since even with 4.30s the theoretical top speed would be about 167MPH, the car would not be limited by gears to if your target speed was160MPH.
The trick (I think) is to choose a gear ratio that puts you in the power band before the air/friction drag stops your acceleration. This way your car is working with the maximum amount of HP it can generate, to hopefully push just a little bit further. It doesn't appear that the stock gears quite get you to the power band at 140MPH, but obviously choosing a gear which is going to limit your theoretical top speed to less than your target speed also doesn't make sense.
On the other hand, you could make the argument for 2.73s and try for 140MPH in 4th @ a bit over 4700MPH, but you may actually be running into the same non-power band problem you'd have with the stock gears in 5th!