Question about shortened gears!
Veetec
02-20-2002, 02:51 PM
Okay, I´ve got a bet with another german Honda owner: He said that if he would make one or two gears of his Civic shorter (3rd and 4th gear) it would accelerate faster and I think that´s logical and true. But he also said that you won´t lose topspeed with shortened gears and I´m pretty sure that you WILL lose topspeed! Who is right?? Please drift, del, fierce or anybody else who knows what he´s talking about, I need some good help and maybe even a good and short explaination!
Thanx in advance!
PS: I´ve posted this in the "Let´s get...forum", too! So don´t answer it two times. ;)
Thanx in advance!
PS: I´ve posted this in the "Let´s get...forum", too! So don´t answer it two times. ;)
supafly1024
02-20-2002, 03:14 PM
Okay, a Civic SI is a 5 speed, correct? I'm basing my answer on it being a 5 speed. Now I would think, and notice I say think because I'm not 100% sure, that if he left the 5th and final gear the same then his top speed would be the same. Now on the other hand it would take him longer to get up to top speed because he would be at a lower speed when he shifted from 4th into 5th with the shorter 3rd and 4th gear. Since 5th isn't really a hard pulling gear it would take a longer amount of time for the car to pull itself to top speed with the shorter gears. That's my theory and it makes sense to me but I could be wrong.
:huh:
:huh:
Kaneto
02-20-2002, 03:58 PM
k, if I'm wrong with anything here, someone correct me.
If he shortened his 3rd and 4th gear then he should theoretically quicken his acceleration while still having the potential for the same top speed. However, he may have some serious problems getting there.
In order to achieve acceleration in each gear you need a minimum amount of rpm in each gear. 1st is a small gear so you can pretty much start below 1k rpm. As the gears get larger, it takes more power, or higher rpm, to get them going. That's why it's harder to accelerate from a stop if you start in 3rd or 4th gear.
If he's using shorter 3rd and 4th gears, he be shifting lower into 5th than if he were using the stock gears, for the same shift point. I know on my Civic if I'm at 2500rpm in 5th, I can mash the pedal all I want, but it isn't going to make much of a difference unless I'm on a downhill slope. Depending on how short he goes with his 3rd and 4th gears, he'll either have to run 4th way up in the rpms before going to 5th, or he may find that he'll never be able to accelerate in 5th gear, in which case he has no hope of getting anywhere near his top speed.
If he shortened his 3rd and 4th gear then he should theoretically quicken his acceleration while still having the potential for the same top speed. However, he may have some serious problems getting there.
In order to achieve acceleration in each gear you need a minimum amount of rpm in each gear. 1st is a small gear so you can pretty much start below 1k rpm. As the gears get larger, it takes more power, or higher rpm, to get them going. That's why it's harder to accelerate from a stop if you start in 3rd or 4th gear.
If he's using shorter 3rd and 4th gears, he be shifting lower into 5th than if he were using the stock gears, for the same shift point. I know on my Civic if I'm at 2500rpm in 5th, I can mash the pedal all I want, but it isn't going to make much of a difference unless I'm on a downhill slope. Depending on how short he goes with his 3rd and 4th gears, he'll either have to run 4th way up in the rpms before going to 5th, or he may find that he'll never be able to accelerate in 5th gear, in which case he has no hope of getting anywhere near his top speed.
fritz_269
02-20-2002, 04:05 PM
Originally posted by supafly1024
Okay, a Civic SI is a 5 speed, correct? ... if he left the 5th and final gear the same then his top speed would be the same. Now on the other hand it would take him longer to get up to top speed...
Bingo. :D
A lot of road-course cars use that exact trick to create what's called a "close-ratio" tranny. You increase the numerical gear ratio difference from 1st to second and from 4th to 5th, and decrease the ratio difference between 2 to 3 and 3 to 4. Why that works is because with a numerically closer ratio, you don't have as much RPM drop between shifts, keeping the engine higher on the power curve.
1st and 5th don't really matter, because you rarely use them on the road course - 1st just gets you going from the start, and you might occasionally use 5th if you have a long straightaway.
If you're talking about drag racing though, you have to carefully analyze the gear ratios to give you maximum acceleration throughout the precise length of the drag. A road-racing close-ratio box will probably be worse at the drags because of the large gap from 1->2. If you just shorten 3 and 4 slightly, you'll probably be faster (in those gears) unless you end up hitting another shift point where you didn't have one before. e.g. In my Prelude, I get near redline in 3rd gear at the end of a 1/4 mile drag (~90mph). My 3rd gear redline limited top speed is 94mph. Were I to lower the ratio in 3rd by 10%, I would now be limited to about 85 mph. Now I'd have to shift to 4th before reaching the end of the drag strip - that's a good 1/2 second where there is no power being applied. Although it may 'feel' faster, I guarantee that my ET will actually end up worse because I had to add a shift.
PS> Does your friend know anybody who modifies ratios for Honda trannies?
:cool:
Okay, a Civic SI is a 5 speed, correct? ... if he left the 5th and final gear the same then his top speed would be the same. Now on the other hand it would take him longer to get up to top speed...
Bingo. :D
A lot of road-course cars use that exact trick to create what's called a "close-ratio" tranny. You increase the numerical gear ratio difference from 1st to second and from 4th to 5th, and decrease the ratio difference between 2 to 3 and 3 to 4. Why that works is because with a numerically closer ratio, you don't have as much RPM drop between shifts, keeping the engine higher on the power curve.
1st and 5th don't really matter, because you rarely use them on the road course - 1st just gets you going from the start, and you might occasionally use 5th if you have a long straightaway.
If you're talking about drag racing though, you have to carefully analyze the gear ratios to give you maximum acceleration throughout the precise length of the drag. A road-racing close-ratio box will probably be worse at the drags because of the large gap from 1->2. If you just shorten 3 and 4 slightly, you'll probably be faster (in those gears) unless you end up hitting another shift point where you didn't have one before. e.g. In my Prelude, I get near redline in 3rd gear at the end of a 1/4 mile drag (~90mph). My 3rd gear redline limited top speed is 94mph. Were I to lower the ratio in 3rd by 10%, I would now be limited to about 85 mph. Now I'd have to shift to 4th before reaching the end of the drag strip - that's a good 1/2 second where there is no power being applied. Although it may 'feel' faster, I guarantee that my ET will actually end up worse because I had to add a shift.
PS> Does your friend know anybody who modifies ratios for Honda trannies?
:cool:
Veetec
02-20-2002, 04:13 PM
Originally posted by fritz_269
Bingo. :D
A lot of road-course cars use that exact trick to create what's called a "close-ratio" tranny. You increase the numerical gear ratio difference from 1st to second and from 4th to 5th, and decrease the ratio difference between 2 to 3 and 3 to 4. Why that works is because with a numerically closer ratio, you don't have as much RPM drop between shifts, keeping the engine higher on the power curve.
1st and 5th don't really matter, because you rarely use them on the road course - 1st just gets you going from the start, and you might occasionally use 5th if you have a long straightaway.
If you're talking about drag racing though, you have to carefully analyze the gear ratios to give you maximum acceleration throughout the precise length of the drag. A road-racing close-ratio box will probably be worse at the drags because of the large gap from 1->2. If you just shorten 3 and 4 slightly, you'll probably be faster (in those gears) unless you end up hitting another shift point where you didn't have one before. e.g. In my Prelude, I get near redline in 3rd gear at the end of a 1/4 mile drag (~90mph). My 3rd gear redline limited top speed is 94mph. Were I to lower the ratio in 3rd by 10%, I would now be limited to about 85 mph. Now I'd have to shift to 4th before reaching the end of the drag strip - that's a good 1/2 second where there is no power being applied. Although it may 'feel' faster, I guarantee that my ET will actually end up worse because I had to add a shift.
PS> Does your friend know anybody who modifies ratios for Honda trannies?
:cool: Okay. But let´s say it´s just a normal daily driver and he just wants to reach his topspeed on. Will he reach his topspeed with a shorter 3rd and 4th gear?? I´m not sure if I´ve understood everything you wrote so I´m not sure if I would explain it to him righ!:confused: What is the drawback with that on a daily driver?
Bingo. :D
A lot of road-course cars use that exact trick to create what's called a "close-ratio" tranny. You increase the numerical gear ratio difference from 1st to second and from 4th to 5th, and decrease the ratio difference between 2 to 3 and 3 to 4. Why that works is because with a numerically closer ratio, you don't have as much RPM drop between shifts, keeping the engine higher on the power curve.
1st and 5th don't really matter, because you rarely use them on the road course - 1st just gets you going from the start, and you might occasionally use 5th if you have a long straightaway.
If you're talking about drag racing though, you have to carefully analyze the gear ratios to give you maximum acceleration throughout the precise length of the drag. A road-racing close-ratio box will probably be worse at the drags because of the large gap from 1->2. If you just shorten 3 and 4 slightly, you'll probably be faster (in those gears) unless you end up hitting another shift point where you didn't have one before. e.g. In my Prelude, I get near redline in 3rd gear at the end of a 1/4 mile drag (~90mph). My 3rd gear redline limited top speed is 94mph. Were I to lower the ratio in 3rd by 10%, I would now be limited to about 85 mph. Now I'd have to shift to 4th before reaching the end of the drag strip - that's a good 1/2 second where there is no power being applied. Although it may 'feel' faster, I guarantee that my ET will actually end up worse because I had to add a shift.
PS> Does your friend know anybody who modifies ratios for Honda trannies?
:cool: Okay. But let´s say it´s just a normal daily driver and he just wants to reach his topspeed on. Will he reach his topspeed with a shorter 3rd and 4th gear?? I´m not sure if I´ve understood everything you wrote so I´m not sure if I would explain it to him righ!:confused: What is the drawback with that on a daily driver?
brians97accordSE
02-20-2002, 08:14 PM
k, here is my take on this, if he shortens his gear's ie. 3 and 4th, his acceleration will be quicker in those gears because he will hit his max acceleration and max torque a lot quicker, but, and i say but because now the bad part comes, if you shorten those two gears and your racing on the highway by the time you shift from 4th to 5th your rpm's will be substantially lower thus it will take a whole heck of a lot longer for him to accelerate in that gear due to boggin of his engine, depending on how far he has shortened them he'll hit 5th gear most likely below 4 thousand and bog his engine, and probably not be able to accelerate, but if your at the strip, watch out, those gears will rip up the track, just my two cents
Rice-Rocketeer
02-21-2002, 01:54 PM
Originally posted by Veetec
Okay. But let´s say it´s just a normal daily driver and he just wants to reach his topspeed on. Will he reach his topspeed with a shorter 3rd and 4th gear?? I´m not sure if I´ve understood everything you wrote so I´m not sure if I would explain it to him righ!:confused: What is the drawback with that on a daily driver?
I answered in the techy forum but I'll add it here. If he only changes 3rd and 4th gears, he'll only limit the top speed in those two gears. Top speed is deteremined by your highest gear (5th) and your final drive. If those two stay the same, top speed is the same.
And the only way the rpm difference for 5th gear will matter is if he wants to get maximum acceleration from 5th gear. Seeing as you already top out 4th gear at like 100mph, are you really gonna be that crazy/think headed to be racing at speeds over 100mph on a public highway with a car that hardly has enough horsepower to keep it above 100 anways? And 4000 rpm in 5th gear is not gonna bog the engine. In fact, I have pity for any engine that cruises at more than 4-5000 rpm on the highway for any extended period of time.
Okay. But let´s say it´s just a normal daily driver and he just wants to reach his topspeed on. Will he reach his topspeed with a shorter 3rd and 4th gear?? I´m not sure if I´ve understood everything you wrote so I´m not sure if I would explain it to him righ!:confused: What is the drawback with that on a daily driver?
I answered in the techy forum but I'll add it here. If he only changes 3rd and 4th gears, he'll only limit the top speed in those two gears. Top speed is deteremined by your highest gear (5th) and your final drive. If those two stay the same, top speed is the same.
And the only way the rpm difference for 5th gear will matter is if he wants to get maximum acceleration from 5th gear. Seeing as you already top out 4th gear at like 100mph, are you really gonna be that crazy/think headed to be racing at speeds over 100mph on a public highway with a car that hardly has enough horsepower to keep it above 100 anways? And 4000 rpm in 5th gear is not gonna bog the engine. In fact, I have pity for any engine that cruises at more than 4-5000 rpm on the highway for any extended period of time.
Veetec
02-21-2002, 09:16 PM
Okay, thanx a lot again! That should be enough input!:)
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