Installed 3.9 FD and worse acceleration
04-02-2008, 10:36 AM
#41
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ok raditz, think about it this way:
you and your friend with an identical car, hypothetically shift exactly as fast as one another. ideally, you should run head to head and come out even when stock.
now you installed your new 3.9 final drive, and for the sake of argument lets say it takes you (and your friend) .5 seconds to shift. if your race requires you to shift 3 times (due to shorter gears) while your friend only has to shift twice, he has a .5 second advantage over you. lets say your new gears only cut your time by .3 seconds for this particular distance/race. mathematically, your friend should be .2 seconds' worth of distance ahead of you. while you still reap the benefits of acceleration, it seems that the acceleration gained through your new final drive just doesnt outweigh the time required for that extra shift in my scenario. i hope that example helps. with shorter shifts, you will be faster than your friend.
you and your friend with an identical car, hypothetically shift exactly as fast as one another. ideally, you should run head to head and come out even when stock.
now you installed your new 3.9 final drive, and for the sake of argument lets say it takes you (and your friend) .5 seconds to shift. if your race requires you to shift 3 times (due to shorter gears) while your friend only has to shift twice, he has a .5 second advantage over you. lets say your new gears only cut your time by .3 seconds for this particular distance/race. mathematically, your friend should be .2 seconds' worth of distance ahead of you. while you still reap the benefits of acceleration, it seems that the acceleration gained through your new final drive just doesnt outweigh the time required for that extra shift in my scenario. i hope that example helps. with shorter shifts, you will be faster than your friend.
Last edited by invazn; 04-02-2008 at 10:40 AM.
04-02-2008, 11:54 AM
#42
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why did my 5at g35 get slower with the 3.53's? it seems a bit faster to 60 maybe but then it starts to die, and by the time i hit 4th at about 100 its dead.
04-02-2008, 11:58 AM
#43
Originally Posted by Motormouth
there is no need to be fair, it clearly shows the difference between shifting and maintaining momentum and losing momentum, which was the point. it does not matter turbo or not, you lose momentum Alberto's is the only clear cut visual aid to the difference.
and raising the rev limiter has already been brought up.
and raising the rev limiter has already been brought up.
edit-lol try and watch this. Its me vs a non driver in an STI AND me vs another Z. Watch how when they shift they lose 1 car immediately, plus momentum from the slowness = a$$ whoopin! Vid wont play for me at work, hope it works for you. This is from back in the day!
http://videos.streetfire.net/video/A...n-STI_3564.htm
Vid above wont work, here is a GOOD example of how losing momentum on a slow shift can = you losing the race, even with much more power. I can show you vids like this all day long, from NA to ST, to TT, I usually end up showing people they need work and trying to help them out lol, except for this guy he was cocky as fawk, and was embarressed after this.
http://videos.streetfire.net/video/A...obra_44550.htm
Last edited by Alberto; 04-02-2008 at 12:08 PM.
04-02-2008, 11:59 AM
#44
Originally Posted by GrayG35
why did my 5at g35 get slower with the 3.53's? it seems a bit faster to 60 maybe but then it starts to die, and by the time i hit 4th at about 100 its dead.
It should get faster, but if you dont hit a good launch-at least the same as before then you hit 4th gear SOONER down the 1/4 and 4th gear in auto's = dead acceleration. Whereas stock you hit 4th right at the a$$ end of the run, I know cuz Ive also raced auto Z/G's down the drag strip
04-02-2008, 12:43 PM
#48
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Originally Posted by Alberto
Slower against a friend or down the 1/4? With same wheels/tires? 60ft's? Weather?
It should get faster, but if you dont hit a good launch-at least the same as before then you hit 4th gear SOONER down the 1/4 and 4th gear in auto's = dead acceleration. Whereas stock you hit 4th right at the a$$ end of the run, I know cuz Ive also raced auto Z/G's down the drag strip
It should get faster, but if you dont hit a good launch-at least the same as before then you hit 4th gear SOONER down the 1/4 and 4th gear in auto's = dead acceleration. Whereas stock you hit 4th right at the a$$ end of the run, I know cuz Ive also raced auto Z/G's down the drag strip
04-02-2008, 04:18 PM
#49
Originally Posted by Motormouth
there is no need to be fair, it clearly shows the difference between shifting and maintaining momentum and losing momentum, which was the point. it does not matter turbo or not, you lose momentum Alberto's is the only clear cut visual aid to the difference.
Alberto's statement about shifting faster is certainly relevant since under most circumstances, moving to a higher FD ratio in our cars will necessitate a shift sooner during a critical period in the overall acceleration curve of the car. Maintaining momentum in the earlier shifts when the car has the opportunity to maximize torque to the ground is critical.
Originally Posted by Motormouth
and raising the rev limiter has already been brought up.
Originally Posted by raditz
Do you think that the problem could be the top speed that you loose in every gear? increased redline will improve top speed...
Last edited by rcdash; 04-02-2008 at 04:43 PM.
04-02-2008, 04:22 PM
#50
Originally Posted by Alberto
+1 Do you need me to show you a video of NA also rcdash? Trust me when I tell you NA from a 1st gear roll through 3rd its an even bigger difference cuz the shifts come up quicker. The 1-2 and 2-3 shift make or break a race. Turbo, S/C, N20 whatever, momentum is momentum, and if only 2 shifts can make up 4+ lengths on a "regular" driver imagine what the OP is going through now having to shift more often.
edit-lol try and watch this. Its me vs a non driver in an STI AND me vs another Z. Watch how when they shift they lose 1 car immediately, plus momentum from the slowness = a$$ whoopin! Vid wont play for me at work, hope it works for you. This is from back in the day!
http://videos.streetfire.net/video/A...n-STI_3564.htm
Vid above wont work, here is a GOOD example of how losing momentum on a slow shift can = you losing the race, even with much more power. I can show you vids like this all day long, from NA to ST, to TT, I usually end up showing people they need work and trying to help them out lol, except for this guy he was cocky as fawk, and was embarressed after this.
http://videos.streetfire.net/video/A...obra_44550.htm
edit-lol try and watch this. Its me vs a non driver in an STI AND me vs another Z. Watch how when they shift they lose 1 car immediately, plus momentum from the slowness = a$$ whoopin! Vid wont play for me at work, hope it works for you. This is from back in the day!
http://videos.streetfire.net/video/A...n-STI_3564.htm
Vid above wont work, here is a GOOD example of how losing momentum on a slow shift can = you losing the race, even with much more power. I can show you vids like this all day long, from NA to ST, to TT, I usually end up showing people they need work and trying to help them out lol, except for this guy he was cocky as fawk, and was embarressed after this.
http://videos.streetfire.net/video/A...obra_44550.htm
The NA vid is not working for me - would love to see it but I'm willing to take your word for it!
Last edited by rcdash; 04-02-2008 at 06:28 PM.
04-03-2008, 07:05 AM
#51
Originally Posted by rcdash
As has been alluded to, the fact is that identical drivers in identical cars with perfect traction and different gearing will reach different points in different positions (winning vs losing) on a straight track...
04-05-2008, 08:45 PM
#52
check these graphs.
one is comparing the acceleration between 3.5 (real value) and 3.9 (theoretical value), and the other one is comparing the first two and 3.9+tomei272 cams+7200rpm rev limit (real value).
Blue and Red are based on my actual dyno results. The black one which is a theoretic guess of 3.9 might produce a little bit less in real world due to slightly increased drive train loss but i think it is reasonably close.
Notice the different patterns of shaded areas. Those are the areas that each gears are taking advantage of its gearing compared to others.
If you look at the graph comparing 3.5 and 3.9, the shaded areas are jumping between the two. As the speed goes up, or gears go up should I say, the advantage of using shorter gear slowly fades away because you will be lacking power between the shifting points compared to stock gears, while making more when stock car has to shift. So you gain some acceleration during the second half of a gear, but you lose some during the first half.
Besically the graph shows who wins where. Black wins, then blue wins, over and over, in term of acceleration. So, there is no point of arguing 'my 3rd gear is better than your 3rd gear' because about 40% of your 4th gear will be slower than stock's 3rd gear. Its not just the 'duration' of 0.5sec or whatever you need to spend to shift up that matters, but its the powerband you are on is gonna be weaker when you shift up. You will eventually catch up as the graph shows, but as the speed goes up, the 'advantage' is less prone because it takes longer time to accelerate, and the amount of 'boost' you get from each gear is not that great compared to low speeds.
So if you have 3.9 gear and compare to a stock car from 0-90kph, you will win everytime unless something has seriously went wrong because the whole 1st gear of 3.9 will blast ahead of stock's 1st gear and 80% of second gear will also pull much harder than stock's 2nd. but if you race from 130-185kph, you will lose because your gearings unfair on you compared to stock gearing.
Now if you look at the other graph with red in it, the car is now revving to 7200rpm opposed to 6600rpm and its top speed per gear with 3.9 is very close to stock gears' speeds. And the red is running 272deg cams shaft which produces more power from 6000rpm onwards while losing some in the lower band.
Notice the shaded areas of this graph, there are not much of black ahead of red, plus, the height of black ahead of red is quite short. And blue is not ahead of any of red.
Again, the black lines are only theoretic values and the height of black lines probably will be a little bit less in real world value but you can still see the patterns there. And red/blue are real world values from my car dynoed so the difference is definately correct between those two.
So yeah, I think it gives a good advatage when raising rev-limit to higher number when doing the 3.9 gear upgrade, as the curve you draw will be better than stock in every gear, and you can take even more advantage by giving up low end and gaining top end with matching cams.
Central20 claims that the 3.9 final drive gears they sell will make the car reach higher top speed because it makes the car to accelerate in 6th gear while stock car would lose speed in 6th compared to 5th due to lack of power. That is because a car with 3.9 gear in 6th will sit in the area where the car can accelerate while stock's 6th cant anymore (235-265kph).
hope this helps
one is comparing the acceleration between 3.5 (real value) and 3.9 (theoretical value), and the other one is comparing the first two and 3.9+tomei272 cams+7200rpm rev limit (real value).
Blue and Red are based on my actual dyno results. The black one which is a theoretic guess of 3.9 might produce a little bit less in real world due to slightly increased drive train loss but i think it is reasonably close.
Notice the different patterns of shaded areas. Those are the areas that each gears are taking advantage of its gearing compared to others.
If you look at the graph comparing 3.5 and 3.9, the shaded areas are jumping between the two. As the speed goes up, or gears go up should I say, the advantage of using shorter gear slowly fades away because you will be lacking power between the shifting points compared to stock gears, while making more when stock car has to shift. So you gain some acceleration during the second half of a gear, but you lose some during the first half.
Besically the graph shows who wins where. Black wins, then blue wins, over and over, in term of acceleration. So, there is no point of arguing 'my 3rd gear is better than your 3rd gear' because about 40% of your 4th gear will be slower than stock's 3rd gear. Its not just the 'duration' of 0.5sec or whatever you need to spend to shift up that matters, but its the powerband you are on is gonna be weaker when you shift up. You will eventually catch up as the graph shows, but as the speed goes up, the 'advantage' is less prone because it takes longer time to accelerate, and the amount of 'boost' you get from each gear is not that great compared to low speeds.
So if you have 3.9 gear and compare to a stock car from 0-90kph, you will win everytime unless something has seriously went wrong because the whole 1st gear of 3.9 will blast ahead of stock's 1st gear and 80% of second gear will also pull much harder than stock's 2nd. but if you race from 130-185kph, you will lose because your gearings unfair on you compared to stock gearing.
Now if you look at the other graph with red in it, the car is now revving to 7200rpm opposed to 6600rpm and its top speed per gear with 3.9 is very close to stock gears' speeds. And the red is running 272deg cams shaft which produces more power from 6000rpm onwards while losing some in the lower band.
Notice the shaded areas of this graph, there are not much of black ahead of red, plus, the height of black ahead of red is quite short. And blue is not ahead of any of red.
Again, the black lines are only theoretic values and the height of black lines probably will be a little bit less in real world value but you can still see the patterns there. And red/blue are real world values from my car dynoed so the difference is definately correct between those two.
So yeah, I think it gives a good advatage when raising rev-limit to higher number when doing the 3.9 gear upgrade, as the curve you draw will be better than stock in every gear, and you can take even more advantage by giving up low end and gaining top end with matching cams.
Central20 claims that the 3.9 final drive gears they sell will make the car reach higher top speed because it makes the car to accelerate in 6th gear while stock car would lose speed in 6th compared to 5th due to lack of power. That is because a car with 3.9 gear in 6th will sit in the area where the car can accelerate while stock's 6th cant anymore (235-265kph).
hope this helps
04-06-2008, 02:09 PM
#53
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i think a longer gear would better our powerbands better.
3.3 vs 3.5
taken from comparing before and after racing.
were basically head to head to about 4th gear then i put about a car length in between.
-this was with 3.5 gears same as mine.
however,
-with 3.3 gears
he is held with me till 140
minus 2 car difference ..... lol if anything i think i want to gear a taller gear.
06350z 6sp me
vs
04 g35 auto (friends car)
3.3 vs 3.5
taken from comparing before and after racing.
were basically head to head to about 4th gear then i put about a car length in between.
-this was with 3.5 gears same as mine.
however,
-with 3.3 gears
he is held with me till 140
minus 2 car difference ..... lol if anything i think i want to gear a taller gear.
06350z 6sp me
vs
04 g35 auto (friends car)
04-06-2008, 06:35 PM
#54
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3.08 FTMFW. forza doesnt lie lol. i think getting shorter gears only helps from a stop but once you pass 100 the car is slower for sure. Longer gears help you stay at peak hp for a longer time. might take a bit longer to get there but when your doin 100+ and you get to peak hp an stay there longer instead of running threw it you will notice a difference.
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