2.20 to a 2.73 Will I feel a difference?
04-14-2006, 02:45 PM
#61
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I have a 79 2:73 5-speed w/LSD I'm willing to trade for an 85+ 5-speed w/ LSD. Only has 66,000 miles on it.
2nd gear synchro is iffy- doesn't downshift into 2nd very well.
2nd gear synchro is iffy- doesn't downshift into 2nd very well.
04-14-2006, 03:17 PM
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Jim, I don't know how interchangable all the gears in a 928 transmission are, but there's also 1.6500(83-84 US) and 1.4583(GTS) for layshafts. 77-82 trannies also have 1.7727, 1.3077, and .9655 instead of 1.7272, 1.2307, and .931 for 2nd-4th like 83+ trannies. That may allow a little more mixing and matching.
04-14-2006, 04:32 PM
#63
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Yes are are some other numbers I believe bascially much of the 78-84 trans internal parts interchange as one family ,the 85-86 early borgwarner , the 1987-91 , GTS is unique but even there some parts may interchange. There has been little work done on this subject most just run what they have. The trans evolved to be stronger...
04-14-2006, 05:12 PM
#64
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Not entirely true. i have information on the cars i run against ive also studied what the cars in speedGT run, as welll as their repective rear wheel hp.
Its not rocket science, but it is subjective to the tracks, expected speeds and Hp of a car in discussion. I dont think you can argue this.
I run a car 20 years older than the grand Am cup racers of 996s, 997s, factory race car mustangs and professionally build M3s driven by the worlds best drivers, on probably worse tires. why do my times get close to them?
(same HP to weight, all sorts of gear options, etc)
One reason, is that i do have a lot of time at Laguna, but the main reason,my car, for a few reasons, is really well suited to laguna seca, both in set up and gear ratios. cars with different ratios seem to do better against me at tracks like sears point, where ill be the first to admit, a 2.73 or 2.64 may help a car like mine. This is not based on guess work. its based on maximizing the hp to the wheels over a lap. the more hp you can take advantage of, the faster you will be, its that simple. (as long as your car can brake, corner and exit).
Take a track like Laguna. the formula is simple. you want a gear box that allows you to get to redline on approach to most all of the turns. since WE cant change the gear spacing, going to a gear box that blindly gives me another shift, will in no way help the maximizing of HP. (ie 2.75 vs a 2.2 at laguna) why, because of the trade offs up to max speed, and the time spent in a gear at the top speeds where you spend most of the time, and run at lower ave hp utilization.
road america for example, the 2.2 gives me 155mph in 4th gear over a lap, on 2 of the main straights. gives me near max torque acceleration out of the carocell, and im never between gears on any other turns or exits. (watch andersons older video clips with his 2.2 vs today ) as you get more hp, your expected speeds increase and suddenly those ratios dont work. Hence, anderson with the 2.75 and near 500rwhp, fits perfect, as he now can get up to 170mph on those same straights.
Im fully aware while racing, of what gears i would need to be to be fastest, sometimes there are trade offs for not having to shift, by sacraficing the HP utilization, but those areas are rare. (usually, where you are between gears and you cant apply full hp there anyway!) Again, as i aways say, "it depends"
it depends on the track, it depnds on the car, it depends on the HP/weight and many other factors. the proof is when you race the car and see where your shift points are. with STACK and MOTEC, its easy to analyse your data to see what the advantages would be and optimize the gear ratios if you could have gear change options. but to say, adding a gear always helps, is not true. without paying close attention to gear spacing and expected speeds in those gears, you are shooting in the dark.
Take one straight at laguna off turn 11
apex speeds are close to 45mph
with a 2.2 , you can shift into 1st and run to 55mph for a quick launch, but hard on the gearbox and you have to be good with the gear box, second from 4500 to 6500rpm, third from 4500rpm to 6500rpm and you are near 120mph, and then a quick shift to 4th for maybe 5mph more to 125 , which is the max speed of that straight. with a 2.75 gear box, you dont have the advantage to use 1st on the curve, there are trade offs in 2nd and 3rd, mostly 3rd, where you spend most of the time as far as applied HP/seconds. now, if i had 500hp, suddenly, that quick shift to 4th for a second or two, would be much longer and the losses would be greater, and offset the time spent in 3rd gear advantage (ie anderson has this issue and thas why the 2.73 is better for more hp)
so, thats how it works. simple integration of the HP curve. its how all the analysis of gear box optimization works in racing.
so, acutally, with the wide spacing of the 928, which we are kind of stuck with, i get 1st once and through to a little of 4th. If my car could run to 7000rpm, i could get 1st once still, but never touch 4th. thats 3 gears. 2 gears besides turn 11. now a porsche cup car is in the same boat. same first gear speeds, at 55mph, but, two gears where we have one (2nd) then, its 4th gear is the same speed as our 3rd gear maxing out at 120mph. what did it gain?? well, it gained 8% more to the rear wheel hp due to its engine being kept near max hp longer between 55 and 95mph. this is based on a stock cup car running the supercup race or most of the SpeedGT cup cars too. also, close to the vet, viper and the 6speed audi that was the fastest car in the series.
Sure, I run what i got, but im fully aware of what i would need at some tracks, if i had options. do i make the best of it? SURE . Now do we have options that make a difference?? not really, we dont have a close ratio option, we have rear end changes that can optimize or make things much worse. It depends.
MK
PS, just did a time measurement of each gear at laguna's final straight.
1st 1.37seconds (45mph to 55mph) 6500rpm
2nd 3.32 (55mph to 80mph) 6200rpm
3rd 5.37 (85mph to 115mph) 6200rpm
4th 3.5 top speed near 125 ? rpm
if you intergrate the hp on the curve, you can clearly see what gear box would yield the greatest average acceleration. the more HP/seconds used, the greater the acceleration overall. many of these exersizes will yield not much difference. splitting hairs more often then not. is there a reason why Anderson also is running the same times at laguna too, not just willow springs with a 2.73:1 vs his old 2.2?? When i asked him how it felt with the new gear box a few years ago, he said " i dont know, but im shifting a lot more".
Its not rocket science, but it is subjective to the tracks, expected speeds and Hp of a car in discussion. I dont think you can argue this.
I run a car 20 years older than the grand Am cup racers of 996s, 997s, factory race car mustangs and professionally build M3s driven by the worlds best drivers, on probably worse tires. why do my times get close to them?
(same HP to weight, all sorts of gear options, etc)
One reason, is that i do have a lot of time at Laguna, but the main reason,my car, for a few reasons, is really well suited to laguna seca, both in set up and gear ratios. cars with different ratios seem to do better against me at tracks like sears point, where ill be the first to admit, a 2.73 or 2.64 may help a car like mine. This is not based on guess work. its based on maximizing the hp to the wheels over a lap. the more hp you can take advantage of, the faster you will be, its that simple. (as long as your car can brake, corner and exit).
Take a track like Laguna. the formula is simple. you want a gear box that allows you to get to redline on approach to most all of the turns. since WE cant change the gear spacing, going to a gear box that blindly gives me another shift, will in no way help the maximizing of HP. (ie 2.75 vs a 2.2 at laguna) why, because of the trade offs up to max speed, and the time spent in a gear at the top speeds where you spend most of the time, and run at lower ave hp utilization.
road america for example, the 2.2 gives me 155mph in 4th gear over a lap, on 2 of the main straights. gives me near max torque acceleration out of the carocell, and im never between gears on any other turns or exits. (watch andersons older video clips with his 2.2 vs today ) as you get more hp, your expected speeds increase and suddenly those ratios dont work. Hence, anderson with the 2.75 and near 500rwhp, fits perfect, as he now can get up to 170mph on those same straights.
Im fully aware while racing, of what gears i would need to be to be fastest, sometimes there are trade offs for not having to shift, by sacraficing the HP utilization, but those areas are rare. (usually, where you are between gears and you cant apply full hp there anyway!) Again, as i aways say, "it depends"
it depends on the track, it depnds on the car, it depends on the HP/weight and many other factors. the proof is when you race the car and see where your shift points are. with STACK and MOTEC, its easy to analyse your data to see what the advantages would be and optimize the gear ratios if you could have gear change options. but to say, adding a gear always helps, is not true. without paying close attention to gear spacing and expected speeds in those gears, you are shooting in the dark.
Take one straight at laguna off turn 11
apex speeds are close to 45mph
with a 2.2 , you can shift into 1st and run to 55mph for a quick launch, but hard on the gearbox and you have to be good with the gear box, second from 4500 to 6500rpm, third from 4500rpm to 6500rpm and you are near 120mph, and then a quick shift to 4th for maybe 5mph more to 125 , which is the max speed of that straight. with a 2.75 gear box, you dont have the advantage to use 1st on the curve, there are trade offs in 2nd and 3rd, mostly 3rd, where you spend most of the time as far as applied HP/seconds. now, if i had 500hp, suddenly, that quick shift to 4th for a second or two, would be much longer and the losses would be greater, and offset the time spent in 3rd gear advantage (ie anderson has this issue and thas why the 2.73 is better for more hp)
so, thats how it works. simple integration of the HP curve. its how all the analysis of gear box optimization works in racing.
so, acutally, with the wide spacing of the 928, which we are kind of stuck with, i get 1st once and through to a little of 4th. If my car could run to 7000rpm, i could get 1st once still, but never touch 4th. thats 3 gears. 2 gears besides turn 11. now a porsche cup car is in the same boat. same first gear speeds, at 55mph, but, two gears where we have one (2nd) then, its 4th gear is the same speed as our 3rd gear maxing out at 120mph. what did it gain?? well, it gained 8% more to the rear wheel hp due to its engine being kept near max hp longer between 55 and 95mph. this is based on a stock cup car running the supercup race or most of the SpeedGT cup cars too. also, close to the vet, viper and the 6speed audi that was the fastest car in the series.
Sure, I run what i got, but im fully aware of what i would need at some tracks, if i had options. do i make the best of it? SURE . Now do we have options that make a difference?? not really, we dont have a close ratio option, we have rear end changes that can optimize or make things much worse. It depends.
MK
PS, just did a time measurement of each gear at laguna's final straight.
1st 1.37seconds (45mph to 55mph) 6500rpm
2nd 3.32 (55mph to 80mph) 6200rpm
3rd 5.37 (85mph to 115mph) 6200rpm
4th 3.5 top speed near 125 ? rpm
if you intergrate the hp on the curve, you can clearly see what gear box would yield the greatest average acceleration. the more HP/seconds used, the greater the acceleration overall. many of these exersizes will yield not much difference. splitting hairs more often then not. is there a reason why Anderson also is running the same times at laguna too, not just willow springs with a 2.73:1 vs his old 2.2?? When i asked him how it felt with the new gear box a few years ago, he said " i dont know, but im shifting a lot more".
Originally Posted by Jim bailey - 928 International
look at 98 911 PET and there are 3 differents stock 3 rd gear ratios available 35:23, 38:27,35:33 plus 3 different 4th gears 41:33, 36:29, 38:34 , then 5th 42:41,33:32 and these are just SOME of the factory ratios. Early 911s you can stack he 3-5 th gear sets just about anyway you wish Porsche "racing" suggestions listed recommended gear ratios depending on the type of track which brings me back to the comments about what gears Mark Kibort is racing AGAINST in other cars ....they could be anything ! Mark sometimes you are like a guy who only owns a 5 lb sledge hammer maybe a 10 lb would be better but all you have is a 5 lb so you just hit it twice... it works for you. But trust me on this you could benefit from being able to use more than 2 or 3 gears at a track. Unfortunately we have few options with the 928 transmission other than the 11:30 (2.7272) ring and pinion , 15:33 ( 2.20) or 11:29 (2.6363, the 89 5 spd not GT) and the chioce of two layshaft ratios which are part of gears 1-4 ratios select a 1.4545 or 1.5714.
Last edited by mark kibort; 04-14-2006 at 05:35 PM.
04-14-2006, 05:32 PM
#65
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Originally Posted by Jim bailey - 928 International
Yes are are some other numbers I believe bascially much of the 78-84 trans internal parts interchange as one family ,the 85-86 early borgwarner , the 1987-91 , GTS is unique but even there some parts may interchange. There has been little work done on this subject most just run what they have. The trans evolved to be stronger...
04-14-2006, 06:12 PM
#67
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Ok then, still looking for an 85+ 5-speed with LSD to trade for a 79 2:72 with LSD with 66k on it.
04-14-2006, 06:19 PM
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A 79 would be a 2.75. Good luck with the trade. Hmm... maybe I can find somebody to trade my normally functioning 80-81 2.73 with LSD for an 85-89 2.73 or 2.64 with LSD. I doubt it.
04-14-2006, 08:22 PM
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More trans trivia seems the 5th gear input which carries the layshaft gears S-4 and GT do NOT interchange the splines on the hub are a different depth interesting.... anyone have a "spare" GT 5 th gear ?