Why not 2.72 as the beter choice?
07-09-2006, 04:20 AM
#1
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Why not 2.72 as the beter choice?
Of the 928s I've owned, my favorite was a green 1980. It weighed in at just over 3,00 pounds and had the low ratio final drive. It was a blast playing with the gears in corners.
My wife's 84 has a bit more horsepower and only a tad more weight, but in addition to being an automatic, the trans and shifting is lackluste - plus you hit speed limits at least by 3rd, if not 2nd gear.
Do I REALLY need to go 200 mph in my 86 1/2. Maybe a more serious question is do I really want to be able to go that fast as an option? Maybe I'd take it some day - and could not if I did not have that choice.
Suppose the day ever came that on some absolutely desolate back road I decide to see what it really can do - and just as I top 180 mph and climbing - radar comes over the hill the other way.
Lose of license. Car towed. Probably tickets beyond fine misdemeanors to reckless driving and even felony endangerment (endangering yourself)...
...or not stop at all and go for it.
Once, in a twin turbo Maserati many years ago I had to make decision and decided to go for it. There was no chase, though. Never even read lights behind me - as I was just gone off into the barren and unpopulated backroads of nothingness.
So I am not sure I want a 200 mph 928 as when is that ever a reality in terms of usage? Isn't 145, 150 mph fast enough?
Lower final drive alway equates to relatively higher horsepower (relative to acceleration). It makes for an overall closer ratio transmission (I wish there was a kit to make 5th gear really tall).
This leads, though, to my REAL question. Early model low ratio 5 speeds are not expensive because early model parts cars are cheap. But the sychros are always out - usually 2nd and 3rd.
Granted, a total trans rebuild might be in order, but can just new sychros be put in for a few hundred dollars - and are they still avaiable?
I miss shifting downshifting to 2nd and coming out of a high speed curve in 4th. Or even just the downshifting using motor braking when coming to a stop light
.
Mark
My wife's 84 has a bit more horsepower and only a tad more weight, but in addition to being an automatic, the trans and shifting is lackluste - plus you hit speed limits at least by 3rd, if not 2nd gear.
Do I REALLY need to go 200 mph in my 86 1/2. Maybe a more serious question is do I really want to be able to go that fast as an option? Maybe I'd take it some day - and could not if I did not have that choice.
Suppose the day ever came that on some absolutely desolate back road I decide to see what it really can do - and just as I top 180 mph and climbing - radar comes over the hill the other way.
Lose of license. Car towed. Probably tickets beyond fine misdemeanors to reckless driving and even felony endangerment (endangering yourself)...
...or not stop at all and go for it.
Once, in a twin turbo Maserati many years ago I had to make decision and decided to go for it. There was no chase, though. Never even read lights behind me - as I was just gone off into the barren and unpopulated backroads of nothingness.
So I am not sure I want a 200 mph 928 as when is that ever a reality in terms of usage? Isn't 145, 150 mph fast enough?
Lower final drive alway equates to relatively higher horsepower (relative to acceleration). It makes for an overall closer ratio transmission (I wish there was a kit to make 5th gear really tall).
This leads, though, to my REAL question. Early model low ratio 5 speeds are not expensive because early model parts cars are cheap. But the sychros are always out - usually 2nd and 3rd.
Granted, a total trans rebuild might be in order, but can just new sychros be put in for a few hundred dollars - and are they still avaiable?
I miss shifting downshifting to 2nd and coming out of a high speed curve in 4th. Or even just the downshifting using motor braking when coming to a stop light
. Mark
07-09-2006, 01:37 PM
#2
Rennlist Member
glad you asked! 
the ole 2.72 vs 2.2 discussion. remember,
Acceleration= Power/(mass x acceleration)
gearing doesnt change power, but what a rear end can do is optimize it for a range of speeds. the ONLY way to get more power over all operational ranges, is to closen the gear ratios , like on a GT3cup car. (ie .83 rpm drops per shift vs our 928s that ALL have close to .7 rpm drops, except for the 2.2's 5th which is near 50%)
That said, because the gear ratios of the 2.2 vs the 2.72 are spaced the same, the acceleration will be the same over most all speed ranges. however, a quick look will find slightly faster acceleration of one vs the other depending on the target speed or operational range. an example of that would be 0-55mph may favor the 2.2, while 0-50 may favor the 2.72. 60-100 may favor the 2.2 while 50-90 may favor the 2.72. think of our 928s as 4 speeds with overdrive. 5th isnt really a consideration due to its fuel efficient goals . the 2.2 is a 4 speed with a top speed in 4th of 155mph while the 2.72 has a top speed in 4th of 135mph.
Keep in mind the difference of the 2.2 vs the 2.72 is not 2.72/2.2 the internal ratios are differnet to make the total difference of only near 12%
Ive raced both gear boxes. both will have their advantages at certain tracks and with certain HP 928s . the key is maximizing the time you spend at near max hp. track, hp, driver, all determine which gear box will be best to achieve that goal.
Mk
the ole 2.72 vs 2.2 discussion. remember,
Acceleration= Power/(mass x acceleration)
gearing doesnt change power, but what a rear end can do is optimize it for a range of speeds. the ONLY way to get more power over all operational ranges, is to closen the gear ratios , like on a GT3cup car. (ie .83 rpm drops per shift vs our 928s that ALL have close to .7 rpm drops, except for the 2.2's 5th which is near 50%)
That said, because the gear ratios of the 2.2 vs the 2.72 are spaced the same, the acceleration will be the same over most all speed ranges. however, a quick look will find slightly faster acceleration of one vs the other depending on the target speed or operational range. an example of that would be 0-55mph may favor the 2.2, while 0-50 may favor the 2.72. 60-100 may favor the 2.2 while 50-90 may favor the 2.72. think of our 928s as 4 speeds with overdrive. 5th isnt really a consideration due to its fuel efficient goals . the 2.2 is a 4 speed with a top speed in 4th of 155mph while the 2.72 has a top speed in 4th of 135mph.
Keep in mind the difference of the 2.2 vs the 2.72 is not 2.72/2.2 the internal ratios are differnet to make the total difference of only near 12%
Ive raced both gear boxes. both will have their advantages at certain tracks and with certain HP 928s . the key is maximizing the time you spend at near max hp. track, hp, driver, all determine which gear box will be best to achieve that goal.
Mk
Originally Posted by DFWX
Of the 928s I've owned, my favorite was a green 1980. It weighed in at just over 3,00 pounds and had the low ratio final drive. It was a blast playing with the gears in corners.
My wife's 84 has a bit more horsepower and only a tad more weight, but in addition to being an automatic, the trans and shifting is lackluste - plus you hit speed limits at least by 3rd, if not 2nd gear.
Do I REALLY need to go 200 mph in my 86 1/2. Maybe a more serious question is do I really want to be able to go that fast as an option? Maybe I'd take it some day - and could not if I did not have that choice.
Suppose the day ever came that on some absolutely desolate back road I decide to see what it really can do - and just as I top 180 mph and climbing - radar comes over the hill the other way.
Lose of license. Car towed. Probably tickets beyond fine misdemeanors to reckless driving and even felony endangerment (endangering yourself)...
...or not stop at all and go for it.
Once, in a twin turbo Maserati many years ago I had to make decision and decided to go for it. There was no chase, though. Never even read lights behind me - as I was just gone off into the barren and unpopulated backroads of nothingness.
So I am not sure I want a 200 mph 928 as when is that ever a reality in terms of usage? Isn't 145, 150 mph fast enough?
Lower final drive alway equates to relatively higher horsepower (relative to acceleration). It makes for an overall closer ratio transmission (I wish there was a kit to make 5th gear really tall).
This leads, though, to my REAL question. Early model low ratio 5 speeds are not expensive because early model parts cars are cheap. But the sychros are always out - usually 2nd and 3rd.
Granted, a total trans rebuild might be in order, but can just new sychros be put in for a few hundred dollars - and are they still avaiable?
I miss shifting downshifting to 2nd and coming out of a high speed curve in 4th. Or even just the downshifting using motor braking when coming to a stop light .
Mark
My wife's 84 has a bit more horsepower and only a tad more weight, but in addition to being an automatic, the trans and shifting is lackluste - plus you hit speed limits at least by 3rd, if not 2nd gear.
Do I REALLY need to go 200 mph in my 86 1/2. Maybe a more serious question is do I really want to be able to go that fast as an option? Maybe I'd take it some day - and could not if I did not have that choice.
Suppose the day ever came that on some absolutely desolate back road I decide to see what it really can do - and just as I top 180 mph and climbing - radar comes over the hill the other way.
Lose of license. Car towed. Probably tickets beyond fine misdemeanors to reckless driving and even felony endangerment (endangering yourself)...
...or not stop at all and go for it.
Once, in a twin turbo Maserati many years ago I had to make decision and decided to go for it. There was no chase, though. Never even read lights behind me - as I was just gone off into the barren and unpopulated backroads of nothingness.
So I am not sure I want a 200 mph 928 as when is that ever a reality in terms of usage? Isn't 145, 150 mph fast enough?
Lower final drive alway equates to relatively higher horsepower (relative to acceleration). It makes for an overall closer ratio transmission (I wish there was a kit to make 5th gear really tall).
This leads, though, to my REAL question. Early model low ratio 5 speeds are not expensive because early model parts cars are cheap. But the sychros are always out - usually 2nd and 3rd.
Granted, a total trans rebuild might be in order, but can just new sychros be put in for a few hundred dollars - and are they still avaiable?
I miss shifting downshifting to 2nd and coming out of a high speed curve in 4th. Or even just the downshifting using motor braking when coming to a stop light
. Mark
07-09-2006, 01:53 PM
#3
Under the Lift
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140 is way too slow. As Ander's remarked while we were riding along averaging 152 and spending a lot of time at 165-170 to get there from a dead stop, "This feels slow." Do it legally and there is no problem: http://www.openroadracing.com/
