Gear ratios...
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From: Loveland, CO
Hello all,
Matt was kind enough to send this my way for review, and it is great info. I wonder if the max rpm should not be lifted to 7800 rpm (I know they're street cars, but I do extend to redline from time to time, and it is instructive to see the true max speed in gears).
But, herewith for further discussion:
EDIT: Matt, file is coming up as invalid on Rennlist
Matt was kind enough to send this my way for review, and it is great info. I wonder if the max rpm should not be lifted to 7800 rpm (I know they're street cars, but I do extend to redline from time to time, and it is instructive to see the true max speed in gears).
But, herewith for further discussion:
EDIT: Matt, file is coming up as invalid on Rennlist
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Hello all,
Matt was kind enough to send this my way for review, and it is great info. I wonder if the max rpm should not be lifted to 7800 rpm (I know they're street cars, but I do extend to redline from time to time, and it is instructive to see the true max speed in gears).
But, herewith for further discussion:
EDIT: Matt, file is coming up as invalid on Rennlist
Matt was kind enough to send this my way for review, and it is great info. I wonder if the max rpm should not be lifted to 7800 rpm (I know they're street cars, but I do extend to redline from time to time, and it is instructive to see the true max speed in gears).
But, herewith for further discussion:
EDIT: Matt, file is coming up as invalid on Rennlist
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To all the guys that want something different
What you see in the graph is a ss model of what is felt by thew driver when driving the car.
Inputs are engine rear wheel torque curve, max rpm(7800 here) trans gearing, wheel rolling radius(for a typical 295/30x20 tire), weight(3155# w/ driver), & aero characteristics(Cd .32, S 2.00). It is a model that is only as good as the input values which I tried to implement as accurately as possible.
It shows what you need to know, ie when to shift up, the actual shift points are where the tail of a lower gears curve crosses the next gears curve. You go a little long because of lags in the process but to remain in a lower gear after that is to have less acceleration available at wot,
the higher a curve the more acceleration is available from the car
What you see in the graph is a ss model of what is felt by thew driver when driving the car.
Inputs are engine rear wheel torque curve, max rpm(7800 here) trans gearing, wheel rolling radius(for a typical 295/30x20 tire), weight(3155# w/ driver), & aero characteristics(Cd .32, S 2.00). It is a model that is only as good as the input values which I tried to implement as accurately as possible.
It shows what you need to know, ie when to shift up, the actual shift points are where the tail of a lower gears curve crosses the next gears curve. You go a little long because of lags in the process but to remain in a lower gear after that is to have less acceleration available at wot,
the higher a curve the more acceleration is available from the car
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From: saratoga, ca
In otherwords, there is a trade off.
as long as the car is in the max HP range, it will be accelerating with the same forces for a given vehicle speed, over all.
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From: saratoga, ca
Someone PM'd me that I had a technical oops on this post. The 2.7 runs a 1.46 3rd, not a 1.48, though that doesn't change the math I actually ran since I had the actual toothcount input into my gearchart. I use a 7400 rpm shiftpoint because these are street cars and track toys and in my experience most owners don't rev to the rev limiter in that application. Given those parameters, the upshift to 3rd is at 5250, which is the basis for my "barely" 5000rpm...
It's better than stock, but still far from optimized.
It's better than stock, but still far from optimized.
(edited for the detune matt used and the 2.7 vs GT4 stock comparison)
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From: saratoga, ca
Good graphs again.. did you use the stock factory dyno output data or an actual run... the ones ive seen on the dyno dont seem to fall off that much at max RPM ranges, but if you go off the stock graph, there is some short shifting that is needed, but almost negated if you factor in the time to shift, which you mentioned. good stuff again!
Mark
Mark
To all the guys that want something different
What you see in the graph is a ss model of what is felt by thew driver when driving the car.
Inputs are engine rear wheel torque curve, max rpm(7800 here) trans gearing, wheel rolling radius(for a typical 295/30x20 tire), weight(3155# w/ driver), & aero characteristics(Cd .32, S 2.00). It is a model that is only as good as the input values which I tried to implement as accurately as possible.
It shows what you need to know, ie when to shift up, the actual shift points are where the tail of a lower gears curve crosses the next gears curve. You go a little long because of lags in the process but to remain in a lower gear after that is to have less acceleration available at wot,
the higher a curve the more acceleration is available from the car
What you see in the graph is a ss model of what is felt by thew driver when driving the car.
Inputs are engine rear wheel torque curve, max rpm(7800 here) trans gearing, wheel rolling radius(for a typical 295/30x20 tire), weight(3155# w/ driver), & aero characteristics(Cd .32, S 2.00). It is a model that is only as good as the input values which I tried to implement as accurately as possible.
It shows what you need to know, ie when to shift up, the actual shift points are where the tail of a lower gears curve crosses the next gears curve. You go a little long because of lags in the process but to remain in a lower gear after that is to have less acceleration available at wot,
the higher a curve the more acceleration is available from the car
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Hello all,
Matt was kind enough to send this my way for review, and it is great info. I wonder if the max rpm should not be lifted to 7800 rpm (I know they're street cars, but I do extend to redline from time to time, and it is instructive to see the true max speed in gears).
But, herewith for further discussion:
Matt was kind enough to send this my way for review, and it is great info. I wonder if the max rpm should not be lifted to 7800 rpm (I know they're street cars, but I do extend to redline from time to time, and it is instructive to see the true max speed in gears).
But, herewith for further discussion:
Just for comparison here's what a pretty well geared race box, g50 /30, used in the 993 Cups would look like
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From: Loveland, CO
Bill,
The chart provided to Pete does NOT change the stock 6th because he has indicated that it is already too short. Furthermore, the version you have reposted is only changing 3-4-5 because of the mainshaft constraints and should be analyzed within those parameters. It is intended as a workable solution to DE drivers wishing to drive to and from the track on the highway.
The chart provided to Pete does NOT change the stock 6th because he has indicated that it is already too short. Furthermore, the version you have reposted is only changing 3-4-5 because of the mainshaft constraints and should be analyzed within those parameters. It is intended as a workable solution to DE drivers wishing to drive to and from the track on the highway.
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From: ^ The Bay Bridge
All I'm looking for is how to replicate the effective ratios of 1-5 and 7 in a 991-1S gearbox within the GT4 transaxle with its stock R&P. I think that setup would be the bees' knees.
Btw, some "friends within" are watching this thread, and one noted that while the 2.7 gears may be strong enough, the rest of the 981 2.7 transmission is not. I am not sure what, exactly, is the issue, but I thought I'd pass this along. Curious as to Matt's thoughts.
Btw, some "friends within" are watching this thread, and one noted that while the 2.7 gears may be strong enough, the rest of the 981 2.7 transmission is not. I am not sure what, exactly, is the issue, but I thought I'd pass this along. Curious as to Matt's thoughts.
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From: ^ The Bay Bridge
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From: Loveland, CO
Quite easy to add a cooler and should be done on any car tracked regularly. The factory cooler is inadequate.
Skeptical about a weak case. Might just be marketing spin.
Skeptical about a weak case. Might just be marketing spin.
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Joined: Feb 2003
Posts: 29,828
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From: saratoga, ca
All I'm looking for is how to replicate the effective ratios of 1-5 and 7 in a 991-1S gearbox within the GT4 transaxle with its stock R&P. I think that setup would be the bees' knees.
Btw, some "friends within" are watching this thread, and one noted that while the 2.7 gears may be strong enough, the rest of the 981 2.7 transmission is not. I am not sure what, exactly, is the issue, but I thought I'd pass this along. Curious as to Matt's thoughts.
Btw, some "friends within" are watching this thread, and one noted that while the 2.7 gears may be strong enough, the rest of the 981 2.7 transmission is not. I am not sure what, exactly, is the issue, but I thought I'd pass this along. Curious as to Matt's thoughts.
just curious as the discussion continues.... by the way, Bill's spreadsheet is very nice having most of the data right there to analyse. my advice is to drive a car with the closeness in the lower 1-2nd gear range and see how awkward i can be. is i mentioed, i have a street car with the same gears as the GT4 and 1st is really low. (12.7:1) and 2nd is the same as the GT4 as well. its nice to get out of the starting gear and into the reall gears at a RPM and torque that doesnt spin the wheels as much and has the perfect spot to engage max HP ranges, which is around 55mph (after the first few hundred RPM of 2nd)
imho