View Poll Results: Would you swap out a 2.73 R/P transmission for a 2.2 R/P one on a >400rwhp 928?
Yes, I think it would be worth it and the lower gears would suit the additional power better
57.14%
No, I don't think it would be worth it, plus it would inevitably make the car *seem* slower
42.86%
Voters: 21. You may not vote on this poll
Question for the >400rwhp club
03-03-2008, 04:12 PM
#1
Race Car
Thread Starter
Question for the >400rwhp club
If you have a supercharged 928 with a 5-speed 2.73 rear pinion transmission, do you think it would be worth it to swap the transmission out for one with a 2.2 5-speed?
Dan
'91 928GT S/C
'86 928S 5-spd w/LSD *sale pending*
Dan
'91 928GT S/C
'86 928S 5-spd w/LSD *sale pending*
03-03-2008, 04:19 PM
#2
Administrator - "Tyson"
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I'm planning on swapping the 2.73 for a 2.20 transmission in my 81. With the extra power the 2.73 is not needed.
Problem is, with your GT you have one of the best transmissions you get get for a 928. I wouldn't swap that out for a 2.20 box just because the GT box is stronger.
Problem is, with your GT you have one of the best transmissions you get get for a 928. I wouldn't swap that out for a 2.20 box just because the GT box is stronger.
03-03-2008, 05:11 PM
#4
Administrator - "Tyson"
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03-03-2008, 05:30 PM
#8
Rennlist Member
This goes back to many discussions, but gearing doesnt make HP and acceleration is proportional to power at any given speed.
Acceleration = Power/(mass x velocity)
There are trade offs through the gears , so it really depends on the target speed range that you will be driving the car in. on the race track, you would choose a gear box that would put you at close to redline for the majority of the straights, before the turns. on a drag strip, depending on traction limitations, there will be some slight gains, even if the final speed is not optimized for the final gear ( ie, 2.2 vs 2.75) the big variable there is traction. in that comparison, if you cant take advantage of the lower 1st gear, then there might be situations where you could be slower.
For example. I did some tests in my first gear, where i have 300+ rwhp. at near max torque or 4000rpm, there is no way that i can keep the wheels from spinning on the street with warm 305x18s race rubber. even if i floor it from a rolling 2000rpm, when it gets to near max torque, it spins the tires. This means that there is a limitation of grip that wont be helped by any additional HP. better traction, launch control, etc will be the most dominant factors. the rest of the gears will have grip and the overall acceleration will be a blend of the HP available in all the gears up to the target speed.
Again, when Anderson changed from 2.2 to 2.72, he didnt see a drop in lap times. IN fact, he is just starting to be about .5 seconds faster than he has been over the past 10 years, with the 2.73, but im sure that 80 more hp hasnt hurt that improvement!
the answer is no. the main reason to use the 2.72 would be for the stronger gears as was mentioned. both the GT and the GTS are stronger gear boxes, and thats why i would do it. I would also do it with 400rwhp, because the tracks i visit are perfect for the 2.2 gear speed ranges. that changes when you get more more HP.
Lots of factors
mk
Acceleration = Power/(mass x velocity)
There are trade offs through the gears , so it really depends on the target speed range that you will be driving the car in. on the race track, you would choose a gear box that would put you at close to redline for the majority of the straights, before the turns. on a drag strip, depending on traction limitations, there will be some slight gains, even if the final speed is not optimized for the final gear ( ie, 2.2 vs 2.75) the big variable there is traction. in that comparison, if you cant take advantage of the lower 1st gear, then there might be situations where you could be slower.
For example. I did some tests in my first gear, where i have 300+ rwhp. at near max torque or 4000rpm, there is no way that i can keep the wheels from spinning on the street with warm 305x18s race rubber. even if i floor it from a rolling 2000rpm, when it gets to near max torque, it spins the tires. This means that there is a limitation of grip that wont be helped by any additional HP. better traction, launch control, etc will be the most dominant factors. the rest of the gears will have grip and the overall acceleration will be a blend of the HP available in all the gears up to the target speed.
Again, when Anderson changed from 2.2 to 2.72, he didnt see a drop in lap times. IN fact, he is just starting to be about .5 seconds faster than he has been over the past 10 years, with the 2.73, but im sure that 80 more hp hasnt hurt that improvement!
the answer is no. the main reason to use the 2.72 would be for the stronger gears as was mentioned. both the GT and the GTS are stronger gear boxes, and thats why i would do it. I would also do it with 400rwhp, because the tracks i visit are perfect for the 2.2 gear speed ranges. that changes when you get more more HP.
Lots of factors
mk
03-03-2008, 05:36 PM
#9
Administrator - "Tyson"
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This is another big reason why I'm chaning boxes. The 85+ 2.20 is a stronger box than the early ones and 1st gear is useless on my car.
03-03-2008, 05:38 PM
#10
Race Car
Thread Starter
Dan
'91 928GT S/C
'86 928S 5-spd w/LSD *sale pending*
03-03-2008, 05:43 PM
#11
Captain Obvious
Super User
Super User
03-03-2008, 05:49 PM
#13
Race Car
Thread Starter
Well I use my car as a daily driver. Sometimes I do not worry about gas mileage and drive her hard. Other times if I'm going 400 miles one way, it's nice to be able to get 24 - 25mpg. I'm not saying it's a big factor, just something to throw in to the discussion. Is it wrong to want a car that can "do it all"? 
Dan
'91 928GT S/C
'86 928S 5-spd w/LSD *sale pending*
Dan
'91 928GT S/C
'86 928S 5-spd w/LSD *sale pending*
03-03-2008, 06:32 PM
#15
Race Car
Thread Starter
Dan
'91 928GT S/C
'86 928S 5-spd w/LSD *sale pending*