Jun 15, 2006 9:12:32 AM
- easy_rider911
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Jun 15, 2006 1:00:30 PM
- JJBlade
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Jun 15, 2006 3:23:03 PM
- SoCal Alan
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Re: Max/min speeds in each gear ?
DRIVETRAIN
Transmission: 6-speed manual
Final-drive ratio: 3.44:1, limited slip
Gear, Ratio, Mph/1000 rpm, Max test speed
I, 3.91, 5.6, 40 mph (7200 rpm)
II, 2.32, 9.4, 68 mph (7200 rpm)
III, 1.61, 13.6, 98 mph (7200 rpm)
IV, 1.28, 17.1, 123 mph (7200 rpm)
V, 1.08, 20.2, 146 mph (7200 rpm)
VI, 0.88, 24.8, 179 mph (7200 rpm)
http://www.caranddriver.com/roadtests/8683/porsche-911-carrera-s-page4.html
Transmission: 6-speed manual
Final-drive ratio: 3.44:1, limited slip
Gear, Ratio, Mph/1000 rpm, Max test speed
I, 3.91, 5.6, 40 mph (7200 rpm)
II, 2.32, 9.4, 68 mph (7200 rpm)
III, 1.61, 13.6, 98 mph (7200 rpm)
IV, 1.28, 17.1, 123 mph (7200 rpm)
V, 1.08, 20.2, 146 mph (7200 rpm)
VI, 0.88, 24.8, 179 mph (7200 rpm)
http://www.caranddriver.com/roadtests/8683/porsche-911-carrera-s-page4.html
Jun 15, 2006 4:00:31 PM
- easy_rider911
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Just what I wanted... Jun 15, 2006 8:44:12 PM
- 69bossnine
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Re: Max/min speeds in each gear ?
Always keep in mind that unless you downshift to a gear that results in having at least 1,500 rpm or more left until redline, you're not really making any haste, because before you know it, you're going to have to upshift again. The closer you are to the redline after a downshift, the more the act of up-shifting effectively negates the advantage of the lower gear..
(Example)
You're cruising along at 60 mph, and up along side you pulls a 6-speed C6 Corvette. Do you
1. Downshift into 2nd gear?
2. Downshift into 3rd gear?
The answer is option #2. Why? Because the extra gearing you gain by going to 2nd is negated by the time it'll take you to almost immediately fiddle with the 2-3 shift. In short, while you're sitting there flailing through a downshift and then an almost immediate upshift, your foe has jumped a length on you, that you won't likely be able to make up.
When you downshift, you're not aiming for the lowest gear you can grab. You're better off aiming for peak torque, which is around 4,800 rpm, whatever gear gets you there or higher (don't go under that) letting the car get some work done, and then shifting.
(Example)
You're cruising along at 60 mph, and up along side you pulls a 6-speed C6 Corvette. Do you
1. Downshift into 2nd gear?
2. Downshift into 3rd gear?
The answer is option #2. Why? Because the extra gearing you gain by going to 2nd is negated by the time it'll take you to almost immediately fiddle with the 2-3 shift. In short, while you're sitting there flailing through a downshift and then an almost immediate upshift, your foe has jumped a length on you, that you won't likely be able to make up.
When you downshift, you're not aiming for the lowest gear you can grab. You're better off aiming for peak torque, which is around 4,800 rpm, whatever gear gets you there or higher (don't go under that) letting the car get some work done, and then shifting.
Jun 15, 2006 9:00:15 PM
- MMD
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Re: Max/min speeds in each gear ?
Quote:
69bossnine said:
Always keep in mind that unless you downshift to a gear that results in having at least 1,500 rpm or more left until redline, you're not really making any haste, because before you know it, you're going to have to upshift again.
Absolutely, there's no point in downshifting to near-redline.
I do it for fun, so my car-inclined passengers say, "Holy cr*p, 70mph in SECOND gear!" It's just a touch mis-infomative; for the sake of cheap thrills you understand.
Jun 16, 2006 3:01:29 PM
- 69bossnine
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Re: Max/min speeds in each gear ?
My pop's Ford GT is 2.61 to 1 ratio IN FIRST GEAR...
1st 64 mph
2nd 96 mph
3rd 133 mph
4th 172 mph
5th 214 mph
6th 259 mph
Kinda sick, huh?? Of course, these are purely mathmatical figures, we all know that the car succumbs to the forces of nature (wind) at bit over 210.
But at 70 mph in 2nd gear, it's revving only 4,600 rpm...
Should anybody care to wave the BS flag, my data source is a 20 page long Roush Industries/Ford Motor SAE Technical filing.
1st 64 mph
2nd 96 mph
3rd 133 mph
4th 172 mph
5th 214 mph
6th 259 mph
Kinda sick, huh?? Of course, these are purely mathmatical figures, we all know that the car succumbs to the forces of nature (wind) at bit over 210.
But at 70 mph in 2nd gear, it's revving only 4,600 rpm...
Should anybody care to wave the BS flag, my data source is a 20 page long Roush Industries/Ford Motor SAE Technical filing.
Jun 16, 2006 3:30:04 PM
- Grant
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Re: Max/min speeds in each gear ?
Quote:
69bossnine said:
My pop's Ford GT is 2.61 to 1 ratio IN FIRST GEAR...
1st 64 mph
2nd 96 mph
3rd 133 mph
4th 172 mph
5th 214 mph
6th 259 mph
Kinda sick, huh?? Of course, these are purely mathmatical figures, we all know that the car succumbs to the forces of nature (wind) at bit over 210.
I'm not calling BS, but I am calling "Poor Gearing". Seems that Ford took a page from the Corvette playbook where 6th gear is only a tack-on item for fuel mileage. The car would offer better performance if it could reach terminal velocity (~210mph) at its power peak (rpm) in top gear (6th). Then the ratios could be lowered and made closer together, offering significantly better acceleration...
Jun 16, 2006 5:16:27 PM
- 69bossnine
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Re: Max/min speeds in each gear ?
It's not that simple... There are many variables to consider when matching gearing to an engine. The Ford GT has a massive torque curve, and the gearing is set to optimize the location of the rpm drop from gear to gear. Trying to translate Porsche's gear spacing to that of a Corvette or Ford GT is an exercise in apples/oranges.
The engineers also had a goal of achieving optimal 0-60, and since the engine is such a torque animal, it allows you the luxury and advantage of eliminating the need for a 1-2 shift. Furthermore, if you made 1st gear any steeper in that car, you would just boil the tires, rendering 1st gear useless, hijacking performance. There's no point in gearing a car so steeply that it can't apply its power to the ground effectively. We're spoiled with the 911, with the engine squatting over the drive wheels.
And then you could argue that 6th gear is useless, which it really is except as a mileage gear on the highway... But on a track, isn't 1st gear "useless" in our 997's? 1st gear in our cars is only good for parking lots and driveways, and getting the car rolling since it's not torquey down low.
In any race-bred car, no matter how many "speeds" are in the gearbox, you're only really going to utilize 3 or 4 of them in series on the track. The others are just "there" for more pedestrian pursuit.
Lastly, you can't argue "poor gearing" with a car that does 0-60 in 3.3 seconds, and runs 11.5 second quarter miles at 128+, with 3400 lbs of pork to haul. It's obvious to me that Ford did their homework, and geared the car for optimal performance, especially on a larger track. The engine is meaty enough that it can pull that tall 1st gear right out of the hole, giving you the payoff of incredible dead-stop sprinting ability, without the futility of lost traction.
My S351 won't hook up under full-throttle until 3rd gear, and even that goes up in smoke in cold weather. All that power, steep gearing, and virtually impossible to exploit to its full potential.
Cars with big-time torque work better with long gearing on street tires.
Besides, the engineering work on the GT is absolutely brilliant, as I've discovered behind the wheel, and as has been borne-out by most of the major magazines. I highly doubt that the engineers on that project bumped their heads and had a moment of redneck delusion when they mapped their gear spacings. You can bet it was quite scientific, as they had a clean sheet of paper to work from.
The engineers also had a goal of achieving optimal 0-60, and since the engine is such a torque animal, it allows you the luxury and advantage of eliminating the need for a 1-2 shift. Furthermore, if you made 1st gear any steeper in that car, you would just boil the tires, rendering 1st gear useless, hijacking performance. There's no point in gearing a car so steeply that it can't apply its power to the ground effectively. We're spoiled with the 911, with the engine squatting over the drive wheels.
And then you could argue that 6th gear is useless, which it really is except as a mileage gear on the highway... But on a track, isn't 1st gear "useless" in our 997's? 1st gear in our cars is only good for parking lots and driveways, and getting the car rolling since it's not torquey down low.
In any race-bred car, no matter how many "speeds" are in the gearbox, you're only really going to utilize 3 or 4 of them in series on the track. The others are just "there" for more pedestrian pursuit.
Lastly, you can't argue "poor gearing" with a car that does 0-60 in 3.3 seconds, and runs 11.5 second quarter miles at 128+, with 3400 lbs of pork to haul. It's obvious to me that Ford did their homework, and geared the car for optimal performance, especially on a larger track. The engine is meaty enough that it can pull that tall 1st gear right out of the hole, giving you the payoff of incredible dead-stop sprinting ability, without the futility of lost traction.
My S351 won't hook up under full-throttle until 3rd gear, and even that goes up in smoke in cold weather. All that power, steep gearing, and virtually impossible to exploit to its full potential.
Cars with big-time torque work better with long gearing on street tires.
Besides, the engineering work on the GT is absolutely brilliant, as I've discovered behind the wheel, and as has been borne-out by most of the major magazines. I highly doubt that the engineers on that project bumped their heads and had a moment of redneck delusion when they mapped their gear spacings. You can bet it was quite scientific, as they had a clean sheet of paper to work from.
Jun 16, 2006 6:48:01 PM
- Grant
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Re: Max/min speeds in each gear ?
I realize that the GT is very quick as it is, but don't you concede the possibility that it might be even quicker with a close-ratio 6spd as I described (not shortening 1st, but making all the rest closer together so that the car tops out in 6th), if they weren't constrained by trying to maximize fuel economy in 6th?
Jun 16, 2006 7:25:52 PM
- 69bossnine
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Re: Max/min speeds in each gear ?
By squeezing the gears closer together, making 6th gear meet top speed near redline, you run the risk of screwing up the gear spacing as it relates to the "sweet spot" between the engine's torque peak and horsepower peak, and the graduation of that spot as speed increases and horsepower is more desireable than torque. It's the engine that really dictates the optimal gear spacing. I've posted the chart so you can see exactly what I mean, and why you wouldn't want to screw with that.... Transmission gear ratio spacing should be matched to the engine, and not dictated by external goals of certain speeds in certain gears, lest you sacrifice overall performance. My 997S has the best matched tranny ratios to engine of any car I've ever owned BTW, at least by "feel" I believe that. Where you would make the adjustment to bring the 6th gear into play is not in the gearbox, but the final drive ratio. Problem is with this car, if you increase the final drive ratio, then you run into the problem of effectively increasing the 1st gear ratio to where you lose your 0-60 in one gear goal, and likely induce 1st gear wheel spin. So you're damned if you do, damned if you don't. That's the thing with gearing, is you can't just play with it while forgetting about the engine's power curves. For optimal performance you match the gear spacings in the tranny to the engine, and don't mess with it. Racing teams go the extra mile to play with the gearing to obtain certain personalities from the engine for specific tracks or courses. Then, do what's best with the final drive ratio.
Quite honestly, given the engine's power and the breadth of the power band, a race-version of the Ford GT would be best-off with a 5-speed tranny.
Quite honestly, given the engine's power and the breadth of the power band, a race-version of the Ford GT would be best-off with a 5-speed tranny.
Jun 16, 2006 7:30:56 PM
- 69bossnine
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Re: Max/min speeds in each gear ?
You've gotta imagine that Ford engineers played with NUMEROUS transmission and final-drive gearing scenarios, using computer simulations, to find the optimal setup for performance. I guarantee they didn't give a rat's patootie about mileage, as the car comes with a gas-guzzler tax anyhow. I don't know why they would leave even a DROP of performance on the table, for no reason.
Jun 16, 2006 8:08:39 PM
- Grant
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Re: Max/min speeds in each gear ?
Thanks for posting the chart! I'm certainly no expert on these matters, but I do have some experience in selecting my own ratios for my custom 5-speed in my 73RS (which has quite a different type of motor than the GT).
Anyways, my understanding is that for road racing (and I assume drag racing too), you want to maximize the engine's power on the curve.
I understand gearing to act as a torque multiplier, so that a lower gear will apply more torque to the road (assuming the same torque output from the motor). The lower the gear the better, until you run out of revs or exceed the tire's ability to stick to the track. And the gears should be spaced so closely that the car picks up the next gear as close as possible to the power peak (not torque peak).
I think an ideal transmission (like a CVT tranny that works)would keep engine revs consistently at the power peak, not the torque peak (and not between the torque and power peaks).
In a non-CVT tranny, this translates to an infinite number of ratios with minimal rev-drop between gears.
The only downside here is the time lost while shifting or a lack of traction to use the available power.
Since the GT has fat tires and is mid-engined, I just assumed (maybe wrongly) that it could benefit from at least 6 closely spaced gears. If it can't, that tells me that the shift times are too long to benefit from that and/or the traction is insufficient (gearing has to be artificially tall to prevent wheelspin), or the motor's power curve is flat (very different from a flat torque curve which creates a perfectly diagonal power curve)
Do you also have the power/torque curves for the GT?
Anyways, feel free to correct any of my assumptions, as I know you will
Anyways, my understanding is that for road racing (and I assume drag racing too), you want to maximize the engine's power on the curve.
I understand gearing to act as a torque multiplier, so that a lower gear will apply more torque to the road (assuming the same torque output from the motor). The lower the gear the better, until you run out of revs or exceed the tire's ability to stick to the track. And the gears should be spaced so closely that the car picks up the next gear as close as possible to the power peak (not torque peak).
I think an ideal transmission (like a CVT tranny that works)would keep engine revs consistently at the power peak, not the torque peak (and not between the torque and power peaks).
In a non-CVT tranny, this translates to an infinite number of ratios with minimal rev-drop between gears.
The only downside here is the time lost while shifting or a lack of traction to use the available power.
Since the GT has fat tires and is mid-engined, I just assumed (maybe wrongly) that it could benefit from at least 6 closely spaced gears. If it can't, that tells me that the shift times are too long to benefit from that and/or the traction is insufficient (gearing has to be artificially tall to prevent wheelspin), or the motor's power curve is flat (very different from a flat torque curve which creates a perfectly diagonal power curve)
Do you also have the power/torque curves for the GT?
Anyways, feel free to correct any of my assumptions, as I know you will
Jun 16, 2006 8:17:55 PM
- Grant
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Re: Max/min speeds in each gear ?
Quote:
69bossnine said:
You've gotta imagine that Ford engineers played with NUMEROUS transmission and final-drive gearing scenarios, using computer simulations, to find the optimal setup for performance. I guarantee they didn't give a rat's patootie about mileage, as the car comes with a gas-guzzler tax anyhow. I don't know why they would leave even a DROP of performance on the table, for no reason.
I'm sure that they wouldn't for "no reason". I can only imagine that they did it for fuel economy, passenger cabin noise reduction, and drivetrain longevity.
Since the GT has the Gas Guzzler Tax already, is it possible that they are worried about it affecting the CAFE standard (manufacturers need to meet an average mpg across all models)?
I KNOW the Z06 has artifically tall gears for these reasons (and mostly to avoid the Gas Guzzler Tax) - performance was left on the table for the Z06 (at least on a road course and maybe 1/4 mile too)...
Jun 19, 2006 7:17:24 PM
- 69bossnine
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Re: Max/min speeds in each gear ?
Grant, I see some factors that could take your recipe for gearing, and blow holes in it one way or the other. The way that you would optimize a car that has a high ratio of horsepower to torque (997S 355 hp / 295 lb-ft) would be different than how you would optimize a car with a lower ratio of horsepower to torque (Ford GT 550 hp / 500 lb-ft). I would think that for a car making 500 lb-ft of torque vs. 550 hp, your target for the rpm drop on an upshift would be a bit deeper than a car like the 997S where the smaller displacement motor makes a higher percentage of horsepower relative to its peak torque. Let's put it this way, any diesel engine would take your above theory for gear spacing, and turn it upside-down. The decision of whether one exploits the torque peak, rather than the h.p. peak, or somewhere in-between, depends on the nature of the engine in question, and how it translates itself into power, and I know I'm talking in generalities. At THIS point, I am in over my head!!! LOL!!! 
I doubt CAFE standards would sway them, as not enough were built to put a dent in the average, even if they got 2 mpg average.
Gearing is weird, I'll admit it boggles me if I think too hard about it....
I doubt CAFE standards would sway them, as not enough were built to put a dent in the average, even if they got 2 mpg average.
Gearing is weird, I'll admit it boggles me if I think too hard about it....
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