Gear ratios...
#76
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All good to know and get answers from someone who is knowledgeable. Thanks.
Understand the gear spinning faster will wear faster; probably pretty negligible however, right? Much in the way guys running small tires on their GT4s are wearing everything out sooner but will probably not feel the effects unless they keep the car until 200,000 miles, etc.? Increased rpm didn't stop me from running 205/55R15 tires on my 914 for 15+ years, and while I am back on 185/70 Avons, I am not sure I have seen any adverse effect from running the short tires.
On the point of not manufacturing a taller sixth because of Daytona. Does that mean you won't make them under ANY circumstances? Such as if you had more street customers requesting a taller sixth gear than race customers?
Understand the gear spinning faster will wear faster; probably pretty negligible however, right? Much in the way guys running small tires on their GT4s are wearing everything out sooner but will probably not feel the effects unless they keep the car until 200,000 miles, etc.? Increased rpm didn't stop me from running 205/55R15 tires on my 914 for 15+ years, and while I am back on 185/70 Avons, I am not sure I have seen any adverse effect from running the short tires.
On the point of not manufacturing a taller sixth because of Daytona. Does that mean you won't make them under ANY circumstances? Such as if you had more street customers requesting a taller sixth gear than race customers?
Hey Mark! This is/was understood from the start, and why the 996 GT3 comment was interesting but kind of a non-sequitur. Point of original post was to start an intelligent discussion on gearing from two premises:
1. The GT4 is an amazing car, and an amazing value. This thread has made me think more about that, and I am glad the GT team spent the money it had where it did. They put a 3.8-liter engine into a Cayman, added GT3 front suspension, developed new rear suspension pieces, added a full GT3 brake system, did real aero work that required unibody changes, and added the best shift linkage any Porsche has ever had. The result is a new GT car that's fast, handles beautifully, brakes hard, and is amazingly practical. For $85k, with a warranty? Wow.
2. Many have found the gearing of the GT4 to be unsatisfactory, and a recent road trip really drove it home for me. Some members within the GT team itself made it clear with facial expressions that they would have loved to do a gearbox for the GT4. In the grand scheme of things, gearing is something that the aftermarket CAN do, and do well.
To your post above, yes, this is exactly what we're talking about—just not about GT3s. And the GT4 gear set is a less than optimum hp/torque multiplier because it is bolted directly to an engine it wasn't designed to work with. The GT4 uses a 991-1S engine delivered with a gear set PAG optimized for the 981-1S engine according to its emissions and fuel efficiency needs with only six cogs to work with. The 991-1S uses a 991-1S gear set PAG optimized for 991-1S engines according to its emissions and fuel efficiency needs with seven cogs to work with. I suspect 1-5 plus 7 from the 991-1S gearbox—or something close—would make the GT4 a better car on all fronts except maybe cases where the 991-1S sixth gear is useful. I'm sure that scenario exists somewhere in North America (Bonneville? oval racing?), but I haven't experienced it—and it sounds like there are already two or three 6th GT4 gear ratios to choose from for the few who need that.
1. The GT4 is an amazing car, and an amazing value. This thread has made me think more about that, and I am glad the GT team spent the money it had where it did. They put a 3.8-liter engine into a Cayman, added GT3 front suspension, developed new rear suspension pieces, added a full GT3 brake system, did real aero work that required unibody changes, and added the best shift linkage any Porsche has ever had. The result is a new GT car that's fast, handles beautifully, brakes hard, and is amazingly practical. For $85k, with a warranty? Wow.
2. Many have found the gearing of the GT4 to be unsatisfactory, and a recent road trip really drove it home for me. Some members within the GT team itself made it clear with facial expressions that they would have loved to do a gearbox for the GT4. In the grand scheme of things, gearing is something that the aftermarket CAN do, and do well.
To your post above, yes, this is exactly what we're talking about—just not about GT3s. And the GT4 gear set is a less than optimum hp/torque multiplier because it is bolted directly to an engine it wasn't designed to work with. The GT4 uses a 991-1S engine delivered with a gear set PAG optimized for the 981-1S engine according to its emissions and fuel efficiency needs with only six cogs to work with. The 991-1S uses a 991-1S gear set PAG optimized for 991-1S engines according to its emissions and fuel efficiency needs with seven cogs to work with. I suspect 1-5 plus 7 from the 991-1S gearbox—or something close—would make the GT4 a better car on all fronts except maybe cases where the 991-1S sixth gear is useful. I'm sure that scenario exists somewhere in North America (Bonneville? oval racing?), but I haven't experienced it—and it sounds like there are already two or three 6th GT4 gear ratios to choose from for the few who need that.
I'm just going to bold within the quotes...
Shorter gears will not last as long as the stock ratios. Reduce the ratio and it spins more rotations per engine rotation. It will wear out faster. But we aren't talking about a 1.722 Cup 3rd gear that gets 25 hours. Not really something for recreational users to think about too much unless you are getting 100 hours a year on track.
Lastly, I will not manufacture a batch of taller than stock 6th gears. Stock 6th is already too tall for Daytona.
Shorter gears will not last as long as the stock ratios. Reduce the ratio and it spins more rotations per engine rotation. It will wear out faster. But we aren't talking about a 1.722 Cup 3rd gear that gets 25 hours. Not really something for recreational users to think about too much unless you are getting 100 hours a year on track.
Lastly, I will not manufacture a batch of taller than stock 6th gears. Stock 6th is already too tall for Daytona.
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#77
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I found this from a guy posting dynos of the following cars
check out the pink line.. is that the 991 engine you are refering too? what is teh redline... isnt it over 7500rpm stock?
edit: added a 3.8 L cayman dyno and 991 specs with gear ratios.
The chart are 911s dyno'd on a Dynojet 248. As follows:
dark green: 2.4 MFI
teal blue: 3.2 Carrera, chipped
red: 964 3.6
bright green: 993 3.6
brown: 2003 996 3.6
pink: 997S 3.8
blue: GT3
check out the pink line.. is that the 991 engine you are refering too? what is teh redline... isnt it over 7500rpm stock?
edit: added a 3.8 L cayman dyno and 991 specs with gear ratios.
The chart are 911s dyno'd on a Dynojet 248. As follows:
dark green: 2.4 MFI
teal blue: 3.2 Carrera, chipped
red: 964 3.6
bright green: 993 3.6
brown: 2003 996 3.6
pink: 997S 3.8
blue: GT3
Last edited by mark kibort; 12-02-2016 at 03:41 PM.
#78
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Brian Copan built several gear boxes for me. On the first 993 I picked the gears against Brian's suggestions. In 4 weeks I was back having the box done again. This time per Brian's suggestions and his rpm splits chart. Huge difference and an expensive lesson.
#80
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by the way.. the redline for the 3.8 looks to be 7500, so you need to take that into account too.
just think about it.. take the 997 3.8 dyno graph above with the pink line... if you can use the HP curve from 6000rpm to 7500rpm there is never a need to change out the gears. there is a dip in that particular graph... it would be far cheaper to fix the dip in the HP graph with a tuner like Vision motorsports then replace the gears in the gear box. once you have the HP curve working for you and optimized, there is not a gear change that can improve the effectiveness of its ability to put accelerative forces at the wheels at any vehicle speed , anywhere on the track.. IF the driver knows the operating RPM range to stay in.
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Last edited by mark kibort; 12-02-2016 at 04:26 PM.
#81
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Hey Mark, simple question, asked honestly and with zero desire to start a flame war: How much seat time do you have in GT4s? 0 miles? 100 mile? 10,000 miles? I ask because a lot of professional road and track testers have noted their dissatisfaction with the GT4's gear ratios, as have a lot of owners. This, after gleaning real-world impressions.
There are charts and theory, and then there is rubber meets the road. I've tested a lot of Porsches over a lot of years, and probably have 8,000-10,000 miles in GT4s on a variety of roads and on track, as well. I feel the gearing in the GT4 offers an area for real improvement—and that the gear ratios from the 991S that the GT4 gets its engine from would make for a significant improvement.
There are charts and theory, and then there is rubber meets the road. I've tested a lot of Porsches over a lot of years, and probably have 8,000-10,000 miles in GT4s on a variety of roads and on track, as well. I feel the gearing in the GT4 offers an area for real improvement—and that the gear ratios from the 991S that the GT4 gets its engine from would make for a significant improvement.
#82
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My first VW had short gears and I was always shifting, hated that car, I thought it would be great if it had long gears.
Now forty years later the company has finally put the engine in the right place, and I'm thinking it would be great if it had short gears.
Now forty years later the company has finally put the engine in the right place, and I'm thinking it would be great if it had short gears.
#83
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Hey Mark, simple question, asked honestly and with zero desire to start a flame war: How much seat time do you have in GT4s? 0 miles? 100 mile? 10,000 miles? I ask because a lot of professional road and track testers have noted their dissatisfaction with the GT4's gear ratios, as have a lot of owners. This, after gleaning real-world impressions.
There are charts and theory, and then there is rubber meets the road. I've tested a lot of Porsches over a lot of years, and probably have 8,000-10,000 miles in GT4s on a variety of roads and on track, as well. I feel the gearing in the GT4 offers an area for real improvement—and that the gear ratios from the 991S that the GT4 gets its engine from would make for a significant improvement.
There are charts and theory, and then there is rubber meets the road. I've tested a lot of Porsches over a lot of years, and probably have 8,000-10,000 miles in GT4s on a variety of roads and on track, as well. I feel the gearing in the GT4 offers an area for real improvement—and that the gear ratios from the 991S that the GT4 gets its engine from would make for a significant improvement.
so, my question back to you would be what is the deficiency in the ratios?
sure the 3.8 liter that came from the 911 , has a different gear box in that car. there are plenty of reasons to change the gear box.. porsche had the same model of car with the same HP with several different gear boxes based on where the destination was for the car, and options.
if we are talking racing, a change to a different set of ratios or a final drive change seems like a lot of expense for little gain, unless you need that little gain for a particular track. (this is not a one fits all discussion)
however, in respect to hyway use, sure depending on your neighborhood and driving style, and speed ranges, a different gear box might suite you better.
contrary to GTGears comments, putting a taller rear end vs lower rear end ratio shouldnt change much, other than cruising RPM. (which is a concern and preference of mine by the way), so for that reason, i would endorse the change, but he doesnt want any part of that, because " the car as is, can go Daytona speedway speeds in 6th". so, what are we left with? changing the gears for what reason. this is my question to you . what are the deficiencies of the gear box with its different ratios to the 991, where the base engine comes from and what do they mean to you? seems like a fair question to have summarized about now, no?
Mark
ps here are the speeds in each gear from this thread . so , all we need now is the 991 stock gears with its stock final drive. do you have that handy?
to keep the discusssion simple.. lets see the stock 991, with the stock GT4 speeds in each gear at redline.
Speeds at redline with a 4.75 final drive -
39.85
67.64
93.55
116.73
138.84
162.84
@stout, Curious if you thinks this will address the 2-5 being too long issue (obviously, it won't help your 6th not long enough complaint)? For comparison, 1-5 speeds with 911S ratios mated to stock GT4 3.89 final drive -
41.19
70.33
103.91
123.89
149.13
and compare to stock gearing what does it buy you ?
Gt4 gearing as was posted. (if this is at the 8200rpm, then slow down by 5%)
1 48 45.6mph at 7800
2 82 77.9
3 114 108.3
4 142 134
5 169
6 198
from specs:
Number of gears
6 Speed
Transmission type
Manual
Ratios
1st
3.31
2nd
1.95
3rd
1.41
4th
1.13
5th
0.95
6th
0.81
7th
-
Reverse
3.00
Front Axle Ratio
-
Rear Axle Ratio
3.89
Final Drive Ratio
3.89
Water-cooled horizontally-opposed six-cylinder
911 Carrera
911 Carrera S
Gearbox
Manual
Gear Ratios
1
3.91
2
2.32
3
1.56
4
1.28
5
1.08
6
0.88
7
0.62
Final Drive
3.44
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Last edited by mark kibort; 12-02-2016 at 06:25 PM.
#84
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It's evident in other situations—street, autocross, back roads, freeway cruising, gas mileage—and how.
Conversely, the best racers can outdrive all but a handful of writers—and I am not one of those—but a large percentage of them can do precisely bupkis to improve the car or tell you how it works. I'm told Milt Minter was the classic example: He was fast in anything (anything), and could get all it had to offer—but he could not tell you how it drove or how to improve it. He sure told great stories about Vasek, though. I've been told there are a lot of racers today who are in the same boat—they are fast, and can extract a lot from the car, but can't tell you much that is useful to you, or help develop the car. At all.
sure the 3.8 liter that came from the 911 , has a different gear box in that car. there are plenty of reasons to change the gear box.. porsche had the same model of car with the same HP with several different gear boxes based on where the destination was for the car, and options.
Fair question, but again this implies you skipped a lot of posts....
Last edited by stout; 12-02-2016 at 06:22 PM.
#85
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991S (PDK in parenthesis)
1st 3.91 (3.91)
2nd 2.29 (2.29)
3rd 1.55 (1.65)
4th 1.30 (1.30)
5th 1.08 (1.08)
6th 0.88 (0.88)
7th 0.71 (0.62)
F/D 3.44:1 (3.44:1)
981S (PDK in parenthesis)
1st 3.31 (3.91)
2nd 1.95 (2.29)
3rd 1.41 (1.65)
4th 1.13 (1.30)
5th 0.95 (1.08)
6th 0.81 (.88)
7th -- (0.62)
F/D 3.89 (3.89)
This info may have appeared earlier in the thread, but maybe it can be filled out with the maximum speeds in gear, and perhaps even a better way of comparing the effective gear ratios given the 3.44 vs 3.89 final drives. I suspect that means that, since custom gears would be required, those gears could be made to take into account the difference in final drive between the two while trying to create effective parity with the 991S in gears 1-5 plus 7. If, of course, that was the goal. It would be mine, and I suspect it would be a good setup for a lot of GT4 owners. Or maybe it could be optimized from there if a gear expert laid out a better plan to maximize acceleration and flexibility in gears 1-5 with a nice, tall cruising cog for 6th.
Last edited by stout; 12-02-2016 at 06:52 PM.
#86
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We're talking about how the power delivery of the car feels on the road, in comparison with other manual Porsches. No theoretical argument can override that empirical experience. If it feels sluggish, it feels sluggish. The question is how to fix that, not how to rationalize the problem away.
#87
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We're talking about how the power delivery of the car feels on the road, in comparison with other manual Porsches. No theoretical argument can override that empirical experience. If it feels sluggish, it feels sluggish. The question is how to fix that, not how to rationalize the problem away.
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#88
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you know the reason for that, right? the bug had about 70hp on a good day, and needed the gears to keep the hp up in the RPM range , so they needed to be very short... just like the old datsun pickups. i remember driving one for work in highschool and it woudl go through three gears before it got through the intercection after a stop light! tall gears would fry clutches in 1st, as you would need big slip to get rolling, AND, the next gears needed to be low to get the car accelerated to highway speeds. they couldnt go much over 80mph so, they were geared just about right back then. race car versions with more HP could go taller..............like the love bug. ;)
I thought of it as Hitler's revenge, when I got a face full of asbestos changing the rear drum brake pads.
;)
#89
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The 991S has more power,less drivetrain loss and better traction. One thing I've noticed in the GT4 that I didn't notice in the 991 S is wheel hopping. If you throw the Powerkit in you're talking 45HP more than the GT4. You feel that! The talk we hear during GT cars presentation about " GT horsepower " is just marketing talk. The GT4 makes exactly what it is rated for. Same goes for the GT3. It's been proven on the dyno.
The only complaint I have is the 2nd gear,that's it. If you want to go to the redline and shift it takes a while... But I've learned to live with that. Most drivers don't have that fine tuned sensibility. Perhaps I'm most drivers... And that's ok...
I wouldn't risk losing the warranty for the " gains " I'm reading about here.
One thing that the GT4 is not it's " sluggish ". Pete,this thread combined with your other one and I'm starting to believe your GT4 is defective...
The only complaint I have is the 2nd gear,that's it. If you want to go to the redline and shift it takes a while... But I've learned to live with that. Most drivers don't have that fine tuned sensibility. Perhaps I'm most drivers... And that's ok...
I wouldn't risk losing the warranty for the " gains " I'm reading about here.
One thing that the GT4 is not it's " sluggish ". Pete,this thread combined with your other one and I'm starting to believe your GT4 is defective...
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#90
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I've driven the GT4 back to back against the Cayman R and 997.1 C2S, all 6-sp manual. On the road, the latter two feel significantly peppier than the GT4, despite having less power and peak torque, whereas the exact opposite should be the case. This can only be explained by the torque curves and how they work with the gearing in each car.