mousecatcher

Nice guesswork, but rather than a guess, use a spreadsheet! It's not just gearing, it's the combination of available power and gearing (gearbox + rear). I added the gear ratios and final drive for a 991.2 GTS PDK to my spreadsheet and generated these charts:




Wow. So 2nd gear in the GTS is a little closer to 1st, but overall all the gears are taller and the spread is wider as well. Using the GT4 power, you don't even make it out of 5th! I didn't even graph 7th as the sheet is only configured to go up to 6th, but no worry since we didn't even get there. You're saying you liked the gearing better, but it turns out what mattered here most was the power.

For a real comparison you'd need to add the power curve for the 991.2, but that's more work than I care to take on myself.

I suspect you would be pretty happy with a different final drive in the gt4, gearing-wise. It would "feel" more like the 991.2 as far as shifting.

stout

Kibort would like these charts, and they do have their value—for performance/track work. If that's the measure that matters to you most, that's cool. It matters to me, too—but in a street car/fun car, seat of the pants observation (not guesswork) and fun factor matter more, at least for me. Not winning any races on the street...or DEs, for that matter. It's about pleasure in use. And my observation is that the gearing and powertrain in general of the base 991.2 Carrera MT along a back road shred my old GT4 both in terms of fun and performance. YMMV, and that's okay.

For me, it's about winding an engine out. The pleasure of it. So in-gear mph at redline is a big part of it. Now, part of the other part of it in my case may be the crappy flat spot from 3500 to 5500 rpm in my GT4 on CA 91 fuel...which was far more annoying to me than the minimal turbo lag/throttle response delay in the 991.2 Carrera. GT4 felt flat-footed in that "trough," then came on hard again at 5500 rpm. Not so pleasurable. Probably not great for performance (or driver confidence, which has a big effect on performance), either. At Thunderhill at high rpm much of the time, this wasn't much of an issue.

So now who's guessing?

I'd be miserable, actually. I think you're right when it comes to the lower gears, let's say 2-4 (and 1 and 5 also), but one of my biggest beefs in living with the GT4 was how many revs it turned in sixth on long freeway cruises. I can see where that cog is needed/useful for top speed on the autobahn, but it's useless for our road courses and pretty awful for our freeway drives.

I can see where I might like a shorter final drive in a track-dedicated GT4—but most people I know with GT4s who track them usually have to drive them a couple of hours (or more) to and from the track. So a shorter final drive exacerbates the freeway cruising issue...more revs = more fuel for no good reason, more wear & tear on all engine parts, and more subtle stress on long drives. It's actually really hard to overstate how nice the gearbox in the 991.2 Carrera is. Not quite as nice a shifter as the GT4, but the ratios feel better chosen 1-6 and 7th is such an ahhhhhhh on long trips. In all but the shift action, it's a vastly superior contraption in use. That said, I could easily sacrifice 6th gear—and would if there was some way to import the philosophy of 1-5 and 7 from the 991 into the 981 GT4 gearbox. For use here in the U.S., anyway.

I know this will be the contrarian position in this thread—it is a forum, after all—but I view installing a shorter final drive in the 981 GT4 as a band-aid fix for a street car...one that may leave some customers very unhappy in the long run. Yes, the upside is it preserves the gear splits and improves effective torque where we all want it (out of turns), and fine if it fits someone's use/needs and they don't care about turning 3700-4000 rpm on long freeway drives. But my worry is that some will make this switch and regret it once they have to live with it.

Now, if I was trailering a GT4 to and from the track and looking for performance, I think you are precisely right...if the track(s) I favored worked well with the shorter final drive. But if I was trailering a GT4 to and from the track, it would have a six-speed PDK gearbox.



pete

mousecatcher

Thank you for the observation!

You are right, the main value is for the track. There's little interpretation required.

For street use, however there is still some value. Reduce the redline and pay attention to the speed range per gear bar chart. That will give you a sense of the gearbox action.

said observation can be reduced to a chart and analyzed. would you trust someone's observation for a power upgrade, over a dyno graph? some things are very very difficult to quantify in a meaningful way, like exhaust tone. some things, like power over a given speed range, are easy to quantify.

Is that response directed at me, or as a general observation?

If directed at me, yup, can't agree more. It's not something that can be disagreed with as its your personal observation, and nothing I presented here challenges that. Since I didn't do the power graph for a 991.2, the difference in gear ratio don't reflect the reality, as I made clear. The point I was making is that it's not just gears. I demonstrated that if you just plopped the 991.2 gears into the GT4, it would be worse, not better.

I'm not sure what I'll do yet personally, but the long highway drive aspect isn't a factor for me. Even with a 3.x hr drive to thunderhill, it's such a small fractional use of the car that it's not a consideration. I'm more worried if the LWBs will be comfortable for such a long stretch!

If the freeway cruise is an important factor, then you are right, a shorter diff ratio is a terrible bandaid. Myself, I use the GT4 purely for recreational/pleasure drive and would just suck it up for the rare long cruise.

stout

^ All good, mousecatcher, and wasn't "after you" per se—just offering a different point of view, and one that might prevent someone from ending up with a GT4 they hate living with on long freeway hauls. If that's a non-issue for you, then your position makes sense to me, and I might even share it. My GT4 had to do everything, so long freeway runs were part of its use. And, even with the stock gears, I found sixth far too short with real consequences (noise, fuel consumption, and to a lesser extent wear/tear).

So making sixth even shorter shorter would be a nonstarter for me. But it sounds like we are in agreement on this point. Actually agree with all your points except exactly what can be charted and is inevitable: what a shorter effective final drive will do to (already high) revs at freeway speeds in sixth gear. That's it. As for just adding 991.2 gears to a 981 6MT, that's not what I meant. I'd be intrigued by those effective ratios...is all. What's in the GT4 isn't great, else we wouldn't be here. Actually, the shorter effective final drive would be great for me (and, I suspect) a lot of customers out there if it could somehow be partnered with a taller sixth.

Cheers,

pete

GTgears

mousecatcher

For street use, agreed. I reckon Porsche's thinking was that they had to chase nurburging numbers for the car to be the success they were hoping for. To their credit, they seem to have nailed it.

Alan C.

Tried a ring and pinion only once on a dual purpose car. After a Cincinnati/Road Atlanta round trip the R&P came out and I went with a set of short gears.

mousecatcher

Just as a thought exercise, how about a R&P to shorten all the gears, then a tall 6th to make up the difference.

In practice, this would be just as expensive as swapping gears only.

Alan C.

I'd still worry about the strength/longevity of the short R&P in a GT4.

stout

If so, then fixing the actual gears is the way to go for the reason Alan C. noted.

Still think the "money" setup would be effectively similar gearing to 991.2 S/GTS/T transmission's 1st through 5th gear + 7th. Add that along with exhaust + tune and I suspect the GT4 would really wake up.

mousecatcher

Well sure, I mean after you do all that you'd have a mid-engined 991.2! :P

GTgears

I believe the product exists from the company who is selling the ring and pinions. I have no idea who is supplying their 6th gears, but they claim it is available on their website. It's not something we will ever produce.

Be sure to buy a fixed 3rd gear while you are at it. 3rd gear should be part of every ring and pinion job a GT4 owner does and factored into the cost if comparing gears versus CWP costs.