8:32 lower final drive

Has anyone in the UK done it and does it work well on the road? It seems to be significantly cheaper that cracking the gearbox and changing individual ratios but changing the final drive alone potentially makes 1st and 6th become less than optimum.

No answer but I've wondered this too. Not going to improve motorway fuel economy but I don't spend a lot of time on the motorway in mine. Time to pop a LSD in at the same time?

Not myself, and probably wouldn’t unless I was building a track focussed car. Not a 996, but a friend of mine had a lower FD installed on his 981GT4, and within a year had it swapped back, annoyed he wasted money and didn’t have it re-geared (or whatever the correct phrase is). 1st gear wasn’t so much the problem. Given the quality of your project, why not have the gearbox opened and tailored to what you really want/need?

We’ve talked about opening the gearbox and it’s possible but if I remember correctly he said no one has ever asked on a 996, which leads me to think it might not be needed and to try it first. Porsche themselves have lowered ratios on the new 992 plus they did it on some RS and the ST, so I need to compare ratios really but I’m busy (and lazy) so I thought I’d ask here to try and save myself the work. Someone did it on a new Spyder and said it was brilliant but I can’t find the thread now.

Have you much seat time in a 996? I find that the gearing works really well in the 3.4, even with its relatively narrow power band and sub-300 bhp. The spread is good and all six ratios are usable. Add another litre of displacement and I don’t think you’ll feel that it’s too leggy. Do the 3.4 and 3.6 have the same ratios? Our five speed 2.7 Boxster on the other hand… is a lovely car but feels so slow when you’re between two ratios. I’d put a six speed and a short diff in that in a heartbeat.

The gearing on the 930, 996 and 997 is too tall. Basically all three 911s feel a bit flat under 3k revs and by the time you’re up at about 5,000 you’re into license busting speeds. I’d rather have more torque at lower revs to make it interesting, which means engine work or lower ratios to effectively do the same.

Agreed, I’d trade some top end for a bit more shove at lower speeds. Easy fix on a motorbike and usually well worth it. Smaller wheels?

My experience of changing the diff ratios is with Triumph TR5/6. Cars exported to the USA had a higher final drive so had terrific acceleration even with the de tuned export engines (emissions) and the UK cars had the lower ratio plus slightly more power so the acceleration was on par but the top speed was better and when cruising the revs were lower thus more economical ( an oxymoron when describing Triump fuel economy). So I can understand changing a low to a high to improve acceleration, but not high to low unless the engine was revving it's thingies off at 70 mph. It might be cheaper to buy a 997?

4:1 ratio is a quite a difference from the factory 3.44, 5th is ~1:1 if I recall correctly. I think 6th is 0.84, so roughly speaking at 3k rpm it would be around 75mph with the factory final drive and 65mph with a 4:1. I'd not be that worried about 1st and 2nd and would have thought this would possibly be a good way to go to save some cash if you want short gears. To answer the q on 3.4 and 3.6 gear ratios, they're the same, 997 a smidge shorter iirc. 996tt/gt2 much longer, gt3 similar but a smidge longer I believe. I think basically for an m96 (or basically any other NA Carrera engine), under 3k rpm just isn't where it's at and it's always going to be a bit flat (esp compared to modern turbo cars!) - even if you bump the capacity you're not going to change that much. Really if that's the aim you want something more like a 991.2 engine for that which can do something like nearly 400ft/lbs from 1700rpm. But it is a fun engine and has quite a lot of character with loads of midrange. I think the 3.4 engine is quite fun needing a bit more encouragement too, even if it's a way off in outright performance. Going a little bit off topic, the 996.2 carrera is already a fair bit more usable at lower revs than either the 3.4 or the gt3 - the 3.6 with variocam+ makes a bunch more torque from lower revs than the 3.4 while still having much bigger valve size/better flowing head. Mine has a massive shove of torque at just under 3k rpm (it has a bit of a bump like the 3.8 below) and holds its power right up to the red-line - it's had a lot of top end and inlet work to make it do that - the midrange makes it really good fun to drive and the engine is eager to be used a bit without needing to really wring it out.. Porsche 3.4 and 3.6 power and torque curves below: 996 gt3 and 997 carrera s

I'd love a lower final drive but i don't see how it's possible without splitting the gearbox (apart from smaller wheels!) What is the process here?

Which gearbox are you using?

I was going to post the same, to change the final drive ratio normally involves changing both the crown wheel and pinion, and the pinion is the end part of a shaft that goes inside the gearbox and has all the cogs on. Can't see how not going inside the box is possible but would love to be proved wrong!!

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Completely agree with this. There are some Porsches that do have painfully long gears in my experience, but I’ve never once thought the 996 was one of them. Half the joy is working these engines.

I agree about the joy of working the engine. I learned most of everything I know in this regard from racing small two stroke motorcycles and the caveman version is that if you down gear them then you’ll get better acceleration whilst going forward slower than you would otherwise have been going with the old ratio. So at somewhere like Three Sisters I’d be using all my revs but going slower than I would be at Snetterton using all my revs. I preferred the smaller tracks because I’m into acceleration and bends, rather than outright speed. Same in my cars, I’d rather be topping out in 3rd at 75mph and having to engage another gear, than be doing 110mph and doing the same. The maths isn’t terribly complicated but it’s less interesting than explaining it like that.

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Not so much recently, like the last few years, so perhaps my memory is playing tricks. I remember them as being very sharp, handle brilliant, but less than thrilling in acceleration and too tall gear ratios to use anything above 3rd at the top of the rev range unless you’re on a track or looking to lose your license. Perhaps I should just use it for a bit before deciding on doing anything with the gearbox. My 997 is the same, in fact so is the 930, as soon as I’m making noises high up in 3rd I’m looking out for speed cameras. I’d rather they were all doing what they do but at slower speeds.