DR.S

I´m one of the guys who guess the gearing could be a tad lower.
However I guess the known to me offered ratios with 4.5 or 4.62 are too short.
So I finally asked our supplier to calculate a ring and pinion set in 9/39 which leads to a final drive ratio of 4.333.

With this ratio speeds at 7800 rpm are
km/h / mph
70.0 / 43.8
118.7 / 74.2
164.4 / 102.8
204.2 / 127.6
243.6 / 152.3
286.3 / 178.9

If I find four enthusiasts this can come true for 3000,- Euro each with a lead time of 4-5 months.
Happy to hear your thoughts / suggestions.

RoadrunnerGTS

I understand that R&P sets are prone to fail/break vs the more expensive option of changing gearbox ratios.

mrd_spy

74mph in 2nd still a bit high imo

GT4 RS revs to 9k and only does 72mph at 9k in 2nd..

TDT

Yep.. doesn’t seem to be that much of a difference, if you were to rev right out to 8k.

@DR.S who is offering the CW&P?… is it RPM Technik? As I’ve seen they are now shipping parts for their kit out to shops.
Also… does it also require software...as I believe it does else CEL on 718 4.0

DR.S

No, not RPM but I would offer a small series, up to five sets.
Made by a German specialized company, which makes the parts from 18CrNiMo7-6; stress relieved; case hardened; centerings, fittings, contact surfaces, gear profile and teeth grinded; shot peened (hardening process)

I currently don't know if a ratio of 4.333 would need a coding (to avoid CEL)

Examples from them:

NiteCrawlr

These top speeds in each gear are very close to the DeMan ratios which I have. I can tell you the driving experience is much more enjoyable and it doesn't have much to do with the top speed in each gear. The added engagement from shifting earlier and more frequently, having the RPM drops between gears much closer, and no longer having to use 1st gear as a working gear because second is short enough is what makes it worthwhile. I am shifting more often but not excessively on the street and seem to always be in the right part of the power band even after shifting which makes it more fun during spirited drives or on track.

While this solution is by far more cost effective than a total regear, I would be worried about the R&P reliability and lack of units already out in circulation. DeMan has excellent customer service and reliability. If you are willing to spend more I would highly recommend their product.

DR.S

Thanks for your input regarding the usability of similar gear ratios

The failed pinions I have seen had 8 teeth, so one less than stock.
This normally leads to higher pressures on the teeth flanks due to lower intervention between ring and pinion (is this correctly described in English?).
Could this be reasons for failures?
Or failures in material / machining / hardening process?
I don't know how transparent other suppliers are regarding this topics.

RoadrunnerGTS

I asked 2 specialist Porsche independent workshops. Both said that CWP sets had not proven a successful method on 911's and they wouldn't recommend that as a way to change ratios.

Unfortunately, I have found that the aftermarket companies making these various gear sets are a bit secretive as to the quality of the materials used.

There's a reason why DeMan & Sharkwerks don't just change the CWP set and rather do the gear set. RPM Technik does CWP, but offer little comfort as to warranty and quality of that CWP set. IIRC, they told me they ha da GT4 with 5000 miles on their CWP. CWP requires ECU update.

The way I see it is that their is only one correct way to do it, and that's via new gearsets 2nd to 6th. The CWP is the cheaper method and there the saying "buy cheap, buy twice".

My 2c is that the long gearing is not really an issue.

Maxhouse97

Interesting first I heard of ECU update for modified CWP. Would be interested to hear what others think about this. Also what other downsides are there with changing the CWP, ones I have heard:

- Difficult to install, set lash
- Need to change 6th gear as stock is already somewhat short
- Due to the above, you have to break into two separate modules (trans and diff) as opposed to just trans (warranty purposes)

Downsides to regear:

- Gear noise/whine
- More expensive

DR.S

From technical (i.e. objective) POV I do not see any argument why CWP should / must fail (every car has one and do these fail?).
Here specifically regarding a 9/35 to 9/39 change.

It would not be the first time that, due to other perspectives, a solution would be possible, although this has been ruled out by some before.

If someone has some detailed / comprehensive information or stumbling blocks to share, please enlighten us

mrd_spy

regarding the 911 comment above, the 997.2 3.8 RS has a CWP change oem and seems ok and a lot of people fit the CUP final drive on 997's

mrd_spy

if you are Germany based have you looked into this company ?
Porsche 982 Cayman Archives – KMP Drivetrain Solutions

jmartpr

One more thing to keep in mind...While the R&P is way more economical and maybe easier to do it doesn't address one issue that the 2-6 gear sets does, the gap/spacing between gears (RPM drop).

DR.S

Thanks mrd_spy, I have seen this but the ratios are not what I want.

I have not checked this, but NiteCrawlr mentioned the ratios with a 4.333 CWP would be similar to Deman gear set.
So why / how should there be different spacings between the gears, jmartpr?

RoadrunnerGTS

Ideally you want to close the drop in revs between 2nd & 3rd. CWP won't change that delta. Other big issue is the drop in top speed and higher 6th gear cruising revs.