jmartpr

Because you are still keeping the exact same OEM gears...the R&P will just allow the gears to spin faster, all of them. One thing is separate from the other.
You want to close the gap/rpm drop between gears while optimizing the gear ratio.
This will not only help accelerate faster but also keep the car in the optimal power band.
Also, with the gears you can change from 2nd to 5th and leave 6th alone as a highway gear, you can't do that with the R&P.

enduro

This. Especially the 1-2 spacing.

burnergt4

For visual folks like me, here's the DeMan ratios with a 8000 RPM redline:

DR.S

Thanks burnergt4.
The values for the 4.333 CWP at 8000 rpm are:
km/h / mph
71.8 / 44.9
121.7 / 76,1
168.7 / 105.4
209.5 / 130.9
249.9 / 156.2
293.6 / 183.5
so basically the same as in the shown diagram despite a bit shorter 1st and 6th gear.

You may consider the math again jmartpr, if you change the CWP ratio, the split between the gears changes in the same way, since this is a multiplier

Maxhouse97

Can anyone provide further detail on why the smaller CWP is less durable, especially considering the cup CWP seems to be of the same relative size? Would think it’s fairly durable.

Also yes the CWP does not fix the spacing between gears, but the delta in mph is less as all gears are reduced (relative to mph). See beloweMan

MPH:49 / 75 / 103 / 131 / 157

MPH change: (1-2) 26, (2-3) 28, (3-4) 28, (4-5) 26



RPM Technik CWP

MPH: 42 / 71 / 99 / 123 / 146

MPH change: (1-2) 29, (2-3) 28, (3-4) 24, (4-5) 23

I say this as someone who is leaning against changing the CWP.

jmartpr

That just just shows the speed is the same but not the change in revs between gears, which is the main gain with a re-gear.
You can achieve same speeds between the two methods.

DR.S

Speed and revs are connected via linear functions (can be clearly seen in the diagram above) with the same origin (0 revs = 0 speed)...

But anyway, I didn't intend to start (another) debate about regearing vs. CWP change.
I´m just offering a small series of mentioned final drive with 4.333 = 39/9 ratio.
I do not see technical disadvantages compared to the stock 3.889 = 35/9 ratio.
Other offered CWP ratios do not suit my needs, e.g. reaching 200 km/h in 4th gear.

There are failed aftermarket final drives out there, but I don't know the material / machining / hardening process background (here I want to be max transparent from beginning).
What I know is that these failed CWPs had 8 teeth pinions.
Reducing the teeth count normally leads to higher tooth flank pressures which MAY explain failures due to material fatigue...

jmartpr

Not to extend this beyond and derail even further the topic.....what I'm talking about has nothing to do with the R&P.
If the stock car has a drop on 3000 rpm between 2nd and 3rd you can put any R&P you will still get the same drop because this is determined by the gear ratios of 2nd and 3rd not the R&P.
But yes, if a good R&P can be sourced it will be cheaper and you can achieve most of the results you are looking for.

DR.S

Yes but 2nd and 3th gear are changed, what your are talking about is, if just one gear would be changed (e.g. see 1st <-> 2nd change)
But no drama, I made the math for you, so everybody can compare speeds and revs (drops)

GT4 / DRS / Deman
80,0 / 71,8 / 80,0 km/h at 8000rpm in 1st
4720 / 4720 / 5260 rpm after shifting to 2nd (DRS is at 5260 rpm in 2nd at 80 km/h)
3280 / 3280 / 2740 rpm drop

135,6 / 121,7 / 121,6 km/h at 8000rpm in 2nd
5770 / 5770 / 5810 rpm after shifting to 3th
2230 / 2230 / 2190 rpm drop

187,9 / 168,7 / 167,5 km/h at 8000rpm in 3th
6440 / 6440 / 6340 rpm after shifting to 4th
1560 / 1560 / 1660 rpm drop

233,4 / 209,5 / 211,6 km/h at 8000rpm in 4th
6700 / 6700 / 6660 rpm after shifting to 5th
1300 / 1300 / 1340 rpm drop

278,4 / 249,9 / 254,3 km/h at 8000rpm in 5th
6810 / 6810 / 6470 rpm after shifting to 6th
1190 / 1190 / 1530 rpm drop

*rounded to 10 rpm

user1029

I thought about this once since autoquest did have a similar offering of a lowered final drive. It does shorten all the gears but the new small ring and pinion has a higher failure rate.

I spent $5000 USD on shortened Guards gears (buy 3 give one free holiday special) 1-4th with 2nd topping out at 68mph. The gears are still holding strong with my 4.5L conversion. I’d say the prudent thing is to just paid a little more and get the gears done upfront than change the final drive ratio.

another consideration is that changing the final drive will result in 6th gear being shorter too. You have to get a longer 6th gear unless you want to be cruising the highway at 4000 rpms
​​​​​​

DR.S

You should probably say what kind auf final drive you are referring, i.e. pinion and crown combination.
Otherwise it is an apple orange comparison

Speeds, rpm drops etc. are compared above so it's up to everybody himself if this would suit his needs...

Just to be clear:
I´m very happy to hear / read some technical arguments / aspects why a final drive with 9/39 teeth configuration should fail "faster" than the OEM 9/35 one.
As I know, all failed final drives were with 8 teeth pinions.

Alan C.

I’ve used Guard gears in 4 different cars I ran in Club Racing, HSR and NASA. Never an issue. All boxes built by Brian Copan. Do it right and forgot it.

Snowy999

another rennlister put together the attached spreadsheet so people can play with the gear options, there is little in it between 20-125mph between the guards regear and a 39/9.

here for people to play with. my conclusion is that for sprinting and road speeds a cwp is a fine option if not perfect from rev drop/power band 1st and second.

r

ps thx to the anonymous rennlister who built this.

justbob

I agree. Second should be done at around 67 mph and 3rd around 95 and so on.