If you had to...

[turn9]

Rebuild the transmission on your 3.3 1979 930 would you keep the factory gearing or would you take advantage of the opportunity and do something "special" with it ?

Please discuss and "learn" me.

t9

[TroyN]

I personally don't like the ratios in 2nd and 3rd. 2nd is way too tall and the gap between 2nd and 3rd is too big. That or maybe a shorter ring and pinion. Do you like the stock ratios?

[bolt]

I did the ring and pinion..if I had to do it over again I would shorten 1,2,3 and keep 4th stock. Do you plan to autocross or track your car?

[cole930]

I have an 80 ROW 930 with most of the usual mods. I street drive only, by that I mean no track time. Originally red line 3rd gear topped out at about 140-145 and unless your on the track or insane 4th gear was pretty useless. I changed to an 8:37 R&P and short gears and it is the single most amazing mod I ever did. It
completely transformed the car.

Cole

[pkracer21j]

short gears...top speed is down to about 165-170, but man it gets there F***in quick. and that speed is movin on public roads.

[TroyN]

Cole, you also shortened your gears? What sizes did you end up going with?

[Jim2]

I pulled down 2,3,4 but I found I went a little to low on 4th. Like cole says it's a really good mod though it's costly for parts.

Funny, a guy I know asked me to come have a look at a damaged 930 he bought for a song. Been a couple months but I just got there today. The car has a ruf 5 speed in it! Lucky bum.

My ratios:
1st 2.25:1 (16/36) standard
2nd 1.444:1 (18/26)
3rd 1.04:1 (26:27)
4th 0.767:1 (30:23)

[billjam]

Absolutely do it!
If you have the opportunity, $$ and some mechanical aptitude (or additional $$ to pay someone else) ... DO IT.
As Cole noted, it transforms the car.

I opted to keep 1st as is, but go for the same ratios as 2nd, 3rd and 4th that are used in the G50 5 speed box rather than change the diff ratio because I can do the gear swaps, whereas I'd have to pay someone else to setup the diff.

The performance improvement is really incredible, especially in 3rd and 4th.
Long freeway runs are a bit of a pain with my lower top gear, but that is a small price to pay. If I was going to do this again, I would go for a slightly higher top gear just to improve highway comfort level and fuel economy.

My car pulls really strongly all the way to redline in 4th with this gearing. I backed out at 6500 rpm last week which was right on 250kph on my GPS.

My gearing is ...
1st 2.25:1 (16/36) standard
2nd 1.53:1 (17/26)
3rd 1.04:1 (26:27)
4th 0.79:1 (29:23)

I bought my gears from Albins (in Australia) for about $US700 per set, but I am sure you can also get them in US.

[turn9]

Originally Posted by billjam

Absolutely do it!
If you have the opportunity, $$ and some mechanical aptitude (or additional $$ to pay someone else) ... DO IT.
As Cole noted, it transforms the car.

I opted to keep 1st as is, but go for the same ratios as 2nd, 3rd and 4th that are used in the G50 5 speed box rather than change the diff ratio because I can do the gear swaps, whereas I'd have to pay someone else to setup the diff.

The performance improvement is really incredible, especially in 3rd and 4th.
Long freeway runs are a bit of a pain with my lower top gear, but that is a small price to pay. If I was going to do this again, I would go for a slightly higher top gear just to improve highway comfort level and fuel economy.

My car pulls really strongly all the way to redline in 4th with this gearing. I backed out at 6500 rpm last week which was right on 250kph on my GPS.

My gearing is ...
1st 2.25:1 (16/36) standard
2nd 1.53:1 (17/26)
3rd 1.04:1 (26:27)
4th 0.79:1 (29:23)

I bought my gears from Albins (in Australia) for about $US700 per set, but I am sure you can also get them in US.

ROTFL !!

Billjam, man ...you gave me the best laugh of the day !!

" Thank yous" to all the respondents. To clarify, this is a street car. No DE or track events foreseen. The main issue is to optimize driving pleasure under normal driving.In other words, compensate for turbo lag ( I'm getting a new turbo as well, G35) so that I don't grow a beard waiting for the turbo to kick in...

Keep the suggestions coming. TIA.

t9

[turn9]

Originally Posted by Jim2

I pulled down 2,3,4 but I found I went a little to low on 4th. Like cole says it's a really good mod though it's costly for parts.

Funny, a guy I know asked me to come have a look at a damaged 930 he bought for a song. Been a couple months but I just got there today. The car has a ruf 5 speed in it! Lucky bum.

My ratios:
1st 2.25:1 (16/36) standard
2nd 1.444:1 (18/26)
3rd 1.04:1 (26:27)
4th 0.767:1 (30:23)

Jim2,

Your 1st and 3rd gears are the same as billjam's. 2nd and 4th are slightly different. Knowing this, what are the advantages/disadvantages of one over the other in terms of on the road performance/driveability?

t9

[DDDD]

Never go back to stock gearing IMO.

I have the Andial ring and pinion and I am pretty convinced that it is as close to ideal as you can get from a pure acceleration point of view. Andial did their homework.

My first gear hits about 45 at redline, 2nd gear about 80, 3rd about 115, 4th about 156 mph.

Things I would tweak, a slightly taller first would make that gear much more flexible, say 52 mph. You would still get a great hole shot. 2nd gear I would take to 84 mph, because I can fry the hide off the tires in second gear above 45 mph. 3rd is devestating and perfect. 4th I would just put at whatever top speed you want, maybe 165 mph? 156 mph is rather buzzy at highway speeds but pulls like a freight train, you could go a little taller.

[Jim2]

turn9, the slight differences between my ratios and Billjam's would hardly be noticable when driving. Not all these ratios are available from all suppliers since they are old 935 and 962 parts, though lots of production now comes from the company down under mentioned by billjam.

First Gears
14:39 2.79 DZ
15:38 2.53 EC
16:36 2.25 FA stock 1st
17:34 2.00 GY
18:33 1.83 HX
19:33 1.74 IX
20:33 1.65 KX
20:32 1.60 KW
18:27 1.50 HR
18:26 1.44 HQ

Second Gears
14:27 1.93 DR
19:34 1.79 IY
19:33 1.74 IX
20:34 1.70 KY
20:33 1.65 KX
20:32 1.60 KW
17:26 1.53 GQ
18:26 1.44 HQ
18:25 1.39 HP
23:31 1.35 NV
23:30 1.30 NU stock 2nd
24:30 1.25 OU
24:29 1.21 OT
26:30 1.15 QU
25:28 1.12 PS
26:28 1.08 QS
26:27 1.04 QR
26:26 1.00 QQ
27:26 0.96 RQ

Third/Fourth Gears
21:29 1.38 LT
21:28 1.33 LS
23:30 1.30 NU
18:23 1.28 HN
24:30 1.25 OU
18:22 1.22 HM
24:29 1.21 OT
25:29 1.16 PT
26:30 1.15 QU
20:23 1.15 KN
25:28 1.12 PS
26:28 1.08 QS
26:27 1.04 QR
26:26 1.00 QQ
27:26 0.96 RQ
28:26 0.93 SQ
28:25 0.89 SP stock 3rd
29:25 0.86 TP
29:24 0.83 TO
29:23 0.79 TN
30:23 0.77 UN
30:22 0.73 UM
31:22 0.71 VM
32:22 0.69 WM
33:22 0.67 XM
32:21 0.66 WL stock 4th
31:20 0.65 VK
32:20 0.63 WK
33:20 0.61 XK
39:20 0.51 ZK

Final Drive Gears
9:38 4.22 stock
8:37 4.63
8:39 4.89
8:41 5.13

[911st]

Many build there motors around making big HP. -- Another approach is to build the motor around the transmission.

I am a big believer in gears.

The rear wheel diameter is of importance. A 930 running 24.5" 245's compared to a 25.7" 275 or 315's are going to respond diffenently to a given gear set.

HP dyno plot and how a given build is making power should also be taken into account when designing a gear set.

A motor built around a K27-7200 with SC cams compared to a build that is say around a K29 or HF style turbo maybe with a higher RPM cam may benefit from different gear set ups.

If a street build I would first look at what speed one likes to cruse at and make a choice of of fourth hear based on what RPM you can live with. Then look at what top speed will be and if that is ok.

Then look at first and where and how you want boost to come in and how far you want it to take you before a shift point. Ones boost/hp curve might be a factor here to.

Second is important as we do not want boost or TQ to drop as much as stock so our average HP is significantly higher. This can make a big difference in acceleration. What RPM/HP drop do we want or can live with when going to second.

Third might continue with looking at what the HP will be at the shift point. Also it is worth noting what RPM/HP we would come in at if we have to make a down shift at cruse to accelerate, whether it may be down to 2nd or to 3rd.

Fourth having been set out of the gate for proper cruse might have a larger gap than stock but should still come in at a point where we are making good HP.

A track build is totally different.

It would be worth contacting a gear suppler and get there input based on your dyno curves, wheel size, and use - for there input and advice. They can often value engineer around what is actually available or even used gear sets that might be available.

[turn9]

Jim2

That is great info, thanks.

DDDD

Never go back to stock gearing IMO.

I have the Andial ring and pinion and I am pretty convinced that it is as close to ideal as you can get from a pure acceleration point of view. Andial did their homework.

<
Things I would tweak, a slightly taller first would make that gear much more flexible, say 52 mph. You would still get a great hole shot. 2nd gear I would take to 84 mph, because I can fry the hide off the tires in second gear above 45 mph. 3rd is devestating and perfect. 4th I would just put at whatever top speed you want, maybe 165 mph? 156 mph is rather buzzy at highway speeds but pulls like a freight train, you could go a little taller >>

What are your final ratios?

Man, I love this forum, so much to learn, so little time...

[bolt]

All great advice above!

If you use your car as daily driver (as I used to but no longer do) I really enjoyed the RP upgrade (sourced from F1 gear maker from UK). Great for stop light to stop light, AX and track. The only downside was freeway driving in the shorter 4th gear...higher rpms--lower my hwy mpg from 20 to 15. Fuel head mod took it down much further-another story.

If considering the upgrade note some mfrs RP's made lots of gear noise/whine. Not sure which current manufacturer makes ones louder than others. Its been awhile, I upgraded in '92 but do lots of research first.

[turn9]

Originally Posted by 911st

Many build there motors around making big HP. -- Another approach is to build the motor around the transmission.

I am a big believer in gears.

The rear wheel diameter is of importance. A 930 running 24.5" 245's compared to a 25.7" 275 or 315's are going to respond diffenently to a given gear set.

HP dyno plot and how a given build is making power should also be taken into account when designing a gear set.

A motor built around a K27-7200 with SC cams compared to a build that is say around a K29 or HF style turbo maybe with a higher RPM cam may benefit from different gear set ups.

If a street build I would first look at what speed one likes to cruse at and make a choice of of fourth hear based on what RPM you can live with. Then look at what top speed will be and if that is ok.

Then look at first and where and how you want boost to come in and how far you want it to take you before a shift point. Ones boost/hp curve might be a factor here to.

Second is important as we do not want boost or TQ to drop as much as stock so our average HP is significantly higher. This can make a big difference in acceleration. What RPM/HP drop do we want or can live with when going to second.

Third might continue with looking at what the HP will be at the shift point. Also it is worth noting what RPM/HP we would come in at if we have to make a down shift at cruse to accelerate, whether it may be down to 2nd or to 3rd.

Fourth having been set out of the gate for proper cruse might have a larger gap than stock but should still come in at a point where we are making good HP.

A track build is totally different.

It would be worth contacting a gear suppler and get there input based on your dyno curves, wheel size, and use - for there input and advice. They can often value engineer around what is actually available or even used gear sets that might be available.

911st,

Very well put,thanks. I was forgetting to factor in tire sizes. I'll probably stick with the 245s. The motor will have SC cams and a Garret35 turbo.

Any suggestions? (I won't hold you responsible )

t9

[911st]

I used to play with calculating gears do not have the skill anymore nor know the gears.

As noted above, somtimes just changing out the R&P can make one happy.

There are gear calculator's out there you can probably down load. Also the suppliers are very happy to make a professional proposal or chart gears based on your info.

Maybe someone here...

[DDDD]

Originally Posted by turn9

[B]Jim2

That is great info, thanks.

DDDD

Never go back to stock gearing IMO.

I have the Andial ring and pinion and I am pretty convinced that it is as close to ideal as you can get from a pure acceleration point of view. Andial did their homework.

<
Things I would tweak, a slightly taller first would make that gear much more flexible, say 52 mph. You would still get a great hole shot. 2nd gear I would take to 84 mph, because I can fry the hide off the tires in second gear above 45 mph. 3rd is devestating and perfect. 4th I would just put at whatever top speed you want, maybe 165 mph? 156 mph is rather buzzy at highway speeds but pulls like a freight train, you could go a little taller >>

What are your final ratios?

Man, I love this forum, so much to learn, so little time...

Andial uses stock ratios but changes the ring and pinion from stock which is 9.38 down to 8.41.

You can just keep your ring and pinion and go to custom gears to get the most custom tailored set up. I think 52 mph, 84 mph, 115 mph and 162 or 165 mph is about perfect.

[DDDD]

Originally Posted by bolt

All great advice above!

If you use your car as daily driver (as I used to but no longer do) I really enjoyed the RP upgrade (sourced from F1 gear maker from UK). Great for stop light to stop light, AX and track. The only downside was freeway driving in the shorter 4th gear...higher rpms--lower my hwy mpg from 20 to 15. Fuel head mod took it down much further-another story.

If considering the upgrade note some mfrs RP's made lots of gear noise/whine. Not sure which current manufacturer makes ones louder than others. Its been awhile, I upgraded in '92 but do lots of research first.

yeah 4th gear will normally whine a bit on a shortened ring and pinion.

You have the most options by keeping a stock ring and pinion and just going with custom gears.

Swapping to the lower ring and pinion is kind of a quick but imprecise way to do it.

[cole930]

Just a personal note here:

I drove a friends 930 with a 8:41 R&P and no gear changes and while acceleration was fantastic there were things I did not care for. An 8:41 R&P is an 18% lower gear ratio across the board. First gear would melt tires and never move if you tried a hole shot and you had to shift to 2nd. very quickly in normal driving as it gets you moving and not much more. 2nd. and 3rd.
were pretty good but street driving made it a little tricky to keep it from boosting if you accelerated at all aggressively. I did not like 4th at all, primarily because of whine. If the R&P is not set up precisely it's a piercing never ending whine and on a road trip it will make you crazy.

I installed a 8:37 R&P which is a 9% difference from stock and then went with a HQ 2nd and a QQ 3rd and chose to leave 1st. and 4th stock. I find this combination quite nice. First get a little kiss from the R&P 9% and 4th doesn't
suffer too much on the big end. 2nd. and 3rd will pull your face off.

Cole