915 or 930 tranny

atr911 · 12-26-2003, 06:59 AM

I'm planning on doing a 3.6 into my 80 targa that I purchased as a roller, no engine OR tranny.

Just wondering if anyone's used a 4 spd 930 tranny to combat the problem of excessive wear on a 915 transmission under high load.

With a 300+ HP 3.6 (cams and all the toys) I really can't see a need for a 1st gear so 4 speeds don't bother me. Also I'd be willing to do a full rebuild and regear if the 930 gears aren't suitable for the 3.6 torque curve.

Any thoughs on this? Are all 930 trannys created equal or have they changed them over the years?

What are some other options for transmissions for 911's and 930's? Ruf or some such made a pretty sweet 930 tranny for the CTR but i'm sure it's silly dollars. Anyone with a 930 in rough shape they need to sell?

Sorry bout all the questions, I'm just very inquisitive this morning!

Adam
a_roseneck@hotmail.com

beepbeep · 12-26-2003, 08:27 AM

Pity you ask now, we had zero-mile 930 transmission a month ago, sold for 1200$.

There are basically two types of 930 transmissions: ones with short bellhousing and others with long one.

Those with short bellhousing (930/30) existed in 930 bade between 75 and 77. Long ones (930/34,36) can be found in 930's from 78 to 88. Apart from bellhousing and cutch, they are all the same. Unfortunately, short-bellhousing ones are pretty rare (they were manufactured during only three years) so they command somewhat higher prices.

Reason for longer bellhousing is that some wiseass at Porsche tought that rubber-damped clutch was just what we need, so whole engine was pushed further back in order to accomodate larger pressure plate.

It ended with center of balance being pushed back even more in already back-heavy car and clutches that were prone to "exploding"...rubber damping pieces usually crack when they get old and jam the clutch. Many were converted to ordinary spring-damped lutches after that.

Why am I telling you this? Beacuse you will need to move rear engine-mounts further back in order to use 930/34 or 930/36 long-bellhousing 930 tranny.

Other than that I think it's very nice transmission that is properly over-dimensioned and can stand up to torque of all N/A engines that Porsche produced, RSR or not.

There are custom ring and pinions to be installed that will make it somewhat less long-legged and very usable at track. Unfortunately, it uses same sort of Porsche synchromesh that 915 uses, so shifts are little balky but it's much much sturdier. G 50 uses Borg & Warner conical synchromesh that is better than Porsche synchromesh.

So you have four alternatives:

1. Short bellhousing 930...more or less plug & play
2. Long bellhousing 930...needs to be cut or engine moved back
3. G50...needs to be cut or rear firewall redone.
4. 915...crunch...whine...crunch...$$$$$$$...crunch

You decide...

beepbeep · 12-26-2003, 08:32 AM

Short bellhousing (with custom billet sidecover):

Long bellhousing (and LSD):

Gearing:

masraum · 12-26-2003, 10:47 AM

While a 300 hp 3.6 will be plenty powerful and the newer motors have a much flatter torque curve, I think it is still worthwhile to have a tranny that keeps the motor more in the middle of it's sweet spot. Seems a beefed 915 or some other 5 spd would be the way to go, but probably none of those are cheap. If the first gear of the small displacement trannies is too low then you could always re-gear.

The Carrera GT is good for 1000 rpm in 6th (something like 20 mph) all the way to over 200, but they still gave it a 6 spd.

atr911 · 12-26-2003, 04:20 PM

I read a really near article about torque that someone posted specifically refering to gearing in cars. Anyone remember or have the site written down?

Just seems the 930 if it can be had at the same price, would be the more logical choice due to the substansial strenght.

Adam

Bothari · 12-26-2003, 04:24 PM

what is the diference in weight? can a long-bellhousing 930 be easily (and reliably) moded to have the same length as the short-bellhousing?

dean · 12-26-2003, 05:18 PM

If you are talking about buying then regearing a 930 tranny. I would think that would cost a bunch. You might as well go with the G50 and have 5 speeds.
The 930 can be shortened like the G50 can.

blue72s · 12-26-2003, 09:33 PM

How much heavier is the 930 4-speed than the 915 5-speed?

atr911 · 12-26-2003, 10:41 PM

Yes, another issue to consider is weight, and i'm sure that the money to buy a distresses 930 tranny and regear it is nowhere near the cost of the G50 conversion. I don't know for sure though, i'm just guestimating.

Adam

beepbeep · 12-27-2003, 12:32 AM

Dryweight of 930 transmission is 53kg.

AES · 12-27-2003, 05:31 AM

Since none of the 3.6 guys are jumping in,

You might want to read this
3.6 gearing

another

and another

There are alot of similar ones, search works great!

Bill Verburg seems to have thought about wheels/tires and gearing a lot, judging by some of his posts

Jack Olsen also regeared his

and of course Wevoid is the acknowledged master