No longer impossible! 996/997 transmission onto air cooled engines!

[TopTuning]

Working on the tunnel cover tonight! 3d scanner is priceless for this job.

Rear seat delete / luggage dump nearly complete.

Using 997 center console with self adjusting ebrake etc. It's a nice fit!

[winders]

Ho much of the torsion car tube do you have to cut and how are you reinforcing both sides if you have to cut a section out? Photos?

[JonT]

does anyone know of a shop that I can drop my car off for this swap?

[chrisbalich]

Originally Posted by winders

Ho much of the torsion car tube do you have to cut and how are you reinforcing both sides if you have to cut a section out? Photos?

Originally Posted by TopTuning

Looks like the entire TB tube between the banana arm mounts is removed.
I don't see any reinforcements...at least not in this picture.
And that will be a lot of work to seal up for a street car. *Even though I exclusively associate winders with racing.

I'd also like to see some more pictures of the 'finished' chassis/tub modifications.
I'm also worried about what this would do to the tub's rigidity wihout a full cage.

[TopTuning]

Originally Posted by chrisbalich

Looks like the entire TB tube between the banana arm mounts is removed.
I don't see any reinforcements...at least not in this picture.
And that will be a lot of work to seal up for a street car. *Even though I exclusively associate winders with racing.

I'd also like to see some more pictures of the 'finished' chassis/tub modifications.
I'm also worried about what this would do to the tub's rigidity wihout a full cage.

You are correct, the tube must be completely removed in that section! This is similar to how all of Porsches period race cars were modified like the 935s.

The control arm inner mount side of the bracket was removed and a new thicker piece of steel welded on in its place. The new parts are boxed onto the cut tube and to the opening cut into the sheet metal between the rear seat hump.

The lower control arm "banana arm" forward mount does significantly less work on a car with coilovers, so I'm not too concerned. I've considered making a hoop of cage tubing over the top of the control arm mounts but it's probably overkill.

As a bit of a test I supported the weight of the car on the control arm bracket after welding and measured zero deflection.

My car does have a rear bolt in cage and all, but seems to drive great, if anything feeling more ridged than before.

If you look at the 964 models and some of the race cars in detail, you can also see that mounting point or it's equivalent is pretty basic, it's now just where the arm swings from vs heavy load control.

[winders]

Originally Posted by TopTuning

The lower control arm "banana arm" forward mount does significantly less work on a car with coilovers, so I'm not too concerned. I've considered making a hoop of cage tubing over the top of the control arm mounts but it's probably overkill.

I don’t see how changing from torsion bars to coil overs does anything to reduce the loads placed on the trailing arm inner pickup points. The fore/aft loads during braking and acceleration are significant and must be resisted.

Please show some photos of what you are doing to lock the torsion bar tubes (now there are two) down….

[safe]

Originally Posted by winders

I don’t see how changing from torsion bars to coil overs does anything to reduce the loads placed on the trailing arm inner pickup points. The fore/aft loads during braking and acceleration are significant and must be resisted.

Please show some photos of what you are doing to lock the torsion bar tubes (now there are two) down….

Agree, the loads on the inner mount is significant and does not change much with coilovers, if anything more load is put on it without torsion bars.
If you completely cut the torsion tube it needs proper reinforcement but it's surrounded by flimsy sheet metal only.
If you look back at the 73RS the torsiontube was reinforced by brackets tying into the center tunnel.

[chrisbalich]

I agree with Scott & Magnus.
Switching to coilovers doesn't diminsh the loads through the banana arms. Much of your thrust, engine braking, and rear braking forces run through those mounts. The spring plate takes some of those forces, but not all.

[winders]

Originally Posted by TopTuning

I've considered making a hoop of cage tubing over the top of the control arm mounts but it's probably overkill.

A hoop from one mount to other really doesn't do anything. First, a hoop, by itself, is not strong. Second, the forces acting on the mounts are most often in the same direction. So it won't actually do anything.

[TopTuning]

I'll be pulling the drivetrain backout to install a wavetrac in the 996 box. I'll get some more pictures for you guys off all the reinforcement work done at that time.

Overall it's working great! Really enjoying the car.

Here's a closer to finished rear seat delete and tunnel adapter.

I can not believe how much quieter the car is with all this! Also, The cheap 6x9s mounted in the vertical panel sound amazing now. Removed speakers from package tray that weren't really helping much honestly.

[pep fab]

Originally Posted by TopTuning

Pretty much!

I'm using a complete tilton pedal set with dual brake masters

what diameter master are you using?

[djb25]

This is extremely interesting and exciting, but I really am not in love with the massive tunnel cover.

It looks like the cover was made to match up with the 997 center console. If someone were to make their own replacement cover, could it be smaller?

[3rd_gear_Ted]

Originally Posted by TopTuning

I'll be pulling the drivetrain backout to install a wavetrac in the 996 box. I'll get some more pictures for you guys off all the reinforcement work done at that time.

Overall it's working great! Really enjoying the car.

Here's a closer to finished rear seat delete and tunnel adapter.

I can not believe how much quieter the car is with all this! Also, The cheap 6x9s mounted in the vertical panel sound amazing now. Removed speakers from package tray that weren't really helping much honestly.

Wavetrac is an interesting choice.
Where is my popcorn?
BTW mine is 12 yrs old, all track use against short gears.

[eastbay]

Originally Posted by TopTuning

I'll be pulling the drivetrain backout to install a wavetrac in the 996 box. I'll get some more pictures for you guys off all the reinforcement work done at that time.

Overall it's working great! Really enjoying the car.

Here's a closer to finished rear seat delete and tunnel adapter.

I can not believe how much quieter the car is with all this! Also, The cheap 6x9s mounted in the vertical panel sound amazing now. Removed speakers from package tray that weren't really helping much honestly.

Looks great!

[TopTuning]

Originally Posted by djb25

This is extremely interesting and exciting, but I really am not in love with the massive tunnel cover.

It looks like the cover was made to match up with the 997 center console. If someone were to make their own replacement cover, could it be smaller?

Yeah it's larger than needed. A 964 / 993 style center seat hump would probably fit fine with the transmission. This was my first plan, but I couldn't find the sheet metal new or used....

Also, the rear seats are completely useless, especially with the roll bar etc.

The 997 center console is a great fit for the car, but I completely understand why someone would want to keep it more original looking. You will have to do something with the cables as they need to run over the top of the center tunnel.

[TopTuning]

Originally Posted by chrisbalich

I agree with Scott & Magnus.
Switching to coilovers doesn't diminsh the loads through the banana arms. Much of your thrust, engine braking, and rear braking forces run through those mounts. The spring plate takes some of those forces, but not all.

I mean to say the forces on the tube it self are much less without the torsion bars. All the system does now is locate the control arm pivot point.

With the design of the early 911 rear suspension, the loads for braking and acceleration are mostly held by the spring plate mount. I am using the Elephant racing ASP rear suspension and have of course used the reinforcement weld on plates.

Basic math will tell you that the inner LCA mount takes about 20-30% of load inline with vehicle. This is not a small amount so reinforcement is absolutely required. I believe the boxing of the control arm mounts to the cut tube and opening cut in the chassis is enough, but triangulating the tube to the chassis and perhaps adding additional tube supports could be worth while.

I've put about 500 (hard) miles on the setup and have been inspecting everything often. No issues yet... My car is making about 350whp/tq currently.

[winders]

Originally Posted by TopTuning

Basic math will tell you that the inner LCA mount takes about 20-30% of load inline with vehicle. This is not a small amount so reinforcement is absolutely required. I believe the boxing of the control arm mounts to the cut tube and opening cut in the chassis is enough, but triangulating the tube to the chassis and perhaps adding additional tube supports could be worth while.

I can tell you from having a race car with raised inner pickup points using pivot boxes that a significant amount of force is run through the inner pickup points. With the torsion tube of 1987 930 chassis completely intact, my race experienced cracking in the chassis where the gearbox tunnel met the rear firewall. On top of that, the top of the pivot box above the bolt that holds the trailing arm in place was cracking as well. Yes, my race car runs big slicks so the loads are exaggerated compared to what a street car would see. The point is that loads are quite high.

If you cut a section of the torsion bar tube out, I don't see how you can get enough strength without adding one or more tubes to triangulate the two torsion bar tubes to the chassis.

[Notagoodperson]

Hi there, just in this forum but was browsing and found this thread.

https://forums.pelicanparts.com/porsche-911-technical-forum/185692-fitting-6-speed-g50-89-carrera.html

Curious as to why you chose the "removal" option as opposed to the method which preserved the torsion bars and structural integrity in a simpler fashion.

No worries either way, just trying to understand

Peter

[Peteinjp]

OP- once you get this flushed out you might want to mention this on the 964 and 993 forums. Pretty common for people to be looking for 6 speeds to replace 5 speeds or tiptronnics and as you know there are no 993 boxes available.

[chrisbalich]

Originally Posted by TopTuning

...Basic math will tell you that the inner LCA mount takes about 20-30% of load inline with vehicle. This is not a small amount so reinforcement is absolutely required. I believe the boxing of the control arm mounts to the cut tube and opening cut in the chassis is enough, but triangulating the tube to the chassis and perhaps adding additional tube supports could be worth while.

I've put about 500 (hard) miles on the setup and have been inspecting everything often. No issues yet... My car is making about 350whp/tq currently.

If the spring plates were channeling 70-80% of the forward & rearward thrust, the rubber bushings therein would fail along the 9 o'clock - 3 o'clock plane. Counter to your 'basic math', they fail at 6 o'clock from the weight of the vehicle levering against the TBs et all.
My smooth brain managed to figure that out with zero math required, just a basic understanding of what every car on this board has experienced at some point in the last 50 years.

I am not your enemy. I am just trying to understand how these modifications are being completed in a safe, reliable way without a full cage.