Inverted 915 Project, No Description needed Options

[pcar916]

Hi Folks,
I'm returned after a brief hiatus with a question. Some of you remember I have Penelope, a 914/993 machine. I have decided to replace the 914 transaxle with an inverted 915. How many of you have done it and do you have stories? :-) My thinking is as follows...
1. Billet side plate. I've already paid the price several times for deflection. The 993 is not a huge hp machine, maybe 270hp with a bit less torque depending on the RPM/throttle.
2. Cable shifter (any suggestions that don't include making one myself.) It would be fun but might take longer than I want to wait.
3. Already have the turbo flanges/CV's to accommodate the deflection angle.
4. Oil cooler already installed whether I need it or not. Already addressed in the trans cooler thread from years ago.

Thought seriously about building a side shifter 915 with Bott's kit, but as good as it is, and it is. I don't want to take the gear-stack out every time I want to check the LSD plates/R&P.

I've gotten a replacement 993 engine while I jazz up her (tired) original engine, but since I haven't done one of these builds, I figured I'd ask this crowd about it because I'd rather drive her while I build the engine.
Glad to be back!
Ron

[Cracker]

No matter what you do with a 915...it is still a 915 (same goes for the 930)! I would suggest you consider purchasing a unit that adapts a G86-20 (Boxster S 6-speed) to your motor. Clay was showing us parts of this kit over dinner Saturday evening. You would get the close-ratio box with immense strength - plenty of aftermarket shifters to chose from too! Just my 2 cents...

Tony

[mepstein]

Why don’t you flip the differential. It’s been done many times on the 914-6 conversion. An added benefit is eliminating the need for a billet side plate.

[Cracker]

...and in the end, it still shifts like a crappy old box! There in lies the issue for anyone who wants a slick shifting transaxle. I have yet to see an impressive system first hand - maybe it exists, dunno. (IMG:style_emoticons/default/confused24.gif)

Tony

Why don’t you flip the differential. It’s been done many times on the 914-6 conversion. An added benefit is eliminating the need for a billet side plate.

[mepstein]

I agree, a 915 box shifts like a 915 box but I learned how to shift on an early, worn out 914 tailshifter so everything else is more than acceptable to me. The conversion is also quite straight forward. The boxster trans will not just bolt up so it depends how far you want to take things. Tony’s cable shifted boxster trans with custom shift tower puts everything else to shame. (IMG:style_emoticons/default/driving.gif)

...and in the end, it still shifts like a crappy old box! There in lies the issue for anyone who wants a slick shifting transaxle. I have yet to see an impressive system first hand - maybe it exists, dunno. (IMG:style_emoticons/default/confused24.gif)

Tony

Why don’t you flip the differential. It’s been done many times on the 914-6 conversion. An added benefit is eliminating the need for a billet side plate.

[Justinp71]

How does the 915 shift compared to a 901? I have a 915 with a Velios Kit ready to go in, but the 901 has been holding up well.

[pcar916]

Sorry folks... busier than a one-armed paper hanger. The one 911 I've had shifted fine but never as delightfully as a well maintained side-shifted 914 box.

Flipped R&P: Thought about it a lot. But inversion rather than a flipped R&P seems to me easier since taking the diff out to inspect the LSD clutches every year is far easier when I don't have to remove the gear-stack. That said, if that's what I wanted to do I'd get Martin Bott's side shifter kit. Seems like a really nice conversion.

930: Thought about that too. Found a few even, but I'm not convinced I'd have an easy time finding the right gear ratios for those four big clunkers.

Boxster trans: Haven't thought about it at all since I heard there was a starter placement issue. Is there a detailed thread about it here somewhere? If I did that I'd have several 914 and a few 915 transaxles to find a new home for.
Tony's cable shifted Boxster trans... gotta read up on it.

I'm in Oklahoma City helping a friend build a 1960 356 Roadster he started years ago.
Between that, work at home and an ailing mother I'm not making any events this year. But I just bought a Cayman to take the edge off. With so much time on the road it might as well be in a PCAR!

Thanks for the thoughts guys.

[Cracker]

If you would seriously consider the Boxster/Cayman S box yiu want to PM Clay Perrine. This setup isn't cheap but then again it appears far more rugged + a slicker shifting manual I have never known. Best of luck.

T

[campbellcj]

I've always circled around this topic myself as I prefer to keep the 901/914 if possible and so far that's worked out for me (~200 lbs-ft at the wheels, minimal hard standing starts). But if I swapped I would likely look to the boxster direction too. The 915 seems like so much expense and work for what's still a vintage, compromised solution.

[brant]

I've always circled around this topic myself as I prefer to keep the 901/914 if possible and so far that's worked out for me (~200 lbs-ft at the wheels, minimal hard standing starts). But if I swapped I would likely look to the boxster direction too. The 915 seems like so much expense and work for what's still a vintage, compromised solution.

Chris,
your going to end up racing that car in vintage racing someday I predict...
keep a legal box. The boxter is bound to be better but it will keep you out of a log book with a vintage organization some day

[campbellcj]

I've always circled around this topic myself as I prefer to keep the 901/914 if possible and so far that's worked out for me (~200 lbs-ft at the wheels, minimal hard standing starts). But if I swapped I would likely look to the boxster direction too. The 915 seems like so much expense and work for what's still a vintage, compromised solution.

Chris,
your going to end up racing that car in vintage racing someday I predict...
keep a legal box. The boxter is bound to be better but it will keep you out of a log book with a vintage organization some day

I have no intention of swapping trans on 914R...

[pcar916]

I agree, a 915 box shifts like a 915 box ...
Tony’s cable shifted boxster trans with custom shift tower puts everything else to shame. (IMG:style_emoticons/default/driving.gif)

Ok, maybe it's my lack of search skills, but can you point out a link to Tony's cable shifted Boxster trans that I can take a look at?

Ron

[mepstein]

I agree, a 915 box shifts like a 915 box ...
Tony’s cable shifted boxster trans with custom shift tower puts everything else to shame. (IMG:style_emoticons/default/driving.gif)

Ok, maybe it's my lack of search skills, but can you point out a link to Tony's cable shifted Boxster trans that I can take a look at?

Ron

I’m not sure if it’s explained on his build thread. I sat in the car so I’m just mentioning it from personal experience.

[Cracker]

Ron,

I never posted a "build thread" for my car - there is not too much to it really. If you have any questions you can PM me your info and we can talk about it. If you are running an AC engine, which I believe you are, adapting the G86 (and G87) trans is your biggest challenge. For shits and grins - a picture of my system is below...

Tony

I agree, a 915 box shifts like a 915 box ...
Tony’s cable shifted boxster trans with custom shift tower puts everything else to shame. (IMG:style_emoticons/default/driving.gif)

Ok, maybe it's my lack of search skills, but can you point out a link to Tony's cable shifted Boxster trans that I can take a look at?

Ron

[pcar916]

Ron,

I never posted a "build thread" for my car - there is not too much to it really. If you have any questions you can PM me your info and we can talk about it. If you are running an AC engine, which I believe you are, adapting the G86 (and G87) trans is your biggest challenge. For shits and grins - a picture of my system is below...

Tony

Thanks and nice looking machine! What's an AC engine? Mine is a NA 3.6L 993 engine which now is attached to a LSD 914 transaxle. Can't believe I ran it as an open-diff car for so long. Yours is a great cable setup and I'd like one that sits up next to the steering wheel as well. Did you fabricate it or buy it?

I'd also like to talk to someone who has built and installed a 915 inverted just to hear any words of wisdom before I start designing and building everything from scratch. I have two 915's that can be used and the aluminum one is a 8:31 R&P. The mag-case is a 7:31, which I like a lot, both for weight savings and low-end grunt.

I suppose I'll use the aluminum case box just for longevity sake.

I know I'll have to do the following to the box...
1. Move the vent to the "bottom"
2. enlarge the oil pathways on the "top" of the inner case
3. fabricate a hoop-mount to mate with the 914 rear trans mounts
4. completely change my clutch/PP/Flywheel system
5. at least consider a hydraulic clutch system
6. cut a relief for the DME speed sensor
7. I don't know if the oil level remains at the side hole

You know, gems of wisdom from someone who's done it!

Ron

[ConeDodger]

McMark has the design for a cable shifted 915 in his head and computer. I have my flipped, quaffed, side plated 915 sitting at his shop waiting for my car. I have a project that comes before that so...

In short, he may consider doing up the first on yours?

[jeff]

What about this option,

https://www.wevo.com/Products/TransmissionP...15SideShift.htm (IMG:style_emoticons/default/lol-2.gif)

[Cracker]

Ron,

Converting the shift method that was originally a mechanical rod system to a cable system does not make it shift better - rather, just different. What inherently creates the poor-er shift is internal - not the method. I currently own a G-Box prepped G50-52 box inverted with all the bells and whistles - it still shifts like an old box regardless. I have attached a video from our first track weekend and check out how QUICKLY and EFFORTLESSLY they occur - that simply is not happening with a 915. I have had this video "locked" for quite awhile now - it is no public. However, based upon your inventory of 915 bits, I would think it makes sense to just stick with that moving forward. It was fun at least to think about...

Regarding my set-up...the actual shifter is made by CAE out of Germany. Since the G86-20 actually can easily be adapted to my engine - it is a no brainer - not so easy for you.

The reference to AC engine = Air Cooled.

Tony


https://www.youtube.com/watch?v=pTgOCuiczAE

[pcar916]

Thanks Gents,
ConeDogger: "McMark has the design for a cable shifted 915 in his head and computer"
I'll follow up and see if his shifter is aftermarket or not. Also, I wish I could move the Guard LSD from the 914 to the 915 box... the bearing surfaces aren't the same size though.

Jeff: Wevo's a nice solution. But it's for a non-inverted 915. Inversion puts the shift rod on the top where a standard rod system doesn't reach without universal joints, cams and levers. Non-inverted leaves me with a flipped R&P and more complicated diff maintenance.

Cracker: That shifting is wonderful!
Since I can't start working on my 914 until I get finished with current projects I have time to noodle over this a bit. If I can figure out how to do the G86/20 box I'll sell off the 915's and a few of the 914 boxes... clear out some space!

Lookin' forward to ceasing the engineering work and building it instead!

Thanks again guys.
Ron

[stownsen914]

I know I'll have to do the following to the box...
1. Move the vent to the "bottom"
2. enlarge the oil pathways on the "top" of the inner case
3. fabricate a hoop-mount to mate with the 914 rear trans mounts
4. completely change my clutch/PP/Flywheel system
5. at least consider a hydraulic clutch system
6. cut a relief for the DME speed sensor
7. I don't know if the oil level remains at the side hole

I haven't done an inverted 915 myself, but I own a 911 with an inverted 915, and am somewhat aware of the mods that were done. Add a couple items to your list. The mating pattern for the 4 bolts where the trans bolts to the engine are not symmetrically oriented, so you'll need to open up (oval out) one (or maybe two?) of the holes in the trans case to get it to fit on the engine. One of those holes is where the starter bolts on, so one of the starter mounting holes needs to be ovaled out too. Not a big deal - you can do it with a die grinder, or possibly with a drill if you are patient.

Also, the starter will now hang off the bottom of the trans instead of the top, and it runs near the headers on my car. 914 headers are different of course, but I expect you'll see the same issue. May be worth doing some measuring and/or test fitting to make sure your exhaust fits OK. I created a little heat shield to keep the starter from cooking due to sitting right near the headers.

I don't recall the amount of oil I put in mine, and I don't have a non-inverted 915 to compare so probably never thought about it. I use the oil fill hole method to determine when it's full.

When you say you need a different clutch/flywheel, do you mean because you are converting from a 901? Hydraulic clutch actuation may be a good idea because the lever on the trans will be on top instead of on the bottom, although I suppose you might be able to creatively route a cable if you wanted. My setup is hydraulic using (I think) 911/944 master and slave cylinders and a custom bracket for the slave cyl. mounting to a couple of the differential side cover bolts.

Scott