Hello 914world… Just renewed my Membership !! Now looking to get my moneys worth...

I’m having a ’75 914 built into a 914-6.
Maybe 10 or 20 years ago I might have tried to do (some of) it myself.
Now I’m more a “pay the money, turn the key” guy.
Here’s a “silly” question. Likely the first of many….
How does a 915 Transaxle work when converted to a mid engine application ??
Not looking for a “how to” just an overview for personal info.
I’ve searched for articles, webpages and / or videos and don't find much.
I find acknowledgements of the conversion but no detailed or even general description.
I see the term “flipped ring and pinion”.
Does the whole gear system run backwards ??
Does just the differential run backwards ??
How would a LSD work in a converted 915 ??
Are the available 916 Kits good ??
Etc...
Any info or links to info would be appreciated !!

Welcome. Contact Patrick Motorsports in Phoenix, AZ. They wrote the book on this modification.

You also have to be ready to drop $10-15K (or 15-20K for PMS). I'm not saying it's not worth it but it's a bit of a commitment.

I’m running the setup in my 914. Works great and love it. You’re also buying a piece of 916 history. The car that never was and personally mine is better without the 916 price tag.
Check out this link for more information.
http://www.914world.com/bbs2/index.php?showtopic=102988

If you'd like to do a 915 in a 914, you might keep your eyes open for an already converted box to save a few $$. I saw one recently on the Pelican forum.

To answer your q, yes you need to flip the R&P or you'll have 5 reverse gears in a 914. The shift mechanism is the other challenge area - there are a few solutions out there, some NLA.

PMS sells all the conversion parts and shift linkage.

I just re-read the entire linked thread....really want a 915 with this complete conversion process. Very jealous Steve @Steve .

Ring and Pinion Ratios are Motor specific.. early versus late.. 911 engine and or choice..

PMB was just advertising a conversion package on Facebook earlier this week. Not sure if it’s the same as Patrick’s kit.

Short answer about the 915

In the 911 that it was designed for….

The tranny is “flipped”. In orientation
With the motor in back of the engine compared to a 914

So flipping the ring and pinion for a mid engine application
Gives you 5 forward gears

Instead of 5 reverse gears

Eric and the PMB team just finished the 916 conversion on my car.
I am looking forward to picking this up soon.

I am so very jealous. PM sent.

Did the conversion myself except for R&P set up.
Used the Martin Bott kit from Germany.
Early mag 915 with ZF LSD and mechanical speedo drive.
Not a picnic.
Driven it about a hundred miles before putting the car aside for a while, so not enough
to have a strong opinion.
Nice to have a conventional H shift pattern
Felt I needed it behind a 3.0 or a 3.2 short stroke.

The thing I don't love about 915 conversions for the 914 is that the 915 shifter adds complexity to an already complex 914 shift linkage. The 915 shift reverses rotation of the shift rod not unlike the early tail shifter linkage.

No different than a 911….

Some basics, here--

The "ring and pinion" are the parts that change the rotation axis of the transmission's output to be the same axis as the wheels spin. (It does more than that, but that's the part that matters here.)

This isn't from a 915 or any Porsche transmission, but it does show a ring and pinion assembly:



If you move the ring gear (the big one whose axis is side-to-side) onto the other side of the pinion gear (the small one whose axis is fore-and-aft) you change which direction the ring gear spins when the pinion gear spins a given direction.

Since a 911 has the transmission in front of the engine, it spins the ring gear (and therefore the wheels) so the bottom of the wheel goes toward the bellhousing when the transmission is in a forward gear. The 914 has the transmission behind the engine, so spinning the bottom of the wheels toward the bellhousing would be spinning it in reverse. So you have to move the ring gear to the other side of the pinion gear in order for the wheels to turn the correct direction when a forward gear is selected.

Other issues with the 915 transmission include the mounting setup, the shift linkage, and the clutch linkage. All of those need to be different when the transmission is installed in a 914. The transmission linkage usually is rather more complicated than a standard 914 linkage, unless you can find the now-rare parts to convert the 915 box to use a 916-style linkage.

--DD

Martin Bott has the 916 conversion parts for sale.

https://www.bugat5speed.de/en/beetle-co/tra...mission-901-914

CCSmith58 Question for ya, what size engine / HP are you running ? Depending on HP you may be better off with a beefed up 901 and save you tons of $$$.

If you still want a 915 another contact would be Joe Cogbill @ CogsCogs.com; he's just finished another flipped 915 with the Martin Bott kit.

In preparation for my factory 6 build I purchased a rebuilt '71 914-6 901 ($3,800), had it converted to side shift ($250), replaced the intermediate plate, bearing retainer and bearing ($1200), 108mm output flanges & hubs ($700) for a mild twin plug 3.0 ..

The deal with the 3.0 engine fell thru; I ended up buying a package deal out of a failed 914-6 race program; 330 hp 3.4 with a flipped 915 for less than a bare bones 3.0. Not trying to sell you anything but my 901 is available if interested.

There are downsides to a flipped 915, weight and shift linkage are 2 most common issues.

Good luck, add pics when you can..

Todd

I would spend time researching Joe Cogbill before making a decision. I have no personal experience with this shop, but in looking and considering a 915 his name came up so I looked around.

I agree. Do your homework.

Test drive one if you can. 915 trans sfifts more balky than a 914 trans. IMHO not worth it with 2.7 and smaller motors. Same thing with a 7:31 r&p 915 trans. Why bother?
Beware of shops that have no experience with this kit.

To the OP
You need to check also the gearing you want to end up with
As mentioned the R/P used will change your ratios

Also depending on which motor, the size, and intended use .... the weight and expense of the conversion may or may not be needed

For example I believe Andy runs a 3.6 on the street with a 901

The 915 also adds weight for racing
The reason we don’t run one on our racecar
At 1800 lbs wet

The question of hp/torque limits on the 901 transmissions always comes up and I have commented on my experiences a few times, but here they are:

My car was strictly track only for 23 years and originally had a 3.0 l making about 275 hp and for the last 20 years had a twin plug 3.4 l making about 335 hp (290 to the wheels). I used a 901 gear box with the billet intermediate plate. I had two transmission failures over the years, one was the R&P and the other was broken tooth on 4th gear. During the last 15 or so years I had no failures at all but pulled the transmission every 3-4 years to freshen which included bearings, synchros and any other parts that looked questionable. I also drained and replaced the gear oil every season. I looked for gold-colored bits in the oil to get a sense of the condition of the bearing cages. I only used first gear with a light throttle and most race tracks involved gears 3-4-5 with a rare few needing 2nd gear on a tight, slow corner.

I think that you can save a huge amount of money going this route if you are sensible about first gear and do an occasional refresh. My race shop told me when I asked about a 915 conversion, that the money not spent on the conversion could buy a lot of 901 rebuilds. I fact, I built two race boxes, a long gear box and a short gear box. I always ran the long gear box and kept the short gear box as a spare. My long box has a Guard limited slip and the short box was built with a Torsen style differential.

Now that I have retired from racing and have converted the car to a street hotrod that just goes to shows or a little local canyon carving, I think the transmission may outlive me. Many years ago when I pulled my box during the winter off-season and sent it to be freshened, I got the freshened box back and re-installed it only to find that I had one forward gear and five reverse gears. My shop was very apologetic and instead of me pulling the box and replacing it had me trailer the car to the shop and they made it right. The tech obviously though he had a 911 box instead of a 914 and flipped the R&P.

One other advantage of the 901 transmission is that it is a true race shift pattern with the upper 4 gears in the "H" pattern rather than dog legging into and out of 5th gear. For street it's a wash on whether or not you want to dog leg on 1st or 5th.

we flush our gear oil every 3rd event for the same reason.
oil is cheap comparatively

(motor oil changed ever event)

@slivel - Excellent feedback re your 901 experience. Quite honestly, it is why I am so up in the air about doing a 915 conversion. It's a good chunk of change to make it all work.

My 901 is an original tail-shifter 914-6 Dr.. Evil converted to side-shifter and went through it replacing anything that even looked remotely worn. I run a 3.2 with about 240 HP and it is a street driven, narrow-bodied car with 195x55x15 tires- soon to be 195x65x15 tires. I am always gentle with 1st gear as I know that is the week link of the equation.

I guess I will really need to try to find a sorted 915 in a 914 and drive it to see if the juice is worth the squeeze.

The other day a good fried was questioning installing a Boxster S 6-speed behind a 3.2. That would be a nice transaxle if it would fit and if the shifter could somehow be made to resemble a stock shifter. I just want it to look as stock in appearance as possible.

GrEaT input here !! Thanks !!
My 914 build is "in process" although still a year out...
I've already bought the '95 993 3.6 and a rebuilt / beefed up 915 transaxle.
The 915 was being built to use in a 400hp 911.
The Gentleman I bought it from decided to go to a G50 unit.
PMB is building the car.
I'm just trying to educate myself about crazy alterations and conversions all you 914ers
have been dreaming up and perfecting.

DD, thanks for your post. That's the kind of info i'm looking for...

So, How do you "flip" the ring gear ?? Do you replace the pinion shaft (gear) ??
Would an OS Giken lsd work in the 914 application ??
Again not looking for a how to, just info...

Check out this link regarding flipping the rear gear / diff.
http://forums.pelicanparts.com/porsche-911...-ring-gear.html
It is just flipping the diff, but the article does mention clearance and rubbing issues.
I switched to the latest 915 trans because the 914 trans drove me up the wall with my 3.2 motor on the street. I felt like I was shifting all the time. Because my 915 gearing was designed for the 3.2, all the gears are taller and now its like driving a stock 911. It’s also much nicer on the freeway. My trans is a 1986 trans which was the last year they were made. Regarding LSD, most aftermarket LSD sell a course spline LSD and fine spline LSD. The 914 trans and early 915 are course spline LSD’s and can be interchanged. The 8:31 915 is a fine spline LSD. I wanted the Guards TBD LSD, but they were on back order, so I settled on a KAAS LSD. https://kaazusa.com/tech-library/the-kaaz-a...lutch-type-lsd/ I also recently bought a 1995 993 motor. Hope to get it installed this summer. Hope I will still be happy with the gearing. A popular upgrade with a 3.6 is to put the tallest 5th gear "TL" in the box. The motor will now run 80 mph at 3k rpms.

expensive and not worth doing. We have done several for high horsepower engines, usually just to say we can do it, also have the factory 916 in here with a 915 in it with very special unique parts

Good point from Steve:
"I switched to the latest 915 trans because the 914 trans drove me up the wall with my 3.2 motor on the street. I felt like I was shifting all the time. Because my 915 gearing was designed for the 3.2, all the gears are taller and now its like driving a stock 911. It’s also much nicer on the freeway."

My car has 245-45-16 Toyo RA1 all around and is turning 3000 rpm to make 60 mph so it is not optimal for long trips, but it suits my purposes of a once per month C&C or canyon drive. This is with an AFNSY gear set. Using a ZD top gear can get me to 70 mph at 3000 rpm with this size tire. My track tire used to be a Hoosier 274-45-16 which was a little bit taller.
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I have a WEVO based 915 done by Patrick Motorsports with my 3.8... shifts like butter and as Steve pointed out the gearing is a bit different, allows the big 6 to really stretch its legs and feels like the gearing is appropriate to the crazy HP. I was a fan of the 901 shift pattern but honestly with the big 6 the 915 really feels much more suited to the engine.

I was just talking about this with 914Dave today. He used a Vellios kit - NLA. He said it's a lot like the Martin Bott kit. He's a machinist and carefully fit everything together. Even had to make a piece missing from the kit. Says it shifts like butter and handles any abuse from his 3.2. He drives his car thousands of miles per year so it's a real thing, not just a future plan. I know for sure he isn't going back to a 914 trans.

https://frontstreet.media/2019/02/20/how-to...4-6-gt-tribute/

I have a 914 trans in my 3.2 conversion car but the next one is getting a Carrera trans with WEVO and LSD built by Peter Dawe. It came in on a 914 race car and I snagged it up. If you don't like the 915 trans, you just haven't driven one built by Peter. The Dawes built 3.6 went to a friend.

Kelly’s is amazing. With a spherical Firewall bushing and a Rennshift the feel is otherworldly for us 914 owners.

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Thanks Mark for the feedback. I’m also using a Rennshift with my Martin Bott 916 kit. I have also driven my car to several WCR’s and other events. I would never switch back to a 914-4 trans. Since I’m so happy with my setup, I am looking forward to my 3.6 project. It would be great if other people responded to the Martin Bott thread with positive or negative experience with the kit. I got screwed by two local reputable shops that could not make the 916 kit shift right. There was always someone local that I trusted that said “did you try these guys?” I could have saved thousands of dollars if I would have taken it to Patrick Motorsports in the first place. Even JW “RIP” at Otto’s told me he could never get the Vellios and 916 kit to shift right and did not recommend it. PMS told me they thought my car was one of the best shifting 915 cars that they have built. Personally I think this is related to the JWest shifter versus Wevo that they install on the majority of there projects. I know that CFR/Tangerine racing also has great feedback with Vellios and the 916 kit from Martin Bott. Nice to know that PMB is also another resource to build them.

Dave was telling me he was constantly looking at angles and geometry of how things interacted, not just assembling parts. So the answer seems to be to use someone familiar with how these products work or else it’s a science experiment on your dime.

If you've ever messed with a custom shifter setup on a 914 (sounds like essentially what these kits are), there are lots of moving parts. Which means many points of failure, slop, places to have clearance issues, etc. You tackle them one by one, make them right and work together nicely, and it will work.

Shifter information: all 915 conversions that have ever been made use a 911/tail-shift style shifter with the ball cup and support bracket under the shifter.

Some 915 conversions are referred to as "side-shift" but the linkage is not designed to use the 914 side-shift type shifter. If you use the side-shift shifter with a 915, you will end up with the shift pattern flipped left-to-right.

Good to know.
I think Dave had that issue but made some linkage to reverse it. Again, he’s a machinist so he lives for that stuff. A

The only experience I have with a 916 is my own but I realized early on
that the reverse interlock on a 914 side shifter and the change of motion would
not work with a 915.
My trans is a '72. It's the only 915 that uses a stamped steel shift base that looks
just like a 914 rear shifter.......but it is very different down below.
The reverse lockout is on the opposite side and has two additional small springs.
I was lucky to find one.
I think the '73 and on 911 aluminum bases are the correct choice for any
915/916 install. OR, your choice of quality aftermarket 915 replacements.
Rory

I tried them all desperately trying to figure out why it wouldn’t shift right before taking the car to Patrick Motorsports. The 916’s and other period correct GT’s with a 915 gearbox all have this one year 1972 shifter, since that is the year they came out. It looks like a 901 shifter with the reverse lockout on the other side. I still have one in my collection. I sold the Wevo and kept the 915 rennshift that JWest mentioned. The 915 rennshift is much more precise and with the stock short throw, I have zero issues with the 5th reverse lockout. The rennshift and Wevo is spring loaded to the 3rd and 4th gate, but the Rennshift also has a shorter left and right neutral. Literally when shifting from 2nd to 3rd all I do is push up on the Rennshift and it automatically goes into 3rd like butter. The stock 915 shifter and one off 1972 915 shifter is only spring loaded for reverse and 5th. The rest of the gears you have to fish for.
Notice goofy one off part numbers 18,19 and 20 5th reverse lockout. It does work and is period correct, but doesn’t shift like a modern Rennshift.
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Here is a good thread from 914Dave about his "bolt action" shifter:

http://www.914world.com/bbs2/index.php?sho...162451&st=0

Wow!! That thread is over ten years old. With everything available over the counter now, what is advantage of fabricating it yourself? I am jealous of such skills and equipment, but it would be interesting to feel a side by side comparison. Maybe a future WCR or other event.

I’ve never read that thread but Dave has taken me through a lot of the special features of his car. Any one of them blow me away. For instance, not realizing the 914-6 used a longer wire to the heat flapper boxes, they came up short. So Dave machined some extender brackets out of titanium to make up the difference. And then there’s the custom made fire suppression system. It’s all really amazing. @914Dave

I never saw that thread before tonight.
I purchased the Bott kit in 2013 and worked on the trans, shift linkage and clutch
linkage while doing my GT project.
I had contact with Dave over the years but had no idea he was fabricating his own
shift tower. Among other great feats.
My set-up uses all stock parts except for the shift rod below the engine.
I shifts OK but could certainly be better.
I'm hoping that when I get back to it I can make it smoother and decrease the
throw.
Fantastic work Dave. Beautiful.
Can't believe it's been almost ten years.

I ran into the same problem early on with my 914-6 factory heat exchangers. Bug pack/Empi sells short throttle cable extenders that work perfect for this application.
914 rubber also sells the correct length cables.
https://914rubber.com/heater-lever-control-cable-for-914-6

No need to replace any of the major parts. You literally pull out the pinion shaft, grab the ring gear and associated bits, and run them around so they are on the other side of the pinion gear. In the pic I posted, just imagine the "differential carrier/ring gear" part flipped around so that what was toward the top of the image is now toward the bottom of the image, and what was toward the bottom of the image is now toward the top.

Of course, there has to be room for the assembly on the other side of the housing that it lives in. And that's where some of the work comes in, because some trans designs don't really have room for it that way.

--DD

lots of info

I cant believe its been ten years since i did the trans work. I will say that the shifter and trans operate smooth and reliable. I have around 17K on the setup now. Worth the effort. I was fortunate enough to find a Vellios kit cheap and by dumb luck. That made the decision easy to forward with the 915.

Hey DD. THANKS... this is helping me understand.
So... the ring gear + diff + bearings are "symmetrical" from the pinion centerline??
would any brand LSD work ??