economical 915 swaps? Options

[Johny Blackstain]

Since I don't have my original engine & the trans I have has been converted to a side shifter, I was thinking of converting my six to a 915 transaxel & would like to know what everyone thinks is the most practical, or the most economical, or the most bullet-proof, etc... Or should I put in some sort of shifter that will notch me up a bit. The car has new shift bushings & it's still sloppy. I suspect I should check the rear mounts as well. Thanks. (IMG:style_emoticons/default/smoke.gif)

[Joe Bob]

The 915 swap is NOT cheap.....requires a cable shifter. WEVO makes the best....it's pricey. Not to mention that a 915 box is $800 for a core...then you usually have to go thru it.

The 901/914 trans is cheap and can handle up to 300hp reliably as long as you keep the 1st gear burnouts to a minimum.....

[Dr Evil]

There is no excuse for a sloppy shifting 901. Do check the mounts (engine to bar, bar to frame, and tranny), all of the bushings including the ones in the stick shift itself, and the conical screws. If it is still crappy then the internals may have an issue.

[drgchapman]

Economical 915 swap... (IMG:style_emoticons/default/av-943.gif)

Core: ~$1000
LSD: $1500 (if yer doin a 915, ya gots HP and need an LSD)
Flip R and P: do it yerself or have pro do it.
While yer in there: seals, gears, bearing retainer, dog teeth, etc.
WEVO side shifter kit: ~$3500
CV's: 915 to 914/6 stub axels(I used 911 CV's)
Custom fab shift linkage.
New speedometer for magnetic pickup.

I had mine done in the shop.

~$10,000 (IMG:style_emoticons/default/ohmy.gif)

Works like a dream with my 3.2.

[John]

The 901/914 trans is cheap and can handle up to 300hp reliably as long as you keep the 1st gear burnouts to a minimum.....

I respectfully disagree.

In our track only 914 3.2 conversion (~220-230 HP), It took us about 6-7 years to get to the point where we could push the car hard enough (be on the throttle hard enough) to continuously break 901 transmissions. (NO BURNOUTS HERE)

We would routinely break teeth off of the 4th gearset. For the street, I would agree that a 901 would live a long long time. For a track car with two experienced drivers, I would say it is a matter of time.

We went through 4 boxes in 4 seasons (one season 2 boxes). I built three of them, and bought the 4th rebuilt by someone else. All failures were virtually identical.

We attributed the problem to shaft flexure. When the engine produced enough torque in 4th gear, the 4th gearset would seperate enough to start a gear tooth root fracture. When the fracture grew enough for the tooth to break off, the gearset would self destruct. The last time I rebuilt a 901, I used a billet intermediate plate for better bearing support. Instead of using it, we went 915. The rebuilt 901 now resides in my 3.2 street car. That car is never pushed hard, so I believe that it will last a long time. I have another 915 for it if I am wrong.

When we went 915/916, we bought the complete package fully sorted and ready to bolt in. New clutch/pressure plate, shift rods, rebuilt trans, 915 shifter, 911 axles, flipped R/P, assembled kit.

The total price for the complete assembly was above $10,000.

just my $0.02

[Dr Evil]

John, thanks for stating your findings. It is always good to get some actual data from people. One point that I not exactly disagree with you on, but wish to clarify is that your HP did not kill the tranny, the torque did. You explained flexure and such which supports this, but I just want to make sure it is clear as this question comes up A LOT.

What kind of tq were you running through the box?

[Joe Bob]

Well first off....the thread starter was talking about a street ride. SO my comment on the 901 is still valid. 901s are still cheap and plentiful and reliable up to 300hp......

As to the 915s....they also have issues.....on my N/A 3.6 which is performance chipped with headers I put out 280hp. It fractured second gear due to shaft flex. I rebuilt it with the WEVO intermediate plate upgrade (the shaft tie in plate is standard in a 930 box BTW) AND hogged out the bearing race, pressed in a sleeve and fixed the second gear....this was on a 915 that had less than 80K street miles....30 with the 3.6.....

So....my opinion is that a 915 is not the ultimate cure. Now a 930 or G50.....VERY rarely do THOSE break....

[rhodyguy]

a $10k trans. zoiks. that's a lot of straight teeth.

k

[Crazyhippy]

Now a 930 or G50.....VERY rarely do THOSE break....

W/o abuse...

They are breakable though (IMG:style_emoticons/default/burnout.gif) (IMG:style_emoticons/default/driving.gif) (IMG:style_emoticons/default/ar15.gif) (IMG:style_emoticons/default/barf.gif)

BJH

[soloracer]

The 915 swap is NOT cheap.....requires a cable shifter. WEVO makes the best....it's pricey. Not to mention that a 915 box is $800 for a core...then you usually have to go thru it.

The 901/914 trans is cheap and can handle up to 300hp reliably as long as you keep the 1st gear burnouts to a minimum.....

Do you have to use a cable shifter with the 915? The reason I ask is I bought a set of shift rods w/linkages from Patrick Motorsports that I believe is supposed to replace the cable shifter on my side shifting 915.

[Joe Bob]

Or a .75 circlip falls off the back of the reverse idler shaft......

[GeorgeRud]

915s can be setup with a shift rod assembly, they don't necessarily need cable systems.

Remember, Porsche went to the 915 type transmission when it increased torque with the 2.4 liter 911. Now, we're pushing 3.6 liters through them and wonder why they are not bulletproof. The newest ones are now at least 20 years old, so we're talking some vintage stuff even with the 915s.

It's a shame that Boxster transmissions don't easily convert into the 914. Perhaps some enterprising types will research transmission swaps as much as they have engine swaps.

I personally love my 915 Vellios transmission with shift rods in a 2.7 conversion street car. It ran me about $4000 to do the conversion with the transmission being set up by a very good local shop, and me doing the linkage myself. The standard H pattern is particularly nice for day to day driving.

[John]

John, thanks for stating your findings. It is always good to get some actual data from people. One point that I not exactly disagree with you on, but wish to clarify is that your HP did not kill the tranny, the torque did. You explained flexure and such which supports this, but I just want to make sure it is clear as this question comes up A LOT.

What kind of tq were you running through the box?

I don't have the figures in front of me (but I'm guessing 185-195 lb-ft). The engine is/was a stock 1987 3.2 with 914-6 headers and no CAT. The car has never been on a dyno. (My street car is a Euro 1984 3.2)

I'm guessing 300HP with a small displacement engine is different than a 220HP larger displacement engine. (More revs with the smaller one, more torque with the larger one)

SOLORACER:

No you don't need to use a cable shifter with a 915. WEVO makes a shift kit, and VELLIOS made a shift kit. I only have experience with VELLIOS parts. I know they work.

just my $0.02

[Johny Blackstain]

John, thanks for stating your findings. It is always good to get some actual data from people. One point that I not exactly disagree with you on, but wish to clarify is that your HP did not kill the tranny, the torque did. You explained flexure and such which supports this, but I just want to make sure it is clear as this question comes up A LOT.

What kind of tq were you running through the box?

I don't have the figures in front of me (but I'm guessing 185-195 lb-ft). The engine is/was a stock 1987 3.2 with 914-6 headers and no CAT. The car has never been on a dyno. (My street car is a Euro 1984 3.2)

I'm guessing 300HP with a small displacement engine is different than a 220HP larger displacement engine. (More revs with the smaller one, more torque with the larger one)

SOLORACER:

No you don't need to use a cable shifter with a 915. WEVO makes a shift kit, and VELLIOS made a shift kit. I only have experience with VELLIOS parts. I know they work.

just my $0.02

I was curious as to where you got your Vellios gear? (IMG:style_emoticons/default/cool_shades.gif)

[Joe Bob]

link

Above is a link to a street 915 second gear fracture.....it's a 914 V8.....same break I had in my 3.6 powered 915....

It appears he has a custom geared box....gonna cost him a mint.

[GeorgeRud]

I believe that Dr. 914 has some Vellios parts (at least they are on his website), and ebarrettinc.com has some parts still available.

[kdfoust]

John, thanks for stating your findings. It is always good to get some actual data from people. One point that I not exactly disagree with you on, but wish to clarify is that your HP did not kill the tranny, the torque did. You explained flexure and such which supports this, but I just want to make sure it is clear as this question comes up A LOT.

What kind of tq were you running through the box?

Hey Evil:

John's 901 breakages completely make sense when you see this:

Porsche Transmission Torque Limits from Porsche 911 Story, Paul Frere
901........138 lb/ft........sand cast aluminum
901........148.5 lb/ft.....die cast aluminum
915........181 lb/ft........diff. and bell housing die cast aluminum, gear box and cover die cast magnesium
G50........221 lb/ft
930........326 lb/ft

Frere mentions racing applications where the torque inputs considerably exceed the limits shown but says "...where longevity is not a consideration..."

These specs are for road going transmissions as specd by Porsche so they need to outlast the OE warranty as a minimum. I would imagine that Porsche was motivated to have a decent safety margin in these numbers as well but I wouldn't bet on having another 50% available.

Frankly speaking you can put whatever kind of torque you want through a 901 if "...longevity is not a consideration..." My 915 transmission built, strengthened, and hopped up, by a mechanic I trust is going to be right at $8000 without the stuff needed to finish the job...new mounts (WEVO), CVs,...but I don't think I'll make it to $10,000..it'll be close though! Ain't cheap.


Best regards,
Kevin

[grantsfo]

I had mine done in the shop.

~$10,000 (IMG:style_emoticons/default/ohmy.gif)

Works like a dream with my 3.2.

I'm sorry but I just have to (IMG:style_emoticons/default/blowup.gif)

[BigDBass]

I'm sorry but I just have to (IMG:style_emoticons/default/blowup.gif)

I couldn't have put it better myself.

[Dr Evil]

Hey Kevin,
Thank sfor putting that up. I knew the values listed for the 901, but those others are pretty interesting. There is/was a site with similar info (maybe the same), but I lost the link. I find it interesting that 2nd is the one that poops out. I Still do not have any concrete evidence that the billet plate helps this failure at all.