How does a 915 trans hold up to 400hp?

[NY65912]

With the thought of diving into the pool of boost head first the question now becomes............

Can a 915 trans hold up to a 400 hp 3.2???


Thanks

[ischmitz]

A lot depends on whether you plan to drag-race, or run WOT for long periods of time on the track at 120 degrees ambient temps. For every usage pattern there are different challenges to tackle for longlivety.

Make sure it gets properly prepped (intermediate plate insert, solid bearing retainer, OIL COOLER, re-enforced side cover, etc) I would talk to Wevo and see what they have in store for you.

Good luck,
Ingo

[Grady Clay]

How does a 915 trans hold up to 400hp?
Better than a 901/911.
Not as well as a 930.

There is a reason Porsche used that big 930 transmission with the Turbos.

Of course there are the G50 and G64 variants.

Best,
Grady

[rattlsnak]

You will hear all sorts of different opinions on this one. I had a bone stock 915 from a 78 SC behind a C2T engine, (@400HP) for 3 years with hard track use with no problems at all. Now, is it the best solution, of course not, but it worked for me. I did no drag racing, or slamming of gears, or even AX. Your results may vary!

That being said, if you do the above upgrades, you should be fine.

[WydRyd]

Protomotive have the 915 listed for power levels up to their Stage 2 kits (or ~485HP). A 915 will certainly hold up to 400HP. Again, depends how you treat it, just like any other gearbox though. Be preventative and do the above upgrades and treat her nice. She'll love you right back

[jluetjen]

The limiting factor with the Porsche transmissions is not the HP, but the torque.

[charlesbahn]

Needs to be a later model 915 to hold up to 400 HP, according to Protomotive. Not sure exactly where the cut off is.
From a previous thread:

Was curious about ajackson's question about the 300 HP limit for a 915 tranny, so I asked Protomotive what their experience is -
"Depending on the year, they may be right.
The early 2.7 trannies can get bashed by a good 3.2 na engine.
The 1978-up 915's have a aluminum casing and a reinforced mainshaft and we commonly run mid 500's through them.
A strong Stage 3 with about 600hp will trash them though.
But it's not so much power that is killing them, but torque.
Many people are putting them in 930's and killing them with only 400hp, but at the 1.2 bar required from a 930 to get 400hp they're making nearly 500lbft of torque.
With a Carrera based system, at about 1.2 bar, we're making about 600hp due to the rpm capabilities.
So, with our turbosystem, with the high power, lower torque, we're able to run much more power through the 915's without hurting them."

[ChrisBennet]

Originally posted by jluetjen
The limiting factor with the Porsche transmissions is not the HP, but the torque.

I'll add Heat as a factor too. The interference fit of the bearings in a 915 is not that tight. Get that case hot (like racing) and the race will be loose in the case.
-Chris

[Wil Ferch]

All the posts here a true ( torque is the issue more than HP, ...yes it's OK, but Porsche went to larger units for a reason...etc).

Historical factoid is that the 915 evolved as a street version of the 916 box used behind 908's....and they made something like 350 hp and lived for 24 hours at least with a madman behind the wheel !!

- Wil

[RickM]

Interesting info, Wil.



Also,
Chris's info just adds more support to the addition of a trans cooler.

Are the Euro coolers the only ones on the market or is there a $$$ friendly DIY solution?

[Wil Ferch]

The Euro 915's ( at least those w/o cat...there was a choice)..had the gear-driven oil pump / coolers for the transaxle...but they also included an internal spray bar or distribution system, for the return-oil.

We can fab something up as a DIY effort, but it would likely be electric motor driven and would lose the benefit of a spray bar unless you want to do ( or are in the middle of ) a transaxle rebuild.

Look at what Thom Fitzpatrick ( widebody911) did. If I find the link I'll edit and post it here.

- Wil

[charlesbahn]

I also asked Todd at Protomotive about this, in fact I had a cooler to DIY install. He said if I wasn't going to race the car not to bother, so I didn't. That was many thousand miles ago and I've had no trouble.

So my advice is Protomotive stage 1 w/wo intercooler and later 915 tranny don't cool unless you have one fall into your lap.

If you're going to race, cool the tranny. Call Todd, he can tell you how to do it.

[RarlyL8]

My experience with the 915 is similar to rattlsnak. The tranny lived happy for 3 years behind 400HP until I took it to the drag strip. When the trans was tore down we found nothing remarkable that would cause the whinning noise it was making. Further inspection found a warped side plate cover. Wevo parts are on backorder preventing the car from getting back on the road. I chose to add a reinforced side plate cover and dual bearing retainer. It should last for years on the street.

So I guess my answer is don't take it to the drag strip.

[WydRyd]

Drag racing can break anything, but just good, honest power delivery will hold in that box. Just don't kill it when shifting, especially in 2nd gear.

Apparently, EPC or someone like that in Ca. makes pressure plates for the 915 that'll hold 500 lbs/ft of torque or so

"Mike the mechanic" ran a blown 3.2 Carrera using his 915 for years without any issues. He just recently went G50 because he's gone to a TT setup.

[Joe Bob]

MY 83 915 lasted 80K, 40 with a stock euro 3.0 (207ish) and 40 with a 3.6 (280ish). The bearing race at the intermediate plate got loose and trashed second gear.

EVERYTHING else was fine......back together with a wevo BEARING RACE retaining piece.

No whines no issues.

[RarlyL8]

Where is Mike these days? I never saw his finished TT. The video he made of the blown 3.2 doing a holeshot is one of the most phenominal events I've ever seen a 915 put through and survive.

[WydRyd]

hehe, Mike mostly hangs around at c2turbo.com. He's very busy with work and married life these days

[k9handler]

I am on my second 915 mated to the 3.6...not near 400 hp but they don't hold up as I would like. Then again I have not done all the WEVO and cooler upgrades either.