993 engine into an SC ????

[Doug E]

The July issue of 911 & Porsche World has pictures of a 993 engine going into an SC.

Pretty impressive, albeit a tight fit. Article says the cost was 6073 pounds and output to the tranny is 285bhp.

How long can the 915 support that kind of power?

[widebody911]

As Bob Dole said when asked "Boxers or Briefs..."

"Depends"

On the street, under civilised driving - probably about as long as a 915 would normally last.

On the track, driven like a madman - dunno, I'll get back to you when mine goes west. I figure it's got a couple of track days left in it, but the end is near.

Originally posted by Doug E
How long can the 915 support that kind of power?

[Jim Richards]

Doug E, don't get anywhere near my car!

[Jack Olsen]

The 915 from an SC (8:31) should be fine for a good long while, if it's in good shape. The earlier 915's (7:31) don't have as good a chance.

[Doug E]

Jim - welllllll, now that you are onto me ...

I was thinking that for the next NoVa Pelican drive we might need to "impound" the cars overnight in my garage just to make sure everything is up to spec. I figure that between Marc, Richard and myself we could have your engine out and back in my car before we hit the road at 8 am.

[rattlsnak]

The weak part on the 915 behind big H.P. seems to be the input shaft or the housing cover where the axle stubs comes out. However, I know several guys, including myself, that are running well over 400 H.P. on the track with no problems.............. yet

[PORSHIN]

Yeah Doug, there should be an overnight tech inspection, of course that would mean I would have to drive up a day earlier...unless you could give me a waiver...
Rob

[CamB]

I have been reliably informed that the 7:31 is too weak for track work, and you have to suck it up and go down the route Jack has (8:31 with custom gears and a cooler) to get a long lasting short ratio box. For those who don't remember, Jack's 7:31 died at his hands

An aluminium cased box (rather than magnesium) is preferable too.

[CamB]

Well, since I can only relay what I have been told, I am a pretty weak source of info - sorry

The major source was my own mechanic, but I don't know if it is an aluminium case thing or a 7:31 thing.

Steve Weiner at Rennsport has this on his site:

http://www.rennsportsystems.com/~porsche/1-d.html

So I then asked the BBS:

7:31 vs 8:31 ring and pinion

And although I was quite keen on the idea of a 7:31 I have ended up with an 8:31 (I will live with too long ratios until I feel very very rich at ~$500/gear set).

Note Jack's experience (I think he is well pleased with the new box!!):

915, Chapter Two

Inside my transmission

[Brian993]

Why not sell your car and get the real deal!

[pwd72s]

Brian? It's called pounds per horsepower. When in Rothsport (Tualatin, Oregon) some time ago I saw a rather plain looking silver 9111SC...up front it was running an RSR spoiler with a big cooler...it also had Turbo brakes, and under it's rear lid a varioram 3.6. I was assured it was an easy swap...I have no idea how much lighter this car would be than your 993, but the weight difference would be hundreds of pounds. IMHO, this silver SC would smoke a stock 993....and that's the "why"...some guys prefer performance over luxury and the status of "new". This isn't a slam on your choice, it's just saying that not everybody has a dream for a 993...

[Brian993]

I hear ya Paul. Makes good sense, it didnt occur to me.

[Bill Verburg]

The weak link in the 915 transmission is indeed the 7 tooth pinion. It won't last long in either an al. or a mg. box with a large diplacement motor. The 1 tooth difference on the pinion is just enough weaker to cause major reliability problems The load limit for a gear set is ~ 2N₂/(N₁ + N₂) for the 7:31 the ~constant is .36897 for the 8:31 it is .41025 a strength increase of ~12% . An interesting possibility is an 8:35 r/p that was once available, Steve Weiner told me that they last used them on the 935s. It is sure that they are rare.

I used a mg. case 8:31 on my 964 transplant for quite a few years with no problems and in fact was advised by Gary Fairbanks(among other knowledgeable folks) to just continue to use it.

I think that the most reliable is the Al case with a cooler, and internal spray bar, either aftermarket as Jack uses or factory as I am using. For street use the cooler is overkill but as with a large oil cooler the peace of mind is priceless!!

[Early_S_Man]

Actually ... I suspect that a lot of people racing against RSR's from '73 thru '80 or so wished the 7:31 r & p was quite a bit weaker ... seemed to hold up in quite a few 24 hour races under the punishment of 330 DIN hp!

[Bill Verburg]

It's not the hp that is the problem it's the torque and the RSRs all had transmissions hand built from selected non oem pieces w an external cooler and at least an internal spray bar, often with additional cooling/lubrication add ons. With fluid that was changed after every outing and a full rebuild after every race. A very good friend who was the facilitator of my transplant and my mentor in all things Porsche for the last 30 yrs was a factory team mechanic/engineer from '69-75. He has been an invaluable source of info/parts/contacts. His advice bolstered by conversations with highly placed engineers at the factory all agreed that any of the 915s would work fine, its just that some versions will be more durable than others. How often do you want to rebuild your transmission is really the only question

[john_colasante]

not everybody has a dream for a 993

Fair enough, but the 993 isn't exactly a luxury boat either.

A stock USA spec 993 has approximately the same power to weight ratio as a '73 RS lightweight. It has a better power to weight ratio than any early 911 S. So if you're pointing out great power to weight ratios of sporting 911's put the 993 up at the very top of your list.

The 993 has a modern multi-link rear suspension making it a better handling car than any previous 911. Earlier model's semi-trailing arm suspension looks primative by comparison.

Also, the idea of the "sport 911" didn't die in '73. The European RS version of the 964 and 993 were built in the same spirit as the early RS versions right down to the minimalist creature comforts, lightweight and extra power.

[Bill Verburg]

I agree whole heartedly with John. If a 993RS were available for street use here I would be on it in a sec. It just galls me that all the really desireable cars are not sold here, a 993S is nice but just knowing the RS is/was available prevents the purchase. That was why I bought my Carrera in Germany and brought it over privately.

[Rick Lee]

I saw a lady at Summit Point last weekend who had a 3.6 in a '72 911. I forgot to ask her what type of tranny she had in there. It was a bada$s ride. Now I'm debating what to do with the equity windfall when I sell my house. Unload the Carrera and get a 993 (Carrera S), or get my body all fixed, stripped, resprayed and swap the 3.2 for a 3.6. Life is tough.

[CamB]

You'll have to excuse my complete lack of knowledge of East Coast geography, but could she have driven from Delaware:

http://instant-g.com/Cars/Midnight72/index.html

'Cause if you are looking for info on a 3.6 swap, look no further.