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GT40 Tech - Powertrain/Transaxles Transaxles and driveline - don't dare post engine things here!

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Old 31st May 2007, 09:35 PM   #1 (permalink)
Howard Jones's Avatar
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Can a Porsche 915 be inverted ?

I have been checking out several other forums and websites and I can't seam to get a really solid answer on this one.

Can a Porsche 915 gearbox be inverted (input shaft center line below the output shafts center lines) like many people do with the 930's, 50/ XX boxes?

There seams to be some belief that inverting a 915 causes oil starvation of the gear-set. I do know that many have been run in a mid engine car by flipping the ring gear around. Some machine work is necessary but not really beyond the capability's of several recognized Porsche gearbox re builders and can be done at the same time as a rebuild without huge increase in the rebuild cost.

My interest is in the added attraction of lowering the center of gravity of the overall power-train and the lower price/availability of the 915 gearboxes.

The 915 seams rather well suited for a engine making somewhat less torque at low vehicle/engine speeds than a V8 but also capable of holding up well to moderate power levels. Something on the order of 300-350HP is what I expect to run through this gearbox.

If it becomes necessary to use a G50 variant or one of the other new gearboxes like the Quaife, Mendeola or the others then the project's budget becomes much larger as the power goes up with the gearbox capacity. The increase in buget will also push out any startup so you can see why I am interested in the 915/ 350HP engine combo.

I am asking here among my friends because at this point I am not far enough along with my plan to waste vendors time on the phone filling me in on background. I prefer to have at least several ducks lined up before I get to the nut cutting.

If anyone really has experience with a 915 and the inversion question along with its capibility at known REAL power levels I will thank you in advance for your reply.
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Old 1st June 2007, 01:23 AM   #2 (permalink)
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Re: Can a Porsche 915 be inverted ?

The Porsche factory rating is 237 ft. lbs. which I'm sure is conservative. 300hp sounds okay, 350 might be pushing it. Seem to recall they run external oiler rails to up the capacity, don't know about the invert.

This is a small transaxle, the input shaft is small and the total weight is about 100 lbs. Limited slip diff is available.
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Old 1st June 2007, 09:54 AM   #3 (permalink)
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Re: Can a Porsche 915 be inverted ?

I know they are sometimes used in V8 914's.

So either the ring gear carrier (diff) is flipped or the gearbox can be run inverted.

They have steep ratios that are closely spaced. Good for small displacement high rpm engines, with low amounts of torque.

They will break easily behind even a mild SBC or SBF.

The UN1, when available, is relativley inexpensive and should hold 350 hp without mods, with the single piece input shaft and 5th gear mods, that number goes up quite a bit.

I pick them up every chance I get.

Sorry for the slight thread drift.

Best,
S
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Last edited by Scott Calabro; 1st June 2007 at 10:00 AM. Reason: content
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Old 1st June 2007, 10:12 AM   #4 (permalink)
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Re: Can a Porsche 915 be inverted ?

The 915 can be flipped or inverted....along with the 930 it is one of the easier boxes to work with.
Until the G50 boxes became more available it was THE box for mid-engine V8's.....
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Old 1st June 2007, 10:18 AM   #5 (permalink)
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Re: Can a Porsche 915 be inverted ?

Howard,

Visit... Renegade Hybrids

They have very good info on the 915 axle.

Best,
S
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Old 1st June 2007, 04:01 PM   #6 (permalink)
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Re: Can a Porsche 915 be inverted ?

Scott, I did spend quite a bit of time at renegades website. I did not however see a definite answer to whether they can be inverted. Fran has made it clear they can be however, thanks Fran.
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Old 4th June 2007, 04:00 PM   #7 (permalink)
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Re: Can a Porsche 915 be inverted ?

Yeah, the Corvair guys like to use the 915 as well. They disagree about
flipping the ring gear (it's possible, but they seem to think it's better to
reverse the Corvair's rotation).

914 owners also like to drop a flipped 915 in as it performs much better than
the 914 transaxle (really a modified 901).

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Old 4th June 2007, 07:24 PM   #8 (permalink)
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Re: Can a Porsche 915 be inverted ?

Have a look here. It may answer some questions.
Trans 915 - Lambo Lounge
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Old 5th June 2007, 03:14 AM   #9 (permalink)
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Re: Can a Porsche 915 be inverted ?

Quote:
Originally Posted by gt40fran View Post
The 915 can be flipped or inverted....along with the 930 it is one of the easier boxes to work with.
Until the G50 boxes became more available it was THE box for mid-engine V8's.....
Mr. Hall gave you the exact answer. Yes they can. The splash oil lubes everything just fine.

The trick to a long lasting 915/930/G-50 box is this:
They don't like speed shifting. Smooth is the way. G-50s are more forgiving with their GM style synchros.
They don't like short shifter kits.
The synchros won't work well with anti friction additives.
Start an engine with no oil in the gear box and kiss the needle bearings good-bye in 60 to 90 seconds
Use limited slip gear oil with LSDs. Swepco is the best for any Porsche gear box.
Don't downshift into first unless you are under 15MPH.
Don't pop the clutch to burn off. Get off the clutch completely and then you can floor board it and burn tires to your heart's content.
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Old 8th June 2007, 06:25 PM   #10 (permalink)
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Re: Can a Porsche 915 be inverted ?

DCrage, Thanks for the info. Do you think the 915 is stronger than a Audi gearbox like the 016? The Audi's seam to take quite a bit of power if you treat them as you have described for the 915. The problem is they can't be flipped over, at least I don't know anyone who has. You would then need to deal with the wrong way around ring gear, too much hassle I would think. Therefor the original interest in the 915 as a budget minded gearbox for moderate power/torque level.
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