Back Date G50 Car to 915

[jamesjedi]

Hi,

I have found a roller that I am interested in. It is a G50 car. Is it a "bolt-on" solution to convert it to a 915?


As always...thanks for any help.

[McLovin]

Can't see how that would be a simple "bolt on" thing.

For one thing, the G50 is a hydraulically operated clutch. Therefore, there is no provision for a clutch cable to run through.

Anything can be done with enough $$ and work, but I'd think this would take quite a bit of cutting out of parts from a 915 chassis, and welding them onto the G50 chassis.

[spuggy]

From what I can gather, most of the issues with fitting a G50 into a 915 car relate to shortening the G50 so that it fits into the available space without moving the motor too far back, and clears the 915 torsion bar tube. You need a G50 shifter and pedal box as well, of course.

I've heard this described as "almost bolt-in", if you start with an appropriately machined G50 and other conversion parts, including a custom transmission cross-member.

In the reverse direction, it's probably much simpler, as you've got all that extra clearance you don't need for the 915.

[sc_rufctr]

Originally Posted by spuggy

...

In the reverse direction, it's probably much simpler, as you've got all that extra clearance you don't need for the 915.

And with that extra space, you could mount the engine and gearbox further forward in the car...
Better weight distribution. And the 915 is lighter! It would also make it easier to install a 930 engine and gearbox... Ye Ha, hehehe

If you go ahead be careful not to over extend the CV joints.

[jamesjedi]

I like the 915 because of weight, cost to own and fix. Is this process fairly straight forward, or headache? I would have thought that there would be a few people doing it for racing?

[porschenut]

I suspect anyone who wanted a 915 for racing would have started with a 915 car. It seems unlikely one would swap out a G50 for a 915, since everyone seems to covet the G50 these days. Maybe it's been done, but it is most certainly not a simple swap. You'll have to modify the car and probably the transmission as well. Not easy, not cheap.

[petevb]

Originally Posted by jamesjedi

I like the 915 because of weight, cost to own and fix. Is this process fairly straight forward, or headache? I would have thought that there would be a few people doing it for racing?

There is a weight difference, but it's not as substantial as you might think (depends on the 915). Regarding cost to own and fix I think you'd save money with the G50 vs a swap to 915. The cost of the swap might start the G50 and 915 out about even, but the 915 will require maintenance more often. Even though the parts are cheaper the frequency of maintenance, especially if you put power through it, would likely tip the scales in favor of the G50. I'd do the G50 (or find a different roller) if I were you.

[AirKuhl]

Originally Posted by jamesjedi

I like the 915 because of weight, cost to own and fix. Is this process fairly straight forward, or headache? I would have thought that there would be a few people doing it for racing?

A 915 is lighter, but any performance advantage would be more than made up for by the faster/easier shifts of the G50.

[Packy]

dude, keep the G-50. If you want more power in the future you already have a tranny that can handle it.

[89911]

Originally Posted by jamesjedi

I like the 915 because of weight, cost to own and fix. Is this process fairly straight forward, or headache? I would have thought that there would be a few people doing it for racing?

I think someone here has the weights of a G-50 compared to a 915. What is it, less then 50lbs? Hardly worth spending $1000's in fabrication and custom work to put in a.....915??. Cost to own? Thats a new one on me. Racing? Is there problems the heavier, beefier G-50 can't handle over a 915??

[jamesjedi]

I dont know anything about the G50. The 915 can handle a higher hp engines. It may have difficulty with torque. It would not be a good tranny for a high output turbo motor that pours on the torque once the turbos spool. With the increase in torque, there will be a diminished life expectancy.

This is what I like about it; It can be nearly torn down with 13 mm rench. The gearing is changable, parts are reasonable. It is lighter, but I am not sure by how much? I have read one account of 20 lbs, which is not allot.


Thanks for the replies. They are informative.

[DanielDudley]

The G50 is the stronger box.

[JeremyD]

from people much more informed than I am. (I keep this for this type of post)

G-50 vs 915 Transmission

Originally Posted by Tyson Schmidt

The weight difference between a G50 and a late model aluminum 915 is 25#. That's with similar clutch and flywheels set-ups. The stock G-50 clutch and flywheel are what add on the extra weight between a stock G50 car and a stock 915 car.

Originally Posted by 911-32

FWIW, the difference G50 vs 915 is 45lbs, but that includes everything flywheel forwards. The bare trannies are about 27lbs. You can fairly easily save 20lbs on the G50 by going for a lightweight aluminium pressure plate, a spring centred clutch and L/W flywheel. Now you are only 25lbs difference and you get the benefit of an engine that revs much quicker between gears and has less reciprocating mass for better acceleration. That's not to say you can't save some weight on a 915 as well, but you get the idea.
Richard

Originally Posted by jwerion

I have weighed the late 80's G50 and the aluminum 915 and there is 20.5 lbs difference stock trans to stock trans. I figured by the time I beef up a 915 and add a cooler I would only have about a 10 lb savings, not worth sacrificing the reliability of the G50 in my opinion. My G50 is bullet proof with out a cooler and I have been very happy with the decision. There is another 10 lbs savings if you use an older mag case 915 but that would not hold up to a 3.8 RSR motor from what I hear.

Originally Posted by Peter Zimmermann

Let's look at this a little closer. The weight of a filled 915 RoW version 915/67 with cooler is approximately 60 kg (132 lbs). The cooler weighs almost nothing (I can testify to this because I've cleaned a number of them), so let's call the USA 915/68 at 130 lbs. The weight of a filled RoW G 50 version 950/00 is 66 kg (146 lbs), which is virtually identical to the USA version 950/01. So we have a weight difference between the two transmissions of 16 pounds.

The 915 flywheel weighs 12 lbs, and so does the G 50 flywheel, so that's even.

The stock 915 clutch weighs 18 lbs, the G 50 clutch weighs 29 lbs. So, in total, the G 50 package is approximately 27 lbs heavier, which was offset (in 1986) by an increase in rear torsion bar size from 24.1mm to 25mm. Something else comes into play here that contributes to the 915 car "feeling quicker" to some drivers. Back in the day of Hemi-Cudas, 427 Vettes, etc., the ticket to really quick quarter mile times was having a "short", 4.11 rear end (final drive) ratio, or an even shorter 4.56 ratio. Of course, the big compromise with a short ratio was having to run at much higher revs at freeway speeds. Cars with a taller, aka longer, 3.00, or 3.30 rear end (ring & pinion ratio) just wouldn't come out of the hole as quick, and the race was usually over in 2nd gear. In 1974, 911s were fitted with a 7:31 ring & pinion, which is a final drive ratio of 4.43 (remember, the bigger the number the shorter the ratio). Later SCs and early Carreras w/915s had an 8:31 (3.88) final drive ratio, BUT, G 50s are fitted with a 9:31 (3.44) final drive ratio. Yes, the factory fitted all new, "shorter" ratios to 1st-5th to try and make up for it, but, while striving for better mileage and reliability, couldn't overcome that "longer" ring and pinion, which can make, combined with the extra pounds, a G 50 car feel more sluggish than a 915 car. A lightweight clutch will help the G 50 car, but on a road course there should be very little difference between the two because the rpm drop between second and third, between third and fourth, and between fourth and fifth, is very similar when comparing a 915 to a G 50. Yes, the 915, in some situations, will "feel" quicker, but can it generate quicker lap times on a road racing course? I doubt it.

[jamesjedi]

JeremyD, that is great information. I have read it several times.

[RoninLB]

915 differences?





then from another thread

Originally Posted by Early_S_Man

You can always go to 'S' or GE-60 cams later with those RS pistons riding comfortably in their Nikasils ... after building a Donohue-geared 915 transaxle like the one charted below!