Converting a GT3 engine to reverse rotation? - Page 7

Matt Monson · 09-22-2010, 09:45 AM

I would think that would significantly hurt the value of the gearbox. If you're gonna spend that kind of money you're up into the range of some pretty serious custom gearboxes.

However, I may be able to help you if you go with that 962 box. I can get new castings made and potentially using that housing as a sample we could make up one that has a bell housing but has all the other things in the right location. Obviously it would be big money, but that's what you pay for one-off stuff.

Flieger · Flieger's Garage

Sorry if you alreday mentioned it, but why not a GT1 box? Was that flipped?

Cupcar · Cupcar's Garage

Is the 4-speed 930 boxe's ring gear flippable like a 915's?

If so, maybe a 930 box with a RUF 5 speed conversion kit and then have WEVO do a "one off" shifter kit for it?

Or, isn't the 962 box based on the 930 internals? If so, maybe castings and shafts from the 930 and 962 could be fitted together?

Cupcar · Cupcar's Garage

Hmm...Looking at my 962 parts book, it looks like the 962 differential casting could be exchanged for the standard 930 casting along with a standard 930 input shaft and viola it would bolt up to GT3 engine.

All without modifying the 962 box and preserving its value.

Matt Monson · 09-22-2010, 12:46 PM

You can flip a 930 ring and pinion, but it requires cutting both the case and the outer edge of the ring gear. Patrick Motorsports can do the conversion.

The 930, 935 and 962 are all the same "family" of gearboxes and there are certain cross compatible parts.

Schwarzeritter · 09-22-2010, 01:31 PM

I have to agree with Matt, you are really going down a very expensive very custom route.
I don't even think you should be worried at this point about re-sale values. And just as I believe Matt had stated the 1990's Subaru boxs were " Glass ", and I just wouldt go there.
I am not a fan of ( cross breeding. ) It really sounds like you bite the bullet and go very custom or go sequential.

Good luck-

Interesting project -

blue72s · 09-22-2010, 03:00 PM

Cupcar,
Sent you a pm.

blue72s · 09-23-2010, 06:04 AM

Quote:

Originally Posted by Matt Monson

However, I may be able to help you if you go with that 962 box. I can get new castings made and potentially using that housing as a sample we could make up one that has a bell housing but has all the other things in the right location.

That sounds good. Any idea how much? (I think Porsche casings are pressure diecast, not sand cast.)

Matt Monson · 09-23-2010, 07:17 AM

Quote:

Originally Posted by blue72s

That sounds good. Any idea how much? (I think Porsche casings are pressure diecast, not sand cast.)

I can look into it for you. Might take a week or so to get an answer since it's not something we do in house. But there's a guy we've used on other project and custom castings. I'll let you know.

The other thing that will need to be considered with this route is the comments about using the 930 output shaft to build a 962-930 hybrid are not accurate if you wish to keep it a 5spd. The 930 shaft isn't long enough for 5 gears. We'd need to do a mainshaft from scratch that is truly a hybrid between the 962 and 930 with the right quill length for the bellhousing, but the right shaft length for the gear stack.

blue72s · 09-24-2010, 03:51 PM

I've been looking at availability of ring & pinion ratios today and it seems there are only two, 4.66:1 and 4.22:1.

Obviously the 4.66 is far too high and I think the 4.22 is still too high for the GT3 engine.. I was hoping for 3.89 like the 2010 RS or straight 4.0 like the GT3 cup car. The top speed of the cup car is about 25mph less than the street GT3, and if I use 4.22 ratio the top speed will only be about 140 or 150mph. Getting the gearing right will be very hard if not impossible with this gearbox.

Matt Monson · 09-28-2010, 08:25 AM

What are you using as your 5th gear ratio? I've got 962 5th gears as tall as 0.61

blue72s · 11:40 AM

I am surprised that 962's have been racing with an overdrive as tall as 0.61. I thought overdrives were for economy driving on the highway?

Overdrive (mechanics) - Wikipedia, the free encyclopedia

Ideally I would like my top gear to be 1:1 or a tooth shorter. As the gearbox shift pattern is like the 901 (dog-leg) meaning the 4th and 5th gear is on the same plane, I think it would better for the 5th to be non-overdrive otherwise it should be on a different plane from the 4th IMHO.

Matt Monson · 09-28-2010, 01:34 PM

Most 962's have 4th and 5th overdriven. The stacks we set up for most customers run somewhere around a 1.08 or 1.12 3rd gear and then .96 or taller for 4th.

blue72s · 09-29-2010, 09:06 AM

Correct me if I'm wrong but I think gear overdrives like that are more for twin turbo's (because of high engine torque), not really suitable for n/a engines.

Flieger · Flieger's Garage

Aside from issues of material strength with a big difference in diameters and tooth count, I do not see any issue with an overdrive. If you want top speed, you will need the gearing one way or another- ring+pinion ratio or the actual ratio on the mainshaft/countershaft.

Matt Monson · 09-29-2010, 10:46 AM

The stock ratios on a GT3 use an overdrive 6th. The 996 GT3 is 1.00 5th and .85 6th. The 997 uses a 1.06 5th and .92 6th.

blue72s · 09-29-2010, 12:31 PM

Quote:

Originally Posted by Flieger

but why not a GT1 box? Was that flipped?

Yes

Quote:

Aside from issues of material strength with a big difference in diameters and tooth count, I do not see any issue with an overdrive. If you want top speed, you will need the gearing one way or another- ring+pinion ratio or the actual ratio on the mainshaft/countershaft.

I was talking about driveability, not about strength.

blue72s · 12:35 PM

Quote:

Originally Posted by Matt Monson

The stock ratios on a GT3 use an overdrive 6th. The 996 GT3 is 1.00 5th and .85 6th. The 997 uses a 1.06 5th and .92 6th.

Yes but you were talking about 0.6! Anyway, with the 4.222 r&p, what you think of this set up? :-

1st 2.53
2nd 1.74
3rd 1.30
4th 1.00
5th 0.83

7,400rpm 996 GT3 engine - Top speed 164mph (tyre rolling radius 13”). The 2.53 (shortest available) is a little tall for 1st gear, should be about 2.90 but unfortunately to no avail.

By the way, in case I decide to get a custom R&P and 1st gear made, what is the shortest 1st gear that could physically fit into the gearbox in question without any modifications? Will 13/46 or 12/41 fit?

Matt Monson · 09-29-2010, 04:22 PM

We make a 2.786 (14:39) 1st gear. Though in all honest 165 mph isn't as fast as one might think, though it depends on where you're going to run this thing. The Caymans we sponsor in Grand Am hit 175 at Daytona, and that's on the stock engine and stock geared transmission.

johnman001 · johnman001's Garage

Quote:

Originally Posted by Matt Monson

We make a 2.786 (14:39) 1st gear. Though in all honest 165 mph isn't as fast as one might think, though it depends on where you're going to run this thing. The Caymans we sponsor in Grand Am hit 175 at Daytona, and that's on the stock engine and stock geared transmission.

How much power/torque can a Cayman transmission handle?