G50/50 gears vs. G50/02 gears on a turbo box

[Newbie911]

Hi,

I was thinking about swapping my G50/50 2nd, 3rd, and 4th gears out to G50/02 gears. I've heard they are more fun to drive with a turbo engine. The gears aren't so long. I hear the gears are the same it's just the ring pinion that is stronger. Any ideas if this will weaken my gear set? I was going to CRYO and super finish all the gears, the ring and pinion, and add a stronger side plate. The engine can produce 700Hp

Thanks for any advice.

[Newbie911]

Bump

[Matt Monson]

There’s no strength difference in the gears. Save your money on finishing them too. It doesn’t make them any stronger either. Using the NA gear is turbo boxes is something people have been doing for 20 years.

[Newbie911]

Thanks Matt,

Well no cryo or micro will save me money.

[Matt Monson]

Just buy like new or new if you can find them. I think I’ve got a 1.074 4th here. That’s a tick shorter than the g50-02 ratio though. I definitely don’t have any of the others.

[Newbie911]

Do you have a gear set you think would be best?

[Matt Monson]

Originally Posted by Newbie911

Do you have a gear set you think would be best?

That’s a can of worms. i own guard transmission. I manufacture gears and LSDs for a living. But I don’t come here to sell. I’m the guy you call up when you’ve got $10-15k to spend.

My advice would be along the lines of what I’ve already said…find the best condition used factory gears that you can. Whether they are g50/00, g50/02, or G50/03 is splitting hairs. It’s like Bruce Anderson’s old advice about buying a car. You buy the nicest one you can afford.

Up in the 930 turbo forum there have been some good threads over the years. Search up there, or make another thread. Not only will you get more people commenting, you’ll get contacts of people who might have the kind of parts that you want.

[spuggy]

In the process of regearing my SBH G50/01 right now. With an EFI 930, N/A ratios are just insanely short - the 3.500 N/A 1st is basically useless for a turbo, except in parking lots or moving around in your garage.

I sourced a G50/02 1st; (3.154; same ratio as /50 and 993RS). Together with a /50 2nd, /02 3rd/4th, /50 5th for cruise.

This gives a tall 1st/2nd & 5th. And close-ratio 2/3/4 - seems to me that's where you are ~95% of the time when you're not parking/pulling away from a stop or cruising.

I found a tall 2nd extremely useful in even a CIS 930 (loved the one in my 915). Was briefly tempted to use a really tall 1st (like 2.5 or 2.00) - but then you'd need another non-factory ratio (or 3) to space gaps/shift(s) optimally - and racing gearsets are not as quiet as factory, so not especially desirable for a street car.

Ordered my 3rd/4th G50/02 sets new. Thought they were surprisingly reasonably priced, considering. One was "ship from Germany" and took a few weeks.

Optimal gearing is both personal and depends on many variables; how you drive, where you drive - and how the motor is tuned. I run SC cams, 3.2-sized ports and manifold. So my configuration makes useful boost by 2500 RPM w/ load, 80% of peak torque by 3000 RPM, peak torque is 4500 RPM, peak HP is 5500 RPM . The motor was built to be "safe" to rev out a lot higher. Although, semi-obviously, power is falling off a cliff by then according to the dyno charts...

You can always short-shift a tall 2nd, if you have torque - and a taller 2nd gives the flexibility to defer or avoid a shift in many situations. Or to drop down into it at a higher road speed, if that's advantageous. If your power band is higher or narrower - or a large turbo doesn't spool well low - this might not work as well for you.

Personally, for a primarily street-driven car, I'll happily trade many potential horses at high RPM (that I would get to use less than 1% of the time) against a flexible configuration delivering low/mid-range kick-in-the-pants throttle response. Because that gets used much more often in comparison.

No single set of gears can work in all situations/uses, they're all compromises. Why there's so many ratios offered/available ...

[Matt Monson]

You can’t put the NA 3.5 ratio mainshaft into a turbo case due to the 7.5” versus 9” ring gear. The shaft length and seal location are wrong. Only 2-3-4-5 are directly cross compatible.

[Newbie911]

Thanks for all the info Matt I really appreciate it.