993 6 Speed into 964 C2

[drola]

i'm contemplating putting a g50/20 6 speed from a 1998 993 into my 1990 C2.
from everything I've read so far it is a pretty easy swap. a little mod here and there but overall not too bad.
my question is - is it worth the trouble?
I always read that 6 speeds are THE way to go. now i see that the g50/30,31 are the way to go. the g50/20 not so much
i did a gearing comparison between my stock and the 993.
964 - 3.5, 2.059, 1.407, 1.086 and 0.868
993 - 3.818, 2.048, 1.407, 1.118, 0.921 and 0.775
are these differences in ratios worth the swap? the car is primarily a street car with an occasional track day.

[Bill Verburg]

Originally Posted by drola

i'm contemplating putting a g50/20 6 speed from a 1998 993 into my 1990 C2.
from everything I've read so far it is a pretty easy swap. a little mod here and there but overall not too bad.
my question is - is it worth the trouble?
I always read that 6 speeds are THE way to go. now i see that the g50/30,31 are the way to go. the g50/20 not so much
i did a gearing comparison between my stock and the 993.
964 - 3.5, 2.059, 1.407, 1.086 and 0.868
993 - 3.818, 2.048, 1.407, 1.118, 0.921 and 0.775
are these differences in ratios worth the swap? the car is primarily a street car with an occasional track day.

Depends the 964 g50/03 is much better than the 964 g50/05 the g50/20 is

here's a visual comparison


and a survey

[Matt Monson]

Not worth it imo. I like the 1 piece synchros on 1-2 on the 5spd better than the 3 piece design on the 6 spd. It’s serviceable when the dogs go bad. A g50/03 and a g50/20 are nearly identical 1-4. The real difference is 5th versus 5-6. For a lot less money add an LSD and regear your existing box and never look back.


Also, have you shopped for a six sod yet? singer is buying them all cuts made finding them hard and driven up the core price $2000-2500 over what they were a couple years back. Ymmv.

[Bill Verburg]

here are the thrust curves comparing an /03, /05 & /20 in the same chassis


the /03 & /20 are clones in 2nd and 3rd, the differences are in the other gears

One of the better features of the /20 is it closes up the gap between 4 and 5 in the 5 speeds then gives a better cruise in the top gear

[drola]

What would be the ideal regear? i don't want to lose the comfort of the 5th gear ratio
what about putting a shorter final drive on the g50/20? (since i already have the box)
the reason i mention 5th gear is because a buddy of mine put a shorter final drive on his 1990 C2 and his highway cruising in 5th gear was dramatically changed. he's at 4k rpm's at 80 mph while mine is at 100 mph at 4k rpm's

[Bill Verburg]

Originally Posted by drola

What would be the ideal regear? i don't want to lose the comfort of the 5th gear ratio
what about putting a shorter final drive on the g50/20? (since i already have the box)
the reason i mention 5th gear is because a buddy of mine put a shorter final drive on his 1990 C2 and his highway cruising in 5th gear was dramatically changed. he's at 4k rpm's at 80 mph while mine is at 100 mph at 4k rpm's

No such thing as one size fits all ideal, it depends on what you want out of the car,

look at the above thrust charts to see the effects of different gearing, a 1990 964 C2 gas a g50/03 which is pretty nicely matched to the torque curve and weight of a stock 964.

The benefit of a g50/20 iis better acceleration in 1st, look at the red curve vs the blue

2nd & 3rd are a wash as there is no change

as you go to 4 the /20 has the edge in acceleration and because there is a smaller rpm drop 3 to 4

go to 5 the /20 has an even bigger edge in acceleration and smaller rpm drop.

here the /03 is done , the /20 then has that tall 6th for cruise. My opinion is that it's too tall but that is subjective, others will like it.

IMO For sporting use w/ almost no freeway cruise the /30 is best
here is the same comparison as above but w/ a /30 instead of a /20


Here the red line is a /30
in 1 the /30 has less acceleration but higher speed, this is great for pit road, getting on/off a track, no so good for drag racing same thing in 2

3 - 5 are the money gears on track the /30 is lower and closer together, better acceleration and lower drops

6 is still a reasonable cruise though slightly busier than an /03

[Matt Monson]

Porsche Classic has a 4.00 final drive (avoid the Albins unit, they are loud and poorly wearing) but it's pretty expensive. I think it's close to $4k. And then it's about twice the labor to install as doing a gear stack.

What we usually end up doing for people is something closer to a 996 Cup than the 993 Cup ratios. Something along the lines of 1.57 3rd, 1.33 4th and 1.12 5th and then the stock 5th in the 6th gear position. That puts you at around $3500 in gears and +/-$1000 in labor. That doesn't count new synchros or sliders, that you would want to consider anytime you go into the box since the labor is already being done to "rebuild" it.

If you stuck with the 5spd, we've recently gone back to making 5spd ratios and have been doing a stack for Sharkwerks that's been written up in a few cars like Joe Rogan's and Matt Farah's personal 964s. It's a 2.19 2nd, 1.53 3rd and 1.174 4th. 5th gets left stock for cruising.

Our gears do make noise since they are motorsports parts and designed for strength, durability and minimum driveline loss, whereas the factory gears emphasize NVH. But that's why we tell you to use the stock 5th in either configuration so you can still highway cruise. The only time the 5spd version I've suggested would require one of our 5th gears is if you are tracking the car a lot and drive it places where you go over 120mph. I won't take a car with the big 4-5 gap out to Daytona, but a lot of the shorter country club tracks are just fine with it.

[Bill Verburg]

Here's a survey including some 996 Cup & RS transmissions



I do like the slightly taller 6 in the 996 Cup /91 w/ 3.44 CWP. I totally dislike a CWP change as all it does is make everything shorter, it's ok for an 8500 rpm motor but does little to nothing for a street or dual use car.

[drola]

Thanks for the insight. Since i already the gearbox i need to decide what to do with it. Either put it in or sell it and use the funds to upgrade my original. From what Bill is saying it still sounds like it’s an improvement in gearing over the five speed

[Matt Monson]

Since 2 &3 are the same on 5 and 6spd all the gains are above 100mph. If you are looking for daily driving and country road performance it will offer no gains.

[Bill Verburg]

Originally Posted by Matt Monson

Since 2 &3 are the same on 5 and 6spd all the gains are above 100mph. If you are looking for daily driving and country road performance it will offer no gains.

I agree the advantage of the /20 vs an /03 is in 1 and 6. 1 is better off the line, 6 gives a more relaxed cruise. Don't knock the relaxed cruise, I am always reaching for 6 in my street car w/ 3.6 and 915 even though I don't do much freeway driving.

[jjeffries]

One of the things i like about modern cars, even the most prosaic, is the high gearing for top gear highway cruising. Granted, they have the engine management to make it work.
Bill, I'm always amazed at how much info you present to us. You must have a seriously capable noggin! I always learn something. Kind regards to all on this thread, John

[Matt Monson]

Originally Posted by Bill Verburg

I agree the advantage of the /20 vs an /03 is in 1 and 6. 1 is better off the line, 6 gives a more relaxed cruise. Don't knock the relaxed cruise, I am always reaching for 6 in my street car w/ 3.6 and 915 even though I don't do much freeway driving.

Not knocking it at all. I think my previous posts actually warn against giving it up if you require it and encourage people to make highway cruising a consideration in their decisions.