993 Tranny into 964
02-15-2012, 08:59 PM
#16
Here is a comparison of the thrust curves of a stock 993 G50/20 6 speed compared to a stock 964 G50/03 5 speed, same engine and wheel/tire setup
/20 in red, /03 in blue, 3rd is identical in both so is shown in green, 2nd is almost identical but the /03 will provide a tad more torque, /20 has way more 1st gear torque and way better 6th speed cruise
Both can be made much better for track use w/ regearing
the stock 964 does have some nice advantages in materials, like steel syncros and steel bearing cages, for track us the brass 993 syncros and plastic bearing cages suck
/20 in red, /03 in blue, 3rd is identical in both so is shown in green, 2nd is almost identical but the /03 will provide a tad more torque, /20 has way more 1st gear torque and way better 6th speed cruise
Both can be made much better for track use w/ regearing
the stock 964 does have some nice advantages in materials, like steel syncros and steel bearing cages, for track us the brass 993 syncros and plastic bearing cages suck
02-16-2012, 03:17 AM
#17
Rennlist Member
Thread Starter
Join Date: Feb 2010
Location: San Francisco, CA
Posts: 431
Likes: 0
Received 0 Likes
on
0 Posts
Boy am I glad I asked you guys before pulling that trigger ... And how I would love to regear my tranny if the costs were not so astronomical, I just can't bring myself to do it. 3k for final drive!?!? It only seems so much when compared to your average final drive costing around $500 to $1000 ...
But yes, thank you all for your input!
But yes, thank you all for your input!
02-16-2012, 02:17 PM
#18
Boy am I glad I asked you guys before pulling that trigger ... And how I would love to regear my tranny if the costs were not so astronomical, I just can't bring myself to do it. 3k for final drive!?!? It only seems so much when compared to your average final drive costing around $500 to $1000 ...
But yes, thank you all for your input!
But yes, thank you all for your input!
1 & 2 have been raised in the /30, 2 is actually usefully in 3 places on local tracks
3 - 6 have been lowered in the /30 combined w/ the taller 1-2 the rpm drops between gears have been reduced, 3,4, 5 are the primary track gears where the /03 would be limited to just 3 - 4
, Bill, How on earth do you have every graph and every picture ever taken in regards to every topic on here?!?!
02-16-2012, 04:11 PM
#21
Nordschleife Master
I love Bill's thrust force charts. Shows people what's really going on.
Though one remark I would make is that the G50/20 versus G50/03 chart has one item that's a little deceptive on paper. 1st gear has more thrust force in the 6 speed gearbox, but in actuality, that gear ratio is just too danged short. The practical reality is that either ratio provides more than enough power to the ground, and thus why the 1st gear in the G50/30 is yet even taller than either the G50/20 or G50/03 1st gear. What matters at the end of the day is the rpm drops on the 1-2 shift, which both the G50/03 and the G50/30 do better than the G50/20.
For building a race geared box, that G50/03 5spd is a pretty good starting point both because of that 3.50 ratio first gear and the fact that 2nd gear is swappable without investing in a new mainshaft. On all but the early (first +/-1.5 years of production) G50/20's 2nd gear is stuck on the shaft as well as first, and when gearing one for the track you've either got to work around that 2nd gear ratio or bite the bullet and get both a new mainshaft and 2nd gear. When a mainshaft cost $2-3k, you can double the cost of your regearing with one single part on a 993 box.
And then there's the synchros. 6spd motorsports steel synchros for 2nd gear cost about $1800!!! A steel 2nd gear synchro for a 964 is more like $275. On a 964 box, you can usual skip the expense of a new mainshaft unless you're chasing a national championship in your class, and avoiding those stupid expensive Cup 2nd gear 3 piece steel synchros is a set of tires contributed to your consumables budget...
Though one remark I would make is that the G50/20 versus G50/03 chart has one item that's a little deceptive on paper. 1st gear has more thrust force in the 6 speed gearbox, but in actuality, that gear ratio is just too danged short. The practical reality is that either ratio provides more than enough power to the ground, and thus why the 1st gear in the G50/30 is yet even taller than either the G50/20 or G50/03 1st gear. What matters at the end of the day is the rpm drops on the 1-2 shift, which both the G50/03 and the G50/30 do better than the G50/20.
For building a race geared box, that G50/03 5spd is a pretty good starting point both because of that 3.50 ratio first gear and the fact that 2nd gear is swappable without investing in a new mainshaft. On all but the early (first +/-1.5 years of production) G50/20's 2nd gear is stuck on the shaft as well as first, and when gearing one for the track you've either got to work around that 2nd gear ratio or bite the bullet and get both a new mainshaft and 2nd gear. When a mainshaft cost $2-3k, you can double the cost of your regearing with one single part on a 993 box.
And then there's the synchros. 6spd motorsports steel synchros for 2nd gear cost about $1800!!! A steel 2nd gear synchro for a 964 is more like $275. On a 964 box, you can usual skip the expense of a new mainshaft unless you're chasing a national championship in your class, and avoiding those stupid expensive Cup 2nd gear 3 piece steel synchros is a set of tires contributed to your consumables budget...
02-16-2012, 07:48 PM
#22
I love Bill's thrust force charts. Shows people what's really going on.
Though one remark I would make is that the G50/20 versus G50/03 chart has one item that's a little deceptive on paper. 1st gear has more thrust force in the 6 speed gearbox, but in actuality, that gear ratio is just too danged short. The practical reality is that either ratio provides more than enough power to the ground, and thus why the 1st gear in the G50/30 is yet even taller than either the G50/20 or G50/03 1st gear. What matters at the end of the day is the rpm drops on the 1-2 shift, which both the G50/03 and the G50/30 do better than the G50/20.
For building a race geared box, that G50/03 5spd is a pretty good starting point both because of that 3.50 ratio first gear and the fact that 2nd gear is swappable without investing in a new mainshaft. On all but the early (first +/-1.5 years of production) G50/20's 2nd gear is stuck on the shaft as well as first, and when gearing one for the track you've either got to work around that 2nd gear ratio or bite the bullet and get both a new mainshaft and 2nd gear. When a mainshaft cost $2-3k, you can double the cost of your regearing with one single part on a 993 box.
And then there's the synchros. 6spd motorsports steel synchros for 2nd gear cost about $1800!!! A steel 2nd gear synchro for a 964 is more like $275. On a 964 box, you can usual skip the expense of a new mainshaft unless you're chasing a national championship in your class, and avoiding those stupid expensive Cup 2nd gear 3 piece steel synchros is a set of tires contributed to your consumables budget...
Though one remark I would make is that the G50/20 versus G50/03 chart has one item that's a little deceptive on paper. 1st gear has more thrust force in the 6 speed gearbox, but in actuality, that gear ratio is just too danged short. The practical reality is that either ratio provides more than enough power to the ground, and thus why the 1st gear in the G50/30 is yet even taller than either the G50/20 or G50/03 1st gear. What matters at the end of the day is the rpm drops on the 1-2 shift, which both the G50/03 and the G50/30 do better than the G50/20.
For building a race geared box, that G50/03 5spd is a pretty good starting point both because of that 3.50 ratio first gear and the fact that 2nd gear is swappable without investing in a new mainshaft. On all but the early (first +/-1.5 years of production) G50/20's 2nd gear is stuck on the shaft as well as first, and when gearing one for the track you've either got to work around that 2nd gear ratio or bite the bullet and get both a new mainshaft and 2nd gear. When a mainshaft cost $2-3k, you can double the cost of your regearing with one single part on a 993 box.
And then there's the synchros. 6spd motorsports steel synchros for 2nd gear cost about $1800!!! A steel 2nd gear synchro for a 964 is more like $275. On a 964 box, you can usual skip the expense of a new mainshaft unless you're chasing a national championship in your class, and avoiding those stupid expensive Cup 2nd gear 3 piece steel synchros is a set of tires contributed to your consumables budget...
when I installed a 3.6 in the C3 I felt that the stock 915/44 was a bit short, I replaced it w/ a 915/67 which is(IMO) perfect for street use and compares favorably to the full race /30
02-16-2012, 08:35 PM
#23
It's great to have Bill and Matt around here, thanks for the info. I went with a tall 1st, ratio is 3, which I think is just a tad taller that a /30 or /31. Second gear ratio is 2.133. My RPM splits are 2023/1585/1345/1224/1138, 1-6 at 7000. This will be street driven for fun.
02-17-2012, 12:50 PM
#24
Nordschleife Master
Bill and Bob, you guys are both welcome. I'm one of these lucky guys who found a job that is identical to his passion. Cars are what gets me up in the morning and the fact that going to work has me associated with them is just a dream come true.
If you're running a 3.00 1st gear, it's quite likely one of ours. We did that on purpose. The Cup 3.154 1st is a 13:41 and the 3.167 is a 12:38 toothcount. Our 3.00 is a 12:36 toothcount. By reducing the toothcount we are able to make individual teeth that have a wider and resultingly stronger root. We've actually got an engineering program that runs the load forces across the teeth at different toothcounts. We're able to calculate what would be too few teeth and would actually weaken the gear by having all the load go through a single tooth at once versus being spread out over several teeth. It's a balancing act to reduce the count to a point that the teeth are bigger but not so much so that one tooth carries too much load at one time. OEMs use high toothcount for NVH. For race gears we toss that out the window and focus on what's going to perform best and last.
Regards,
Matt
If you're running a 3.00 1st gear, it's quite likely one of ours. We did that on purpose. The Cup 3.154 1st is a 13:41 and the 3.167 is a 12:38 toothcount. Our 3.00 is a 12:36 toothcount. By reducing the toothcount we are able to make individual teeth that have a wider and resultingly stronger root. We've actually got an engineering program that runs the load forces across the teeth at different toothcounts. We're able to calculate what would be too few teeth and would actually weaken the gear by having all the load go through a single tooth at once versus being spread out over several teeth. It's a balancing act to reduce the count to a point that the teeth are bigger but not so much so that one tooth carries too much load at one time. OEMs use high toothcount for NVH. For race gears we toss that out the window and focus on what's going to perform best and last.
Regards,
Matt
