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The car is dual purpose both Street in track including the highway. Currently second gear feels too high and that's my main complaint. Basically this box will be very close to what I would do if I kept the five speed and reheated it but it's a 993tt box so all Porsche gears and triple syncros on 1st and 2nd with 6th of course for cruising. 6th would probably only be used on the highway. Also has factory lsd but I plan on switching that out for a GT unit.
The car is dual purpose both Street in track including the highway. Currently second gear feels too high and that's my main complaint. Basically this box will be very close to what I would do if I kept the five speed and reheated it but it's a 993tt box so all Porsche gears and triple syncros on 1st and 2nd with 6th of course for cruising. 6th would probably only be used on the highway. Also has factory lsd but I plan on switching that out for a GT unit.
1st gear: 3.82
2nd gear: 2.15
3rd gear: 1.56
4th gear: 1.21
5th gear: 0.97
6th gear: 0.75
Ring and pinion: 3.44
Pete
There are many ways to look at a transmission
here is a comparison of a few w/ just the ratios
your's is the first one, I don't like it because of the big gap between 4 & 5, the g50/30 is the factory race transmission just about perfect, the g50/21 is the best street trans used in a 993
another way to see whats what is thrust or acceleration curves, here are the acceleration curves for an RSA w/ g50/03 vs the same car w/ your trans, I used this car because as we discussed you need the torque curve to start
Thanks Bill- but are you sure you have the right data point on 5th? It’s 0.97 and should max at 151mph @ 6800rpm
Looking at this is giving me some pause on the unit I’m considering. I’m not finding many other options in the 6 speed flavor and it does pull the gears closer together than the g50/03. I’m also open to regearing a 5 speed as long as I can find a quiet gear for cruise speeds but likely I’d end up with 1-5 similar to the 6 speed I’m considering in the end anyway. So it may not be the best gearing for a 6 speed but it kinda looks like what I’d end up with in a 5 speed.
I lifted this from Steve Wong’s site as I plan on chiping so my car should be very similar. If anyone knows an online source for calculating thrust curves I’d love to put in this data. The blue is with his chip on a stock 964.
There are many ways to look at a transmission
here is a comparison of a few w/ just the ratios
your's is the first one, I don't like it because of the big gap between 4 & 5, the g50/30 is the factory race transmission just about perfect, the g50/21 is the best street trans used in a 993
another way to see whats what is thrust or acceleration curves, here are the acceleration curves for an RSA w/ g50/03 vs the same car w/ your trans, I used this car because as we discussed you need the torque curve to start
There's definitely something wrong with this comparo chart since Pete's proposed G64/51 gearbox has IDENTICAL ratios to a G50/21 for 1-2-3. They only vary on 4-5-6, and not by much.
Thanks Bill- but are you sure you have the right data point on 5th? It’s 0.97 and should max at 151mph @ 6800rpm
Looking at this is giving me some pause on the unit I’m considering. I’m not finding many other options in the 6 speed flavor and it does pull the gears closer together than the g50/03. I’m also open to regearing a 5 speed as long as I can find a quiet gear for cruise speeds but likely I’d end up with 1-5 similar to the 6 speed I’m considering in the end anyway. So it may not be the best gearing for a 6 speed but it kinda looks like what I’d end up with in a 5 speed.
I lifted this from Steve Wong’s site as I plan on chiping so my car should be very similar. If anyone knows an online source for calculating thrust curves I’d love to put in this data. The blue is with his chip on a stock 964.
Pete
yes, I erred on your 5
here is the correct one, the acceleration curves are correct
Don't know what I'm missing then. Your own chart shows that a 50/21 is the same for 1-2-3, but your Peteinjp column is very different than that.
Your own 50/21 chart:
Don't know what I'm missing then. Your own chart shows that a 50/21 is the same for 1-2-3, but your Peteinjp column is very different than that.
Your own 50/21 chart:
I don't know what you are looking at both Pete and g50/21 are the same for 1-3
here' the raw data w/ tires which have an effective 24.6" diameter based on rolling radius(265/35 x18)
Petespeed @6800 38 67 93 119 149 193
g50/21speed @6800 38 67 93 116 141 176
I don't know what you are looking at both Pete and g50/21 are the same for 1-3
here' the raw data w/ tires which have an effective 24.6" diameter based on rolling radius(265/35 x18)
Petespeed @6800 38 67 93 119 149 193
g50/21speed @6800 38 67 93 116 141 176
jebus...i was standing on my head. Sorry, i was reading it upside down .
Thanks everyone for your input. Bill’s charts were useful in my decision specifically looking at the first chart showing various boxes compared. The g50/30- seems fun but I’m guessing the engine that is was intended for has a peakier torque curve than my basically stock 964. At this point I’m thinking of changing just 6th cause I don’t think the 964 will pull such a tall gear all the way to 197mph- and I’m not sure I’d want to anyway without some splitters/spoilers not to mention more experience behind the wheel. A lower 6th would be still fine as an overdrive. This example- just for comparisons sake- g50/21 0.82 6th which looks just perfect. I want a quiet gear for this so I’ll have to see what the builder has access too.
Anyway the point of the thread was for me was to decide about the purchase and that I have done. Hopefully I’ll be able to work out the details with the seller in short order.
In that case the box will be sent off to Bill Rader whom I spoke with this morning- thx Matt!
Also a big thanks to Steve Weiner who has been a very helpful and reassuring with his guidance.
Is there any reason you don't use the correct 6640 RPM rev-limit for the 964 in your spreadsheet?
For the same reason i try to use the same tires, these are gearbox comparisons for the most part , for a meaningful gear box comparison only the gears should be different
for other comparisons obviously other options would be used
Thanks everyone for your input. Bill’s charts were useful in my decision specifically looking at the first chart showing various boxes compared. The g50/30- seems fun but I’m guessing the engine that is was intended for has a peakier torque curve than my basically stock 964. At this point I’m thinking of changing just 6th cause I don’t think the 964 will pull such a tall gear all the way to 197mph- and I’m not sure I’d want to anyway without some splitters/spoilers not to mention more experience behind the wheel. A lower 6th would be still fine as an overdrive. This example- just for comparisons sake- g50/21 0.82 6th which looks just perfect. I want a quiet gear for this so I’ll have to see what the builder has access too.
Anyway the point of the thread was for me was to decide about the purchase and that I have done. Hopefully I’ll be able to work out the details with the seller in short order.
In that case the box will be sent off to Bill Rader whom I spoke with this morning- thx Matt!
Also a big thanks to Steve Weiner who has been a very helpful and reassuring with his guidance.
Fingers crossed........
Pete
You are correct that these cars will be aero limited w/ mosy drivetrains,
I thought I had posted this one, must have slipped up
Thanks Bill- do you happen to know the ratios on that 6 speed? Also would you explain the thrust units? If I understand correctly it’s feet per second- so for 3rd Gear the 6 speed is showing approx avg of say 1.25 ft/s2 over the 5 speed as it accelerats up to peak torque.
04-06-2018, 08:02 AM
How do we feel about these gear ratios?
