993 gear ratio advice
05-02-2011, 09:14 PM
#61
Rennlist Member
Hoosier R6 is actually 24.9. I only hit 135 before the bus stop, but you can still run a 2:07 at that top speed which is respectable with stock power. The other tire option is the 295 which is the same width as the 285, just a little taller 25.3. I would still add a couple hundred rpms top end and some more torque that the chip adds. The added rpm extends your corner gearing and helps get through the entire corner without a shift point.
05-02-2011, 10:12 PM
#62
Have you done a roll out on the Hoosier 285/30x18?? That's what I need.
I have that data for the tires I have used, as I stated for MPSC the 265/35x18 is speced @25.3" but has an actual loaded rolling height of ~24.6" when you do a roll out.
I have that data for the tires I have used, as I stated for MPSC the 265/35x18 is speced @25.3" but has an actual loaded rolling height of ~24.6" when you do a roll out.
05-02-2011, 11:45 PM
#64
Rennlist Member
Since RacerUniversity was brought into this discussion, I need to clarify a few things.
Kibort said it is just like Rennlist and he had a trial membership. Neither is particularly true. RacerU does use forum software but anyone who looks at the 'forums' can quickly see that virtually all of those areas are NOT discussion forums, they are read-only 'Classrooms'. Our model is to present material as short courses and we have a single discussion area to discuss those courses and closely related topics.
snip>>>>
Somehow, I think we can muddle along without Kibort's expertise.
RacerUniversity is very different than Rennlist or other discussion forums because we are NOT a discussion forum. We feel that our existence enhances places like Rennlist and I plan on remaining a participant in both places.
Kibort said it is just like Rennlist and he had a trial membership. Neither is particularly true. RacerU does use forum software but anyone who looks at the 'forums' can quickly see that virtually all of those areas are NOT discussion forums, they are read-only 'Classrooms'. Our model is to present material as short courses and we have a single discussion area to discuss those courses and closely related topics.
snip>>>>
Somehow, I think we can muddle along without Kibort's expertise.
RacerUniversity is very different than Rennlist or other discussion forums because we are NOT a discussion forum. We feel that our existence enhances places like Rennlist and I plan on remaining a participant in both places.
you want to think the few things I discussed and argued. heck you didnt even know what a Hp-second was, You thought it was made up by me based on your vast knowledge as an automotive engineer. Look, we both have equal experience on most of the topics, professionally. and the discussions were very tame. anyway, you then you wrote back and appologized. I was warned about the mulitple posts, i stopped but when winders kept on writing disrepectful posts, I responded to them. Sorry, I dont think I did anything wrong or unprofessional on your list. Im sure you will survive without me, and also sure you will propogate some miscoceptions that seem to plague this sport.
Now, you want to air your dirtly laundry here?
see you at the track!
crybaby, go tell your mamma?
by the way, I would NEVER threaten physical harm! I only suggested that when in person, I bet your spoiled brat attitude is different in person!
what are you , his mamma?
05-02-2011, 11:51 PM
#65
Rennlist Member
since the gears are nice and close, why not just change the rear end to achieve a 155mph top speed, or something in that range, rather than the complete rebuild and rematching of all the gear ratios?
Its seems, at first clance, (without know his tracks, shift points, etc) that it might be an easier solution.
Is there an available rear end that can be swapped out, like the 3.44 going to a 3.90 or something?
Wouldnt that solve the issue, since 1st is basically unused anyway?
thoughts?
Its seems, at first clance, (without know his tracks, shift points, etc) that it might be an easier solution.
Is there an available rear end that can be swapped out, like the 3.44 going to a 3.90 or something?
Wouldnt that solve the issue, since 1st is basically unused anyway?
thoughts?
Rick,
What you have there in gearing is a common budget approach for the G50/20 that I am not particularly fond of. What they have done is worked around your fixed 2nd gear ratio (which is on the shaft and unchangeable) and reused what was your stock 3rd gear in the 4th position. Then they plugged in replacement 3rd, 5th and 6th gears from there as new replacement gears. It makes for the funky RPM drops that Bill Verburg has higlighted with his charts.
In a perfect world, you would have a 993 Cup shaft where you can change second gear and make it an 80mph gear like others have suggested. But you can't. So the solution is generally to shorten up 3rd even a bit more than what you currently have in there. You put in something like a 1.65 or even down to 1.70 so that you are minimizing the number of times you are shifting below 3rd and crossing out of the 3-4 shift axis and into 2nd. 2nd ends up only being used on the one or two slowest corners on the track, otherwise you spend most of your time on the 3-4 axis and going back and forth between those two gears.
And that stock 3rd 1.407 gear in 4th, is still technically too tall of a gear ratio and can be shortened up by several positions as well. Probably 1.429 is what I would look at doing there.
Your 5th and 6th gears are a touch shorter than I would usually want to see on a 993 like yours, but gears are expensive, and if you follow the suggestions of bobt993 with the slightly larger tire and slightly higher redline, then you can probably get away without altering them. On this particular gearbox, you best gains in lap times and acceleration are going to be found in changing out those 3rd and 4th gears. HP and drag don't allow your vehicle much more than another 10mph straightaway top speed on all but the longest tracks. I'm guessing that whomever put that box together either had an engine that revved upward of 8000rpm or just assumed they'd never run their car at somewhere like Mosport or VIR.
And on that topic, 3 and 4 are the high wear gears anyways. You spend more time in 3rd and 4th than most anything else and when they get the box apart they are the gears most likely to be showing significant tooth wear, especially that short 1.632 3rd gear. For anything we make that is 1.632 or shorter in 3rd, we put a 50 hour motorsports life on it. I know that sounds really short, but we're really conversative and we also really only count that as actual "race" hours. So, if you spend a weekend with 3 hours of practice time, 30-45 minutes of qualifying, two 30 minute spring races and one 1 hour enduro, I would call that 2 1/2 hours of race life, even though you physically ran it twice that many hours. So for some people it's easier to just call them 100 hour gears. But the shorter the 3rd gear gets, and it starts to get down to 19 or 20 teeth on the idler, they get worked hard and wear fast.
Just some food for thought withouth getting bogged in that other mess. I've got no comments on the rest of that side conversation.
What you have there in gearing is a common budget approach for the G50/20 that I am not particularly fond of. What they have done is worked around your fixed 2nd gear ratio (which is on the shaft and unchangeable) and reused what was your stock 3rd gear in the 4th position. Then they plugged in replacement 3rd, 5th and 6th gears from there as new replacement gears. It makes for the funky RPM drops that Bill Verburg has higlighted with his charts.
In a perfect world, you would have a 993 Cup shaft where you can change second gear and make it an 80mph gear like others have suggested. But you can't. So the solution is generally to shorten up 3rd even a bit more than what you currently have in there. You put in something like a 1.65 or even down to 1.70 so that you are minimizing the number of times you are shifting below 3rd and crossing out of the 3-4 shift axis and into 2nd. 2nd ends up only being used on the one or two slowest corners on the track, otherwise you spend most of your time on the 3-4 axis and going back and forth between those two gears.
And that stock 3rd 1.407 gear in 4th, is still technically too tall of a gear ratio and can be shortened up by several positions as well. Probably 1.429 is what I would look at doing there.
Your 5th and 6th gears are a touch shorter than I would usually want to see on a 993 like yours, but gears are expensive, and if you follow the suggestions of bobt993 with the slightly larger tire and slightly higher redline, then you can probably get away without altering them. On this particular gearbox, you best gains in lap times and acceleration are going to be found in changing out those 3rd and 4th gears. HP and drag don't allow your vehicle much more than another 10mph straightaway top speed on all but the longest tracks. I'm guessing that whomever put that box together either had an engine that revved upward of 8000rpm or just assumed they'd never run their car at somewhere like Mosport or VIR.
And on that topic, 3 and 4 are the high wear gears anyways. You spend more time in 3rd and 4th than most anything else and when they get the box apart they are the gears most likely to be showing significant tooth wear, especially that short 1.632 3rd gear. For anything we make that is 1.632 or shorter in 3rd, we put a 50 hour motorsports life on it. I know that sounds really short, but we're really conversative and we also really only count that as actual "race" hours. So, if you spend a weekend with 3 hours of practice time, 30-45 minutes of qualifying, two 30 minute spring races and one 1 hour enduro, I would call that 2 1/2 hours of race life, even though you physically ran it twice that many hours. So for some people it's easier to just call them 100 hour gears. But the shorter the 3rd gear gets, and it starts to get down to 19 or 20 teeth on the idler, they get worked hard and wear fast.
Just some food for thought withouth getting bogged in that other mess. I've got no comments on the rest of that side conversation.
Last edited by mark kibort; 05-03-2011 at 12:17 AM.
05-03-2011, 12:29 AM
#66
Rick - just as a data point, my box was rebuilt with the following GT gears:
3rd gear 19 to 30 1.578947368 93.147
4th gear 21 to 27 1.285714286 114.391
5th gear 24 to 26 1.083333333 135.761
3rd gear 19 to 30 1.578947368 93.147
4th gear 21 to 27 1.285714286 114.391
5th gear 24 to 26 1.083333333 135.761
05-03-2011, 08:59 AM
#67
05-03-2011, 09:00 AM
#68
05-03-2011, 09:12 AM
#69
Rennlist Member
bill, that will wait since the car is up off the ground right now. Rick sending you my gearing info, but it is not that relevant since I have an open main shaft (2nd was changeable) and run a 25.6 tall tire now.
05-03-2011, 09:17 AM
#70
05-03-2011, 09:19 AM
#71
just some info on the fixed 1 & 2 gears
all of the /20 & /21 can have 3-6 changed easily enough, 1 & sometimes 2 are integral w/ the main shaft, the changeover trans #s are
G50.20 - 02693
G50.20 - 02174 (M220)
G50.21 - 05072
G50.21 - 03094 (M220)
before only 1 is fixed after 1 & 2 are fixed, to change them a new mainshaft is required(last price I saw Was ~$2000, I'me sure it's much more now)
check to see where yours lies wrt these #s
all of the /20 & /21 can have 3-6 changed easily enough, 1 & sometimes 2 are integral w/ the main shaft, the changeover trans #s are
G50.20 - 02693
G50.20 - 02174 (M220)
G50.21 - 05072
G50.21 - 03094 (M220)
before only 1 is fixed after 1 & 2 are fixed, to change them a new mainshaft is required(last price I saw Was ~$2000, I'me sure it's much more now)
check to see where yours lies wrt these #s
05-03-2011, 01:27 PM
#72
Nordschleife Master
Sorry for my redirection. I just saw the 3rd and 4th issues of the current stack and it's my opinion that your greatest gains in lap times and acceleration will be had by addressing them.
As for the top end issue, it could be addressed by simply changing your current 6th gear from a 1.063 to a 1.040. That would still leave you with an acceptable rpm drop on the 5-6 shift of just a bit over 1000rpms and probably get you to where you want to be.
Just an FYI, I tend to approach these sorts of questions as if it were my own money and don't assume bottomless pockets. When gears are going to run you more than $1000 each, every additional unit you have to add to the stack is not an insubstantial hit. When your builder gets that box apart, be sure they give that 3rd gear a really good inspection. If it's been in there a while it may need to come out whether or not you change the ratio on it.
Lastly, if it were a spare no expense build, I would suggest something close to what Bill posted yesterday following my initial post.
05-03-2011, 02:12 PM
#73
Bill - thanks for generating that data. I've had both 6th gear configurations (0.775 and 0.929) and since I don't use 6th on the track I opted for going with 0.775 for highway driving.
Rick - you're welcome to drive my 993 and see how you like it.
Rick - you're welcome to drive my 993 and see how you like it.
05-03-2011, 04:37 PM
#74
Addict
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Thread Starter
Join Date: Oct 2005
Location: On Rennlist, apparently
Posts: 4,447
Likes: 0
Received 37 Likes
on
18 Posts
Hi Blaine
I'd like that; transmission is headed off to G-Box tomorrow and so hopefully next week I'll be making some decisions.
Looks like I won't make it to LCMT for Blues Festival with NER this summer, due to a family wedding, but once this box gets back in the car I'll be ready!
I'd like that; transmission is headed off to G-Box tomorrow and so hopefully next week I'll be making some decisions.
Looks like I won't make it to LCMT for Blues Festival with NER this summer, due to a family wedding, but once this box gets back in the car I'll be ready!
