3.09 ring & pinion
11-17-2005, 07:33 PM
#421
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Originally Posted by Jim bailey - 928 International
Mark .." remember the beaten to the ground 26% net gain?" so how are you determining this 26 % ? In 50 words or less please...
11-17-2005, 08:18 PM
#422
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They say you only get 10% retention for reading and comprehending the written word. so, 10% of 500 is about 50! 
mk
mk
Originally Posted by heinrich
SWEET ... Mark's reply was only 543 words Jim
11-17-2005, 09:22 PM
#423
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The comprehension depends greatly on who is doing the writing... the numerous assumptions about what happens from zero to 25 mph have skewed what is probably a reasonably accurate mathematical exercise. Running the engine 40 percent faster from zero to 39 MPH means that when the 2:20 is putting out 125 hp at 2,500 rpm the 3:09 is running at 3,500 rpm and about 200 hp. that is a 75 hp difference but a whopping 60 percent increase in horsepower driving through a much lower gear. The 2.20 at 3,500 is racing against the 3:09 at 4,900 rpm 200 hp against 270 hp or so still some 35 percent more horsepower. Old pickup tricks used to have a "granny gear" a super low low or creeper gear. You could put it in gear let out the clutch and get out of the truck and walk along beside it . It allowed rather small engines to move big loads or climb very steep grades just not very quickly. I believe that horsepower can become torque by using lower gears.
11-17-2005, 10:29 PM
#424
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I went on the gear ratio quest and came up with this:
Direct link to thread
Originally Posted by kjcracer
Well since my name has come up in this thread, maybe you'd like to know the story about what we were up to with 928 gearing and modifications, as I see (saw back over 10 years ago) them? If so, please read on...oh, it's a bit long... it's a complicated subject.
There is a standard old trick: narrow up the gear "splits" in the car...so it can have a narrower power band, and then cam it wilder for that narrower rpm band. A lot more power in a narrower rpm band...and the (new) narrower gear splits make it work effectively. When I looked at the manual 928 gearbox, I saw factory gear splits that look something like this: 1st to 2nd and 2nd to 3rd, approximately 2000 rpm drops (when shifting near the engine redline) and 3rd to 4th and 4th to 5th about 1500 rpm drops. The exception is the USA 83-88 "EPA" gearboxes that also put in a 2000 rpm drop between 4th and 5th, along with the 2.20 r&p. (OUCH, if you ever need 5th gear at your racetrack with that gearbox!)
Why was Porsche up to? (When not trying to get around some arcane EPA rules.) Well, notice that they're "narrowing" the splits some, as the speed goes up. They know the engine had better be in the best part, think of it as the "sweet spot," of the power band as the speeds go up (I'm sure you've all noticed the available acceleration is less at higher speeds/gears.)
My idea? A real close-ratio gearbox for the 928...really enabling us to "cam up" the engine, too...just applying classic theory to our car. So, building on all the discussions so far on this thread, here was my three part plan:
1) 3.09 ring and pinion (deepest that fits the case, keeping-up the strength
of the parts)
2) close-up the layshaft ratio even more (makes the 4-5 shift "closer")
3) pull-up 1st and 2nd gear, too... (close them up, more, too)
This would give gear splits like this:
1-2 shift 2000 rpm (vehicle is least sensitive to power band at this speed)
2-4 shift 1,750 rpm (closer)
3-4 shift 1,500 rpm (stock)
4-5 shift 1,300 rpm (really close)
I think you get the idea. As the speeds go up, we'd operate in a narrower, just the best, part of the rpm band of the engine. We'd be able to highly cam the engine, and really make it really work...there is a synergistic effect. We'd have more ideal gearing for nearly any roadrace track, as we weren't working so close to the edges of the engine band.
So what happened to this idea? I had a couple PCA 928 S4 and a new GTS owner who wanted to try this idea. Finding a company to make parts for an o.e. transaxle wasn't easy (do this aftermarket limited slip, please!) but I did find Houseman Automotive in London, Ontario, Canada. I sent o.e. samples to Jamie, and he went to work.
The first part was the 3.09 ring and pinion. I drove Jim's car at Lime Rock in 1995 with it. Fast. The in-car camera videotape "agrees"...we made mincemeat out of the instructor group, after being first told they didn't feel 928s were fast enough for the (red) group. That notion got settled, then...
Next? It was time for the next steps. To change the layshaft and also make the custom 1st & 2nd gearset. While the 3.09 had been utterly reliable, these parts had subsequent failures. To this day, I can't even be sure what happened....I couldn't believe that some shop had machined the parts after they got them, installing them without consulting anybody. And then took no responsibility. I think we may have worked through the problems on these parts...but...the affected members were out of patience. Hey, development work sometimes is painful, so while I was disappointed, I understood the choice to continue/or not was theirs.
About the same time, PCA National nixed my proposed 4-valve 928 follow-up story to my 2-valve "Project 928" trilogy (from back in the summer of '91) so I now had little personal reason, or funds, to move forward alone. The whole project was stopped, "mid-stream." The 3.09 ring & pinion is the only product that I could call reliable, without any further work.
This concept would have fullfilled all the criteria to make a great close-ratio 928 gearbox...allowing us to do classic camshaft hotrod power boosts! Thought you'd like to know what the original idea was, and what happened to this little-known project...the close-ratio 928 gearbox.
If you look at details, you'll see that the stock 4-5 shift is much tighter than the 2-3 shift (on the "good" USA gearboxes, anyway ) I feel the 3.09 r&p, alone, is often a small improvement (again, not the "EPA" boxes, those need more changes.) Why? At least you're using the closest "gear splits" the factory offered...the 3-4 and 4-5, 1500 rpm splits...eliminating the 2000 rpm drop 2-3 shift at all but the slowest tracks. Yes, you will be limited to 150- 155 mph top speed depending on your actual engine rpm limit...but there aren't many tracks where you actually go faster than that.
If want to argue about this, please spare me. Take it up with the race guys at the factory! Yes, I was reading a copy of the new/revised "Excellence Was Expected" three-volume history book series on Porsche last week. Great reading, with plenty of 928 details in the appropriate chapters.... including? Guess what ring and pinion the factory came up for a race 928 Euro S, in 1983, for several races? A 3.09. Page 1070, Chapter 47 which is called: "Ultimate Eights" (in Volume Three.) You can check it out yourself...oh, and send congrats to Mark Anderson for getting mentioned on the same very page! I am not foolish enough to argue basics with the factory motorsport engineers, people like Helmet Flegl...those guys have probably "forgotten more" than any of us will ever know. Certainly if they thought enough of this idea to make a custom race part, there is merit. I hope I've explained (somewhat) the overall view of "why," and I'm only sorry to report that the close-ratio 928 gearbox project never got finished, only the 3.09 ring & pinion made it through the development process. With 20/20 hindsight, I am glad to see the factory agreed, valdidating the idea for motorsport application. Hope all this clarifies things some. Thanks for listening. Kim
There is a standard old trick: narrow up the gear "splits" in the car...so it can have a narrower power band, and then cam it wilder for that narrower rpm band. A lot more power in a narrower rpm band...and the (new) narrower gear splits make it work effectively. When I looked at the manual 928 gearbox, I saw factory gear splits that look something like this: 1st to 2nd and 2nd to 3rd, approximately 2000 rpm drops (when shifting near the engine redline) and 3rd to 4th and 4th to 5th about 1500 rpm drops. The exception is the USA 83-88 "EPA" gearboxes that also put in a 2000 rpm drop between 4th and 5th, along with the 2.20 r&p. (OUCH, if you ever need 5th gear at your racetrack with that gearbox!)
Why was Porsche up to? (When not trying to get around some arcane EPA rules.) Well, notice that they're "narrowing" the splits some, as the speed goes up. They know the engine had better be in the best part, think of it as the "sweet spot," of the power band as the speeds go up (I'm sure you've all noticed the available acceleration is less at higher speeds/gears.)
My idea? A real close-ratio gearbox for the 928...really enabling us to "cam up" the engine, too...just applying classic theory to our car. So, building on all the discussions so far on this thread, here was my three part plan:
1) 3.09 ring and pinion (deepest that fits the case, keeping-up the strength
of the parts)
2) close-up the layshaft ratio even more (makes the 4-5 shift "closer")
3) pull-up 1st and 2nd gear, too... (close them up, more, too)
This would give gear splits like this:
1-2 shift 2000 rpm (vehicle is least sensitive to power band at this speed)
2-4 shift 1,750 rpm (closer)
3-4 shift 1,500 rpm (stock)
4-5 shift 1,300 rpm (really close)
I think you get the idea. As the speeds go up, we'd operate in a narrower, just the best, part of the rpm band of the engine. We'd be able to highly cam the engine, and really make it really work...there is a synergistic effect. We'd have more ideal gearing for nearly any roadrace track, as we weren't working so close to the edges of the engine band.
So what happened to this idea? I had a couple PCA 928 S4 and a new GTS owner who wanted to try this idea. Finding a company to make parts for an o.e. transaxle wasn't easy (do this aftermarket limited slip, please!) but I did find Houseman Automotive in London, Ontario, Canada. I sent o.e. samples to Jamie, and he went to work.
The first part was the 3.09 ring and pinion. I drove Jim's car at Lime Rock in 1995 with it. Fast. The in-car camera videotape "agrees"...we made mincemeat out of the instructor group, after being first told they didn't feel 928s were fast enough for the (red) group. That notion got settled, then...
Next? It was time for the next steps. To change the layshaft and also make the custom 1st & 2nd gearset. While the 3.09 had been utterly reliable, these parts had subsequent failures. To this day, I can't even be sure what happened....I couldn't believe that some shop had machined the parts after they got them, installing them without consulting anybody. And then took no responsibility. I think we may have worked through the problems on these parts...but...the affected members were out of patience. Hey, development work sometimes is painful, so while I was disappointed, I understood the choice to continue/or not was theirs.
About the same time, PCA National nixed my proposed 4-valve 928 follow-up story to my 2-valve "Project 928" trilogy (from back in the summer of '91) so I now had little personal reason, or funds, to move forward alone. The whole project was stopped, "mid-stream." The 3.09 ring & pinion is the only product that I could call reliable, without any further work.
This concept would have fullfilled all the criteria to make a great close-ratio 928 gearbox...allowing us to do classic camshaft hotrod power boosts! Thought you'd like to know what the original idea was, and what happened to this little-known project...the close-ratio 928 gearbox.
If you look at details, you'll see that the stock 4-5 shift is much tighter than the 2-3 shift (on the "good" USA gearboxes, anyway ) I feel the 3.09 r&p, alone, is often a small improvement (again, not the "EPA" boxes, those need more changes.) Why? At least you're using the closest "gear splits" the factory offered...the 3-4 and 4-5, 1500 rpm splits...eliminating the 2000 rpm drop 2-3 shift at all but the slowest tracks. Yes, you will be limited to 150- 155 mph top speed depending on your actual engine rpm limit...but there aren't many tracks where you actually go faster than that.
If want to argue about this, please spare me. Take it up with the race guys at the factory! Yes, I was reading a copy of the new/revised "Excellence Was Expected" three-volume history book series on Porsche last week. Great reading, with plenty of 928 details in the appropriate chapters.... including? Guess what ring and pinion the factory came up for a race 928 Euro S, in 1983, for several races? A 3.09. Page 1070, Chapter 47 which is called: "Ultimate Eights" (in Volume Three.) You can check it out yourself...oh, and send congrats to Mark Anderson for getting mentioned on the same very page! I am not foolish enough to argue basics with the factory motorsport engineers, people like Helmet Flegl...those guys have probably "forgotten more" than any of us will ever know. Certainly if they thought enough of this idea to make a custom race part, there is merit. I hope I've explained (somewhat) the overall view of "why," and I'm only sorry to report that the close-ratio 928 gearbox project never got finished, only the 3.09 ring & pinion made it through the development process. With 20/20 hindsight, I am glad to see the factory agreed, valdidating the idea for motorsport application. Hope all this clarifies things some. Thanks for listening. Kim
Direct link to thread
11-18-2005, 01:17 AM
#425
Rennlist Member
oh god, please dont even go there. i dont think there is a sentence in this that isnt a little wrong , if not completely wrong.
Let me know if you want the corrected version sent to you via PM. dont want to bore anyone with the rebuttle. I think my replies may be on the thread.
In a nut shell, we have very good gear box spacing. in fact, the 3.09 on a GTS gear box, makes even more of a S4 gear box than an S4 2.2 with a 3.09.
He noticed a differnce, but Ive seen his incar video tapes. Ive also seen his 6 second variances of tire tests, with DOT tires, where ive never seen more than 1 seconds variance with any number of DOT tires. again, you have the data, right from me and from the computer. besides launch, a 3.09 on a 2.2 box, only modifies the "sub 1st gear" For Kim, a sometimes time trial, instructor, sometimes road racer, he would never even be in that sub 1st gear. wanna know why???? because in road racing there are very very few corners where you are ever below 40mph, if any!! (in the USA) . So, after knowing what you know now, why would you believe anyone that has a 3.09 on a stock S4 or GTS gear box, that says, " I felt the difference!"
Mk
Let me know if you want the corrected version sent to you via PM. dont want to bore anyone with the rebuttle. I think my replies may be on the thread.
In a nut shell, we have very good gear box spacing. in fact, the 3.09 on a GTS gear box, makes even more of a S4 gear box than an S4 2.2 with a 3.09.
He noticed a differnce, but Ive seen his incar video tapes. Ive also seen his 6 second variances of tire tests, with DOT tires, where ive never seen more than 1 seconds variance with any number of DOT tires. again, you have the data, right from me and from the computer. besides launch, a 3.09 on a 2.2 box, only modifies the "sub 1st gear" For Kim, a sometimes time trial, instructor, sometimes road racer, he would never even be in that sub 1st gear. wanna know why???? because in road racing there are very very few corners where you are ever below 40mph, if any!! (in the USA) . So, after knowing what you know now, why would you believe anyone that has a 3.09 on a stock S4 or GTS gear box, that says, " I felt the difference!"
Mk
Originally Posted by Shane
11-18-2005, 01:33 AM
#426
Rennlist Member
Jim,
HP IS torque at any vehicle speed through the gears.
the average hp of the range, not the peak hp differences is what you need to look at , as its the hp applied over time that is important to look at.
you integrate to whatever resolution you want, but use the range all the way to redline. (ie up to 39mph) you can even verify this by plugging in a 60hp difference overall, and seeing the similar acceleration. 60hp was the average differnce or near 20%.
your numbers may be off a bit. here are the ones i used, right from the published baseline s4 curves.
3300rpm 180
3500 rpm 180hp
4000 200hp
4500 210hp
5000 285
5500 260
6000 263
6500 250
this means the aveage torque to the wheels with a 40% ratio difference with the 3.09 gear box looks like this
with a 3500rpm launch with a 2.2 to 39mph is about 195hp ave hp
with a 4500rpm launch with a 3.09 to 39mph is about 250hp.
the launching hp would be 45hp at the start
the ending hp at 39mph would be 35hp at the end.
because we are dealing with curves, the more you integrate, the better the result of the averaging, fits the data.
The difference in hp to the wheels witha stock S4 is about 55hp as shown here.
this is about 20% of a gain overall from 0-39mph, ignoring grip, driver, etc.
dont look at hp through a set of gears. thinking or saying this is redundant. you would look at torque through the gears at a series of rpms. (which actually equals hp at any of the respective speeds.).
Mk
HP IS torque at any vehicle speed through the gears.
the average hp of the range, not the peak hp differences is what you need to look at , as its the hp applied over time that is important to look at.
you integrate to whatever resolution you want, but use the range all the way to redline. (ie up to 39mph) you can even verify this by plugging in a 60hp difference overall, and seeing the similar acceleration. 60hp was the average differnce or near 20%.
your numbers may be off a bit. here are the ones i used, right from the published baseline s4 curves.
3300rpm 180
3500 rpm 180hp
4000 200hp
4500 210hp
5000 285
5500 260
6000 263
6500 250
this means the aveage torque to the wheels with a 40% ratio difference with the 3.09 gear box looks like this
with a 3500rpm launch with a 2.2 to 39mph is about 195hp ave hp
with a 4500rpm launch with a 3.09 to 39mph is about 250hp.
the launching hp would be 45hp at the start
the ending hp at 39mph would be 35hp at the end.
because we are dealing with curves, the more you integrate, the better the result of the averaging, fits the data.
The difference in hp to the wheels witha stock S4 is about 55hp as shown here.
this is about 20% of a gain overall from 0-39mph, ignoring grip, driver, etc.
dont look at hp through a set of gears. thinking or saying this is redundant. you would look at torque through the gears at a series of rpms. (which actually equals hp at any of the respective speeds.).
Mk
Originally Posted by Jim bailey - 928 International
The comprehension depends greatly on who is doing the writing... the numerous assumptions about what happens from zero to 25 mph have skewed what is probably a reasonably accurate mathematical exercise. Running the engine 40 percent faster from zero to 39 MPH means that when the 2:20 is putting out 125 hp at 2,500 rpm the 3:09 is running at 3,500 rpm and about 200 hp. that is a 75 hp difference but a whopping 60 percent increase in horsepower driving through a much lower gear. The 2.20 at 3,500 is racing against the 3:09 at 4,900 rpm 200 hp against 270 hp or so still some 35 percent more horsepower. Old pickup tricks used to have a "granny gear" a super low low or creeper gear. You could put it in gear let out the clutch and get out of the truck and walk along beside it . It allowed rather small engines to move big loads or climb very steep grades just not very quickly. I believe that horsepower can become torque by using lower gears.
Last edited by mark kibort; 11-18-2005 at 03:05 AM.
11-18-2005, 03:20 AM
#427
Rennlist Member
[QUOTE=Shane]I went on the gear ratio quest and came up with this:
Shane, you couldnt just PM me on this one?? now i had to plug it all in the simulator
new values using a stock S4 curve (previous set of values were for the holbert car)
acceleration rates with g forces * from simulator
S4 with 3.09 / S4 with 2.2 / GTS gear box with 3.09 on s4
30mph .71 .51 .71
40 .54 .58 .5
50 .52 .536 .49
60 .38 .383 .41
70 .36 .36 .34
80 .314 .313 .32
90 .256 .245 .239
100 .231 224 .221
you can see that the the GTS and the S4 with the 3.09 get out and have a great launch having much more acceleration from 0-35 to and 0-39mph. (GTS to 35mph)
after that, the gTS has the poorest acceleration rates after 40mph. i think at one point, at 60mph, the GTS has the fastest rate of acceleration, but aside from that, every single 10mph increment, it accelerates slower. the net net of a 3.09 on a GTS gear box, on an S4 engine, is it is a loosing proposition, unless you are a drag racer from a dead stop. actually its 1/4 mile time would match the S4 with 3.09, and its only real advantage would be to 60mph over both, due to the launch. So for a road racer or anyone using a 928 at speeds above stopped (ie road racing, street driving, etc) the 3.09 would be a waste of time and money to put on a GTS gear box.
remember all this changes slightly with differnet engine hp profiles, and net hp levels. you can see this comparison had all 3 cars in the mid 13 seconds and a top speed in the 105mph range.
mk
Shane, you couldnt just PM me on this one?? now i had to plug it all in the simulator
new values using a stock S4 curve (previous set of values were for the holbert car)
acceleration rates with g forces * from simulator
S4 with 3.09 / S4 with 2.2 / GTS gear box with 3.09 on s4
30mph .71 .51 .71
40 .54 .58 .5
50 .52 .536 .49
60 .38 .383 .41
70 .36 .36 .34
80 .314 .313 .32
90 .256 .245 .239
100 .231 224 .221
you can see that the the GTS and the S4 with the 3.09 get out and have a great launch having much more acceleration from 0-35 to and 0-39mph. (GTS to 35mph)
after that, the gTS has the poorest acceleration rates after 40mph. i think at one point, at 60mph, the GTS has the fastest rate of acceleration, but aside from that, every single 10mph increment, it accelerates slower. the net net of a 3.09 on a GTS gear box, on an S4 engine, is it is a loosing proposition, unless you are a drag racer from a dead stop. actually its 1/4 mile time would match the S4 with 3.09, and its only real advantage would be to 60mph over both, due to the launch. So for a road racer or anyone using a 928 at speeds above stopped (ie road racing, street driving, etc) the 3.09 would be a waste of time and money to put on a GTS gear box.
remember all this changes slightly with differnet engine hp profiles, and net hp levels. you can see this comparison had all 3 cars in the mid 13 seconds and a top speed in the 105mph range.
mk
11-18-2005, 10:19 AM
#429
Nordschleife Master
Originally Posted by GlenL
The reason a higher ratio rear end is better off the line is two fold.
1) During launch the engine has a larger mechanical advantage over the wheels
2) After it is hooked up the engine is running more RPMs and producing more power
1) During launch the engine has a larger mechanical advantage over the wheels
2) After it is hooked up the engine is running more RPMs and producing more power
Looks like we've reached the point where I can just quote my own previous posts in the current conversation.
11-18-2005, 02:21 PM
#430
Originally Posted by mark kibort
those look like guesses. 1-2nd 55% drop 2nd to 3rd looks ok and so does 3-4th. but remember, if these are actual speeds thats one thing. but what is the final drive ratios. PLUS , dont forget, what is the tire diameter! just for giggles, what does a drag mustang run for tire diameters? remember this changes the effective gearing vs our cars with 25" diameter tires. PLUS, what do they grow to ? Ive seen slow mo video. man, it looks like they get REAL big. this is also a factor. got to look at the entire system. (not just where the gear shift lever is sitting)
MK
MK
The Stang in question is running 275-60-15's in the rears(usually at 16psi at the track IIRC). BTW, the reason they appear to 'grow' is because they are set at very low pressures, and the centrifigul forces under launch make them momentarilly expand outward. If they were filled to 32psi to begin with they wouldn't get that 'growth' effect.
11-18-2005, 02:26 PM
#431
Rennlist Member
Actually, jim added a little too much. He said, hp " can become" torque by using lower gears" Hp is torque through the gears (kind of semantics) but, his % were off and skewed a little. 20% hp gain due to the 40% advantage, not 60% gains due to the 40% advantage. You have to get realistic about the launch speeds, or you could play with the numbers to get 100% gains too!
the idea, is maximizing hp to the wheels. closer gears do this, and in the "sub 1st 3.09" you maximize hp by getting more rpms out of the shoot, giving more hp at the lower speed range. (just until 39mph).
mk
the idea, is maximizing hp to the wheels. closer gears do this, and in the "sub 1st 3.09" you maximize hp by getting more rpms out of the shoot, giving more hp at the lower speed range. (just until 39mph).
mk
Originally Posted by GlenL
Isn't this what Jim just added?
Looks like we've reached the point where I can just quote my own previous posts in the current conversation.
Looks like we've reached the point where I can just quote my own previous posts in the current conversation.
11-18-2005, 02:31 PM
#432
Rennlist Member
maybe with your drag tires, but in "real" drag racing, the drag slicks actually expand and are part of the gearing equation. but you know this, right?
I guess it depends on what kind of tire you have! street tires may not grow, but real drag slicks do.
Hey, just noticed the tire size. do you know that a 275x60x15 is 28" in diameter??? suddenly , you just brought a 3.09 back to a 2.72:1 !!! (that in itself is a 15% change. if you did this, you need to change a 2.2 to a 2.75 gear box, just to stay even! ie no change.
suddenly your 12.5:1 sub 1st with the 3.09 actually becomes 10.93.
its all about the entire set of ratios.
If anyone learns one small thing from this lengthy discussion, they will forget about rear ends numbers and gear number names and look at total ratios to the ground!
(id also like to think they would also learn that HP = resultant torque through the gears at any speed.) then, they can cringe as do when the professional racing broadcasters talk about the viper and the porsche coming off the final hair- pin and say "watch the viper with all that torque blow by the porsche out of turn 11!" and because you know both cars have the same hp to weight ratio, and are traveling at the same speed, they both put down the same torque to the ground and accelerate in a dead heat to the finish line!!!! (even though the viper has 600ftlbs of engine torque and the porsche had 300ftlbs of engine torque. NOW, some of you guys will know why!
Other things learned:
1. clutch put in, instantaneous deceleration
2. changing rear end doesnt effect gear spacing
3. changing rear end doesnt give a mechanical advantage at all speeds, only in the newly created "sub-1st gear" . that depends on the trade offs in ratios
4. Total gear ratio is not only the gears with rear end, but the tire diameter
and after all that, we still dont know why the universe still seemingly expanding and accerlating, after the big bang!
MK
I guess it depends on what kind of tire you have! street tires may not grow, but real drag slicks do.
Hey, just noticed the tire size. do you know that a 275x60x15 is 28" in diameter??? suddenly , you just brought a 3.09 back to a 2.72:1 !!! (that in itself is a 15% change. if you did this, you need to change a 2.2 to a 2.75 gear box, just to stay even! ie no change.
suddenly your 12.5:1 sub 1st with the 3.09 actually becomes 10.93.
its all about the entire set of ratios.
If anyone learns one small thing from this lengthy discussion, they will forget about rear ends numbers and gear number names and look at total ratios to the ground!
(id also like to think they would also learn that HP = resultant torque through the gears at any speed.) then, they can cringe as do when the professional racing broadcasters talk about the viper and the porsche coming off the final hair- pin and say "watch the viper with all that torque blow by the porsche out of turn 11!" and because you know both cars have the same hp to weight ratio, and are traveling at the same speed, they both put down the same torque to the ground and accelerate in a dead heat to the finish line!!!! (even though the viper has 600ftlbs of engine torque and the porsche had 300ftlbs of engine torque. NOW, some of you guys will know why!
Other things learned:
1. clutch put in, instantaneous deceleration
2. changing rear end doesnt effect gear spacing
3. changing rear end doesnt give a mechanical advantage at all speeds, only in the newly created "sub-1st gear" . that depends on the trade offs in ratios
4. Total gear ratio is not only the gears with rear end, but the tire diameter
and after all that, we still dont know why the universe still seemingly expanding and accerlating, after the big bang!
MK
Originally Posted by m21sniper
They are in fact approxomations due to the fact that my dumbasss doesn't have a photographic memory.
The Stang in question is running 275-60-15's in the rears(usually at 16psi at the track IIRC). BTW, the reason they appear to 'grow' is because they are set at very low pressures, and the centrifigul forces under launch make them momentarilly expand outward. If they were filled to 32psi to begin with they wouldn't get that 'growth' effect.
The Stang in question is running 275-60-15's in the rears(usually at 16psi at the track IIRC). BTW, the reason they appear to 'grow' is because they are set at very low pressures, and the centrifigul forces under launch make them momentarilly expand outward. If they were filled to 32psi to begin with they wouldn't get that 'growth' effect.
Last edited by mark kibort; 11-18-2005 at 02:55 PM.
11-18-2005, 03:13 PM
#433
Sharkaholic
Lifetime Rennlist
Member
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Where can I find the stock gear box ratios for an 86.5 5sp? For each gear
1st-
2nd-
3rd-
4th-
5th-
R-
I would like to figure out what each ratio is when applied through the USA 1.5714 layshaft and the euro 2.72 ring & pinion.
It would be nice to know! This might even be a better way to convert the manual transmissions than buying custom 3.09 gears. If one can pick up a set of 2.72 euro gears and slide it into a US 2.20 and get gear ratios similar to a 3.09 for 1-4, and still get the top speed potential of a 2.72 5th gear all the better!!
1st-
2nd-
3rd-
4th-
5th-
R-
I would like to figure out what each ratio is when applied through the USA 1.5714 layshaft and the euro 2.72 ring & pinion.
It would be nice to know! This might even be a better way to convert the manual transmissions than buying custom 3.09 gears. If one can pick up a set of 2.72 euro gears and slide it into a US 2.20 and get gear ratios similar to a 3.09 for 1-4, and still get the top speed potential of a 2.72 5th gear all the better!!
11-18-2005, 03:17 PM
#434
Rennlist Member
for S4
1st- 4.04
2nd- 2.68
3rd- 1.92
4th- 1.45
5th- 1
for GTS/GT boxes
1st- 3.76
2nd- 2.51
3rd- 1.79
4th- 1.35
5th- 1
Let us know the resultant ratios. dont see how 5th would change though
MK
1st- 4.04
2nd- 2.68
3rd- 1.92
4th- 1.45
5th- 1
for GTS/GT boxes
1st- 3.76
2nd- 2.51
3rd- 1.79
4th- 1.35
5th- 1
Let us know the resultant ratios. dont see how 5th would change though
MK
Originally Posted by Shane
Where can I find the stock gear box ratios for an 86.5 5sp? For each gear
1st-
2nd-
3rd-
4th-
5th-
R-
I would like to figure out what each ratio is when applied through the USA 1.5714 layshaft and the euro 2.72 ring & pinion.
It would be nice to know! This might even be a better way to convert the manual transmissions than buying custom 3.09 gears. If one can pick up a set of 2.72 euro gears and slide it into a US 2.20 and get gear ratios similar to a 3.09 for 1-4, and still get the top speed potential of a 2.72 5th gear all the better!!
1st-
2nd-
3rd-
4th-
5th-
R-
I would like to figure out what each ratio is when applied through the USA 1.5714 layshaft and the euro 2.72 ring & pinion.
It would be nice to know! This might even be a better way to convert the manual transmissions than buying custom 3.09 gears. If one can pick up a set of 2.72 euro gears and slide it into a US 2.20 and get gear ratios similar to a 3.09 for 1-4, and still get the top speed potential of a 2.72 5th gear all the better!!
11-18-2005, 03:27 PM
#435
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Mark the object of the drag racing start is NOT to smoke the tires, a Bill Ball burnout is how you lose the race ! 
So dumping the clutch at 3,500 or 4,500 is just the beginning of the launch (and rather high for street tires). A great smokey burnout has about as much to do with a good drag racing start as "drifting" does to road racing. The engine speed is going to bog down to something much less as the speed of the tires matches the speed of the car and the tires get traction. You can only slip the clutch so much then you must make the pull up to 39 mph or 55 mph with the 2:20 . Horsepower is a measure of work performed over time the more horsepower the more work how I apply it through gearing changes the effective torque. Porsche specs on climbing ability 79 car ; 1st gear a 71 % , 2nd 41%, 3rd 28% , 4 th 18% , 5th 11% ...do we see a trend here ? The 1/2 gear first of the 3:09 obviously will climb a steeper hill.
So dumping the clutch at 3,500 or 4,500 is just the beginning of the launch (and rather high for street tires). A great smokey burnout has about as much to do with a good drag racing start as "drifting" does to road racing. The engine speed is going to bog down to something much less as the speed of the tires matches the speed of the car and the tires get traction. You can only slip the clutch so much then you must make the pull up to 39 mph or 55 mph with the 2:20 . Horsepower is a measure of work performed over time the more horsepower the more work how I apply it through gearing changes the effective torque. Porsche specs on climbing ability 79 car ; 1st gear a 71 % , 2nd 41%, 3rd 28% , 4 th 18% , 5th 11% ...do we see a trend here ? The 1/2 gear first of the 3:09 obviously will climb a steeper hill.