Re gearing
09-07-2012, 06:01 PM
#1
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Re gearing
some posts above....especially Ken's 
comment about going slower at Laguna Seca with a re-geared box (Ouch!), and the shift point graphic above from Bill Verburg. Both Ken and Bill always seem to know their business...so I am really puzzled now as I am getting ready re-gear my 993 stock G50 box. Against any and all evidence, I am going to do it regardless. I have driven a re-geared 993, man does that car seem to come alive across all gears, seemed to me that the sweet spot when the torque kicks in is always just nearby and accessible. I hear there is a huge penalty if you run PCA Stock, move up a class....G stock is tough enough now running against RS America cars, 150 Lbs lighter I believe and about the same HP as a 993 as headers are legal in PCA Stock.
The "Yellow Car" referred to below is Ken Shahoian's "Yellow Zonker", an extremely well built 993 C2 with a re-geared close ratio tranny, built by Jeff Gamroth and Steve Weiner, I believe, about 8 years ago. No expense soared by Kim, the original builder of this car.
I don't know anything about the 964 car referred to below in the graphic above..what I am reading is that a 964 5 speed may well be a pretty good track box, maybe not needing re-gearing. Somehow, I find this difficult to fathom, how about you?
Being very close to laying out the cash for a 993 re-gear, I will be really pissed if I put $10,000 into a close ratio 993 box and lose 1 to 1.5 seconds a lap at Laguna Seca. In my 3200 Lb (wet) 993 (Class minimum weight), I feel that the stock 993 gears are just not right in about 50% of the turns at Laguna Seca:
Basically Turns 2 through 6... in turn 5 that I gear down to, from 4th to 3rd, having a lower gear and maybe getting up that hill quicker would be great, and car more speed through 6, up the hill.
A shorter 3rd gear would give the car more grunt from Turn 11 on to the front straight. This is assuming I stay with stock 1st and 2nd, replacing 3rd through 5th, with my stock 5th becoming my new 6th. I have include a Laguna Seca track map.
Ironically, I find my stock geared 993 to be just fine at Sears and Thunderhill....I copied Ken on this.....maybe I am just a crappy driver, although strangely enough I seem to get decent times at Laguna Seca...I better go to My Laps and see what I do there in case I get called out on this.
It seems to be sad but true, the 993 car, has a few things that need addressing if you want to race it. For DE or Time Trials, the car is good to go...just add some DOT "R" tires.
It needs to lose some weight, and getting it to PCA G Stock weight will all but make the car un-streetable. In PCA Stock, springs are "free", so if you want to run with your "bros" on the track, you'll have to re-spring her and re-valve the shocks. Be prepared to tear up the interior when you install the full cage
I would think, that the factory got it right when they designed the gear chart for the 993 RS and 993 RS Club Sport. Both technically street cars, legal in many countries around the world, but of course not in the US.
Where am I going with this??? If you want a race car, research what will be the best race car in the class you want to run in. In Porsche Owners Club (A SoCal Racing Club), one of the best cars to run is a 964 car, run it in their "J" Prepared where you compete against 84 89 Prepared Carrera cars, them with 220 HP to the rear wheels (These cars are tweaked), the 964 with close to 250 or more to the rear wheels using headers and a chip. In Prepared you get gears too, and you can take additional weight out of the car...but for some reason, few show up with a 964 Prepared car. I have a pal who built one as described above, it ran very well, setting track records, but the guy got the hots for a RS America and sold the car. Now he is hesitant to run the RS America, they are getting too valuable.
When you show up at the track to race a street car that morphed into a race car, you may be at a disadvantage...the clean sheet of paper approach is best. I know this from personal experience, too personal at that.
comment about going slower at Laguna Seca with a re-geared box (Ouch!), and the shift point graphic above from Bill Verburg. Both Ken and Bill always seem to know their business...so I am really puzzled now as I am getting ready re-gear my 993 stock G50 box. Against any and all evidence, I am going to do it regardless. I have driven a re-geared 993, man does that car seem to come alive across all gears, seemed to me that the sweet spot when the torque kicks in is always just nearby and accessible. I hear there is a huge penalty if you run PCA Stock, move up a class....G stock is tough enough now running against RS America cars, 150 Lbs lighter I believe and about the same HP as a 993 as headers are legal in PCA Stock.The "Yellow Car" referred to below is Ken Shahoian's "Yellow Zonker", an extremely well built 993 C2 with a re-geared close ratio tranny, built by Jeff Gamroth and Steve Weiner, I believe, about 8 years ago. No expense soared by Kim, the original builder of this car.
I don't know anything about the 964 car referred to below in the graphic above..what I am reading is that a 964 5 speed may well be a pretty good track box, maybe not needing re-gearing. Somehow, I find this difficult to fathom, how about you?
Being very close to laying out the cash for a 993 re-gear, I will be really pissed if I put $10,000 into a close ratio 993 box and lose 1 to 1.5 seconds a lap at Laguna Seca. In my 3200 Lb (wet) 993 (Class minimum weight), I feel that the stock 993 gears are just not right in about 50% of the turns at Laguna Seca:
Basically Turns 2 through 6... in turn 5 that I gear down to, from 4th to 3rd, having a lower gear and maybe getting up that hill quicker would be great, and car more speed through 6, up the hill.
A shorter 3rd gear would give the car more grunt from Turn 11 on to the front straight. This is assuming I stay with stock 1st and 2nd, replacing 3rd through 5th, with my stock 5th becoming my new 6th. I have include a Laguna Seca track map.
Ironically, I find my stock geared 993 to be just fine at Sears and Thunderhill....I copied Ken on this.....maybe I am just a crappy driver, although strangely enough I seem to get decent times at Laguna Seca...I better go to My Laps and see what I do there in case I get called out on this.
It seems to be sad but true, the 993 car, has a few things that need addressing if you want to race it. For DE or Time Trials, the car is good to go...just add some DOT "R" tires.
It needs to lose some weight, and getting it to PCA G Stock weight will all but make the car un-streetable. In PCA Stock, springs are "free", so if you want to run with your "bros" on the track, you'll have to re-spring her and re-valve the shocks. Be prepared to tear up the interior when you install the full cage
I would think, that the factory got it right when they designed the gear chart for the 993 RS and 993 RS Club Sport. Both technically street cars, legal in many countries around the world, but of course not in the US.
Where am I going with this??? If you want a race car, research what will be the best race car in the class you want to run in. In Porsche Owners Club (A SoCal Racing Club), one of the best cars to run is a 964 car, run it in their "J" Prepared where you compete against 84 89 Prepared Carrera cars, them with 220 HP to the rear wheels (These cars are tweaked), the 964 with close to 250 or more to the rear wheels using headers and a chip. In Prepared you get gears too, and you can take additional weight out of the car...but for some reason, few show up with a 964 Prepared car. I have a pal who built one as described above, it ran very well, setting track records, but the guy got the hots for a RS America and sold the car. Now he is hesitant to run the RS America, they are getting too valuable.
When you show up at the track to race a street car that morphed into a race car, you may be at a disadvantage...the clean sheet of paper approach is best. I know this from personal experience, too personal at that.
re gearing is general has the goal of making the transmission more useful and increasing acceleration rates through lower gearing while retaining highway cruise at a reasonable rpm.
here is a comparison of a stock US /20 and Row /21, US gears were heavily influenced by EPA milage #s and aren't the best for general use. The /20 is what our government gave us, The /21 is what the Porsche engineers intended for all around sporting use
This is a comparison of the /31 used in M002RS(street) compared to the /21, 1 - 3 are taller in the RS, this is a more sporting gear stack designed to get out on the track quickly and up to speed, w/o concern for hill starts
Here is a comparison of a /32 used in the M003 RSCS and /31 used in the M002 RS, the CS 4 & 5 are a tad taller most of the differences were in internal components which are far more durable under track use
Here is a comparison of the /30 used in the M001Cup & RSR vs the /32, again not much change in the gear ratios except to make the top gears a little more useful, the only place I have used 6 in the /30 is Monticello, it would probably be useful at Daytona too
JMO but I think that the /30 is just about perfect for street or track use
More to come if there is any interest
09-07-2012, 07:03 PM
#2
Nordschleife Master
That is really great data to have. Do you happen to have any charts for the 993TT trans? While these gears work great for the big-torque, TT motor, would they work for a NA 993?
09-07-2012, 07:15 PM
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I did the ROW G50/21 gearbox swap way back in 1999 and for anyone considering ... Go For It !
Changes the coupes "street" sports car drive character significantly.
Thanks for the details ! !
Changes the coupes "street" sports car drive character significantly.
Thanks for the details ! !
Last edited by M. Schneider; 09-07-2012 at 10:39 PM.
09-07-2012, 07:36 PM
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09-07-2012, 07:48 PM
#5
Bill, I'd be curious how you think gearing should change as power to weight ratio or redline changes.
09-07-2012, 07:49 PM
#6
Hi Bill - Thanks for this post.
I've mentioned my situation a few times, but I am still in a dilemma as it relates to my gearing. I re-geared 3-4-5-6 off a 4S transmission, with the following ratios:
3.818 / 2.15 / 1.56 / 1.241 / 1.03 / 0.857
My engine has a 7,500 rpm limit, with torque really picking-up at 4,000 rpm (runs on ITBs).
While I really appreciate the low rpm drops resulting from the re-gearing, I am highly disappointed with the 1-2 rpm drop and also from finding myself at too low rpms when taking on slower curves in second gear.
I am therefore considering welding on a 3.0 first gear and changing my ring and pinion to 4.0.
Putting aside the potential wear from the 4.0 R&P, what is the downside of this transmission set-up? By my calculations, it would result in a top speed of 46 mph in first, 64 in second, 88 in third and 110 in fourth (@ 7,500).
While this may not be suitable for a street daily driver, would it not make for an extremely fun weekend hot rod / track car? I am not concerned by the potential times at one track vs. another, but rather with the driving pleasure.
Thanks for your input.
I've mentioned my situation a few times, but I am still in a dilemma as it relates to my gearing. I re-geared 3-4-5-6 off a 4S transmission, with the following ratios:
3.818 / 2.15 / 1.56 / 1.241 / 1.03 / 0.857
My engine has a 7,500 rpm limit, with torque really picking-up at 4,000 rpm (runs on ITBs).
While I really appreciate the low rpm drops resulting from the re-gearing, I am highly disappointed with the 1-2 rpm drop and also from finding myself at too low rpms when taking on slower curves in second gear.
I am therefore considering welding on a 3.0 first gear and changing my ring and pinion to 4.0.
Putting aside the potential wear from the 4.0 R&P, what is the downside of this transmission set-up? By my calculations, it would result in a top speed of 46 mph in first, 64 in second, 88 in third and 110 in fourth (@ 7,500).
While this may not be suitable for a street daily driver, would it not make for an extremely fun weekend hot rod / track car? I am not concerned by the potential times at one track vs. another, but rather with the driving pleasure.
Thanks for your input.
09-07-2012, 08:25 PM
#7
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The taller the gear the wider the speed range that that gear can be used over, more power or lower weight implies better acceleration w/ that gear but you still want to maximize the available power so ideally you would be at the top speed in a given gear when you enter any braking zone. To accomplish that is a trick, gear stack set up specifically to achieve that goal at one track is very likely to be a disaster at another different track, but generally within reason the taller gear will be more flexible in this regard.
In the other thread Ken stated that he liked the 964 gearbix better than his regeared one, the reason can be seen here in the typical track speed range from say 75 to 130mph the 964 will use only 3 & 4, the modified 993 will use 3, 4 & 5, extra up/down shifts can take time and the chance of having to be in the wrong gear at least some of the time because a shift would need to occur at an awkward place go up, somewhere between the 964 ratio and Kens ratios would probably be where to be, but better acceleration also comes from more torque and less weight, so the 964 gears might be better there every car is different
what gearing are you running in yours?
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09-07-2012, 08:39 PM
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Hi Bill - Thanks for this post.
I've mentioned my situation a few times, but I am still in a dilemma as it relates to my gearing. I re-geared 3-4-5-6 off a 4S transmission, with the following ratios:
3.818 / 2.15 / 1.56 / 1.241 / 1.03 / 0.857
My engine has a 7,500 rpm limit, with torque really picking-up at 4,000 rpm (runs on ITBs).
While I really appreciate the low rpm drops resulting from the re-gearing, I am highly disappointed with the 1-2 rpm drop and also from finding myself at too low rpms when taking on slower curves in second gear.
I am therefore considering welding on a 3.0 first gear and changing my ring and pinion to 4.0.
Putting aside the potential wear from the 4.0 R&P, what is the downside of this transmission set-up? By my calculations, it would result in a top speed of 46 mph in first, 64 in second, 88 in third and 110 in fourth (@ 7,500).
While this may not be suitable for a street daily driver, would it not make for an extremely fun weekend hot rod / track car? I am not concerned by the potential times at one track vs. another, but rather with the driving pleasure.
Thanks for your input.
I've mentioned my situation a few times, but I am still in a dilemma as it relates to my gearing. I re-geared 3-4-5-6 off a 4S transmission, with the following ratios:
3.818 / 2.15 / 1.56 / 1.241 / 1.03 / 0.857
My engine has a 7,500 rpm limit, with torque really picking-up at 4,000 rpm (runs on ITBs).
While I really appreciate the low rpm drops resulting from the re-gearing, I am highly disappointed with the 1-2 rpm drop and also from finding myself at too low rpms when taking on slower curves in second gear.
I am therefore considering welding on a 3.0 first gear and changing my ring and pinion to 4.0.
Putting aside the potential wear from the 4.0 R&P, what is the downside of this transmission set-up? By my calculations, it would result in a top speed of 46 mph in first, 64 in second, 88 in third and 110 in fourth (@ 7,500).
While this may not be suitable for a street daily driver, would it not make for an extremely fun weekend hot rod / track car? I am not concerned by the potential times at one track vs. another, but rather with the driving pleasure.
Thanks for your input.
09-07-2012, 09:01 PM
#9
They current ratios work well enough, but are quite compromised and I wouldn't recommend anyone duplicate them. With an 8k redline I get the following speeds in gears:
1- 48
2- 66
3- 100
4- 136
5- 165
6- 197
First and second are specifically for autocross- first is tall so the I can occasionally put all the power down, while second is short because the engine lacks flexibility and it's enough speed for most courses. From there up it's almost a different gearbox, and a bit more traditional. While the car is fast enough, the rhythm of shifting though the gears is broken by the stutter-step 2nd. 6th is obviously cruising only.
Medium term I'm planning to increase the flexibility of the motor to cure the issue.
09-07-2012, 09:21 PM
#10
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Thanks for the chart!
Cheers,
Mike
09-07-2012, 11:08 PM
#11
What RPM are you using for the other transmissions?
09-08-2012, 08:14 AM
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09-08-2012, 09:04 AM
#14
That GT2 is geared amazingly, unbelievably short...
I wonder if the redline is perhaps under-reported. I've seen a GT2 Evo dyno that made clear the actual power output had nearly nothing to do with what Porsche claimed for the car.
I wonder if the redline is perhaps under-reported. I've seen a GT2 Evo dyno that made clear the actual power output had nearly nothing to do with what Porsche claimed for the car.
09-08-2012, 09:18 AM
#15
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Keep in mind those cars run tall slicks which probably brings the final ratio close to the cups/rsr's...?!