Corvette Trans in a 928
02-22-2005, 05:37 PM
#19
Rennlist Member
Anybody know what the Z06 'valved mufflers' consist of? I know the Subaru H6 (240hp, 3litre) has rear mufflers with valves that open to reduce back pressure over ~ 2400rpm.
jp 83 Euro S AT 49k
jp 83 Euro S AT 49k
02-22-2005, 05:56 PM
#20
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Also, dont get too lathered up about just a "6speed" if thats the only goal. remember, its the gear spacing and total ratios. if you look at the ratios of the 6 speed, you see its really a 928 GTS box as far as gears, with a 6th speed. so, basically, its a 5 speed with overdrive. In fact, its really closer to a S4 gear box, and you can hear the gears in my races on video, against C5 corvette race cars. (they are almost matched gear for gear up to 130mph) now, if there was a durability gain, i could see the interest. otherwise, the effort can be spent on hundreds of other areas of our cars.
of other cars with very simular gear boxes, the M3, for which i race often, has a euro 5 speed with a most commonly used 4:10 rear end that is basically Identical to my S4 gear ratios after 1st. In fact, for those that remember the GTS 3.09 discussion, it is just this. 1st gear usless on the track, and 2nd,3rd, 4th, 5th at redline, exactly the same as an S4's 1st , 2nd, 3rd and 4th at redline
Mk
of other cars with very simular gear boxes, the M3, for which i race often, has a euro 5 speed with a most commonly used 4:10 rear end that is basically Identical to my S4 gear ratios after 1st. In fact, for those that remember the GTS 3.09 discussion, it is just this. 1st gear usless on the track, and 2nd,3rd, 4th, 5th at redline, exactly the same as an S4's 1st , 2nd, 3rd and 4th at redline
Mk
02-23-2005, 05:04 PM
#21
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Mark, part of the interest in a Corvette 6 speed is the overall gear ratio, as well as the overdrive 6th gear. Theoretically it *should* improve the acceleration times, while still allowing a higher top end speed, as well as easier/more fuel efficient highway cruising. My GT tachs at around 3100 rpms at 75 MPH, which is quite high for cruising, compared to most cars. It would be nice to be able to cruise at around 2400 rpm at that speed, both for engine longevity, as well as better fuel economy. Just my 2 cents.
02-23-2005, 07:48 PM
#23
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Originally Posted by Chris Lockhart
My GT tachs at around 3100 rpms at 75 MPH, .
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02-23-2005, 08:20 PM
#25
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Originally Posted by Asterix
I've sent Dogmatix off with Obelix... They're hunting for a boar.
The lovely Panacea is washing my 928
The lovely Panacea is washing my 928
02-24-2005, 02:42 PM
#26
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your speedo will not know the difference if you have big or small tires. it will AWAYS be tied to the rpms exactly. by the way, the GT GTS gear box runs at exactly 2850rpms at 80mph. (ie , guess what guys, same as the Z06 transmission in 6TH gear too!!!!!!)
GT with 2.72 and 1:1 ratio = 2.72:1
Vet Zo6 with stock 3.73:1 ratio x .75 6th gear = 2.80:1
not much of a differnce , Huh!
AS FAR AS THE BOTTOM LINE WITH THE GEAR BOXES
redline call it 6500rpm for the GT vs S4 vs VET Z06 is :
VET /3.73:1 --------- 58,83,109,133,157,178 MPH 1-6th gears
S4 /2.2:1 ------------ 55,84,117,155,224 MPH 1-5th gears
GTS /GT 2.72:1 ---- 49,73,104,138,183 MPH 1-5th gears
If you notice, the S4 and the Vet are almost identical from 1-2 gears, and then the S4 has an 7% advantage in 3rd. then, the vet has a 17% advantage in 4th to 133mph and they are then the dame to 155ish. SO, the vet basically has a gear between our (the S4) 3rd and 4th gears. this is why i have a pretty even time at laguna seca with the vets, as the top speed down the main straight is 125ish.
comparing to the GTS, The GTS has a lower 1st gear by 20%, 2nd is lower by 14%, 3rd is lower by 5% and 4th is almost the same. SO, in this case , up to 135ish MPH, the GTS has the better transmission. up to 157, the vet has a 17% advantage and then they are close again to 180ish (vet 6th vs 5th in GTS)
so, in the in this comparison, the Vet then just has an extra gear between 4-5 on a GTS.
MK
GT with 2.72 and 1:1 ratio = 2.72:1
Vet Zo6 with stock 3.73:1 ratio x .75 6th gear = 2.80:1
not much of a differnce , Huh!
AS FAR AS THE BOTTOM LINE WITH THE GEAR BOXES
redline call it 6500rpm for the GT vs S4 vs VET Z06 is :
VET /3.73:1 --------- 58,83,109,133,157,178 MPH 1-6th gears
S4 /2.2:1 ------------ 55,84,117,155,224 MPH 1-5th gears
GTS /GT 2.72:1 ---- 49,73,104,138,183 MPH 1-5th gears
If you notice, the S4 and the Vet are almost identical from 1-2 gears, and then the S4 has an 7% advantage in 3rd. then, the vet has a 17% advantage in 4th to 133mph and they are then the dame to 155ish. SO, the vet basically has a gear between our (the S4) 3rd and 4th gears. this is why i have a pretty even time at laguna seca with the vets, as the top speed down the main straight is 125ish.
comparing to the GTS, The GTS has a lower 1st gear by 20%, 2nd is lower by 14%, 3rd is lower by 5% and 4th is almost the same. SO, in this case , up to 135ish MPH, the GTS has the better transmission. up to 157, the vet has a 17% advantage and then they are close again to 180ish (vet 6th vs 5th in GTS)
so, in the in this comparison, the Vet then just has an extra gear between 4-5 on a GTS.
MK
Originally Posted by martin D
Are you sure Chris ? that would leave you 10mph short at the top end compared to what you should have, I had cruise set at 80mph the other day which was 3000rpm ('90 GT), 2.72 rear which should be the same as yours, unless you have smaller Dia. rear wheels/tyres ? or a u/s tach/speedo ?
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02-24-2005, 02:53 PM
#27
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If you look at the comparison in my last post, you can see at 80mph, the GTS is exactly at 2850rpms and the 6 speed Vet in 6th gear is 2950rpms!! (just the opposite of what you are looking for.) Plus, vs the GTS, the vet has a huge disadvantage all the way passed 100mph vs the gears on the GTS. (also the opposite of what you are looking to find on the vet)
if you look at the comparison again, it would clearly seem that the S4 transmission would be the best of both worlds.
Mk
if you look at the comparison again, it would clearly seem that the S4 transmission would be the best of both worlds.
Mk
Originally Posted by Chris Lockhart
Mark, part of the interest in a Corvette 6 speed is the overall gear ratio, as well as the overdrive 6th gear. Theoretically it *should* improve the acceleration times, while still allowing a higher top end speed, as well as easier/more fuel efficient highway cruising. My GT tachs at around 3100 rpms at 75 MPH, which is quite high for cruising, compared to most cars. It would be nice to be able to cruise at around 2400 rpm at that speed, both for engine longevity, as well as better fuel economy. Just my 2 cents.
02-24-2005, 02:54 PM
#28
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I think racers are the minority on this board.
Most people who would be looking at a Corvette Trans, would probably be looking for a transmission that can take 1000#TQ/HP...
It's mostly the stroker/supercharger guys, who are looking for some kind of option other than stock.
Most normal 928 drivers are pretty happy with the stock 928 transmission.
The 'Vette trans gets mentioned, when people start talking about what happens when you start pushing torque and horsepower up past 600. There have been transmission failures at these levels, so people would naturally look at other cars, whose transmissions can handle a lot of horsepower...
Most people who would be looking at a Corvette Trans, would probably be looking for a transmission that can take 1000#TQ/HP...
It's mostly the stroker/supercharger guys, who are looking for some kind of option other than stock.
Most normal 928 drivers are pretty happy with the stock 928 transmission.
The 'Vette trans gets mentioned, when people start talking about what happens when you start pushing torque and horsepower up past 600. There have been transmission failures at these levels, so people would naturally look at other cars, whose transmissions can handle a lot of horsepower...
02-24-2005, 03:03 PM
#29
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Thread Starter
The Corvette trans can go to 62mph in 1st. I'm not sure about where your numbers are from Mark.
02-24-2005, 03:08 PM
#30
In Your Face, Ace
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The many gearing options a T56 offers is what makes this conversion attractive..a 2.72,3.42,4.11 etc are all options. It's not exclusively the 6-speed or extra gear you would gain. I started to do this on the '85, however I have since sold the project. I had the T56 and C-5 torque tube, and you'd be amazed at how much lighter that stuff is than the Porsche box and TT. The T56 shifts as smooth as a rifle bolt.. I traded emails with Steve C, and he has a easier a better idea on how to do this. You would be able to achieve the same goal without as big of conversion.. I'm not sure that I am at liberty to speak of it in detail, so I'll have to leave it at that. It would be great if Steve works it out though!