951 transmission
08-29-2002, 04:14 PM
#1
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951 transmission
I was curious about the 951 tranny. Is it possible to get longer gears? or shorter gears for that matter? It would be nice to have a longer second gear or to have a longer fifth. If there are, how much would it cost? Thanks.
08-29-2002, 04:41 PM
#3
Race Director
Power Haus II sells gears for racing purposes
<a href="http://www.phii.net/" target="_blank">Power Haus II - Gears</a>
Here is what their site has
Model Gearset Teeth Ratio
951 (944 Turbo) 3rd 19:30 1.578:1
951 (944 Turbo) 4th 22:27 1.227:1
951 (944 Turbo) 5th 25:25 1.000:1
951 (944 Turbo) 5th 25:24 0.960:1
Stock Gears Are Ratio
3rd 1.400
4th 1.034
5th 0.829
Note 1st & 2nd Gears are a part of the mainshaft I do not think that can be replaced.
968 gears are splined in the shaft are not interchangeable with 951 gears.
Here are stock gear in 944/951/968
944 82-87 944/924S 88-89 944S 951 S2 968
F/D 3.889 3.889 3.889 3.375 3.875 3.780
1st 3.600 3.600 3.500 3.500 3.500 3.180
2nd 2.125 2.125 2.059 2.059 2.059 2.000
3rd 1.458 1.458 1.400 1.400 1.400 1.400
4th 1.071 1.071 1.034 1.034 1.034 1.110
5th 0.730 0.829 0.829 0.829 0.778 0.910
6th - - - - - 0.780
Not sure of any other gears for the 951.
<a href="http://www.phii.net/" target="_blank">Power Haus II - Gears</a>
Here is what their site has
Model Gearset Teeth Ratio
951 (944 Turbo) 3rd 19:30 1.578:1
951 (944 Turbo) 4th 22:27 1.227:1
951 (944 Turbo) 5th 25:25 1.000:1
951 (944 Turbo) 5th 25:24 0.960:1
Stock Gears Are Ratio
3rd 1.400
4th 1.034
5th 0.829
Note 1st & 2nd Gears are a part of the mainshaft I do not think that can be replaced.
968 gears are splined in the shaft are not interchangeable with 951 gears.
Here are stock gear in 944/951/968
944 82-87 944/924S 88-89 944S 951 S2 968
F/D 3.889 3.889 3.889 3.375 3.875 3.780
1st 3.600 3.600 3.500 3.500 3.500 3.180
2nd 2.125 2.125 2.059 2.059 2.059 2.000
3rd 1.458 1.458 1.400 1.400 1.400 1.400
4th 1.071 1.071 1.034 1.034 1.034 1.110
5th 0.730 0.829 0.829 0.829 0.778 0.910
6th - - - - - 0.780
Not sure of any other gears for the 951.
08-29-2002, 04:59 PM
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I see that they meake the fifth shorter. Why is that? If you ever wanted to do 200 mph ( just an example) and you had the power to back it up, you can't? I guess that's when a different tranny comes in.
08-29-2002, 06:31 PM
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a stock 951 is drag limited to 157; the air resistances to traveling faster is also a parabolic function so you'd need siginificantly more hp to justify gearing for 200. it wont happen unless your car is stupid fast.
you would want to shorten 5th to have a better quarter mile time. if you can max your gears around your trap speed you're doing good work (this is situation dependent though; the distance between shifts, the engine's powerband, the time between shifts, and the number of gears all have to be accounted for in a cost/profit system to find out the correct gearing for any car).
you would want to shorten 5th to have a better quarter mile time. if you can max your gears around your trap speed you're doing good work (this is situation dependent though; the distance between shifts, the engine's powerband, the time between shifts, and the number of gears all have to be accounted for in a cost/profit system to find out the correct gearing for any car).
08-29-2002, 06:47 PM
#6
Nordschleife Master
I am actually in the camp that they are geared to high. For the tracks i've been to I can barely use 5th. I guess if we are talking highway driving a taller 5th might be nice for gas milage.
I would actually like to do a S2 tranny swap into mine at some point and time, or maybe if i can pick up an S tranny cheap I'll do that. I'm sure it would hold up for a while, I know it is not as strong as the 951 or S2 unit, but I would be fun to have such a low ratio box.....
I would actually like to do a S2 tranny swap into mine at some point and time, or maybe if i can pick up an S tranny cheap I'll do that. I'm sure it would hold up for a while, I know it is not as strong as the 951 or S2 unit, but I would be fun to have such a low ratio box.....
08-30-2002, 05:16 PM
#7
Race Director
[quote]Originally posted by ian:
<strong>I am actually in the camp that they are geared to high. For the tracks i've been to I can barely use 5th. I guess if we are talking highway driving a taller 5th might be nice for gas milage.
</strong><hr></blockquote>
Yep, The gearing requirements are different for the track as for the street. Most tracks in this country are do not have places to reach 200 mph in a street car. Rarely (except for LeMans) have I seen even prototypes going over 180 mph. They can do so, but not in a 1/4 mile.
The secret to race gearing is to find the highest speed point on the track you are on and then regear so that you will fall just short of redline. Then you have just enough to make it.
In realtiy is MUCH more complicated than that since the pros have different gearing for "EACH TRACK" and there are many factors involved in selcting gears.
On the street gearing, especially top gear, is done for reasonable performance and max fuel economy.
<strong>I am actually in the camp that they are geared to high. For the tracks i've been to I can barely use 5th. I guess if we are talking highway driving a taller 5th might be nice for gas milage.
</strong><hr></blockquote>
Yep, The gearing requirements are different for the track as for the street. Most tracks in this country are do not have places to reach 200 mph in a street car. Rarely (except for LeMans) have I seen even prototypes going over 180 mph. They can do so, but not in a 1/4 mile.
The secret to race gearing is to find the highest speed point on the track you are on and then regear so that you will fall just short of redline. Then you have just enough to make it.
In realtiy is MUCH more complicated than that since the pros have different gearing for "EACH TRACK" and there are many factors involved in selcting gears.
On the street gearing, especially top gear, is done for reasonable performance and max fuel economy.
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08-31-2002, 01:24 AM
#8
Race Director
"a stock 951 is drag limited to 157; the air resistances to traveling faster is also a parabolic function so you'd need siginificantly more hp to justify gearing for 200. it wont happen unless your car is stupid fast."
Yeah, I think Porsche claimed 152mph for the 951. Most magazine testers saw 155mph. The TurboS came in at 162mph. Air- resistance goes up with the square of speed while the power required to overcome that air-resistance goes up to the third power. So to go 4.5% faster (951 -> 951S), you would need to increase power by 14%. That is 1.045 * 1.045 * 1.045 = 1.142. Multiplying the Turbo's 217bhp by 1.142 and you get... 248bhp, almost exactly right on what a TurboS has.
Taking that upwards to 200mph, you can compute for the Turbo the power required to reach 200mph (a lot of variables canceled here, but we're assuming the same car under the same conditions before & after)
[ (200mph/155mph)^3 ] * 217bhp = 466bhp
And the TurboS:
[ (200mph/162mph)^3 ] * 247bhp = 465bhp
However, you'd need to match this power-output precisely with the RPM where that speed can be achieved in top-gear. In a 951 with stock gearing, you'd have to get 465bhp @ 7500rpm to go 200mph (and just barely at that).
"you would want to shorten 5th to have a better quarter mile time."
Wow, that'd be some seriously low gearing to get into 5th in the 1/4-mile. I've only managed on rare occasions to get into 4th gear @ 115mph and hold it for just a second or two. What you would want is a 25% shorter R&P to lower all your gears and keep the percentage spread between them the same.
If you really wanted a taller 5th gear, you can just install the 5th gear set from the 944NA cars. I've got a gearing chart on the 924/944/951 cars on my <a href="http://members.rennlist.com/951_racerx" target="_blank">951 RacerX website</a> if anyone's interested...
Yeah, I think Porsche claimed 152mph for the 951. Most magazine testers saw 155mph. The TurboS came in at 162mph. Air- resistance goes up with the square of speed while the power required to overcome that air-resistance goes up to the third power. So to go 4.5% faster (951 -> 951S), you would need to increase power by 14%. That is 1.045 * 1.045 * 1.045 = 1.142. Multiplying the Turbo's 217bhp by 1.142 and you get... 248bhp, almost exactly right on what a TurboS has.
Taking that upwards to 200mph, you can compute for the Turbo the power required to reach 200mph (a lot of variables canceled here, but we're assuming the same car under the same conditions before & after)
[ (200mph/155mph)^3 ] * 217bhp = 466bhp
And the TurboS:
[ (200mph/162mph)^3 ] * 247bhp = 465bhp
However, you'd need to match this power-output precisely with the RPM where that speed can be achieved in top-gear. In a 951 with stock gearing, you'd have to get 465bhp @ 7500rpm to go 200mph (and just barely at that).
"you would want to shorten 5th to have a better quarter mile time."
Wow, that'd be some seriously low gearing to get into 5th in the 1/4-mile. I've only managed on rare occasions to get into 4th gear @ 115mph and hold it for just a second or two. What you would want is a 25% shorter R&P to lower all your gears and keep the percentage spread between them the same.
If you really wanted a taller 5th gear, you can just install the 5th gear set from the 944NA cars. I've got a gearing chart on the 924/944/951 cars on my <a href="http://members.rennlist.com/951_racerx" target="_blank">951 RacerX website</a> if anyone's interested...
08-31-2002, 06:32 AM
#9
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Excellent post Danno.Lets take it one step further. When a nascar car is certified and inspected the aerodynamics of the car are in fact measured by templates for the cars body curves .The aerodynamics are considered to be so important that each car must conform to these set rules to provide a fairness factor.It is one of the reasons they draft one another.In fact ,even the wax on the car or the car being dirty is a factor ,let alone a friendly tap that occasionaly happens.Your explanation on this post yet again shows your in depth knowledge. THX
08-31-2002, 08:37 AM
#10
Excellence had an article about the Powerhaus 2.8ltr 944 turbo. It ended up making 414RWHP and hit the rev limiter in 5th. The author claims that it equates to 193mph limited by the gearing.
The article ran in Dec 1998, if you want to look it up. I know it was available online but I lost the website.
Daniel
<img src="graemlins/burnout.gif" border="0" alt="[burnout]" /> <img src="graemlins/burnout.gif" border="0" alt="[burnout]" /> <img src="graemlins/burnout.gif" border="0" alt="[burnout]" />
The article ran in Dec 1998, if you want to look it up. I know it was available online but I lost the website.
Daniel
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08-31-2002, 02:37 PM
#11
Rennlist Member
If you are thinking of updating to a 944S2 trans take a close look at 2nd. It is lower than the 951. It would be a useless gear at Mid-Ohio and Putnam Park. It might be OK in 7 at Road Atlanta. So, depending on track of choice you might just end up with a 3 speed tranny.
Alan
Alan
