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Would are cars be faster with some lower gearing?
https://forums.tipec.net/viewtopic.php?f=25&t=8870		 Page 1 of 1
Author:  t3rra [ Mon Jun 28, 2010 6:19 pm ]
Post subject:  Would are cars be faster with some lower gearing?
Just looking at the e30 specs and all do it heavier and less power it's stated as quicker, but has a top end off about 20-30 less. So in 4th we would still have a whole gear over it. But really when are we going 120+ understand fual wise taller gear means less revs

I have 944S and it's been said that a n/a gear box would make the most of it's extra power? But how?
1st-40 2nd-65/70 3rd-90 4th 120 5th ???
Author:  tr7v8 [ Mon Jun 28, 2010 6:45 pm ]
Post subject:  Re: Would are cars be faster with some lower gearing?
In theory top speed is when power=wind & rolling resistance, this will normally be at peak power. How ever blasting around at peak power is poor for economy, best fuel consumption is normally around the peak torque point, so top gear is normally set to give a 5-10% reduction in revs from peak power at cruise. Hence most deseasals are higher geared (lower numerical) than petrols because they develop peak torque & power at lower overall RPM.
This is why Porsche 944's feel better at 80-90MPH than at our motorway 70MPH because they are geared for German autobahns.
Author:  J.J. [ Mon Jun 28, 2010 7:22 pm ]
Post subject:  Re: Would are cars be faster with some lower gearing?
This is true. In the case of the S that is best when revved I think Porsche got it wrong & the car would benefit from the lower diff' ratio of the 2.5 8v N/A. It would still rev out at 140 which is fast enough. Standard shocks give up at 130 so it's more about economy than top speed. I'm rebuilding my diff' but sticking with the stock ratio for maximum acceleration. :) Quite a good argument for using a lower ratio for the S2 over here with our ridiculously low speed limits! :wink:
Author:  t3rra [ Mon Jun 28, 2010 8:28 pm ]
Post subject:  Re: Would are cars be faster with some lower gearing?
I think from Porsche selling point, the gearing was geared 4 a taller top end over the n.a as a selling point, must be a reson they changed the gear box. So how would the gear change the power band, if it produces so much power at so many revs.
Author:  tr7v8 [ Mon Jun 28, 2010 8:33 pm ]
Post subject:  Re: Would are cars be faster with some lower gearing?
t3rra wrote:
I think from Porsche selling point, the gearing was geared 4 a taller top end over the n.a as a selling point, must be a reson they changed the gear box. So how would the gear change the power band, if it produces so much power at so many revs.

Changing gearing doesn't change the power band, that is fixed by the engine design. Changing the gearing affects where the power band is in relation to road speed. Think of Harley Davidson one bang per lampost vs Jap Kawisukionda 4 pot which is screaming its nuts off at say 70MPH.
Author:  t3rra [ Mon Jun 28, 2010 8:41 pm ]
Post subject:  Re: Would are cars be faster with some lower gearing?
Sorry Jim
Not really sure I got that?

I just assumed that the gear size rotated in relation 2 the power delivery from the engine and in turn effected the speed of the wheels or power 2 turn them, I understand that revs is the number of rotations inside the engine. Shorter gear would reach max engines revs earlier. I'm wrong no dougt

Thanks
Author:  tr7v8 [ Mon Jun 28, 2010 8:50 pm ]
Post subject:  Re: Would are cars be faster with some lower gearing?
t3rra wrote:
Sorry Jim
Not really sure I got that?

I just assumed that the gear size rotated in relation 2 the power delivery from the engine and in turn effected the speed of the wheels or power 2 turn them, I understand that revs is the number of rotations inside the engine. Shorter gear would reach max engines revs earlier. I'm wrong no dougt

Thanks

Correct but you don't change the power band of the engine ONLY the road speed in relation to it. So lets day with overall gearing at 4:1 & you're doing 100MPH at 4,000RPM. Then you change the overall gearing to 8:1 Then at 100MPH we're doing 8,000RPM The engine power band has stayed the same but the RPM for a given road speed changes. So if peak power is say 8,000RPM then on the 4:1 gearing you have around half the power at 100MPH that you'd have on the 8:1 gearing.
Author:  lindsayhbrown [ Mon Jun 28, 2010 9:18 pm ]
Post subject:  Re: Would are cars be faster with some lower gearing?
With the 944S at 70mph in 5th the engine is turning over at about 3250rpm, the power dosen't come in until 4krpm so 4th gear at 70mph would give you the best performance, albeit with poor economy
Author:  t3rra [ Mon Jun 28, 2010 10:03 pm ]
Post subject:  Re: Would are cars be faster with some lower gearing?
4th gear would take place you just under it, but 3rd would put you in it.
My sales broucher says fuel at 75 is 34mpg 56 is 42.8
So would this be based on 5th gear as the revs would be lowest point, about 3800 rev were the torque takes a sharp rise, were as bhp pecks up 2 a liner inresse at 3000 revs. Reading from the power curves.

From the power curves you can see were a 924s is faster the 944 n/a. Is This is due 2 weight as both have the same engine, but the 924 is only 20kg lighter prob less then the weight off the spear wheel.
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