[flash]

over the last few months, the topic of high speed limits of the 968 has come up a few times



i had a minute, and i thought i would do a little math to point out a few limits of the 968 and it's high speed capabilities - without getting into aerodynamics and how much work would be required for high speed stability (and it's a lot), and without getting into how much horsepower would really be needed (also a lot), i did the following number crunching



given its stock gearing (manual transmission) and stock tire diameters (25"), the following speeds would require approximately the following revs:



156mph 6423 (published stock max speed)

165mph 6794

170mph 7000

175mph 7205

180mph 7412

189mph 7800 (max rev of racer x chip)

200mph 8235



i think you can see here that the liklihood of the car ever going over 185 is very slight, regardless of horsepower



fun thinking about it though

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[BruceWard]

If you had the horsepower to use it a Turbo RS transaxle or custom gearing in a stock transaxle would provide more MPH per RPM.

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[flash]

ok - i started off with the qualification of STOCK gearing, with full knowledge that a change of that might help, but at this point, where do you get such things? the V8 guys would love to know - there is a serious acceleration trade-ff involved too, and it might actually turn out to be a wash, depending on where the torque curve lies in relation to the gearing



if you do manage to get taller gearing, then of course, you get into the very serious aerodynamic limitations of the car - it already lifts badly as it is, moslty in the rear - much work would have to be done to force the car back down - this additional downforce robs horsepower, so you get a trade-off there too



bottom liine, you aren't going to get there by horsepower alone

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[BruceWard]

Is your goal in the post that it become the ultimate proof that a 968 can not exceed 185 MPH?



I do not understand the benefit of such a post?



Powerhaus II http://www.phii.net/ offers custom gear ratios for the 968.



I am not sure of the source of Turbo RS transaxles. Certainly there are some currently installed custom 968s. I would check to see if Porsche has any in the warehouse and then advertise in Pano if I was looking for one.

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[flash]

i was thinking about it as a result of a recent conversation with somebody who wants ot increase their top end for a specific purpose - it got me to thinking about it, so i decided to look at the limiting factors of this car - gearing quickly showed up - the valve train is probably another issue - the hydraulic lifters won't likely keep up for the sustained periods necessary to hit and hold that speed - aerodynamic instability is another huge issue - rear end lift and undercarraige wind will have to be managed a lot better than they are now



the goal was not to indicate any ultimate proof - that is a bit more complicated, but can still be done by math - i don't want to start a fight here - the point was to show that it is a lot more difficult than just having horsepower - way too many people think it is just a simple thing of adding more power - it's a lot more complicated than that - the gearing was just a quick "no go" that i thought would be of interest - there have also been a couple of people lately to claim to have gone 165 - the chart above may help them to see if they really were or not



by the way, i looked at those gears - almost bought them - unless they have another set other than the ones i saw, they actually raise the final ratio, pushing 6th down closer to where 5th is now - nice grouping though - makes the spacing very tight - would be a blast in a road race car - i think jason has them

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