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Man, has this board gotten quiet over the last week or so!! With Spring right around the corner, all us "cold country" folks should start thinking about the driving season!



So, I'll use the silence to start a discussion about something that has been popping up on this and the Net boards: "How high can you rev a 968?". With the redline set well below 7000, there is a lot of talk about running our cars to 7700 and beyond. To my knowledge, the only Porsche's I have seen that could run in those areas, and live, are race prepared cars.....which are set up with rev limits up around 10,000!



It would appear that the individual components (cams, valves, connecting rods, etc) are capable of the high loading that high revs produce, but I worry about things like valve float, bearing loading, cam lobe wear, etc. Without the stiffer valve springs that the race cars run........when can we expect our valves to begin to float......(i.e. not fully allow for full valve closure because the inertial forces can't move them closed fast enough because of the lighter spring rates)? And, with an interference engine, like the 968, how much valve float can be tolerated before we begin running valves into pistons?



And, what about rod bearings or the small end bearings? I know that they are all capable of withstanding higher revs.........but, for how long? Today, it is not unusual to see engines that make 150K+ miles without a rebuild. If the engines are repeatedly subjected to the red line plus region, will these become 80K mile enignes.....or less? I know that in a competitive race car, getting two or three runs out of an engine is about all you can hope for to stay competitive........so, what are we doing to our cars at higher revs? Conversely, if they are capable of the higher rotational speeds, why has Porsche set the rev limiters in the low 6K area?



Having owned a few P-cars, I personally have always felt that they run better if you run them hard.......but, I have always tried to pay attention to red line. And, I have consistently gotten well over 150K miles out of engines and trannies.



Most of the chips for the 968 really don't show much until you hit redline or greater engine speeds..........but, what will that do to the lives of our engines?



Your comments would be appreciated.!



Regards,



Ernie

the engine builders i've talked to say the bottom end is good for over 8 grand - the top end is too, but the hydraulic lifters won't keep it up that high for sustained periods - i would say that if you are doing those kinds of revs, you should defintely check your balance belt tension more often, along the lines of what you should if you were racing, basically 3 times the service frequency of normal - also, make sure your oil is very clean



short bursts to 7500 have been a complete non issue in the 17k miles or so i've been doing it with the racer x chip - no signs of telltale lifter floating or anything of the kind - i don't take it to redline that often, but i have no concerns shifting at 7400



the weltmeister chip has been out there for a very long time, in a lot of cars, which goes to 7700, and i've not heard of any issues - i've spoken to steve dinan too (the designer of that chip) and he also indicates no issues expected



as for what it does to life expectancy, we'll have to wait and see i suppose

[quote name='flash' date='Feb 6 2006, 01:45 PM']the engine builders i've talked to say the bottom end is good for over 8 grand - the top end is too, but the hydraulic lifters won't keep it up that high for sustained periods - i would say that if you are doing those kinds of revs, you should defintely check your balance belt tension more often, along the lines of what you should if you were racing, basically 3 times the service frequency of normal - also, make sure your oil is very clean



short bursts to 7500 have been a complete non issue in the 17k miles or so i've been doing it with the racer x chip - no signs of telltale lifter floating or anything of the kind - i don't take it to redline that often, but i have no concerns shifting at 7400



the weltmeister chip has been out there for a very long time, in a lot of cars, which goes to 7700, and i've not heard of any issues - i've spoken to steve dinan too (the designer of that chip) and he also indicates no issues expected



as for what it does to life expectancy, we'll have to wait and see i suppose

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This information is really valuable to myself as my intention is to have a full-time track car.



I was at VIR last march with the Mazda club and Porsche Club. I got rides with 2 different instructors. 1 had a 1982 911 fully race prepped and lightened, air cooled engine. The other had a 1997 TT with just suspension and exhaust. Both drivers drove in almost the exact same manner when it came to where they shifted, at or right before fuel-cut/rev limiter in all gears. I remember asking both about this and the replies were nearly identical. No problem as long as you pay attention to regular maintenance. 911's are a whole lot different than 968's but it says something of the engineering thought process behind the cars. At least IMHO. Anyway just thought that it was interesting.



Jeremie

somebody will have to do some flow studies on the lifters and oiling system to see how long you could maintain those revs



i know that when i am out playing with it, and it is strictly a toy, that i don't worry about it, as there have been no signs yet of an issue - but, as i said, i don't hang around above 7k very long - i do leave her at 6-6.5k quite a bit though



i think bob blackwell has the same chip as me and runs his on the track - bob? thoughts?