TB993tt

When my 993tt was new, my bum dyno told me it was underpowered compared with my previous 440hp 965. I dynoed the car and saw 380hp at the flywheel. With the car being new, I contacted Porsche in the UK who said they would find the lost power for me (although they objected to the car being rolling road dynoed saying it could overheat and blow the gearbox) The first job to be done was for the supplying dealer to check the cam timing. It was explained to me that to save time in the manufacturing process a jig was used to set the cam timing and this inevitably gave rise to tolerances. They set the timing to factory specs using the old "by hand" method. They showed me the before and after timing figures per bank and they were different - I canīt remember the figures. I dynoed the car again and (again whilst I canīt remember the figures) when the two dyno curves were compared, they were different with the hand set timing giving a better curve and finding 10hp peak. Remember this was mid 1995 so Porsche were quite aware and sensitive about the tolerances of the jig system.
Incidentally, the lack of power turned out to be a wastegate problem.

Edward

Kevin,

Help me out here as I'm a bit confused. You've got a rocker arm and what looks to me like mechanical adjusters (or at least they don't look like the hydraulic ones I replaced). What in the pic was the modification that you did that allows you to alter cam timing? Adjusting valve lash will change timing a bit, but not really the difference that one gets at the sprocket, not to mention that the importance of correct valve lash supersedes other "performance" concerns, wouldn't you say? Perhaps I'm missing something but cam timing is done at the camshaft and gear (as you say, you replaced the cam gear) and not at the lifters.

Edward

Kevin

Edward;

If one tries to adjust the cam timing with a dial indicator, like one would do on an earlier engine, the hydraulic lifter will collapse. In short you will not be to set your required lash at a given degree setting. I have modified the stock hydraulic lifter so that one can dial in each cam. You can not do this with the hydraulic rockers. And in this case I didn't want to switch to solid rockers, because I didn't want to regrind the cams. New rockers=New camshaft surface. Hope this helps

Edward

Kevin,

Thanks. I'm curious, though (you've got my attention on gear-head stuff like this ) as to what you've done to your rocker arms that still allow you to utilize the hydraulic lifter?

Also, you mention that "you will not be [able] to set your required lash at a given degree setting," but one doesn't really "set" lash with hydraulic lifters...they just "do their thing" regardless of how early/late the cam lobe comes in. I hope I'm not sounding argumentative; I'm just trying to understand what you've done as this stuff interests me! Please feel free to tell me where I've missed something.

Edward

Kevin

Edward;

Anything to help, maybe I wasn't explaining it good enough. When you set your cam timing (Dialing in you camshafts)you cannot do this with a stock hydraulic lifter, it will collapse, because the engine is not running (it was on my engine stand) no oil pressure is available to pump up the lifter to close the lash. The only way possible to set the cam timing on both cams it to do this with a solid adjustable rocker. Once you have dialed in you camshafts, reinstall you hydraulic lifters.

Edward

Kevin,

I get it ...uh, duh <img src="graemlins/c.gif" border="0" alt="[ouch]" />


Edward