nick_968

Most 968's are losing hp through the valve guides, this is a well known prob, that is why most are down on power when they dyno. One other thing to remember is that Pazzers car dynoed at 218 before but this is one dyno on one day at one temperature and cannot be used as a base result compared to other 968's so dont read into the figures too much. The before and after are much more important, was the base readout done on the same dyno on the same day?

RajDatta

True, just too many variables. That is why I question the 30hp increase claim.
The valve guide is a well know problem for sure. A head refresh with new guides is not that expensive, especially when done directly thru a machine shop and doing the work yourself.
Raj

pazzer

Hi Raj, no these dyno runs were about 3 years apart im afraid, yes i have the airbox mod and the k&n filter aswell, although they were on the same dyno, as you say a good head refresh could be in order this is why it may off been down on power to start with, plus the car had been standing for about 10 months aswell and really needed some fresh fuel in there, although the odometer is only showing 60000 miles, so maybe the head could be ok, should get a leakdown test done, chris.

Lord_Galva

Not that known. I have never heard that our cars had this problem.
So the machine shop installs the guides into the head then install?

RajDatta

They have to heat the head in the oven to press the old guides out and get the new guides in. Colin/Ninemeister wrote a great article on this and the effect it has on power. In a nutshell, it causes the valves to flutter and creates turbulence in the path of the incoming air into the combustion chamber. I will try to dig the article.
Maybe Pazzer can request 9M to post it for all of us to read .
Raj

Lord_Galva

Cool.

RajDatta

Pazzer, have you discussed this with 9M? I would think he would be the person to talk to as far as freshening your top end.
Raj

968workaholic

The larger gain from changing out the guides is the reduction of oil consumption. If the valves are loose enough to be rocking in the guides then there would be some serious oil loss. As for causing the valves to flutter, its more that they don't open and close on a straight path, causing uneven wear on the face of the valve and the seat. A valve that flutters would be caused more by a broken/weak valve spring rather than a worn guide. Six weeks of engine classes finally paid off!