Quote:
Originally Posted by j.fro
This is why I laugh when I look at the arrangement that some out of work practical Engineer did in his Garage, using a vacuum cleaner blower motor to blow over objects, in an attempt to design a component.
Ouch!
I think that is exactly what they did, how else can a:
2.7L 986 have 217 HP, ~80 HP per liter
3.2L 986 have 250 HP, ~78 HP per liter
3.4L 996 have 300 HP, ~88 HP per liter
I agree with this, and there is further evidence from the current 3.4 liter engines: 350HP in a 911, but only 315 in a Boxster S.
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There's more to it than that... The 986 engine uses the same cams as the 5 chain, 3.4 996, they are even stamped as such right on the cam blanks.
The cylinder head ports and castings are also the same, BUT the 3.2 chambers are 3-4ccs smaller, for the smaller bore size.
4 valve engines respond aggressively to bore size increases, the 3mm difference in bore size between the 3.2 and the 3.4 is HUGE in regard to swept volume, and chamber filling. The entire intake system is different as well, as the 986 intake runners are longer and thinner and extend from the plenum chambers all the way to the cylinder heads without interruption. The 3.4 996 does not do this, at the 70% point it breaks away and changes to a more effective aluminum intake runner that bolts to the head.
The plenum areas are also larger.
We find huge gains with intake manipulation, but thats not meaning bolt on items-
Porsche knew that the engine in the Boxster was in the right place, and the engine needed a handicap to keep the performance differentials between the two cars so the 911 would remain the flagship.
Because of this, we have always been able to increase the percentage of power increase more with the 986 engine more than its 996 counterpart. Its not uncommon for us to produce 100HP more than stock from a 3.2S engine for a totally street able engine, on pump gas, with a red line that can be reduced 500RPM lower than stock.