View Single Post
patkeefe patkeefe is offline
one of the great unwashed
patkeefe's Avatar
Join Date: Apr 2004
Location: Ringwood, NJ
Posts: 2,850
The Hondas and Miatas are also water cooled.

You need to consider the dynamic compression ratio, how effectively you can fill the cylinders with charge, what RPM range you want the optimum power and torque, and a few other things. Don't imagine the head design of a Porsche is inferior, it really seems to me to be quite effective in ventilating the combustion chamber; it's limitation in my mind is the flame front propagation, which is why twin plugging is necessary.

Compare to a 930, which is more apples to apples. They use a lower static compression ratio, evidently because the factory wanted more power in the higher RPM ranges. They also have much higher boost limitations than you would get from a converted n/a engine, but the air cooled powerplants also have heat rejection limitations. So, depending on cams, fuel, intercooling, etc, there may be times when you might have to decrease the compression ratio of a 3.2 n/a engine to make it work for your application.

Bolt on turbocharging is basically a compromise, but it is relatively cheap HP in the Porsche world. I get 251 RWHP from my 3.0 CIS SC engine, and it is just like a plain old SC engine to about 3000 RPM, then it picks up a bit of power. It is quite streetable, and runs well on the track, which is what all Porsches should be capable of. I run the static 8.5:1 CR, and 6 PSI boost. I think I calculated my BMEP to be around 210, IIRC, which is not bad.

Previous posters in this thread are in my opinion some of the sharpest guys on this subject, maybe they will chime in further on this.
Patrick E. Keefe
78 SC
01 Boxster
Old 11-22-2007, 08:55 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #9 (permalink)