[Grady Clay]

Now that we successfully hijacked your thread for a while discussing the vagaries of ignition systems (much has been posted on the Forum) lets discuss your actual questions some more.

There is no substitute for displacement, however you get it. All modern engines are "over-square" meaning the bore diameter is larger than the stroke length. That makes for high revving, high horsepower - but there is a limit. The other issue is rod length compared to stroke length. Remember this was an engine that was originally 80 mm bore and 66 mm stroke providing 1991 cc. With the longer strokes the heads have not moved farther apart. That means shorter rods and greater rod angularity - not necessarily good at the extreme.

When Porsche increased stroke from 66 mm to 70.4 (2.2-->2.4) they kept the bore the same 84 mm. The same was true from 70.4 mm to 74.4 mm (3.0-->3.2) with 95 mm bore. Of course they had already "experimented" with the 3.3 Turbo (97x74.4.)

A general rule of thumb is; increasing the stroke, everything else the same, increases low end torque. Increasing bore, everything else the same, increases high end power. Doing both results in increased displacement and increases both torque and HP.

I'm sure someone is (or has) building a 4.0 - just not out of a 3.0SC

When you say you want to "...build a real torquer hot rod...." Keep in mind air cooled 911s like revs. I am very comfortable buzzing around at 3500-4500. I am uncomfortable at 2500. It is all about air and oil flow. Of course when you stab the loud pedal at 4000, things happen right now.

A 3.5 (100x74.4) is a reasonable mod. I think we built our first one in '79.


Best,
Grady