[911st]

Goran,

Good catch. You are correct, I was thinking of the SC pistons.

On the turbo they needed a flat piston for low compression so a piston that would create swirl in support of better mixing was not an option.

As we know, CIS sprays fuel for two compete turns of the crank (720 deg's) for each one time the intake valve is opened (apx 220 deg). That fuel just sits near the top of the intake valve waiting for air to come by and mix with it. Increasing volocity at the intake port help this and better lifts any wet fuel sitting on the sides of the intake port.

It takes more than an increase in volocity at the intake port to benifit low rpm power. It needs to be combined with just the right intake runner length and volunm to create the pressure waves needed to push more air into the cylinders at the targeted rpm.

Thus, my personal belife is this velocity has little to do with filling the cylinder for stronger low rpm operation and was a trade off to support a weakness that comes with CIS to better meet emissions. I know this is not what most have concluded.

I also wonder if we were not running 2.0 911T sized intake ports, if we might actually increase low rpm filling but as a lower volicity. In any case larger ports should reduce restriction during "spool" time (boost onset to full boost).

Interesting about the shaved cylinders. Bruce Anderson says the same thing in his book about the cylinders being shaved. Could there also be other reasoning?

It is interesting that with the later 3.3 & 3.6 C2 Turbo's did not do that, nor the 993TT. Nor was any of the upgrade P&C kits like the 3.4, RUF short skirt 3.4, or 3.5 kits. I guess as this happened at about the same time Porsche went to a 5 blade fan on the 1977 911's in and effort gain more heat for the thermal reactor exhaust (not increase HP with less drag), it seems easy to think it might possibly be emissions concerns were at least part of the reasion.

The 3.0 turbos has both full fins and larger intake ports.

I am not saying I am right, just what I belive.

Thanks for the input.