i dont quite get it. yes, you can fit an aftermarket supercharger/turbo, and run it at a low boost, but can you resist turning up the boost? big bang theory, right! to be honest, yes, if you want turbo performance, then buy one, fully sorted by the factory, but why even bother? if you have an na, and you want some grunt, then pull your engine, sell it for hard cash, and fit an engine that has the hp you require. i would say the tricky things like engine mounting, and mating up the clutch end with tube are far easier than getting a homemade turbo system to function properly, give power, without blowing any thing up!
plenty of engines going about that will give 200-250hp, but with heaps of torque, and thats really the business end, not the hp. right from idle, great gobs of power. i'd rather see a list of engines, that can be fitted to the 944, in place of the "how do you turbo a na". if you want to do it, then by all means go ahead. i'm all for innovation.
for instance, at work, one of the design engineers, has fitted a 302 mustang engine , into a mazda miata, complete with suitable axle /brakes etc etc...
i have not driven this thing, but have been a passenger, and in a straight line, on a long road, it scared me sh..less. it seems to corner no differently, or drive any different.
it looks standard, 'til it takes off. only drawback--the tires dont last too long. my point? its a fun vehicle, it rides beatifully, and it blows corvettes away at the lights, in fact, it blows anything away!!
just a few observations.
bob.

Cylinder filling is certainly a function of compression (along with valve timing, intake/exhaust manifold, port, and valve geometry, lift), so forth but yes compression ratio is a biggie as well, when determining VE.
Ahmet

Ummm... please explain how increasing the CR will improve VE.

Higher CR will help to extract more hp from the existing charge, but volumetric efficiency is a measurement of cylinder filling.

Higher CR is recommended and sometimes required when running cams with higher lift and longer duration, this is to compensate for valve over-lap and duration which lowers the static compression.

VE changes with engine RPM, an engine at wide open throttle at 3000rpm could have a VE of 90% and at 6000 rpm 60%. This is a rough guide. At maximum RPM modified engines may have a better VE, e.g.: average overhead valve engines 45% to 75%, overhead cam twin valve 65% to 80%, four valves per cylinder 75% to 90%.

I have seen dyno runs where VE of 105% was measured at 5000 rpm.

VE charges of more than 100% can be had with proper porting and intake/exhaust/cam configurations.

Sorry for the misunderstanding. Let me put it this way, take a 944 engine, and put a crank w/a longer throw in it. This will increase the compression (along with the displacement). It's true that now VE needs to be calculated off the new displacement value, thus I should not claim that higher CR will (necessarily) lead to higher VE.
Ahmet

how do insurance companies ever find out about turboing your n/a?

they have agents scan the web boards.

In that case, I just replaced my engine with a Black and Decker....

Just as an FYI, my insurance is exactly the same (to the penny) for my obviously modified 86 turbo, as it was for my 84 NA.

Blackfoot, how are your cars doing nowadays?
Ahmet

some of them feel neglected. will try to find foster homes soon.

Increasing displacement could actually lower the VE, unless other modifications are done to increase airflow into and out of the cylinders.

Increasing stroke in an engine does not neccesarily increase CR. Often times stroker motors will include pistons with a lower height or deeper dish to lower CR for boost conditions.

Many, many variables come into play when modifying engines, often times these little details are overlooked. I have seen many people build/modify engines with mis-matched components and wonder why they fail to perform as expected...