FredR

Boost pressure is a parameter that can be easily measured and data logged to give the driver some idea of what is going on. The pressure in the inlet manifold is irrelevant if the air cannot flow into the combustion chamber but the pressure exists to force air in there -QED.

The dynomometer is mostly of significance with respect to before and after scenarios and acceleraton for any given gear ratio depends entirely on torque at the operating point [thereafter the ability of the tyres to hold it].

The only thiing that generally limits the TS as I am aware is the size of the intercooler that can be fitted. The way the auto box works on a stock S4 motor screams for more low end torque to wake it up. This presumably is why Porsche segregated the S4 and GT models to better mate cams to gear ratios.

Most die hards who fit the likes of Tim's kit invariably seem to be owners of manual transmission cars. Obviously some are autos but I do not know the percentage splits. It would be interesting to know whether the auto owners are as happy as the manual tranny owners are. Similarly a back to back comparison of the auto model with TS versus centrif s/c driven by an independent test driver.

Ultimately, no matter what is done, blowing [if done well] will produce a more exhillarating experience- of that I have no doubt.

Using a blow off valve I have quite a lot of reservations about in the sense of losing more than one gains.

At the end of the day the only thing that matters is the abiity to get the air into the combustion chamber. I think Ted's post says it all- the curve shift at the lower end resulting from different pulley ratio is just not worth much at all on a centrif s/c.

Regards

Fred

hacker-pschorr

BINGO!!

There is one major difference between every known positive displacement supercharged 928 (twin screw) and the centrifugal 928's: The Intake Manifold.

Yes, under pressure the intake manifold & runner length is still a factor.

Every centrifugal supercharged 928 retains the stock intake manifold. We've shown in other threads that a non-functioning flappy on a supercharged car will lose torque down low, just like a stock 928.

If a custom intake manifold were fitting with shorter runners with a centrifugal blower, the engine will lose low end torque, just like a normally aspirated 928.

killav

Just recieved a Pro-Charger kit for my brother in law's 98 LS-1 Z-28. I am installing this for him over the next few weeks. After some initial break-in, he plans to add a wastegate to the charge pipe and performing the modifications discussed in this thread. This is a twin intercooled kit.

I will report back once complete but it might be a few months from now as he is over-seas in Afghanistan.....

dr bob

Mike--

Why not put the wastegate in at initial compressor install time? It will sit closed until you up the pulley ratio.

From a process-control point of view, the easiest solution is to add a second throttle body at the inlet of the compressor. Control that throttle with a spring-backed diaphragm actuator, from pressure on the intake downstream of the pedal-operated throttle. ASSuming that you didn't starve the compressor inlet to the point of surging across the blades (this is a huge assumption), it would take care of the whole thing nicely.

Question-- do Murph-III owners have the abulity to get full throttle in third gear (auto box) now at less than 3000 RPM without tire spin?