Was just doing some light reading on the install for the Stillen SC to see if it was possible for a DIY install.

I did notice however that under the "Care/Maintenance" page they state that headers or racepipes adversely affect the supercharger.

I'm no expert on fluid dynamics but I would assume that extra exhaust gases on an engine putting out more power than in the stock form should require more expulsion of waste or spent air. If you widen the diameter of piping or shorten it then you would decrease resistance and allow faster velocity of the fluid out (in this cas exhaust fumes) so that you could push in new clean (oxygen) air and redetonate.

Why would they want you to avoid this?

 

they say that for the roots blower to opperate most effectively it needs backpressure. Hence they say that racepipes and headers arnt a good idea.

 

i really wish that the stillen would put out more power, that is the nicest aftermarket kit you can buy. the craftmanship is untouchable.

or at least if they made it safe with stock exhaust and when you opened it up, it would make a lot more power??

 

Yup...but the only problem is you need the fugly hood...

 

A lot of it comes from that they're using a roots blower. With a CSC, lysolm or turbo, the air that comes from the turbine outlet is already compressed. With a roots blower, it just comes out faster, but still at atmosphere pressure. They don't compress the air within the unit, like the others do. The compression takes place between the blower and intake valves, in your intake manifold.

On a 4 stroke cycle, when the piston is dropping down the cylinder and the intake valve opens, a vacuum is created in the cylinder. Because of the overlap portion of the cam duration, the exhaust valve is still open. An appropriate level of back pressure allows the incoming air/fuel mixture to completely fill the cylinder. Too much back pressure, keeps exhaust gases in the cylinder, not enough draws the air/fuel mixture out through the exhaust valve.

So on a boosted application, since the intake manifold is no longer at atmospheric pressure, the pressure there is pretty much always higher than the pressure in the exhaust, so during the overlap phase, some of the air/fuel mixture is pushed out the exhaust valve. With a turbo or csc, the air that is added is already pressurized so its easier for the entire intake manifold to retain that air pressure level as air is rushing out the exhaust manifold. With the roots blower, it has to repressurize the entire intake manifold by pushing more ambient air into the chamber.

Since a roots blower is positive displacement, it pushes a fixed amount of air per revolution. So when the intake manifold pressure drops, there is only so much the unit can do to raise it back up and add extra air to the mix. This is extremely tough for the unit at higher rpms, why the Stillen doesn't generate huge peak whp. But at lower rpms, its much easier since the valves stay open longer. Why it generates such great low end torque.

Its not as much that you need a lot of backpressure for the unit to operate. Its that you need the right amount to keep the pressurized air/fuel mix from going straight out the exhaust valve and keeping it in the cylinder for maximum power. And the right amount is pretty much at stock backpressure levels.

 

Yeah stocks definately best with the stillen kit. I installed a stage 2 kit on a coupe a few years ago after I had installed I,H,E. The car made a wopping 30 more horse power than a stock z

 

I am working on that.
I am looking to make some big developements here soon with a true twin screw type, positive displacement SC based off a design similer to that of the Stillen/Eaton unit.

Just be a little patiente everyone. Can you imagine (approx.) 500 WHP, with the Stillen type power delivery??......

 

so if what you're saying is true then then because of the overlap in exhaust valve opening and intake rushing in the result could be a blow by of fuel and air if the exhaust system's resistance was decreased (and pressure decrease) while an increase in flow occurs out of the chamber.


thanks for the explanation. I think my lapse in knowledge was that I didn't realize the exhaust valves stayed partially open. i assumed that hte exhaust valve didn't open until the intake valves closed and vice a versa (single chambered heart came to mind).

anyways. thanks.

 

Yeah, stock NA cams have a decent amount of overlap. That's why aftermarket cams are so good for the bigger FI builds because they have more lift and less overlap. Helps to eliminate the blow by because you don't need the positive / negative pressure areas to draw in the intake charge.

Overlap timing isn't the only problem with the Stillen though, it just helps to explain the backpressure issue. Because overlap decreases at higher rpms, but the intake charge gets hotter and hotter from the blower spinning faster so you get diminishing returns. Its a lot of different things working together.

Scott has pretty much tried everything possible to get more juice from the Stillen setup. Blower size and the nature of the roots design really just make it what it is.

 

So this only effects the stillen supercharger? As in, racepipes/headers are bad for it. How about Vortech or Procharger? Are pipes bad for those guys?

 

will it still need the ugly stillen hood?

Vortech and Procharger work differently than the Stillen roots type.

 

Those are positive pressure systems (similar to putting person on a ventilator). They won't be affected as much by output out the exhaust valves because they do not create a negative pressure system like the roots style suprcharger.

sorry if my engine analogies seem physiological. it's the only way I can manage to understand it properly

 

No, this discussion only pertains to the Stillen. Centrifugal S/C'ers like the Vortech & Procharger will benefit from better breathing mods, as long as the exhaust velocity is matched correctly. Basically, don't over do it on the diameter...

 

Took me awhile, but now I love the hood on the G. Not so much on the Z, though...

But yes, his kit will require that. There's no way any top-mounted Roots or Whipple setup can clear the stock hood, unless maybe you found a way to lower the engine mounts...

 

or you could do it like back in the old days