Supercharger bypass

Wulp, I just found out what happens to the car when the bypass is closed all the time, and now I know why I was spinning the tires off the car last Saturday at the track. Man did I have bottom end torque , AND lots of pinging when going above about 8psi , AND LOTS OF HEAT. I just went up town and drove home and felt the SC and the IC and I think they would have been glowing if it was dark out .... breakfast anyone, I coulda cooked it for ya.

I had broken the hard line going from the plenum to the bypass valve when I was putting everything together, and the break was out of site till I pulled on the tube.

What was your boost gauge reading?

It was nailing 10psi right off the bat and by the time I hit 2500 rpm's it was pegged. Funny thing was at idle it still had vacuum.

The blower can only suck so much air with the throttle closed. So I guess it makes sense that it would still show vacuum at idle.

Of course it will show vacuum. The only real difference is the load on the blower and the fact that you aren't getting cirulation (and hence cooling) during part throttle. Leaving the bypass closed doesn't affect boost though. It will respond slightly quicker but it won't make any more boost.

Well, it seemed the car pegged the gauge at around 2500 rpms and stayed there. Now the car hits 15psi I believe around 4000 RPM's.

Unless the extreme air charge heat going inside the motor was causing alot of back pressure because the motor couldn't handle it????? strange or my bypass valve isn't working right.

fturner said:

Well, it seemed the car pegged the gauge at around 2500 rpms and stayed there. Now the car hits 15psi I believe around 4000 RPM's.

Unless the extreme air charge heat going inside the motor was causing alot of back pressure because the motor couldn't handle it????? strange or my bypass valve isn't working right.

Click to expand...

The supercharger can't create any pressure when the throttle is closed. What does happen, however is that with the bypass closed the air temps will climb equal to engine temps, ie. 200 deg or more and stay that way until you open the throttle at which point the IC starts to work. Normally we get the benefit of the IC at all times and not just when in boost.

It's only physics. When the bypass is closed (anytime vacuum is NOT present in the intake manifold), it's closed and boost level is simply modulated by your right foot. The elevated temperatures may have affected what you saw on your boost gauge but that's all.