[ByronRACE]

The blower is a Vortech V7-JT reverse-rotation. The mounts are custom. Electric water pump; meziere WP-337 I think.

I'm using a Vortech Mondo bypass valve. I built a little fixture that hooks up to shop air to allow you to set the cracking pressure to whatever you want. I played around with springs until I found what I needed. The mondo valve has an adjustment screw that gives you adjustment range on the spring preload. Basically, it's a crude relief valve.

A computer managed waste-gate would be superior. Mine will have some boost creep as pressure gets higher. I have plans to mitigate that if needed using a boost controller to modulate pressure to one side of the diaphram to control boost to the level I need. Much like a conventional boost controller, just optimized for this big bypass valve instead. In this mode, the internal spring will be very weak and both sides of the diaphram will be plumbed to manifold pressure. When the boost set point has been reached, you'll start venting one side of the bypass valve diaphram to atmosphere via a 3-way valve. The resulting differential pressure will cause the diaphram to move and the valve will open...venting off boost. You'll manage this closed-loop using pressure feedback like a conventional boost controller; and should be able to maintain flat boost at any pressure you like, or even define a boost curve...or control boost using some other input like vehicle speed, rpm, wheel slip...etc. This is stuff to play with later...my car has a PC for a dash; so I plan to do all kinds of experiments with such things.

The only disadvantage to the aggressively pulleyed centrifugal is that at all points above your blow-off pressure level, the intake air temp will be higher than it would be had you just pulleyed the blower to achieve that same pressure by a function of impeller RPM alone. That is, pulleying the blower to produce 20psi at 7500rpm then blowing it off to 5psi flat across the board is going to make a lot hotter air than if you would have pulleyed it less agressively. You have to compromise some...don't go too crazy on the drive ratio, and don't blow it off too early, and you're fine. Right now I'm pulleyed for approximately 14psi (that's about max for this combo I think...considering my head flow), and blowing off at 10. That shouldn't hurt much.

The nice part about the Vortech is the efficiency. That V7-JT is 78% efficient. Intake temps at 15psi on other comparable race engines with this blower I've datalogged show 160-180deg air at max pressure; and less (of course) at lower pressures. Low enough that you can avoid intercooling if you simply use a low compression design and tune it conservatively. I chose to build mine 7.88:1. It's running 20deg total now; at what should be around 11:1 AFR...no dyno time yet. If you see yourself doing extended WOT; you should intercool it. After having driven my car...I can tell you now that I'll NEVER be doing extended WOT in this car...just short bursts for grin factor. I've been to WOT once for a brief moment...in 3rd gear at about a 50mph roll. It just went "BLAAAT!", bounced off the limiter (set below 5K for now), and I thought something broke...because I didn't go anywhere. A quick check in the rear and it became quite evident that the tires WERE turning.....to grease in fact.