Less peaky centrifugal supercharger

[BiGANG]

hey guys i was just helping my mate work on his car and we discovered the BOV was leaking boost above 12psi which was why he wasnt making the power he wanted. Anyway although its a bad thing on a turbo motor, could this same theory be used to actuate boost on a supercharged motor to bring in max boost earlier?

For example. Instead of the supercharged car making 10psi at peak revs (which is probably close to 8000rpm) Could a HEAPS smaller pulley (like a 20psi pulley) be used and be actuated by the spring in the BOV to bleed the boost above 10psi? This would in effect might bring maximum boost in heaps earlier maybe 4000rpm and then would flatten off all the way to redline? Would this theory work in the real world or am i forgetting something?

[BLKCRX]

Using a BOV as a so called wastage is something we do on full blown race cars, it’s a very old but very powerful method, and yes it does have that direct effect, of creating maximum possible boost at any time, this setup is very easy to implement on a turbo setup, but as for a supercharger setup I can’t really see it benefiting as much. Full boost on a supercharger is typically made on low RPM 3500rpm on a b18c5 Jackson Racing supercharge, and 3000 on a k20 Jackson Racing supercharger. On a supercharged engine boost typically bleeds off at higher RPM due to the supercharger being inefficient and not able to flow enough air.

Regards James

[saxman]

peak boost on a jrsc and something like a vortech centrifugar charger come at very different points... the vortech is like a spun turbo, only instead of having to wait until 3500 or whatever to achieve full boost like on a turbo, you get to wait until redline(who says superchargers have less lag than a turbo?)

[BiGANG]

so if it is a viable method why dont more people do it in america instead of whinge about the jr system being better. Im just curious because i have been doing heaps of reading and all i seem to get from american websites is that the jr is the better one to have and the vortech is the dyno queen's supercharger. If this method of bleeding boost is so easy to do wouldnt it make the vortech more competitive as well as a shitload more powerful in the midrange?

[Weq]

note compressor efficency of these setups.

A turbo leaking at 10psi of pressure could be making as much as 20~+psi to maintain it. That means big intake temps/less life.

[BiGANG]

note compressor efficency of these setups.

A turbo leaking at 10psi of pressure could be making as much as 20~+psi to maintain it. That means big intake temps/less life.

I understand this, but Say even the supercharger would have to be rebuilt in half the time of a more efficiently running setup. It will make a fair bit more usable power in the rev range so i depends whether its worth paying for it with a shorter supercharger life.

Another question..

Are different pressure springs available for blow off valves or would something have to be made up? Im just curious because ive seen replacement springs for BOVs such as the Greddy one but they say things like for high boost apps, and for low boost apps, they dont say anything about the actual pressure of the spring.

[PhatSol]

Bleeding boost off a supercharger would be inefficient since you are throwing away compressed air that has cost alot of horsepower to create.

[AusS2000]

Also any sort of boost bleeding device or pop off valve would have mechanical inaccuracies. In a steady climb through the rev range you'd see the boost oscillate around the boost point. And in sudden changes you'd probably never maintain your boost target.

[strafe]

You really need to calculate the impeller speed of the supercharger, and figure out a safe limit for how much boost the supercharger can make. Spinning the supercharger faster may not necessarily make more power, as more heat is produced. (40,000rpm is generally the maximum impellor speed for Vortech Superchargers).

This means you could possibly fit a smaller supercharger to bring boost in earlier, but make less bost. (Fitting a larger supercharger will make more boost, but have more aggressive power delivery, and feel very peaky).

Centrifugal supercharger blow-off valves use a spring which keeps the valve open at idle. This is to prevent compressor surge.

You would need a huge electronically controlled wastegate to try and achieve what you want to do in the first post, and...

Even if it did work, you prob. have a supercharger too big for your motor, which would not create much more boost in the mid range anyway.

So what's the solution for mid range power?? Positive displacement superchargers (eg Eaton, on Jackson Racing kits). These displace a specific volume of air per rotation (between the housing and rotors for the eaton). This is why they create boost early, and taper off throughout the rev range (struggles to displace the amount of air required by the engine to create the same amount of boost as in the low revs).

The ultimate solution? Have a centrifigul supercharger blowing INTO a positive displacement supercharger. Used sucessfully by lancia in the '80s for their lancia delta rally cars (dont quote me on that, have to check my facts), this allows low down and top end power to be produced. Costs may be a bit prohibitive on a road car though...

erm, I hope this answers your question

[strafe]

Oh, and i forgot, there's an LS-1 Ute built by Marks Workshop in WA that uses a Centrifigul Supercharger blowing into a Positive Displacement Supercharger, Woot!!

[locote]

Thats 2 S/C waw......
lets see Vortech kit is like 7Gs JR is about 5gs plus install and tuning...
THATS 1 EXPENCIVE SETUP!!!!!
How much heat would a setup like this generate????

[saxman]

the lancia delta used a twin charger set up. turbo + supercharger. The supercharger was used at low throttle, then disabled via an electromagnetic clutch once the turbo took over. IIRC that is.


the real solution to super fast boost, throttle response, no lag, and plenty of high end power is a variable nozzle turbine based turbo that varies the a/r ratio from start to finish. Better in every single possible way.