Supercharger Bov

[Mitch-12]

so my supercharged 4k will be done soon but i can't quite understand how a bov works on a supercharger i know i need it or it will make the engine rev but if they work on vac how does it open at idle cause wouldnt i have boost?

[Evan G]

have you tried googling how a bov works?

[Mitch-12]

yeah everyone says different

[altezzaclub]

So... it opens under high inlet vacuum when you change gear, which means you're right, it could open at idle. However the vacuum under high-rev deceleration (changing gear) is higher than at idle, so picking the right spring or having an adjustable spring should keep it closed at idle and have it open when you change gear.

 

It won't be anywhere near as important as having one on a turbo, the S/C is slowed by the motor as revs drop.

 

Did the car that originally had the S/C have a BOV or surge valve fitted??

 

How about this-

 

You could add a blow off valve to a supercharged engine as it will reduce the amount of horsepower consumed by the supercharger when the throttle is closed (at idle). But this is overkill you really don't need one since power comes from the crank not the exhaust. An oil cooler would be a better investment

[Spencer[RL]]

^^ Agreed , Superchargers don't need BOV. If you craving that noise turbo it. I myself prefer the whinning of a SC

[Mitch-12]

i don't want the noise i just though you needed to have something to relive the pressure at idle cause it will get boost and want to rev the engine?

[Mitch-12]

think it's called a bypass valve?

[Mitch-12]

and it's an sc14 they have electronic plumb back ones

[altezzaclub]

hmm.. the only one I've driven was a S/C Altezza rally car, and it was electric clutched so you could drive it all day without the S/C coming on, unless you booted it...

 

....then all hell broke loose and the noise was amazing!

 

I assume they had the ECU running the switch, not something you can do with a carb.

 

Anyway, it shouldn't rev the engine more than the carb will let it surely? You screw the amount of fuel going in down and down until it idles where you want it to.

[kickn5k]

^^ Agreed , Superchargers don't need BOV. If you craving that noise turbo it. I myself prefer the whinning of a SC

If you run blow though you WILL need a BOV!!!!! Clutched blower pulleys reduce throttle response and are a complete waste of time.

Most factory sc setups run the throttle body before the blower so no need for a bov.

 

Stu.

[Mitch-12]

i have 7k stuff and motec m48 with ign expander and ref and sync special secret dizzy with a flat cap and sequential ign and inj with ls1 coils :) and maybe i can move the tb ?

[Mitch-12]

and i have dry sump tooth belt pulleys not clutch crap

[ninja-philbo]

put tb on intake of blower done

[pol090_ke11]

I am also doing a similar setup on my 7k in my ke11, I will be running twin blow through carbs with a fixed supercharger pulley running off my gilmer drive pulley kit so there will always be boost.

 

Say if you have your supercharger is setup to run 10psi @ 5000rpm this will mean for every 500rpm there will be 1psi of boost, So in this case at idle there would be no more than 2psi which means the spring in the BOV will have to be really soft to take any unwanted pressure off the throttle butterfly or carby.

 

I'm not sure how this will affect the performance of the BOV at gear change or shutting of the throttle at 5000rpm or higher.

 

Not sure if this has actually answered any of your questions but thats my two cents :y: :y: :y: good luck with it mate.

[Mitch-12]

I'm thinking putting a v6 commodore tb on intake of blower an just have a pipe out of my 7k manifold