BOV necessary on SC?

[imoloq]

Hi,

Wanna ask all the sifus here: Is a BOV necessary on a supercharger? I know a person who has a supercharged engine and he says he put the BOV on for fun. And I'm thinking that a BOV might be a safety net in case the throttle is closed suddenly and the manifold pressure can't be bled off fast enough.

Any feedback would be greatly appreciated!

 

[normality78]

i dun think that guy even know what is he talking about. putting bov on SC? whahahhhaha

 

[imoloq]

Maybe he loves the sound?

 

[K_C]

where to put the BOV???
on the air ram???

 

[imoloq]

After the intorcooler maybe?

 

[jswong]

When the throttle is closed suddenly, the crank speed goes down also. The supercharger will reduce in rotation and the air that it pushes out will correspondingly decrease. That's why supercharged systems don't need BOV. Just curious, though.. does his BOV ever makes any sound?

 

[normality78]

spot on jswong. thats why im saying, does the guy even know what is he talking about. I dont even think that guy know how SC work.

Imolog,
Do u know how bov work? If u know thn u will know there is only 1 plc to put bov.

 

[K_C]

SC got I/C ar???

can put BOV ar??? put where ???

roots charger can put???

 

[imoloq]

I know what I'm talking about and I know how BOV and SC works. On turbo systems at least.

I'll try to find out more about his setup.

 

[normality78]

how to be invention as whn u release the pedal, the charger spin will reduce in and the boost will correspondingly decrease. its direct inter-relate. there is no exessive boost press to release thn where you get the sound from?

 

[imoloq]

how to be invention as whn u release the pedal, the charger spin will reduce in and the boost will correspondingly decrease. its direct inter-relate. there is no exessive boost press to release thn where you get the sound from?

I have no idea. I haven't not seen his car in action yet so I can't comment much.

But I have my theories: When you release the pedal suddenly when going full throttle, the throttle plate is closed in a split second whereas it takes the engine some time to rev lower. During this transition, boost is still generated and probably the extra volume of air produces the sound.

 

[imoloq]

Just met up with the guy with the BOV SC. The guy obviously don't know what's he's talking about. He says my car, an NA, has 0.8bar of boost. LOL that's the funniest thing I've heard in a long time! No sound from his BOV though.

We dragged a bit and he got like 2 car lengths in front of me by fourth. Really powerful car, running 4AGZE with 0.6bar boost.

 

[kEn330]

I had BOV on my Beemer and it comes with the Sc kit.... it did work very much like turbo applications, just that it is not as loud as them....

 

[RSI]

It really depends on the SC setup. The throttlebody can be either before or after the SC. If you mount the throttle at the intake of the SC then you do no need a BOV. However a bypass valve is used to gain better FC so that the SC does not need to make boost during cruising. Mini cooper S and all Jackson Racing SC kit uses this configuration.

If the throttle is mounted on the inlet manifold after boost is being made then a BOV/BPV must be used. Mercedes Kompressor engine (C200K, SLK230 etc.) uses this configuration.

 

[RSI]

When the throttle is closed suddenly, the crank speed goes down also. The supercharger will reduce in rotation and the air that it pushes out will correspondingly decrease. That's why supercharged systems don't need BOV. Just curious, though.. does his BOV ever makes any sound?

That theory applies only to turbos. A sudden closure of the throttle also reduces supply of air to the exhaust turbine.

Whereas on a SC system, Letting go the throttle at say 6,000rpm will block the supercharger outlet while the SC is still making boost since the SC is linked together with the engine. And the boost has no where to go but back up into the SC and out thru its mouth! That will damage the SC in short order. On cars using air flow sensor, it is very likely to stall the engine since the engine is detecting air in the reversed direction!

If it is a roots supercharger, having it pumping into a closed throttle will build up a lot of heat and the heated air backing up thru the rotors will kill the SC very quickly not to mention additional heating onto the intercooler if there is one.

 

[imoloq]

Thanks for all the info on SC RSI. Having a BOV or not really depends on the SC setup. What about 4AGZE? What setup are they running?

 

[RSI]

Thanks for all the info on SC RSI. Having a BOV or not really depends on the SC setup. What about 4AGZE? What setup are they running?

If not mistaken it is the conventional system with throttle after the SC.
That is why the 4AGZE engine is very noisy. Throttle mounted in front of the SC will only get noisy at full throttle but will dampen throttle response.

Throttle mounted at the inlet manifold will always be noisy.

 

[imoloq]

If not mistaken it is the conventional system with throttle after the SC.
That is why the 4AGZE engine is very noisy. Throttle mounted in front of the SC will only get noisy at full throttle but will dampen throttle response.

So, no wonder 4AGZE need BOV. What's the reason for the extra noise in throttle after SC setups?

 

[RSI]

So, no wonder 4AGZE need BOV. What's the reason for the extra noise in throttle after SC setups?

The throttle blocks the sound that is made when the roots is pumping when is is not fully opened.

Imagine a throttlebody covering a small speaker. The sound will be loudest when the throttle is fully open and soft when just slightly opened.

 

[K_C]

That theory applies only to turbos. A sudden closure of the throttle also reduces supply of air to the exhaust turbine.

Whereas on a SC system, Letting go the throttle at say 6,000rpm will block the supercharger outlet while the SC is still making boost since the SC is linked together with the engine. And the boost has no where to go but back up into the SC and out thru its mouth! That will damage the SC in short order. On cars using air flow sensor, it is very likely to stall the engine since the engine is detecting air in the reversed direction!

If it is a roots supercharger, having it pumping into a closed throttle will build up a lot of heat and the heated air backing up thru the rotors will kill the SC very quickly not to mention additional heating onto the intercooler if there is one.

thanks for all the explanation bro... any idea how to get over the heated air backing up thru the rotor for roots charger ar??? ehehe