Just curious, when is a blow off valve needed with a centrifigal supercharger and what are the benefits?

 

From what i understand, it will protect your blower when you come off of the throttle and eliminate the pressure going back to the blower. When you let off of the throttle, the valve will open with the intake vaccum to release the excess pressure between the tb and the blower discharge. That is what causes damage or shortens longevity of the blower. I feel it should be used in every blown situation.

 

I agree.

 

I'm no expert but I would say you need one if you are running high boost. Vortech recommends one if you run more than 12psi. A blowoff-valve or bypass-valve will protect your blower from being damaged by compressor surge. I'm running a Vortech unit at low boost (6psi) on my stock L98 for 45K+ miles and I've had no problems so far.

They sure do sound cool though!

 

I'm planning on getting one. How do you adjust a BOV and any recommendations on a model?

Willie

 

Im getting one of the cool ones with the horn to make it extra noisy like the ricers use...

 

no adjustment needed. it opens under vaccum. under boost it will stay closed. i ned to hook mine up too. !

 

no adjustment needed. it opens under vaccum. under boost it will stay closed. i ned to hook mine up too. !

Wait a minute. What you describe is a surge valve. I already have two of these. What I need is a valve that will open when boost spikes, i.e. the moment the throttle is released. Isn't that what a BOV does?

Willie

 

yes

 

Let's say I'm peaking at 20-psig at WOT, then I let off the throttle. For an instant, the pressure will spike above 20-psig. In this scenario, I want to set the BOV to open at 21 - 22 pounds. Can I assume BOV's have an adjustment to accomplish this?

Willie

 

yea they have adjustments.

Right now, (at 8.5#s) I just use a surge valve and it works fine. WIthout it on there, the car shifts rough

 

why wouldn't you want it blowing off at say 20# or 15lbs.? why only 21 or 22 or more lbs.? just curious.

 

Not all BOVs have adjustments.

From what I have seen it's not exactly a pressure adjustment, as far as what pressure it would blow off at, but how hard or soft it will open, once the vacuum is applied to the valve, but because of this it will seem like pressure settings are being adjusted, since a higher pressure will be need in some cases.
Seems to be more for quick or slow opening/closing of the BOV, basically just adjusting how it reacts.

 

its mainly because it is only performing a protective duty, as long as it is opening higher than the max boost the engine is seeing during performance operation but still opening below the threshold damage will occur at when throttle is snapped closed then its getting the job done, thats why some are not adjustable.

Sometimes they come with a 20 and a 30 pound spring thats all the adjustment you get. a car running less than 15 pounds boost would run the 20 spring and a guy with a eclipse running 25 pounds would run the 30.

 

i thought that any extra pressure thrown back towards the blower is bad after the throttle closes. So it should blow off anytime you come off of the throttle/// no?

 

I have seen some that operate purely from pressure under them, some operate from a boost line hooked to them and some that either work alone or to assist some other method of operation using the vacuum to make it open. these either re route between the filter and boost device (blower, turbo) inlet or have a filter of thier own to avoid accidental intake of dirt. Some bypass valves operate this way as well.