Explain spring rate selection for BOV

Can anyone explain the details of spring rate in say a Tial BOV.

The Tial site says measure the engine vaccuum in the plenum at idle and use a table to determine which spring to use.

Does this mean that the spring rate is nothing to do with how much boost you are intending to run. It's more to do with the fact the spring rate is there to stop the bov leaking at idle (ie engines that pull a big vacuum need a stronger spring to keep the bov shut under idle)?

Also under low boost my car has compressor stall noise (as if the BOV isn't opening), is the fact the BOV isn't opening anything to do with the spring rate (ie stronger springs would cause the compressor stall noise to occur at slightly higher boost levels)

Probly not much help but all i know about tial is they recommend a 11lb spring for supras... some find it to stiff and end up with turbo surge before it actualy opens.

People ive spoken to and from things ive read recommend switching to a 9lb spring

thats all i know about spring rates for tial BOV's

Probly not much help but all i know about tial is they recommend a 11lb spring for supras... some find it to stiff and end up with turbo surge before it actualy opens.

People ive spoken to and from things ive read recommend switching to a 9lb spring

 

thats all i know about spring rates for tial BOV's

Cheers Martin

I guess the fact Supras have a rated spring fits in as although all Supras run varying boost, the amount of vacuum they draw should be pretty consistent given a stock engine in good condition.

Technically I have no idea but thinking about it I would say you measure the idle pressure so that you know how high it is when lifting your foot off the accelerator. The higher the suction of the intake manifold, the higher the rate of spring that you can use.

I can't see the advantage of a higher rate of spring though, perhaps it has something to do with it leaking. I don't think the spring rate will change regardless of what type of aspiration you are using as the vacuum inside the manifold will always remain the same..... although built might make a difference?

It was all driven as my mate is thinking of fitting a BOV to a 4.5PSI Supercharged setup & I got into looking at what a 7 PSI spring actually meant (ie would it operate on a 4.5PSI boost setup), I concluded it would (ie it's not related to how much boost you run, rather how much vacuum the engine draws at idle)

It was all driven as my mate is thinking of fitting a BOV to a 4.5PSI Supercharged setup & I got into looking at what a 7 PSI spring actually meant (ie would it operate on a 4.5PSI boost setup), I concluded it would (ie it's not related to how much boost you run, rather how much vacuum the engine draws at idle)

Yeah I'd say so. -7-9psi seems about right

I would say 11 would be a bit high though. Is that what is in your tial BOV?

Yeah I'd say so. -7-9psi seems about right

 

I would say 11 would be a bit high though. Is that what is in your tial BOV?

No idea bud, Michel fitted it when I went single, I always thought it was 10 (but they don't do one in 10) although I do get A LOT of compressor stall on partial throttle, I love it though

it does sound good even if its not doing the turbo much good

from my understanding though if you have to slack a spring it will leak cause the spring isnt stiff enough to keep it shut and to stiff a spring and it will be to slow to react resulting in surge

it does sound good even if its not doing the turbo much good

 

from my understanding though if you have to slack a spring it will leak cause the spring isnt stiff enough to keep it shut and to stiff a spring and it will be to slow to react resulting in surge

That is the way it sounds but that would mean that the efficiency of the BOV depends on the amount of -ive pressure the engine creates. I'm guessing this has changed with the addition of push pull type BOV's though. I think they work a lot like electrical relays now, with the spring being totally seperate from what controls the boost release.