BOV on 4AG-ZE (seriously)

[mic*]

If you dont put a non-return valve in your vacuum line, then you will apply boost to it, like you are saying. In this case i would definitely be plumbing boost to the back of the diaphragm too or you will rupture it because although there is boost on the bottom of the valve, and the top of the diaphragm, the back of it will still be atmospheric pressure and go pop if you boost too high.

[Ben Wilson]

If you download this pdf, you'll see a picture of a BOV in bits.

There is no diaphram to rupture, I've got it hooked up as per the stardard instructions.

[mic*]

Try this.

Put a non-return valve in the vacuum line so it can suck but not blow boost to the BOV. Run a by-pass around the non-return valve with two small same sized restrictors in it, so the the BOV can now get full vacuum but limited boost.

Should be able to vent well with the hard spring.

[Ben Wilson]

But, I want the BOV to close under boost.

Bear in mind that the other boost 'reference' is from the main pipe itself. I think the correct spring will do the job nicely.

[mic*]

Yeah i know you want it to close. I thought the prob was that the softer spring is possibly gonna flutter too much.

Ultimately the spring is what supposed to hold the valve closed, not equal boost on both sides. If you want it to snap open and closed you need a hard spring. What I suggested is just a way to still have a tough spring to do the job, and still vent quickly & well.

Its up to you tho.

The other advantage was going out buying some tube and a valve for a couple of bucks, & fitting it now as opposed to paying more and waiting two weeks for your spring.

[Ben Wilson]

With the big spring, it doesn't even open off load (like a good BOV is supposed to).

I might try lopping a few coils off to lower the preload, but of course that will stiffen the spring.

[mic*]

When you say off-load do you mean cruising or decelleration?

I thought the video i watched was the hard spring venting on sudden decelleration?

Smooth deceleration may not result in such a blast, but that was the idea of my above suggestion. If the boost is limited to the BOV "vac" line, then the pressure differential already exists coz full boost is pressing the bottom of the piston/valve, the spring holds the BOV closed, then a slight increase in the pressure difference (ie smoother decell) and it will start opening.

The clutch will turn the SC off pretty quickly tho, so there is never gonna be a great excess of pre-TB boost to vent i wouldn think...

[Ben Wilson]

I'm still not getting what you mean here.

I'm trying to get the valve to open more easily, I want it to open basically at any time I'm not under full boost.

I want it open a little when I'm under boost but at part throttle to vent the execss.
I want it open at idle/cruise/decelleration to simply eliminate the supercharger from the equation.

[mic*]

Ok i see what you mean mate, and there is no way that what i have said will acheive a bypass (reverse) operation.

BUT;

For the BOV to act as a bypass, when the at part throttle the after TB vacuum level must exceed the pre TB vacuum with the SC off. And it must exceed it enough to overcome the potential of the spring.

I would think that if there is a fundamental need for the stationary SC to be bypassed, then it must create a reasonable vaccum (restriction) itself. Therefore a vacuum would exist between the SC(off) & TB at part throttle & the pressure differential will be very minor, and thus a VERY weak spring would needed for it to suck open - bypass operation.

Conversely, since the BOV is right after the SC, and the boost/vac reference is after the IC and TB, it would be reasonable to expect that the pressure on the bottom of the piston while under boost will exceed the pressure at the reference line, thus a heavier spring is needed to keep it closed.

Particularily when you mash it and the SC boosts instantly the BOV would be wide open till the boost ran down the manifold. Is that what happened with the RC car spring when you say it didnt close in time?

Also, from my thread "GZE intake" (which i thank you for your responses to) i have learnt that sucking throught the SC doesnt seem to make much diff for a 4A, and also that its desirable for the SC to be spinning when the clutch kicks in anyway.

[Ben Wilson]

I see what you are getting at.

With the RC car spring, the piston was completely open at idle (far more than it needed to be). I'm thinking with a springs somewhere between the two, I'll have a decent compromise.

I'll wait for the turbosmart spring to arrive (the've already done the maths), and see how it works then.

I've got a lot of tidying up to keep me busy until then.

[mic*]

Keep me posted Ben. I am genuinely interested to know exactly what results you get. Hopefully the Turbosmart spring will fit the bill.

[Ben Wilson]

I'm going to be 'mildly irritated' if it doesn't

[WindeX]

How did this end up?

[Ben Wilson]

Not bad, it works nicely, it is bloody loud though.

I've got to build up an airbox for it some time.

[Ben Wilson]

Some video of the car in action:

Click here to watch MR2-Khana