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Discussion Starter #3
So when I have my boost controller off/ running stock boost I'm getting a horrid noise as I let off the gas at higher RPM when I noticed that the vavle had snapped and I believe it to be the culprit. I can't seem tonsee anything else wrong.

Thanks for the reply/info I'm very new to the mr2 world/ boosted community.
 

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What is this noise you speak of?

Just hook up the hose directly to the BOV rather than through the vacuum limiter.
This link below explains how the BOV on the MR2 works however some information is not quite correct. I have highlighted these with BOLD Underlined Italics and corrected is in (brackets) in the quote.

Well, Toyota used a two-way recirculating blow off valve on (my) MR2 and I was wondering if this was the same. Another individual on the MR2 board has since said that it is. He also is positive the Porsche valve works this way. Can anyone confirm?

Here's the way it works. As we all know a BOV opens when you come off of the throttle to prevent damage to the impeller from pressure spikes. Well, because the AFM on the MR2 has already metered the air going by it to the turbo if they were to have used a BOV dumping to the atmosphere it would result in a rich air/fuel ratio because you'd be eliminating air from the intake charge. So, Toyota put a recirculating hose that puts the air back in front of the turbo. This maintains the proper A/F ratio and also allows the turbo to spool up just a bit faster when you get back on the gas because it doesn't have to work harder to pull in more air. It's all right there. That's function number one, air going one-way, recirculating.

The second-way is by-passing. The valve also opens under vacuum allowing some of the air to bypass the turbocharger. Why? Well under vacuum the engine has to pull air over/through the impeller blades. This also is a cause of tubo lag. The smart little Toyota engineers figured that if they could get some of the air flow by the turbo the engine would rev faster, produce more exhaust gas faster, there by making the turbo boost faster.

Then when the intake system from the turbo through the intercooler to the intake manifold moves from vacuum to boost the valve closes allowing the car to come on power.

"The large round area at the top is a diaphragm. The area on the top of the diaphragm is larger than the area under the diaphragm. Now note there is hose directly from the manifold to the top (large area) of the diaphragm, and another hose tee's off that goes through a check valve (This is not correct. It is a limiting valve. Check valves would stop air movement in one direction however this is not the case otherwise there would be no point having the valve connected to the system)to the underside (small area) of the diaphragm. When there is pressure (boost) in the manifold, there is equal pressure on both sides of the diaphragm, but since force=pressureXarea, the greater force on the top holds the valve closed. In fact, the higher the boost, the more tightly the valve is held closed. (Yes this last statement is correct but if there is equal pressure on both sides the spring adds the extra pressure on top of the boost pressure and holds it in the closed position. At least this is how I see it working based on other BOVs, maybe no the OEM version.)

Now as soon as you lift, and pressure starts to drop in the manifold, air immediately escapes from the top of the diaphragm, but the "check valve" (restrictor valve) restricts it from escaping on the bottom, and the pressure on the bottom quickly exceeds the pressure on the top, and the valve snaps open. If you reverse or eliminate the “check valve” (VTV) then you can't trap pressure under the diaphragm, and the valve cannot respond as quickly.


The diaphragm section of the valve is connected to a spool in the main section of the valve. That spool opens and closes the connection between the crossover pipe and the intake air pipe. When the diaphragm is pushed (or pulled) to the top, the valve is open, and when it is pushed to the bottom, it is held closed.

There is just a light spring on the spool in the main body. Its only function is to return the valve to its normally closed condition when the engine is not running. "
Here: http://www.mr2-tech.com/bgb/mechani...rger_system.htm
 

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Not a check valve. It's a limiting 'valve'. Think about it, if it was a check valve it would let boost into the BOV but not out. So holding pressure all the time. If you flip it the other way it wouldn't let boost into the BOV so pulling a constant vacuum. Not quite how the BOV is designed.
 

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Discussion Starter #7
What is this noise you speak of?

Just hook up the hose directly to the BOV rather than through the vacuum limiter.
This link below explains how the BOV on the MR2 works however some information is not quite correct. I have highlighted these with BOLD Underlined Italics and corrected is in (brackets) in the quote.
Thanks a ton for the information! I will try this, thanks for saving me some time and money. What a great community!
 

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Not a check valve. It's a limiting 'valve'. Think about it, if it was a check valve it would let boost into the BOV but not out. So holding pressure all the time. If you flip it the other way it wouldn't let boost into the BOV so pulling a constant vacuum. Not quite how the BOV is designed.
I am not that familiar with the factory BOV. I've never held one in my hand before. I don't run a BOV.

If you look at the diagram, there are two inlets to the BOV.
The hose on top has no restrictions. I assume it is connect to intake manifold, therefore it sees vacuum and boost.
The hose on top is tee'dd to the hose that goes to the side, which has the limiting valve.

Why would one port of the BOV need to be limited and the other receive the full flow? It makes more sense to me if that port only needs to see vacuum and not boost, or visa-versa.
 

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