Originally Posted by senna21

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 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.

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 "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

Go to Turbocharger and scroll down to the bottom of page TC-13 and the top of TC-14.

Also see the attached pic and annotations.

Originally Posted by RarlyL8

Pardon the temporary hijacking of your thread, I'll breifly answer the questions posed.
I've been a Rennlist member sense 2001 and a Pelican member before that. I only had time for one BBS and Pelican was more active. Pelican has become less technical these days while Rennlist has become a real 930 tech powerhouse. That's why we're here.

The air breather on my engine is my own "invention" HA! You can "build" one yourself in one hour with $20. It started out as an easy way to tune my car without removing the intercooler and air cleaner assembly every time I needed to adjust the mixture (my car is a '78SC, the engine bay has less room up top). I liked the end result so much I left it on.
The air filter is CP Auto Products part #25108 with dimensions of 6 3/8" diameter by 2 1/2" tall. The lid is 1/8" aluminum scrap, there is no base - the filter fits perfectly on the air meter housing. That's it.
THERE IS NO NOTICABLE POWER ADVANTAGE and none was intended. It does sound really really really cool. A swoooooshhhh sound every time you open the air metering plate.
No power lost, cool sound, did not cost $300, easy access to the engine. It's all good.

Originally Posted by RarlyL8

I have a B&B intercooler as well. It is a short neck made to be a stock replacement. You can use the 965 style BOV if you mod the stock BOV housing or fab a replacement peice.

Originally Posted by RarlyL8

Do you have the Andial unit? If so, look at the opening that mates to the throttle body. Measure the length of the neck from the bottom of the intercooler to the end of the flange that connects to the throttle body. A long neck cooler will have about a 2" or so (equal to the thickness of the BOV housing) longer tube than a stock unit.
If you don't have the Andial unit ask the owner to measure this distance for you (assuming he does not know what type it is).

Originally Posted by RarlyL8

A picture's worth a thousand words.

Sure get rid of a lot of junk don't you.