WERK-I

The over boost switch screws into the fitting provided on the Kokeln IC.

senna21

Are these one-way or two-way bypass valves?

JoeMag

what do you mean by "two way"?

PorscheMD

Tap a hole im your intercooler

Chet 930

Getting rid of that dead weight bypass valve is not hard at all (and yes it is a heavy unit) but can be a little costly if you're not upgrading to a long neck intercooler. I dont know about the rod and keeping it closed thing, I've never tried that. Sounds like it might work.

I chucked two of those things already as I was upgrading to a better intercooler. If you can get your hands on a later diverter valve and the rubber elbow for the valve to go into, then you could have your intercooler neck extended and modded to fit the throttle body. The only other thing would be to fit the overboost switch and boost sender unit somewhere. But I dont see this being worth the cost though. There really isnt any gain per say that you would benefit from. Just remember to get a long neck intercooler if and when you ever upgrade and then there wont be a need for the factory bypass anchor. And by the way, stay away from the plastic Bosch valve, they tend to leak boost.

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.

sand_man

Unfortunately, I've alreaded "upgraded" to a B&B I/C which is not a long neck. I guess I'll save this project for another day. I've got my hands full with the engine rebuild. I thought it was just a matter of jamming the OEM BOV closed in it's housing and then purchasing the 965 style elbow and BOV. The over-boost switch, gauge sender, and other pluming for the turbo. however, add a liitle complexity that I don't really need right now. Granted, none of this is hard, I just don't have time for the additional work

What would be involved in connecting my B&B I/C to the intake once I removed the OEM BOV housing? Could I use like a Samco or silicone hose of some sort to make a "long neck"? Or would the pressure be too much for such a rig?

A930Rocket

Dumb questions....

I have a kokeln so I'm not familiar with the B&B. When you install the B&B, you need the old BOV? It doesn't go all the way to the throttle body? Is this what is meant by long neck? I thought it would install like the Kokeln.

sand_man

B&B might make a "long neck" but mine is not. It fits on and uses the OEM BOV housing.

Chet 930

The right way is to have the neck modified which usually involves cutting and welding. Then you would have to drill and weld a fitting (bung) for the boost override switch and the boost sensor (for the tach guage if you are still using it).

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. It doesn't look difficult but might be time consuming to get all the fittings needed plumbed the way you like and welded up pretty.

sand_man

Thanks...EVERYONE! Good to see you one here Rarely!!!

A930Rocket

Rarly8,

Where is your air cleaner from? Any difference in performance?

Sure cleans up ithe engine compartment!

BTW, where do you usually post? Pelican, 911Turbo, or ? Your screen name is familar.

SGOGT4

Doesn't it look like air circulation to the small cleaner behind the intercooler would be an issue?

PorscheMD

I am also curious as to the performance increase. thought about trying one a few times but never did.