Toyota Celica Supra Forum banner

1 - 4 of 4 Posts

·
Premium Member
Joined
·
5,540 Posts
Discussion Starter #1
Do you have your BOV plumbed in like this?



Or like this

Back about 1999 or 2000 I first saw the SOGI Tech Tips regarding replacing the stock Toyota BOV on a 7mgte with a Bosch BOV from a Saab. They installed it as in the second picture above. I always thought that looked bassackwards so I redid it the other way as in the first picture. Most aftermarket BOVs have the vacuum line directly opposite the pressure side with the output on the side as in the top pic as I now have my Bosch.
The sound is different from the two different installs. The bottom install SOGI-style sounds like a hoooot when you let off the throttle whereas the top install sounds like a PSSSST when you let off. It seems to perform about the same either way and other than the different sound, the only other measurable difference is I get a little better gas mileage with the top install.
There are discussions on other forums about this install on Turbo Mopar, Saab, Porsche, and Audi owners groups (probably others, too) and everyone seems to have different opinions. Most all the discussions state somewhere along the line that the Bosch BOV was designed to be used either way.
Regardless, I like the Bosch because it's cheap and plentiful, and it works.
 

·
Registered
Joined
·
593 Posts
I have mine like the second photo just because I also referenced the SOGI tech tip.
 

·
Registered
Joined
·
102 Posts
Do the 2nd configuration due to direction valve-piston moves. 1st photo config causes boost to creep valve open. In 2nd photo, boost tends to keep the valve closed for more accurate control. Use the 993 part# with brass-reinforced diaphragm for better durability.
 

·
Premium Member
Joined
·
5,540 Posts
Discussion Starter #4
Do the 2nd configuration due to direction valve-piston moves. 1st photo config causes boost to creep valve open. In 2nd photo, boost tends to keep the valve closed for more accurate control. Use the 993 part# with brass-reinforced diaphragm for better durability.
Boost creep?!? BOVs have nothing to do with boost creep, that's a problem with the waste gate.
The discharge of the BOV should be out the side of it like in picture 1 above. When the throttle plate is open, the air pressure on both sides of the piston in the blow-off valve is equal and the spring keeps the piston down. The vacuum line on top of the piston and the line on the other end of the piston will have the same pressure until the throttle plate closes. It's only when the throttle closes that you'll have a difference between top and bottom of the BOV piston because the bottom is upstream from the throttle plate and the vacuum is downstream from the throttle - the throttle plate is the only thing that separates them. So when the throttle closes a vacuum forms in the manifold (downstream from the throttle plate) and this, in combination with the pressurized air from the turbocharger (upstream from the now-closed throttle plate), moves the piston in the valve up which releases the pressure back into the inlet of the turbo (or the atmosphere).
Look at all the aftermarket piston-type BOVs. Greddy, Turbo-XS, and dozens of others all have the BOV discharge out the side like the first photo above.
 
1 - 4 of 4 Posts
Top