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Stock BOV - where did this restrictor plate come from?

mjfawke

By mjfawke,
in Engines & Forced Induction

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mjfawke

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I was working on the car yesterday, and decided to lift the BOV just to have a look. My engine is from an R32, but the PO replaced the BOV, so I wanted to see if it had the R33 model with the passage to the diaphram. Which it does...

Under the BOV, I discover (in order from top pipe), an embossed metal gasket, a paper gasket, a metal plate with a 15mm hole through it and another embossed metal gasket. I removed everything except one of the embossed metal gaskets.

So now the blowoff valve works the way everyone describes - a 'sneeze' instead of a vented BOV kind of sound, the on/off boost transition is nice and smooth, there is no compressor surge when lightly lifting off, and when taken close to redline the revs drop back quickly instead of slowly.

So - why the hell was there a plate with a 15mm hole in it????

  • 2 weeks later...
mjfawke Collaborator

mjfawke

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O.K. - it does have an impact on performance. Without the plate, the valve seems to leak, 'cause the car has been waaaay down on power (I thought it was dodgy fuel). I'm not sure what it did to the boost - the car is a bit of a sleeper, so no boost gauge, but it runs around .9bar normally.

Today I put the plate back in and the power came back - wheelspin in 1'st, spinning over bumps in 2'nd/3'rd just like it used to. So - I've just finished the 'Talon BOV' mod. I've blocked the pressure port into the bottom of the diaphram from the IC piping with a 6mm grub screw, and drilled a 3mm vent hole to atmosphere instead. Can't take it on a test drive until later, but when I do, I'll post back with comments.

mjfawke Collaborator

mjfawke

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Yep - saw that thread, but the claim was that the stock valve didn't leak until around 18psi, but it appears it leaks at 13psi without the restrictor plate. And still no answer as to why there is a plate with a small hole in it anyway...

I finally got a test drive in with modded BOV and no restrictor plate. Pretty much the same sounds & throttle transition, but the performance is back again...

So - don't remove the restrictor unless you mod the BOV at the same time!

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