Making the std BOV adjustable

After I fitted my twin air intake system I found that my std BOV was 'leaking' almost all the time, and must have been doing it for ages without me noticing (as it was recirculating & silent).

This must have been hurting part throttle performance as it was wasting boost nearly all the time except for near WOT.

My solution was to make it adjustable, which was quite easy and only needed a drill, junior hacksaw, file and small blowtorch.

Procedure is:

1) Remove BOV

2) about halfway round the top (narrowest) section of the BOV (yellow wiggly line in the 2nd photo) fasten a jubilee clamp and use this to carefully cut the top in half with the junior hacksaw. Marking a line across the cut line will be useful when it comes to realigning the top & bottom again.

3) take the top off & mark the centre of the top with a centre punch. Use a small round thing ( round piece of wood that fits inside the top) to place the top on so the surface of the top is resting on it.... so it doesn't cave in the top when you centre punch it!!

4) drill to 6mm in 2,4,5 then 6mm steps

5) take a trip to B&Q and buy a M6x20 bolt, a pack of M6 thingys that have a threaded inner portion & a flat base with spikes sticking up (used to hammer into wood to give a threaded insert) & a pack of large washers that just fit inside the top of the BOV with a 3mm hole.

6) stick the M6x20mm bolt in the drill and spin it round while filing the end 4mm or so down to 3mm diameter

7) take the M6 spiked threaded thingy & flatten the spikes down with a pair of pliers.

8) screw the 6mm bolt into the thingy so the 3mm end is sticking out of the flat end of the thingy

9) sand down the top of the BOV & the bottom of the flat end of the thingy

10) the thingy with the bolt in it can now be fitted to the top of the BOV where the 6mm hole was drilled

11) fit the washer over the 3mm end of the bolt & hammer the 3mm end so it squashes up & prevents the washer from coming off. Make sure the washer can move a little & turn though.

12) solder the thingy onto the top of the BOV

13) fit the spring back into the body of the BOV & place the top back on with its threaded adjuster adjusted all the way out

14) clamp the top onto the body using a G clamp from the top of the bolt to the base of the body

15) sand the paint off the area around the hacksaw line

16) block all ports and place the BOV body in water so the water comes up the side of the body to a height above the diaphragm. DO NOT GET WATER INTO THE DIAPHRAGM!!

17) carefully heat the BOV around the area of the split line & solder back together.

Now you have a tuneable BOV. The more the bolt is screwed in the more spring pressure is excerted on the diaphragm, so the higher the vaccum required to make the valve open. From fully wound out (lowest spring pressure) to fully in (highest spring pressure) the difference is from it blowing all the time to it blowing only when the throttle is shut quickly.

Great improvement!

Nice little write up. Not the sort of thing I'd imagine many people would do off their own backs - well done.

Hmm, innovative. How did you solder the thingy?

The thingy solders to the top of the BOV. You can see the bolt sticking out of it.

Just used the blow torch and some solder. Wicked in nicely & was quite smooth after. After painting it almost looks original.

If you wanted it to look more orginal then an allen screw that recesses right into the thingy would be best, like in this pic:

Better than spending £250 notes I suppose.

Better than spending £250 notes I suppose.

Yep, if you haven't got £250 then £2.50 is a bit more reasonable

If anyone wants one doing let me know.