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  • GUIDE : Fitting an atmopsheric dump valve to a 1JZ

    The stock recirculating dump valve (or blow off valve 'BOV') isn't exactly quiet on the 1J but for those (like me) who love the ptsschhh, this is how you do it. Note: The 1J uses MAP (manifold absolute pressure) rather than the AFM like the 7M which means no idling or stalling issues

    Step 1 - Locate the stock unit which is above the rear turbo as shown on the picture

    Step 2 - Check out the pipework, a single vac/boost line goes to 2 points on the valve, one opens the valve on positive pressure and the other on negative pressure. The big tube shown on the right hand side of the valve is the high pressure side and the low pressure side is where the valve body mounts to the intake piping.

    So normally, air is sucked in through the air filter and runs past the (closed) valve. Under boost conditions, the high pressure hose is pressurised but goes straight into the valve body so does nothing. When you come off the throttle on boost, the valve opens and the high pressure is effectively linked to the low pressure i.e. the compressed air output from the turbos routes straight back to the inlet piping

    Step 3 - Slacken and remove the single bolt (10mm IIRC) that holds the flange of the BOV to the inlet pipework

    Step 4 - Use a Philips screwdriver to loosen the jubilee clip that runs the high pressure connection to the valve

    Step 5 - Grab the bend in the pipework and give it a wriggle up and down firmly then pull back off, you may find using a large flatblade screwdriver to push it off helps but don't carve your hand up!

    Step 6 - There is another 10mm bolt holding the piping which I removed for wriggle room

    Step 7 - Now a vac line, squeeze the clip and slide it up the pipe then pull the pipe off the valve

    Step 8 - There's always one 'invisible' bolt, this is underneath the valve and is a 10mm, ring spanner is easiest for this and once cracked off it's easy to get out and thankfully not too long

    Step 9 - The valve should now pull away from the engine and you'll see an O ring (orange in this case) which seals the valve against the inlet pipes

    Step 10 - Remove the final vac line as you did in step 7

    Step 11 - Now you have removed the BOV completely, take out the vac lines and filter by removing the bottom clip and sliding off

    Step 12 - Replace the 10mm removed in step 6

    Step 13 - Grab your shiney new valve, in my case a DV26 which I rate highly (on the 7M too with its dual piston design), you need the single vac source to the top of the valve as pointed in the photo

    Step 14 - I recommend you use silicone for the pipework because it is soo easy to work with and good with high temperatures. Re-use one of the stock clips to fit some silicone hose in place (picture 1) then use a mini jubilee clip on the top of the valve because it is a shorter length than the first pipe so you want it held in place.

    Note you should keep pipe runs as short as possible but give yourslef enough room to work with

    Step 15 - Insert the base of the BOV into the stock high pressure piping and tighten the jubilee clip

    Step 16 - You will notice a gaping hole where the stock vlave used to be, from my investigations people tend to just leave the stock dump valve in place but remove the vacuum lines. While you can do this and there is not much chance of it leaking and causing a problem, it is cluttered and a bit naff! You could leave the hole and have no adverse effect other than unfiltered air entering the engine but the best bet is to blank it off so either:

    1. Buy a blank, they can be found and I believe the 'turbo smart' BOVs used to ship with a blank
    2. Angle grind off the base of the old valve, fill the hole and refit
    3. Cut out a very simple shape and bolt in place. You can use a thinner metal and pad the bolt with washers or use a shorter bolt


    Step 17 - If you want to alter the position of the valve e.g. have it vertical as opposed to horizontal do the following steps. First, slacken the jubilee clip on the main inlet pipe and pull it clear

    Step 18 - Slacken off the outer jubilee clips on the inlet pipe that holds the T piece in place

    Step 19 - Rotate the T piece upwards, you'll need to apply a bit of torque to free it from the rubber pipes at first

    Step 20 - Now you can get a screwdriver in to the jubilee clip holding the rubber high pressure pipe in place

    Step 21 - Rotate the pipe to get desired angle (second pic is just for info of what's behind the pipe), I put it vertical but make sure you have clearance when you close the bonnet!

    Step 22 - I suggest you reposition the jubilee clip so you can get a ring spanner to it rather than a screwdriver which is way better

    Step 23 - Rotate the T piece back down

    Step 24 - Refit the main pipe then tighten the outer jubilee clips from step 18

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