DIY Open-Air Vented Blow-Off Valve I've got a VERY loud pressure surge release valve function. It makes some hellacious blow-off noise and is open-air vented. The system works well and, due to the nature of the additional valve, it does not create a vacuum leak you'd have by open-air venting the BOV by itself. Here's a brief explanation of what I've done: I re-plumbed the blow-off valve, basically. I disconnected the return hose from the blow-off valve to the turbo inlet duct on the output side of the MAF (s-curve shaped 3" black hose coming off the mass airflow meter/air filter). I plugged the turbo inlet duct w/ a 1/2" plug to seal the now new leak. I turned the blow-off valve hose 180 degrees back (facing the firewall instead of the turbo inlet duct now) and plumbed a 3/4" swing-valve at the end of it, after everything was said and done. (I also replaced two factory spring clamps w/ screw clamps) -- This swing-valve acts as a one-way pop-off valve and works under pressure. Under vacuum, the valve seals shut, eliminating the possibility of a vacuum leak. Here's the parts I used: 3/4" Swing-valve tee (or other one-way plumbing valve w/ or w/o tension control) 3/4" to 1/2" galvanized bushing (used to reduce thread-size) 1/2" Close (short) threadded nipple Four screw clamps, to 1/4" smallest diameter 1/2" threadded Plug (steel/galvanized or what have you) 1/2" width hose (about 6 to 8 inches long/Get it anywhere! Steal some!) -- I used a spare ACV hose off of an '88 NA stock airbox, by the way. -- It's a big-dipper shaped hose and worked perfectly. A few zip ties to keep the setup sturdy once it's all built All of these parts can be found at any good hardware store, like Home Depot, for about $10 total. The valve I bought was $5.99 and was the kicker of the bunch. The steps to take with the car preferrably cold (near alot of hot parts): 1. On the back of the turbo inlet duct, the blow-off valve is routed in. From there, remove the existing squeeze clamp and detach the BOV hose. Removed the BOV entirely and replace the existing squeeze clamp on the intake manifold side with a screw clamp (much cleaner). Turn the BOV return hose (from the side of the turbo output) 180 degrees backwards. If I remember correctly, I had to flip the BOV upside down then turn the hose all the way around so it'd be level. 2. Use the 1/2" plug and plug the back end of the turbo inlet duct that now has a gaping hole in it. First things first. Use one of the new screw clamps on the plug and make sure it's good and tight. Be sure not to put the plug too far into the inlet duct. Screw clamp it to the threadded portion of the plug. 3. Threadd the 3/4" to 1/2" bushing on the inlet-side of the new swing-valve and then thread the 1/2" nipple into the end of the bushing. This should leave you w/ about a full inch of space to screw clamp the end of the hose on. Make sure you get the valve on right (where the valve is swinging outward and not inward). This is VERY important and could be detrimental to the life of your turbo. (3/4" swing valve attached to and threadded to 1/2" bushing, threadded to 1/2" close nipple, which is attached and clamped to one end of the 1/2" hose) 4. Attach the other end of the hose to the newly-turned blow-off valve. The stock BOV has about 3/4" to a full inch of room the other end of the hose could be clamped on. Use a new screw clamp for this one and make sure it's tight. 5. Depending on hose length and valve size, route this new setup back and around the upper intake manifold area (above and behind the ACV/EGR area) and zip tie it to some of the metal hoses in the area. I put the valve here for maximum audibility and clarity. Make sure the valve is level/horizontal as possible. I had to experiment with this a few times on mine and was able to create a small vacuum leak when I had the output side of the valve facing at a downward angle. You can experiment angling the valve up a bit, but I wouldn't go too high. The purpose of this valve is to compliment the existing setup and not hinder it. As a result, you should have a T2 that sounds much like a steam engine when coming off mid to heavy throttle. The new setup is open-air venting the air right into the atmosphere near the cockpit, instead of being re-routed into the turbo inlet duct before the turbo, while still retaining the same functionality and efficiency of the stock blow-off valve. If this is setup properly, you should not encounter any 'new' vacuum leaks whatsoever. The only issue I ran into was a slight change in low-end throttle response, but it's barely noticeable, even if at all. Under WOT/high boost, depending on the tension of the valve itself, it may be dead smooth or may flutter some. Mine, with the valve I used, flutters after about 9psi/boost at WOT. It still sounds good, though. Brian D. Cain 1988 Red FC3S-GTR http://homepages.waymark.net/~bcain
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