Question about Ng's TID
09-19-01, 10:47 PM
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Question about Ng's TID
Very new to turbo's. I have a 87. Ng mentions a check valve to replace the blow off valve. When you say bov are you refering to the same thing as the air bypass valve as shown on page 4B-4 illustration of the 88 factory manual? The normally closed valve that is opened by vaccum? Very new to turbo's. The definition in your picture is good but not good enough for me to tell just where the bronze check valve is attached. Thank you.
09-20-01, 01:35 AM
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The Brass checkvalve doesn't actually replace the stock BOV (also known as the compressor bypass valve) it just goes on the end of the valve..
The purpose of the BOV is to vent boost pressure away from the turbo compressor when you lift off on the accelerator while boosting.. without the BOV the boost pressure that is in the intake system has nowhere to go when the throttle plates are shut, but back towards the compressor wheel.. in mild cases this excess boost will slow down the compressor wheel, introducing slow spool up.. however in cases, this excess boost can atually spin the compressor wheel backwards (compressor surge).. as you can pobably guess, this is very bad for the life of the turbo.. That's where the BOV comes in to save the day.. when you lift off the accelerator you go from positive boost to vacume.. a host attached to the BOV to a source of vacum opens the BOV valve and allows the boost pressure to vent out and back into the TID, thereby bypassing the compressor wheel all together...
When you do the TID mod you have 2 choices.. you can somehow rig the outlet of the BOV back into the TID just as it is done on the stock duct, or you can "open vent" the BOV.. And that is where the check valve comes into the picture.. at idle you are pulling vacum.. in most cases there is enough vacume to open the valve in the BOV.. this introduces a rather large intake leak, which in turn makes your car idle like a blown motor .. The check valve is put in place to make sure there is no air leak at idle..
hope that helps..
BTW, choice of checkvalves is kinda tricky.. you can get valves that operate using a flapper door, a light ball that blocks an orifice, or a spring loaded valve .. if you get yourself a valve who's door/flapper is too loose, then you will get valve flutter.. this occurs when you are in transition between going from vac to boost, or are near it.. the vacume from the BOV outlet will not be strong enough to keep the door shut.. and so it flutters.. which introduces intermittent leaks.. however if your doorflapper is help closed too tightly then you may not be able to overcome the pressure requires to open the door and some of that pressure will head back towards the turbo... experiment a little bit, you'll find somethign that works for you..
The purpose of the BOV is to vent boost pressure away from the turbo compressor when you lift off on the accelerator while boosting.. without the BOV the boost pressure that is in the intake system has nowhere to go when the throttle plates are shut, but back towards the compressor wheel.. in mild cases this excess boost will slow down the compressor wheel, introducing slow spool up.. however in cases, this excess boost can atually spin the compressor wheel backwards (compressor surge).. as you can pobably guess, this is very bad for the life of the turbo.. That's where the BOV comes in to save the day.. when you lift off the accelerator you go from positive boost to vacume.. a host attached to the BOV to a source of vacum opens the BOV valve and allows the boost pressure to vent out and back into the TID, thereby bypassing the compressor wheel all together...
When you do the TID mod you have 2 choices.. you can somehow rig the outlet of the BOV back into the TID just as it is done on the stock duct, or you can "open vent" the BOV.. And that is where the check valve comes into the picture.. at idle you are pulling vacum.. in most cases there is enough vacume to open the valve in the BOV.. this introduces a rather large intake leak, which in turn makes your car idle like a blown motor .. The check valve is put in place to make sure there is no air leak at idle..
hope that helps..
BTW, choice of checkvalves is kinda tricky.. you can get valves that operate using a flapper door, a light ball that blocks an orifice, or a spring loaded valve .. if you get yourself a valve who's door/flapper is too loose, then you will get valve flutter.. this occurs when you are in transition between going from vac to boost, or are near it.. the vacume from the BOV outlet will not be strong enough to keep the door shut.. and so it flutters.. which introduces intermittent leaks.. however if your doorflapper is help closed too tightly then you may not be able to overcome the pressure requires to open the door and some of that pressure will head back towards the turbo... experiment a little bit, you'll find somethign that works for you..
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