Mounting a secondary Bosch BPV to an aftercooled SC setup
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Mounting a secondary Bosch BPV to an aftercooled SC setup
I did this a while back on my Comptech Novi 1220 setup based off feedback from a few of the S2Ki SC'd legends (S2000Junky in particular) and have since been asked about it several times. I posted these pictures and a short write-up on a different forum, but figured it would be good archive information for anyone looking to do the same in the future.
My history with aftermarket BOV/BPV's on my Comptech setup ranges from the stock Bosch BPV, to a Turbosmart Dual Port, to a Tial Q, then a Tial QR, and now the Tial QR with the secondary Bosch BPV. I had compressor surge from the stock Bosch BPV and the Turbosmart Dual Port (both ports vented to atmosphere) when making 9k RPM shifts at 7 PSI. The Tial Q (with a custom 1.5" ID adapter flange to my aftercooler) solved this as it evacuated much more air volume. However once I stepped up to 16 PSI the venting noise at cruising RPM's was unbearable. I swapped to the Tial QR which is far more tame under cruising conditions, but the compressor surge at high RPM shifts was back. This is because the Bosch BPV, Turbosmart Dual Port, and Tial QR all have a 1" ID restriction at their inlets, and only so much air volume can be vented through them... this restriction causes the compressor surge.
Adding the Bosch BPV to the air pump port on the aftercooler to act as a secondary BOV/BPV allowed a second escape point for air volume to reduce the duty of the main BOV. This allows me to use a quieter main BOV like the Tial QR and avoid compressor surge at high RPM shifts. Currently I have the secondary Bosch BPV venting to atmosphere, but I might plumb it back into the intake to further reduce blowoff noise. The Bosch BPV is louder under venting than the Tial QR, but still 100x quieter than the Tial Q under cruising conditions.
Anyway, onto the info:
My history with aftermarket BOV/BPV's on my Comptech setup ranges from the stock Bosch BPV, to a Turbosmart Dual Port, to a Tial Q, then a Tial QR, and now the Tial QR with the secondary Bosch BPV. I had compressor surge from the stock Bosch BPV and the Turbosmart Dual Port (both ports vented to atmosphere) when making 9k RPM shifts at 7 PSI. The Tial Q (with a custom 1.5" ID adapter flange to my aftercooler) solved this as it evacuated much more air volume. However once I stepped up to 16 PSI the venting noise at cruising RPM's was unbearable. I swapped to the Tial QR which is far more tame under cruising conditions, but the compressor surge at high RPM shifts was back. This is because the Bosch BPV, Turbosmart Dual Port, and Tial QR all have a 1" ID restriction at their inlets, and only so much air volume can be vented through them... this restriction causes the compressor surge.
Adding the Bosch BPV to the air pump port on the aftercooler to act as a secondary BOV/BPV allowed a second escape point for air volume to reduce the duty of the main BOV. This allows me to use a quieter main BOV like the Tial QR and avoid compressor surge at high RPM shifts. Currently I have the secondary Bosch BPV venting to atmosphere, but I might plumb it back into the intake to further reduce blowoff noise. The Bosch BPV is louder under venting than the Tial QR, but still 100x quieter than the Tial Q under cruising conditions.
Anyway, onto the info:
Purchased what I will term a "secondary bypass valve" for my supercharger setup. Looking to install today and start screwing around with it. My current blowoff valve isn't venting enough at high RPM shifts, so I'm basically adding a second one on an extra port on my aftercooler to see if it will help the issue.
So here's the extra stub on my aftercooler that I'm looking to put my secondary bypass valve on. It used to have a 3/4" hose coming from my secondary air injection system (air pump) but that has since been removed from the car completely (emissionslolwut). The Bosch bypass valve has stubs for 1" hose, so in order to adapt this port to accept a 1" hose, I just cut off a 1/4" long piece of 3/4" hose and am using it as an ID adapter.
The problem is that the bypass valve interferes with the radiator hose that is right near this side of the aftercooler, as shown below:
So to fix this, I measured how deep the port on the bypass valve goes to see how far I can actually stick this stub on the aftercooler down into the bypass valve before it hits the diaphragm, and then I'll cut off some of the length of the port on the bypass valve. I figured out I could actually cut off 3/4" of this stub and still clear everything internally.
At the same time, I'll do away with this little tab that was used for rotational clocking of the valve on the Comptech kit.
After a quick Dremeling, the result is this... a much shorter inlet port stub on the bypass valve. Hopefully this gains me enough clearance to avoid the radiator hose, or at least not be interfering with it so much.
And here's the outcome; it fits well and a 3/4" long piece of 1" hose covers everything nicely. I'll only need one hose clamp to keep everything sealed up. The radiator hose barely clears, but I ended up removing the hose support bracket in this picture as I don't feel its necessary and it gives much more clearance.
I tried to tee off of the vacuum line that runs to my other blowoff valve and run a line to this bypass valve, but I think it reduced the vacuum pull too much. Neither valve was operating properly once they were connected. I later realized that I already had that lined tee'd for my boost gauge, so I was really stretching that vacuum port thin. I've opted to redo my vacuum lines a bit. I've got an open 5/16" port on the manifold from my old air pump circuit. I'm going to run a large line off that port and tee it down to run to the two blowoff/bypass valves. The smaller port that previously fed the BOV and boost gauge will only be responsible for feeding the boost gauge now. Hopefully this will allow full vacuum to be seen at both valves equally.
Edit - My proposed vacuum line routing worked out perfectly. My main BOV and secondary BPV both run off the same 5/16" vacuum port on the manifold which is beefy enough to support both just fine. Both valves close under throttle and open when off throttle simultaneously and completely. It is obvious that the main BOV is venting most of the air (since it has the larger inlet port diameter) by the feel of the air quantity exiting both valves. Even though the Bosch BPV is venting less air, it is still the noisier of the two just due to its design and plastic housing versus the Tial QR's smoother internals and metal housing. I may eventually plumb the Bosch back to the intake to cut the noise down further, but the cruising noise is barely noticeable still (as it was with just the Tial QR) and the high RPM shift blowoff isn't too bad either. More noticeable than before, but still somewhat tame. Overall I'm happy with this setup, and no more compressor surge even at 18 PSI shifts!
So here's the extra stub on my aftercooler that I'm looking to put my secondary bypass valve on. It used to have a 3/4" hose coming from my secondary air injection system (air pump) but that has since been removed from the car completely (emissionslolwut). The Bosch bypass valve has stubs for 1" hose, so in order to adapt this port to accept a 1" hose, I just cut off a 1/4" long piece of 3/4" hose and am using it as an ID adapter.
The problem is that the bypass valve interferes with the radiator hose that is right near this side of the aftercooler, as shown below:
So to fix this, I measured how deep the port on the bypass valve goes to see how far I can actually stick this stub on the aftercooler down into the bypass valve before it hits the diaphragm, and then I'll cut off some of the length of the port on the bypass valve. I figured out I could actually cut off 3/4" of this stub and still clear everything internally.
At the same time, I'll do away with this little tab that was used for rotational clocking of the valve on the Comptech kit.
After a quick Dremeling, the result is this... a much shorter inlet port stub on the bypass valve. Hopefully this gains me enough clearance to avoid the radiator hose, or at least not be interfering with it so much.
And here's the outcome; it fits well and a 3/4" long piece of 1" hose covers everything nicely. I'll only need one hose clamp to keep everything sealed up. The radiator hose barely clears, but I ended up removing the hose support bracket in this picture as I don't feel its necessary and it gives much more clearance.
I tried to tee off of the vacuum line that runs to my other blowoff valve and run a line to this bypass valve, but I think it reduced the vacuum pull too much. Neither valve was operating properly once they were connected. I later realized that I already had that lined tee'd for my boost gauge, so I was really stretching that vacuum port thin. I've opted to redo my vacuum lines a bit. I've got an open 5/16" port on the manifold from my old air pump circuit. I'm going to run a large line off that port and tee it down to run to the two blowoff/bypass valves. The smaller port that previously fed the BOV and boost gauge will only be responsible for feeding the boost gauge now. Hopefully this will allow full vacuum to be seen at both valves equally.
Edit - My proposed vacuum line routing worked out perfectly. My main BOV and secondary BPV both run off the same 5/16" vacuum port on the manifold which is beefy enough to support both just fine. Both valves close under throttle and open when off throttle simultaneously and completely. It is obvious that the main BOV is venting most of the air (since it has the larger inlet port diameter) by the feel of the air quantity exiting both valves. Even though the Bosch BPV is venting less air, it is still the noisier of the two just due to its design and plastic housing versus the Tial QR's smoother internals and metal housing. I may eventually plumb the Bosch back to the intake to cut the noise down further, but the cruising noise is barely noticeable still (as it was with just the Tial QR) and the high RPM shift blowoff isn't too bad either. More noticeable than before, but still somewhat tame. Overall I'm happy with this setup, and no more compressor surge even at 18 PSI shifts!
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The rubber ring in the first picture is still on the port, and it is underneath the larger diameter 1" hose in the last picture. The rubber ring basically acts as a diameter adapter.
