Blow-off valve understanding
03-13-23, 02:06 PM
#1
Blow-off valve understanding
I am not looking to replace my BOV, but messing around with the sequential vacuum line simplification made me want to understand how the turbo control system works.
So... almost all the threads i read on this recommended the Tial 50mm or similar BoV. My confusion comes in with how they installed them. It looks like most people are letting them into the intake pipe between the IC and the TB, closer to the TB. To me, it seems the BOV would be better installed near the turbos so it sees the pressure nearest to the turbos rather than near the TB. i.e., you care what it is at by the turbos, and if the IC has significant pressure drop, by the time the air gets to a BOV by the TB, the turbos will be seeing significantly more pressure.
In effect, to me it seems the BOV would be best installed where the stock one is - right off the Y-pipe.
The next problem to be is that the fitting on the bottom of the Tial is like 2" across, whereas the rubber hose coming off the Y-pipe is 3/4" IIRC. So if a person did install it in the stock location, then you would see a big pressure drop as the air went from a 3/4" opening to a 2" one. It would seem that would make the Tial (or any other similarly-sized one) BOV ineffective if installed in the stock location?
And: even if it functions perfectly fine in the pipe going into the TB, you are cutting a 2" hole in the 2-3/4" pipe going into the TB which would seem likely to cause a lot of turbulence in the flow. (And some installations show this as a short length of the 2-3/4" pipe installed via two silicone couplers in between 2 other short lengths fo aluminum pipe, one at the IC and one at the TB - at least have the mounting flange welded into a single length of the aluminum pipe?)
Also, none of the install procedures I have seen mention removing the stock BoV, so this is at best belt and suspenders, but at worst may be both BoVs fighting each other or the aftermarket one having too weak of a spring and venting first so not maintaining the same pressure as the stock one would.
As I said, I am not looking to replace mine since it is working perfectly fine, just looking to learn more about how this all works, so educate me :-).
So... almost all the threads i read on this recommended the Tial 50mm or similar BoV. My confusion comes in with how they installed them. It looks like most people are letting them into the intake pipe between the IC and the TB, closer to the TB. To me, it seems the BOV would be better installed near the turbos so it sees the pressure nearest to the turbos rather than near the TB. i.e., you care what it is at by the turbos, and if the IC has significant pressure drop, by the time the air gets to a BOV by the TB, the turbos will be seeing significantly more pressure.
In effect, to me it seems the BOV would be best installed where the stock one is - right off the Y-pipe.
The next problem to be is that the fitting on the bottom of the Tial is like 2" across, whereas the rubber hose coming off the Y-pipe is 3/4" IIRC. So if a person did install it in the stock location, then you would see a big pressure drop as the air went from a 3/4" opening to a 2" one. It would seem that would make the Tial (or any other similarly-sized one) BOV ineffective if installed in the stock location?
And: even if it functions perfectly fine in the pipe going into the TB, you are cutting a 2" hole in the 2-3/4" pipe going into the TB which would seem likely to cause a lot of turbulence in the flow. (And some installations show this as a short length of the 2-3/4" pipe installed via two silicone couplers in between 2 other short lengths fo aluminum pipe, one at the IC and one at the TB - at least have the mounting flange welded into a single length of the aluminum pipe?)
Also, none of the install procedures I have seen mention removing the stock BoV, so this is at best belt and suspenders, but at worst may be both BoVs fighting each other or the aftermarket one having too weak of a spring and venting first so not maintaining the same pressure as the stock one would.
As I said, I am not looking to replace mine since it is working perfectly fine, just looking to learn more about how this all works, so educate me :-).
03-13-23, 03:08 PM
#2
RX-7 Bad Ass
iTrader: (55)
I actually got to meet Corky Bell who is one of the masters of turbos many years ago and ask him some questions.
Really, the best place for the BOV is where it can physically fit and work. Mazda put it right off the turbos since they were recirculating them to the air box for noise reduction.
The BOV dumps all the pressure in the system so quickly that I really don't think it makes much of a difference where it is.
That 2" hole for the Tial could cause some turbulence but I don't know if it would be enough that it would cause a loss in power or any noticeable effect.
BTW for the stock twins the stock BOV is perfect. Flows enough, holds pressure, blows off smoothly, reacts quickly. Even makes a little bit of sound if you vent it.
Dale
Really, the best place for the BOV is where it can physically fit and work. Mazda put it right off the turbos since they were recirculating them to the air box for noise reduction.
The BOV dumps all the pressure in the system so quickly that I really don't think it makes much of a difference where it is.
That 2" hole for the Tial could cause some turbulence but I don't know if it would be enough that it would cause a loss in power or any noticeable effect.
BTW for the stock twins the stock BOV is perfect. Flows enough, holds pressure, blows off smoothly, reacts quickly. Even makes a little bit of sound if you vent it.
Dale
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MilesBFree (03-13-23)
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