Okay I don't know if I am just ignorant, or what. But I was just looking at Rx7.com and I for the first time saw a Pop Off Valve. Now the whole idea of it sounds awesome. It is basically a safety feature you attach to your intake track so that if boost creep occurs it releases any extra pressure than what you desire. I would think that it would basically be just like the reverse of a wastegate, by regulating the amount of O2 entering the engine thereby regulating the amount of exhaust that travels through the exhaust housing. To me this sounds like a brilliant idea, how come no one uses them on our cars?
Pop Off valve? How come no one in DSM land uses them?
16g-95GSX
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Okay I don't know if I am just ignorant, or what. But I was just looking at Rx7.com and I for the first time saw a Pop Off Valve. Now the whole idea of it sounds awesome. It is basically a safety feature you attach to your intake track so that if boost creep occurs it releases any extra pressure than what you desire. I would think that it would basically be just like the reverse of a wastegate, by regulating the amount of O2 entering the engine thereby regulating the amount of exhaust that travels through the exhaust housing. To me this sounds like a brilliant idea, how come no one uses them on our cars?
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I think pop off valves are more popular on cars that have very high underhood temps (rx7s) or run in high rpms for long periods of time (again, prolonged high underhood temps thing). Basically when there is a chance of the wastegate vaccum line melting or getting a hole burnt in it and there by disabiling the wastegate, the pop off valve will not allow the turbo to spike over any certian PSI. Wastegate falures don't appear to be very common on DSMs therefore, you dont see pop off valves. On an interesting side note, CART racing leauge officals use pop off valves in order to set the amount of pressure each car can run. Its the round thing that sticks out of the engine lid right behind the drivers head.
Well I just thought about the MAS making it run slightly rich. I can see where you guys are coming from. For a second there it almost seemed like an alternative to the External dump. I don't see how you can talk about boost leaks though as it doesn't leak a crapload but just enough to keep the boost to the desired level.
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This is pure speculation on my part, but since RX7s can't stand a single ping in the engine, wouldn't these also be considered a safety device so that if the boost were to go too high and create an unsafe mix for a very sensitive motor, it would just pop the valve and save the engine. Or do I have the wrong concept?
This can't be a replacement for an external wastegate. The external wastegate bypasses exhaust gas from hitting the turbine wheel, making the wheel not spin as fast when you've reached your desired boost.
If you use the valve to release compressed air in your intake tract, the compressor/turbine wheels are still spinning with your exhaust gas faster and faster to compensate for the lost boost. You'll be overworking your turbo, and blowing hotter air.
If you use the valve to release compressed air in your intake tract, the compressor/turbine wheels are still spinning with your exhaust gas faster and faster to compensate for the lost boost. You'll be overworking your turbo, and blowing hotter air.
No you wouldn't think about it. You can't get "more and more" exhaust gas unless you get more and more boost. At a set boost level there will be the same amount of exhaust gas for any application on our DSM's. If there is a regulated amount of intake O2 going in then there is a regulated amount of exhaust gas coming out, thereby keeping the turbo spooled to a certain spin amount. Get what I'm saying? The turbo wouldn't keep spooling faster and faster because there is nothing there to make it spool any faster than it is already going. It would keep a constant spin speed.
The only problem I see is that it would make your car rich RIGHT as the boost begins to exceed the desired level, as the MAS would have already compensated for the O2 that is now released. But that amount would be very small as the second the Pop off valve senses extra pressure it would release it, so it would catch that extra O2 before the amount got to be too signifigant that the rich mixture would even affect you that much. I bet if you had a VPC that it wouldn't even affect you as far as a rich mixture just because of the way it reads O2.
The only problem I see is that it would make your car rich RIGHT as the boost begins to exceed the desired level, as the MAS would have already compensated for the O2 that is now released. But that amount would be very small as the second the Pop off valve senses extra pressure it would release it, so it would catch that extra O2 before the amount got to be too signifigant that the rich mixture would even affect you that much. I bet if you had a VPC that it wouldn't even affect you as far as a rich mixture just because of the way it reads O2.
I won't argue with you 16g-95GSX.
But the fact stands the higher your RPM, the more exhaust gasses are expelled from the engine. This is why an external wastegate bypasses exhaust gas from hitting the turbine wheel. I know, I run one a Tial 35mm.
If you still feel running a pop off valve is a substitute for an external wastegate except for the fuel mixture problem, then I think it's pointless to argue any further
But the fact stands the higher your RPM, the more exhaust gasses are expelled from the engine. This is why an external wastegate bypasses exhaust gas from hitting the turbine wheel. I know, I run one a Tial 35mm.
If you still feel running a pop off valve is a substitute for an external wastegate except for the fuel mixture problem, then I think it's pointless to argue any further
Heheh. You are forgetting that boost is controlled by a boost controller. How? My manipulating the wastegate to open at a point where the flowing through the exhaust side is enough to compress x psi of air on the intake side. If you use the pop off valve instead of a wastegate, then there is nothing diverting the exhaust so the exhaust side WILL keep spinning up until it self destructs.16g-95GSX said:
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What GSXdream is talking about is exhaust velocity, and you (16g-95GSX) are talking about exhaust volume. Yes, you get more exhaust gases when you increase boost. However, the speed of the exhaust gases can increase independent of boost. Why does your turbo begin to spool when going up a big hill and you have cruse control on? The higher load on the engine increases the exhaust velocity spooling the turbo. or think of it this way, when you go from 0 to 1psi, what caused that 1psi? It wasn't the orginal 0psi going through the engine causing the turbo to spool. The problem with the popoff valve idea is, although yes it might keep the boost under whatever you have the spring set for, you will spin the turbo faster than it needs to be spun for that particular boost level. Hotter air, and more wear on the turbo itself is what you get in return. Also springs aren't the best at regulating boost, because although the pop off valve may open fully at say 15psi, it most likely leaks at 14psi because its near the opening point. The way that they run them is, your engine can handle x amount of pressure.. you get a spring for the popoff valve that opens under x+3psi to insure that it wont leak at the point you want to run it at. Feel free to correct me if I'm wrong about any of the exhaust velocity stuff by the way. Thanks
Thought: Has any hooked up to boost guages, one to monitor inatake manifold psi, and one right off the turbo. Like the little nipple on the lower intercooler pipe. So you can see what the engine is getting, and how much the turbo is actually putting out.
Did the two gauges thing...
I used to have two boost gauges hooked up. The first one was at the turbo outlet, and the second was at the manifold. I did this mainly to see what kind of pressure loss I was getting with the Starion IC when I first installed it.
I still had a T25 on the car. At mid-throttle, I saw a 6 psi drop between the two. It made me wonder about the effectiveness of the mod I had just performed. But at WOT it only read 1 to 2 psi difference. Keep in mind though, that I had the IC inlet and outlet modified and had the endtanks rewelded to make sure there were no leaks out of the unit itself. The pressure loss seemed to be across the IC. But then I decided to to hook up the two gauges to the IC itself, one on the inlet, and one on the outlet. VERY surprisingly, the gauges ran almost in sync with each other, maybe a .75 to 1 psi difference. That's practically unheard of with a Starion IC. Of course, I think it had to do with the turbo itself, the T2small doesn't push alot of CFM. I'm sure it's raised a bit with the 16G, but I haven't done the two gauge thing lately. Lastly, I tapped the upper IC pipe just after the BOV and then back at the manifold. The main pressure loss was coming from the TB plate itself, but only at mid-throttle. With boost in the system, the throttle plate is the single most restrictive part of the intake (Maximum Boost, page 80). That's where 4 of my 6 psi loss came from.
I don't know exactly what point I was trying to make with that whole rhetoric, but that's where I am with measuring pressure loss across the system.
If I could have just said "yes" to your question, well I'm sorry to have wasted your time.
I used to have two boost gauges hooked up. The first one was at the turbo outlet, and the second was at the manifold. I did this mainly to see what kind of pressure loss I was getting with the Starion IC when I first installed it.
I still had a T25 on the car. At mid-throttle, I saw a 6 psi drop between the two. It made me wonder about the effectiveness of the mod I had just performed. But at WOT it only read 1 to 2 psi difference. Keep in mind though, that I had the IC inlet and outlet modified and had the endtanks rewelded to make sure there were no leaks out of the unit itself. The pressure loss seemed to be across the IC. But then I decided to to hook up the two gauges to the IC itself, one on the inlet, and one on the outlet. VERY surprisingly, the gauges ran almost in sync with each other, maybe a .75 to 1 psi difference. That's practically unheard of with a Starion IC. Of course, I think it had to do with the turbo itself, the T2small doesn't push alot of CFM. I'm sure it's raised a bit with the 16G, but I haven't done the two gauge thing lately. Lastly, I tapped the upper IC pipe just after the BOV and then back at the manifold. The main pressure loss was coming from the TB plate itself, but only at mid-throttle. With boost in the system, the throttle plate is the single most restrictive part of the intake (Maximum Boost, page 80). That's where 4 of my 6 psi loss came from.
I don't know exactly what point I was trying to make with that whole rhetoric, but that's where I am with measuring pressure loss across the system.
If I could have just said "yes" to your question, well I'm sorry to have wasted your time.
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