100% Recirc against 50 atmo 50 recirc

[mazdaspeed619sd]

What are the benifits and cons of having a dual port bov? And what are the benifits and cons of running 100% recirc? Isn't it the reason to have a bov is to release pressure from the throttle plate? In this case with mods such as intake, intercooler, and exhuast to help the motor breath better, doesnt it increase pressure overall against stock throttle body and plate is not meant to have? Isn't it the reason why we have something like the dual port bov to release some of the pressure? I am confused on this. Someone help?

[phantom3]

Originally Posted by mazdaspeed619sd What are the benifits and cons of having a dual port bov? And what are the benifits and cons of running 100% recirc? Isn't it the reason to have a bov is to release pressure from the throttle plate? In this case with mods such as intake, intercooler, and exhuast to help the motor breath better, doesnt it increase pressure overall against stock throttle body and plate is not meant to have? Isn't it the reason why we have something like the dual port bov to release some of the pressure? I am confused on this. Someone help?

The purpose of a blow off valve or compressor bypass valve is to prevent large pressure spikes in the intake pipes when the throttle plate is closed while boosting, preventing the turbo from surging. The BOV sits between the turbo and the throttle body and has a vacuum line that is attached to both the other side of the BOV valve and the intake manifold. When you are boosting the pressure on both sides of the valve is essentially equal because the pressure in the intake manifold is the same as in the intake pipes. When you close the throttle plate while boosting all that air slams into the plate and pressure spikes. At the same time the intake manifold pressure drops to a vacuum, and thus so does the pressure on the other side of the valve. The result is the valve opens wide to allow the pressure to vent out. Also included in a good BOV is some form of spring to aid in keeping the valve closed during modulating part throttle situations so that the BOV doesn't open and cause drivability problems.

Why upgrade:

The stock bypass valve is weak. The result is that it leaks at boost levels above about 17 (guessing here) psi. The fix then, obviously, is to install a BOV that doesn't leak until higher boost levels. If you don't, anything you do to increase boost will be fruitless. You even run the risk of damaging your turbo by stressing it trying to get higher boost.

Here is what happens, if you do any mods that increase boost (intake, exhaust, modding stock boost controller, installing after market boost controller, installing larger turbo etc) before upgrading the BOV. Air is sucked into turbo, compressed, sent to the intercooler, then past the BOV, to the throttle body, into the intake manifold, and into the pistons. The BOV vents into the intake system BEFORE the turbo which is effectively like venting it outside in this case because it is allowed to expand back to atmospheric pressure.

Now as the turbo spins faster to increase the pressure in the intake pipes beyond the leak point of the stock BOV, pressurized air in the intake pipes leaks past the BOV. The pressure in the intake pipes thus can't reach the point where the boost controller will keep the turbo from spinning faster and limit boost. So the turbo spins even faster to flow more air to try and get pressure up to the point where the boost controller will start regulating the turbo's flow, but air is still leaking out of the BOV and in fact as pressure increases the BOV opens more and leaks even more. The end result to this cycle is that either:

a) The turbo will eventually spin fast enough to overcome the leak and get the boost pressure up. At this point the turbo is running way outside its efficiency curve and is doing little else than pushing very hot air and working hard to do it. Hot air knocks, detonates, and contains less air mass than the same pressure/volume of air at a cooler temp (remember your physics PV=nRT) and you'll be pissed that your car is slower than a Honda Insight

b) The turbo never really can flow enough air to overcome the leaking BOV, all the steps in a) occur, and your turbo dies an early death.

There are many options out there from HKS, GReddy, Blitz, TurboXS. Which ever way you go you really should do it such that the purged air is routed back into the intake at the turbo. This isn't the time to explain the entire working of the engine management system and besides you should do some of that research on your own. But the long and short of it is this: the ECU measures how much air enters just after the filter and bases how much fuel it injects based on that count. When you shift, if that counted air is vented to the outside rather than back into the turbo inlet, then the ECU will still inject fuel based on the counted air but with the air now gone the car will run VERY rich between shifts resulting in stumbling. Some people seem to be able to get away with it but generally it just isn't worth bothering with. The only performance benefit that i can think of would be the turbo RPM staying higher between shifts. A 50/50 BOV splits the air to compensate for this a little.

Is it worth it? That is up to you. Do you want a big PSSSH! *shift* BANG POP sound? or a more quite sound? also a BOV that is set to VTA (vent to atmosphere) will put added stress on emission components such as the catalytic converter due to the fact that a quantity of unburnt gas will exit the engine. I also have my suspensions that a BOV set to VTA will increase fuel dilution in your oil.

IMO, if your not creating a full on track car with Zero emission equipment I don't feel its worth it to go VTA or Even 50/50.

- David (Dictated but not read/copied from someone else)

[Docnox]

I was actually skimming through Import Tuner in Walmart the other day, and they did a test to see whether a turbo car makes more hp with recirc or VTA. Basically, unless you're running a monster turbo, there are no benefits of VTA, besides the sound.

I think full recirc would be best, but others should chime in about their dual-ports, because they are usually reviewed positively.

[Deadman]

i run 100% vta, and no probs at all... I run the new hks ssqv, the hks being the only one i would recommend to run in vta.

[FCmaniac]

Originally Posted by mazdaspeed619sd What are the benifits and cons of having a dual port bov? And what are the benifits and cons of running 100% recirc? Isn't it the reason to have a bov is to release pressure from the throttle plate? In this case with mods such as intake, intercooler, and exhuast to help the motor breath better, doesnt it increase pressure overall against stock throttle body and plate is not meant to have? Isn't it the reason why we have something like the dual port bov to release some of the pressure? I am confused on this. Someone help?

The same amount of pressure is released... it's just WHERE the pressure is released to is different. The dual port Turbosmart for example simply releases 50% to atmosphere and 50% back to the intake tract. The car is designed for 100% recirculation of this air. The ECU injects fuel assuming 100% of this air is being recirculated. If you release any to the atmosphere, you have less air and more fuel hence the rich condition and higher possibility of backfiring.

I'm running the Turbosmart 50/50 valve. I love it. It does backfire slightly between shifts from time to time but its not a big deal to me. The car runs just as good as it did when I had the Forge BPV (full recirc).

[Meder]

Running the turbosmart here also. A rare slight pop sometimes between shifts, maybe once every 40 miles or so, no problems at all. Running in 50/50

[lestat13]

I've run just about everything. Turboxs hybrid on 2, 3, 4, and 5 washers, greddy type-s in vta and recirc, greddy type-rs in vta and recirc, and hks in recirc and vta with standard fin and no fin. I will say that running anything vta except the hks ssq makes the car idle like shit. Shifting is better with the hks ssq in vta over others, but it still leaves something to be desired. Everything I have run 50/50 or as a bpv ran flawlessly (after tunning the greddy valves of course). I recommend just getting an upgraded bpv or running something like a type-s in recirc for a different sound.

[Driverman5777]

I run the HKS SSQV in full VTA... I absolutely love the sound and drivability isn't affected at all, granted I have the standback and Tune for it... not 100% pop free yet, but getting there... Much much more fun than the stock

[fbpem1]

Originally Posted by Deadman i run 100% vta, and no probs at all... I run the new hks ssqv, the hks being the only one i would recommend to run in vta.

+1

[motocrosser614]

Vta gets way anoying cant stand it especially in traffic cause it echos off cars. I think most cars vta sound awesome, but for my daily its not needed ill run whats recommended for the engine and no backfire

[nighthawk358]

i never had a backfire with my turbosmart dual port and i run it 50/50