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Discussion Starter #1
I've been thinking about getting a bov for my rex and obviously the only thing holding me back is the temporary richness between shifts (the stalling can be solved by making sure the bov stays closed which is easy enough to do). Now I'm coming from a turbo'd s2k that has a MAP sensor behind the throttle body so a bov doesn't affect anything at all.

What I have a hard time figuring out is why the richness period can't be tuned out considering the stock ECU can be tuned. Is it "hardwired" into the ECU to always add fuel upon closing the TB? Seems like that would be a simple parameter to change. I'm not sure how complex of a tune you can perform with a simple reflash, but I know with my s2k and the AEM EMS you can control every darn thing of the car which does include deceleration maps and what not

Any ideas?
 

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(I will try to avoid many of the technical terms and blah blahs)
The difference lies in the sensor location. Where our sensors take in airflow readings prior to the BOV and MAP sensors are within the intake manifold itself. Where the map takes in manifold intake air pressure and compensates fuel curves that are only one step behind the combustion chamber, our sensor takes in total air flow from the intake. The BOV wont affect MAP because the air has been vented before the reading to the sensor, calculations are done after the air release, hence not resulting in a rich mixture. Our vehicles have already calculated total air flow so releasing air after the calculation results in a rich mixture.
It is the same result for vehicles that have Air-flow metering systems like Supras as they also run rich between shifts.
I have tested some tuning approaches to this even altering cell by cells but to no great degree, one solution is to map the conditional "if throttle is closed, then run leaner, or if boost <=0 then leaner" however ECM tuning logic will tell you that these conditions do not cover 100% of the situations where BOVs open so tuners tend to avoid this tuning approach unless specifically told by the customer. Best to recirculate to let the engine run at its best at all times.

However if the cool sounds are more to your liking feel free to do whatever you want. Enjoy your car. ;D
 

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Discussion Starter #3
You can talk technical, I'm in school to be a mechanical / aerospace engineer :)

I understand the part that the air is metered. Now when the air is recirculated, I'm assuming it goes back into the intake pipe (I haven't actually looked at my own engine so this is just a guess) but once the TB is closed there is no need for any "extra" air (recirculated air). So would I be correct to assuming this running rich in between shifts only happens when shifting fast? If you shifted slow the recirculated air would just go back out the filter since the TB is still closed (like I said assuming very slow shifting).
 

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You are correct about the air recirc. back into the intake duct via inlet hose. However, since the air has already been calculated in fuel mixtures, that air is "needed" despite the throttle plate being closed. Air is needed for combustion at all times, so in essence the engine is constantly sucking in air, not blowing it out through the filter. The car thinks there is still more air coming in. Even at idle, the vehicle still sucks air in to run but it calculates much less volume coming in. The computer knows that the BOV is there to protect the turbo and not the engine so it brings fuel into the system due to the large volume of air it still thinks is coming in. (just not at the high velocity as under boost conditions)
Another thing to note would be that despite the recirc design, our cars run rich in between shifts. Hence the fire that comes out when running catless despite the recirc. BOV. The excess air can also be let out through the blow by tube or through oil catch cans back into the intake. There are so many ways to run this extra air to try and let the car run as best as possible. This is much of the reason why many AFM or MAF tuners highly recommend keeping the Recirc design. It's because the system is flawed anyways and runs rich, why would anyone want to make it run worse than it is already? "I want you to run this car for as hard and as long as possible so I am going to do whatever I can to make you rnu as safe and as reliably as I can while still giving you performance gains."
Another note: Many tuners also don't care about the VTA because the car runs rich in-between shifts anyways, that the VTA makes a non significant contribution to overall A/F ratios. "Run it if you like. It wont affect durability enough for it to matter anyways. You are putting on the BOV and modding your car to run it fast anyways and drive it hard. You aren't looking to keep the car forever."
Both sides of the camp have tried to prove both points and success/failures of each study tend to support whichever camp they are on.
As far as the shifting fast.
Try this: Shift fast but with the throttle off. There is no BOV noise because you are not boosting. In this case, running rich will not occur. If you get a VTA BOV here, it wont matter at all since there is no excess air. Shift slow but press the clutch while steping on the throttle and you will get the BOV sound, VTA here will cause u to run rich. There are alot of situations where this can occur, hence the whole can't tune for all situations BOV deal.
Ultimately it is up to you however you view the whole BOV issue.
Hope this helps in some way for you.
 

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I just thought I would throw in my .02 here. If you are looking to here your stock recirculating blow off valve, purchase an intake...the only bad thing about the stock bov or bypass valve is that it drops boost. Has anyone tried crushing it yet? There are several aftermarket bov's like GFB that are hybrids that give you options. They probably hold boost better than stock, but I would only run it in the recirculating option. I personally like the Perrin unit.
 

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I'm still hitting boost targets but then again, I am tuned as well :)
 
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