Can you vent blow off to atmoshere on supercharged car?
- Thread starter cathartic
- Start date
It is ricey when you are going out of your way to do it, spending money and time tinkering around for the sake of adding noise to an otherwise great running car. If your running a 25psi turbo on a DFI setup, Ill jizz my pants. If your running a silly Vortech street setup on a Mass Air car psssshing off, I laugh.88stangmangt said:
88stangmangt
Active Member
i hear ya......................im plan to only buy the HKS and no more..........but you wouldnt be laughing very hard when it blew past you............i think BOV's on S/c's are awesome becuase they are geting more popular but still un-common.................nothing wrong with some one thingking you have a huge turbo under your hood................but on the other hand i have heard that people are plumbing them off there intake to store pressure and blow off like a normal BOV except they have no turbo/SC no that is ricey........RydeOn said:
Let me help point you on the right track on this. Time has nothing to do with how it works. When the throttle is shut, the air becomes diverted in an alternate route so it wont back up against the throttle body. The air reenters the system into the intake side of the blower, but after the mass air meter. Since the charge that is "blown off" is still taking up displacement (the Mass part of MAF, learn how it works) and is contained within a loop in the intake charge system, no additional air can be metered, and thus your ECU has detected that the throttle has been closed. In contrast, had the air been blown off into the world, the vacuum from the S/C inlet would continue to draw air from the MAF while replacing the blown off displacement. This sends the ECU a signal that air is being introduced even though the throttle is closed. Since the MAF is measuring air when the throttle is closed, your mixture is rich.
Alright so that means that when the computer meters the air at the MAF (I do know how it works 
) which is still outside of the intake plenum, it uses that information to add an amount of fuel into the air that is in the cylinders now. I guess I assumed when the MAF first reads a big rush of incoming air which hasn't hit the cylinders yet, that there was a pause if you will, before the fuel was actually added to let the air get there. But I guess the air moves fast enough the discrepency probably isn't even noticable. And it would be far less drastic going from WOT to close than the other way around.
So yeah I guess that makes sense then, I guess I was just assuming a little bit more of a precision system than it is.
) which is still outside of the intake plenum, it uses that information to add an amount of fuel into the air that is in the cylinders now. I guess I assumed when the MAF first reads a big rush of incoming air which hasn't hit the cylinders yet, that there was a pause if you will, before the fuel was actually added to let the air get there. But I guess the air moves fast enough the discrepency probably isn't even noticable. And it would be far less drastic going from WOT to close than the other way around.So yeah I guess that makes sense then, I guess I was just assuming a little bit more of a precision system than it is.
88stangmangt
Active Member
that air is already metered so it must be used so it is put back into the intake or air inlet tube..................but that defeats the whole purpose of a BOV .....................that is why they make by-pass valves..............
It's probably way more complicated than what it's worth, but I wonder if you can set up a BOV than when activated overrides the MAF signal to the computer and tells the computer your at closed throttle. Because what really matters isn't what air is being metered, it's what air is really being used.
Michael Yount
Mustang Master
True, but if it were as simple as that then there would be no reason to blow off back into the intake, the computer would see the closed signal from the TPS, and ignore the fact that the MAF is telling it there is still incoming air passing through it because of the BOV.
So if there is a tuning issue using a BOV, it's because the computer adds the fuel as it sees the MAF signal regardless of TPS signal. So, you need to change the MAF signal to be the same it would be during closed throttle.
So if there is a tuning issue using a BOV, it's because the computer adds the fuel as it sees the MAF signal regardless of TPS signal. So, you need to change the MAF signal to be the same it would be during closed throttle.
Michael Yount
Mustang Master
I understand what you're getting at serijou - I was responding to this statement "...and tells the computer your at closed throttle." The computer doesn't look to the maf to know whether it's at closed throttle or not - it looks at the tps. What I'm getting at is you may want to look at how the ecu treats/deals with the maf reading when the tps says the throttle is closed. You may not have to alter the maf signal depending on what the ecu does when it sees the tps go to closed throttle voltage.
Alright I follow you now. My choice of words was poor. I didn't actually mean to use the MAF signal to tell the computer the throttle was closed, but rather change the MAF signal to reflect what it would look like in a N/A car while the BOV is activated.
Now this is 100% assumption and you know how that goes. But my guess would be that the computer isn't really designed with the notion of the TPS and MAF sensors contradicting eachother.. while both are actually functional and accurate. The computer uses both signals to calculate how much fuel to add. in a N/A situation there will be a natural correlation between TPS readings and MAF readings. As the TPS says the throttle is opening more, the MAF in turn will verify this - there is more air coming in. So, theoretically, by simply looking at one, in a N/A situation, you could ballpark what the other "should" be. The whole BOV to the atmosphere however throws a huge wrench in this, and your computer is going to see;TPS closed = not alot of fuel while the MAF is saying add fuel (probably add fuel somewhere between what full throttle and 3/4 throttle would be in a N/A situation). This situation is gonna be out of paramaters for the computer, because this situation is impossible N/A. So, the computer is going to take the safter route, and add the fuel like the MAF says... there might be a compromise in there somewhere. And I wouldn't be at all surprised if the computer figures at that point in time that the TPS just took a dump and briefly goes into limp mode... which could also be called rich as hell mode. Let me be the first to admit this is all computer-seat theory drawing on my very limited knowlege of the EEC-IV system. And I'm not at all trying to say this or that is how something is or isn't. This is nothing more than just some thoughts I'm throwing out there.
Now this is 100% assumption and you know how that goes. But my guess would be that the computer isn't really designed with the notion of the TPS and MAF sensors contradicting eachother.. while both are actually functional and accurate. The computer uses both signals to calculate how much fuel to add. in a N/A situation there will be a natural correlation between TPS readings and MAF readings. As the TPS says the throttle is opening more, the MAF in turn will verify this - there is more air coming in. So, theoretically, by simply looking at one, in a N/A situation, you could ballpark what the other "should" be. The whole BOV to the atmosphere however throws a huge wrench in this, and your computer is going to see;TPS closed = not alot of fuel while the MAF is saying add fuel (probably add fuel somewhere between what full throttle and 3/4 throttle would be in a N/A situation). This situation is gonna be out of paramaters for the computer, because this situation is impossible N/A. So, the computer is going to take the safter route, and add the fuel like the MAF says... there might be a compromise in there somewhere. And I wouldn't be at all surprised if the computer figures at that point in time that the TPS just took a dump and briefly goes into limp mode... which could also be called rich as hell mode. Let me be the first to admit this is all computer-seat theory drawing on my very limited knowlege of the EEC-IV system. And I'm not at all trying to say this or that is how something is or isn't. This is nothing more than just some thoughts I'm throwing out there.
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