blow off valve

[TURBOGTA1]

I got tired of hearing the marbles in the coffee can noise, just by lightly getting into the accelerator and starting to build boost, then backing off !!! I threw in a Tial blow off valve, and that niose (beating up the turbo) is a thing of the past!!!!

 

[Turbo1dr]

I have a question about that. So you're saying the engine will run rich because the air is already accounted for by the MAF sensor, and the ECM will provide fuel for that air, but the air is being shot out the BOV to atmosphere. Makes sense. But when you get off the gas and the throttle blade snaps shut WITHOUT a blow-off valve, all the air that the MAF measured STILL isn't making it into the engine to be used for combustion, so regardless of having a BOV or not, if the MAF measured a certain amount of air and then you snap the throttle shut, isn't the car going to run rich either way? Whether the air is vented to atmosphere with a blow-off valve, or shot back the "wrong" way through the intake piping until it slams into the turbo and sneezes out your air filter, in either situation the air isn't making it to meet up with the fuel that the ECM provided for it. I'm not saying that you're wrong, I'm just providing you my train-of-thought and hoping you can explain. I figured the air isn't entering the engine regardless of which way it finds its way out, any time you snap a throttle blade shut you will momentarily run rich...

With MAF before turbo inlet and NO BOV:

When the throttle snaps shut the air that's rushing back out of the MAF only lasts for a split second. When all the compressed air is out the MAF will start reading air intake as normal and the engine will run fine. With it happening so fast engine stumbling or rich condition is minimal. The back-rush of air slows the turbo down VERY fast.



With MAF before turbo inlet and BOV in up pipe venting to atmosphere:

When the throttle snaps shut compressed air rushes out the BOV and not backward out the turbo. Since the BOV is open to atmosphere the turbo will still be sucking in air through the MAF and venting it back out the BOV. While this is happening the MAF is measuring the air intake even though the engine is at closed throttle. The ECM will be getting a high MAF reading and will put in more fuel. This is due to the BOV being open due to engine vacuum. It's just sucking in air and blowing it right back out the BOV. This is where the rich condition and engine stalling or stumbling occurs.


With MAF in up pipe and BOV before MAF in up pipe:

I have not had this set-up on my car but I would imagine that no engine running problems should occur. When the throttle shuts the MAF only reads the air that the engine is taking in. The turbo will be sucking in air and venting it all before the MAF.

 

[Boost231]

+1 for the Tial 50mm. i love mine. i dont have one on my TB but i have one of my Turbo Gsxr600

 

[turbojimmy]

I was about to ask you why you thought I had a blow-through set-up, but I see you caught your mistake. :tongue: I actually wanted to do blow-through for a long time but then I got alky injection and I'm sure my MAF sensor wouldn't enjoy taking a methanol bath every day.

The silcone hose on your up-pipe made me think you had a blow-through. I have my alky injection after the MAF in the up-pipe so it doesn't bathe in alcohol unless I let the throttle slam shut under high boost which is why I'm curious about the BOV.

Jim

 

[Nasty]

BOV is not needed on these cars.
Save your money, the "benefits" seem to apply to the manual transmission 4 cyl imports, this reasoning has infected the new comers to the TR world.

Furthermore, of all the automotive turbo applications Porsche, Audi, GM, Ford, Toyota, Nissan, Dodge, Mercedes, BMW.
Of all the Heavy duty applictions International/Navistar, Cummins, Mack, Cat, DetroitDiesel, Mercedes, etc. None were offered with a "BOV".
Why? Its simply not needed, the original design of the CRHA's fully floating bearings with oiling provisions, and the newer ball bearings are able to function in either direction and provide support, because they were designed to function in a severe enviroment.
Once again look at the above manufacturers and see how many did come with manual transmissions and do not have bovs.
Its just a shame to see junk science, seperate people from their money.

The Dodge Turbo III's had BOV's, such as my '93 Daytona RT Turbo had. Its been a long time, but '92-'93 Daytona RT Turbos & Spirit RT Turbo's both had them (they may have made them in '91 too, I forget). Of course they were 5 speed manuals, I never could get used to the farting noise they made-so I just never let up on the gas to avoid it !

 

[White Out]

With MAF before turbo inlet and NO BOV:

When the throttle snaps shut the air that's rushing back out of the MAF only lasts for a split second. When all the compressed air is out the MAF will start reading air intake as normal and the engine will run fine. With it happening so fast engine stumbling or rich condition is minimal. The back-rush of air slows the turbo down VERY fast.



With MAF before turbo inlet and BOV in up pipe venting to atmosphere:

When the throttle snaps shut compressed air rushes out the BOV and not backward out the turbo. Since the BOV is open to atmosphere the turbo will still be sucking in air through the MAF and venting it back out the BOV. While this is happening the MAF is measuring the air intake even though the engine is at closed throttle. The ECM will be getting a high MAF reading and will put in more fuel. This is due to the BOV being open due to engine vacuum. It's just sucking in air and blowing it right back out the BOV. This is where the rich condition and engine stalling or stumbling occurs.


With MAF in up pipe and BOV before MAF in up pipe:

I have not had this set-up on my car but I would imagine that no engine running problems should occur. When the throttle shuts the MAF only reads the air that the engine is taking in. The turbo will be sucking in air and venting it all before the MAF.

The best is to run a bypass valve (bpv). It recirculates the air from the charge pipe into the post maf, pre turbo intake. This prevents the rich condition.
An atmospheric venting bov will give you fireballs out the back of the car.

With a blow through an atmospheric bov is fine. This is the set up that I will be running on my STi soon. The only difficult thing with blow through is not having any air turbulance around the maf. Otherwise the car will never be able to get a good tune because the maf voltage will be all over the place. Generally the bov is between the maf and the throttle body.

Nick

 

[BlackMetal]

Thanks for the clarification about the rich condition, makes sense.

All I can say is I purposely set-off my BOV all the time when I drive my car, love the sound, and I have never experienced the slightest hesitation, stumble, or stall. I guess if I ever run into any of these issues I might think twice about recirculating the air rather than venting.