Negatives of unmetered BOV to atmosphere
 

What are the negatives of venting unmetered air to the atmosphere? I understand it puts fuel into the cylinders that there isnt air to burn. But other than losing some fuel does running this set up long term damage anything?? Thanks

Makes it more difficult to tune. Introduces a variable for no reason. Long term issues would be dependent on how well the tune can compensate for it.

What? I think you've got it backwards.

You can do whatever you like with un-metered air because the MAF hasn't seen this air yet and thus fueling and spark hasn't compensated.

It is bad to vent METERED air because the MAF has seen that air and has told the ecu about this air. So if you dump it after the MAF has seen it then you get issues.

Yea you're right, that makes more sense. I had my car tuned with my BOV set to 100% recirculated. I'm thinking about switching it to 50% vent to atmospheres and am wondering about how my car will react.

If you do that and don't do anything else, you'll be running too rich. Worse mileage, worse response, black smoke out of the exhaust from unburned gas, if you have a cat it will damage it.

If you pay whatever and get a great tune along with it, best case scenario you get no performance benefit, negligible additional wear and all the wooshing noises you want.

Not necessarily. It depends on where the BOV is located. If it is pre-MAF he can vent it 100%. If it is post MAF then do not vent it .

@Whatabouteggs, does sw20kosh's explanation click for you? He is correct but we can discuss some more if you like. This could be a fun, interesting learning experience, IMHO.

As long as the bov is before the maf... There will be no difference. The only difference would occur if your bov is right before or very close to your maf sensor and caused turbulence when open as with mine on my JDL. also if you are 100% speed density it makes absolutely no difference. This question is best left to your tuner... Especially since you haven't mentioned what setup you are actually running. We would just be guessing at random.

That is true. Depends on the MAF placement of the kit though. AVO's kit uses the stock MAF location I believe, so that wouldn't be possible. It uses a MAP sensor that comes with the kit to control for pressure, and the MAF for temperature and total air metered.