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View Full Version : Just a question about the BOV's



Tekdemon
06-24-2003, 07:51 PM
I've been reading around, and a lot of WRX gearheads say an all air venting BOV(like the HKS one) isn't good because it'll dump all the turbo pressure but your fuel system will still be pumping the original amount for a while so you end up with a really rich spike during your shift?

Supposedly a 50/50 air and fuel BOV is optimal? Can anybody shed any light on this?

andy
06-24-2003, 10:06 PM
The reason this is a problem on the WRX is because the stock
BOV recirculates the vented air back into the intake. So the ECU
has already compensated for that air, and you end up running
rich.

I ran a 100% atmospheric (vents all air back to the engine bay)
BOV with no real problems. Yes, I did run a little rich and yes,
my exhaust showed signs of it, and yes I probably was a tad
slower, but otherwise, it was a heck of a lot of fun. That "whoosh"
noise is hard to beat...

On a car where the stock bov doesn't vent to the intake, it wouldn't
really be a problem...

ssvr6
06-25-2003, 04:33 AM
Exactly. On the 1.8Ts, they don't have a BOV at all, they're using a DV (diverter valve) that puts it all back in the intake. Some people were installing the BOVs and getting CELs from running rich.

Cars that are NA and get boosted, don't have to really worry about this.


Steve

FCobra94
06-25-2003, 10:18 AM
Originally posted by andywrx
The reason this is a problem on the WRX is because the stock
BOV recirculates the vented air back into the intake. So the ECU
has already compensated for that air, and you end up running
rich.


That is true. To add to that, the reason that WRX's run rich when going w/ a 100% atmospheric BOV is because those engines are equiped w/ a MAF. Mass Air Flow sensors meter the air coming in BEFORE the blow off valve, right after the air filter. The reason they run rich w/ the 100% atmos BOV is because when it opens to release the boost pressure, they are releasing metered air. All the while, the ECU assumes that all the air that came in through the MAF is going to reach the enigne so it adds more fuel to the mix to compensate. When the air is vented to the atmosphere, it never reaches the engine obviously, but the same amount of fuel is still added by the computer because it still sees that it needs to adjust for all that air that it saw after it first entered the filter.

I'm not exactly sure how it works w/ Honda's but I believe that the MAP sensor detects how much air will be entering the engine at the manifold which is obviously, after the BOV so it reads the actual air coming into the motor and you won't have an abnormally rich mixture (unless you tune for it)even w/ the addition of the BOV, whether it be 100% atmospheric or whatever...

Some one please correct me if I'm wrong, especially about my Honda knowledge :D

SexNTurbos
07-02-2003, 02:16 AM
The Civic motor (or Honda in general) uses a map sensor to decide the level of fuel to mix. Unlike the mass air flow system, the map sensor is in the intake manifold so the air isn't metered before entering the throttle body. Since the air doesn't get measured until it's in the engine, the air in the intake pipe before the throttle body can be expelled to the atmosphere with no driveability issues. Spending the money to plumb it back into the intake pipe would be a waste of money and provide no benefit.

Running a recirc would yield neither a gain/loss. It doesn't hurt anything on the car but it will affect the richness of the A/F ratio between shifts due to the metered air not being present to mix with the fuel.

On my STi, I switched the stock form (recirc) to an atmospheric and noticed some minor tuning changes (mainly turbo responsiveness) between shifts on the dyno, but no power gain.

Good explaination FCobra94

Austin

FCobra94
07-03-2003, 09:11 PM
Originally posted by SexNTurbos
The Civic motor (or Honda in general) uses a map sensor to decide the level of fuel to mix. Unlike the mass air flow system, the map sensor is in the intake manifold so the air isn't metered before entering the throttle body. Since the air doesn't get measured until it's in the engine, the air in the intake pipe before the throttle body can be expelled to the atmosphere with no driveability issues. Spending the money to plumb it back into the intake pipe would be a waste of money and provide no benefit.

Running a recirc would yield neither a gain/loss. It doesn't hurt anything on the car but it will affect the richness of the A/F ratio between shifts due to the metered air not being present to mix with the fuel.

On my STi, I switched the stock form (recirc) to an atmospheric and noticed some minor tuning changes (mainly turbo responsiveness) between shifts on the dyno, but no power gain.

Good explaination FCobra94

Austin

Nice follow-up yourself! :D

Just curious, but wouldn't you have a 2004 STi (just going through your sig)? That is of course, unless you imported one from Japan ;)

I'm next on the list to recieve one in blue w/ gold wheels but things kinda fell through when I found out that my school sched next semester involves a 60+ mile commute every freakin day and not the 2-3 days I had planned on instead! I wouldn't feel comfortable puting that many miles on it. :sigh: One day though, it will be mine..I think I'm gonna cry when I go to get my deposit back from the dealership :'(

Until then, I'll prob be enjoying the company of an 03 Si :D

Oh! Anyways...how do you like yours? :)