I have repeatedly heard that it is acceptable to leave the CRV and the ABV venting into the atmosphere. However, under 9" of vacuum to port A (see picture below) it is possible to blow through from port B to C. And we all know that a healthy engine will pull 16"+ at idle.

If in fact, the engine is under vacuum, wouldn't the engine be pulling air in through port B to C and into the engine? I can even feel air being sucked in the ABV and CRV under vacuum at idle. Why is it ok to leave these vented?

 

The ABV is used to release excess boost from the intercooler piping so that you dont get surge which can force the turbo's to spin backwards which can potentially damage them. Stock, the ABV vents to the intake and venting to the atmosphere will give the typical "woosh" heard from a BOV. I dont see how that will do any damage to the engine.

Under acceleration, the engine isnt a vacuum pump its being forced fed air from the turbo's so, technically the ABV wouldnt be working under vacuum, and when you release the throttle and the throttle plate snaps closed, the vacuum pulls the ABV open to vent the pressurized air in the Intercooler piping.

 

the crv and abv both suck in air under vacuum to make it easier for the engine to get air instead of the engine trying to get air from going through the turbines of the turboes its just an eaiser way for them to flow. you can leave them vented to atmosphere to get the whoosh sound but put a small filter at the end of the crv and abv.

 

Who told you that it's okay for these to be vented?

Everything I've seen, people frown on venting the stock ABV and CRV. They do suck in air at idle, and that's not a good thing if they arne't filtered. Remember, when they are hooked up they are suck air from the air box, which is filtered.

If you want the "woosh" sound, it's best to get an aftermarket hard-pipe intake, which has nipples for the ABV and CRV to get air from when opperating under vacuum.

In general, it's never okay to suck unfiltered air into any engine...that's why we have air filters

 

Can say the standard SP version over here had them venting to atmosphere with no filtration - the pressurised airbox had no provision for connections. To the best of my knowledge, standard Mazda warranty applied, so wouldn't consider it much of an issue.

 

Unless you actually test yours, then any answer saying it is wrong to be unfiltered is pointless.

Even though the engine at idle and cruise may be under vacuum (after the throttle body) , the turbos are still pumping some air under very light pressure. Pull one of your hoses and test it yourself.

My single GT35R definitely blows at idle and my BOV is closed.

 

my abv and crv suck in air at idle so it would be a good thing to filter them

 

If the CCV is working, the CRV should never draw air. Mine sure doesn't. When it's open, the CCV is closed, isolating the secondary tract from the rest of the intake. No need to filter it unless your CCV is leaking.

My ABV does draw a TINY amount of air at idle. The vacuum source is after the TB, so the actuator port sees vacuum at idle and cruise, which opens the valve (see the FSM test of the ABV to confirm that this is by design, fully open at 9in/Hg). Still, I don't bother filtering mine, since it's a negligible amount of air going in there - covering it with my finger, I can barely feel the pull. The vast majority of intake air goes through the filter, since as Chuck pointed out, the primary turbo is pulling some air through the filter.

 

o yeah i forgot to say mine is non sequential

 

IF you change the spring in the valves they can be closed untill the vacuum pulls 17 inches when you let off the throttle at above idle . With the spring changed the boost will come on sooner . The people who had the valves I modified liked the quicker spool ,it was enought to be noticed . The valves did not let air flow into the intake track so venting without a filter was no problem . This was useing them as blowoff valves .

 

^--link?

 

Before going single, I was non-seq with many mods. Originally I used the stock BOV. I tested mine and it was closed at idle and did not suck in any air.

 

hmmm mine must be broken because i can definatly feel air being sucked in and i tried to put a fd bov on my fc and it didnt work because my fc has a MAf and the fd bov was sucking in unmetered air so it didnt run right.

 

A stock one in working order will be open at around 4 inches vacuum. Fully open at about 9-10 inches, if I remember correctly . I did this some years ago .After I changed the spring they opened at 17 inches vacuum .When going down the road when I let off to shift the vacuum went to 19 -21 inches and the valve releaved the pressure and the turbos stay spooled for the next gear .With the valve closed the from tip in spool up was faster .

 

Sounds like a good idea. Where'd you get the spring?

 

The spring was from an 80cc two cycle Yamaha clutch built in the 1960s . I will look to see if I have any more of them .I modified four or five valves back then .All went to different parts of the country .

 

i have mine vented with the Pettit TKT intake kit... works perfect, no problems yet

 

i just pulld my ABV and its blowing air out at idle. the ABV is fed off the y-pipe and the turbos are still boosting, more actually than the throttlebody will let through hence why the excess pressure is leaving through the ABV

 

+1

 

mine blows air about the same as if you hold your hand an in from your mouth and exhale normally