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Discussion Starter #1
I'm not exactly sure how a blow off valve works, but has anyone with the vortech kit ever thought about replacing the recirc valve with a BOV? It would work, right?
 

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If you use a BOV that vents to atmosphere you'll run into problems. The Cougars uses a mass airflow sensor that calculates fuel maps from the airflow values. For example, the MAF would read 15 lbs of air entering the MAF (based on voltage calculations) and the PCM will fire the fuel injectors accordingly. When you close the throttle plates (shift gears or take your foot off of the accelerator) the BOV will vent that air into the atmosphere. The PCM still thinks you're putting 15 lbs of air into the engine, but in actuality there's no air..........and it'll be running really rich at that moment.

A recirculation valve or by-pass valve sends the vented airflow back into the intake tract, which keeps the A/F ratio correct. You could run a BOV vented into the atmosphere, but you may run into stalling problems and your engine may bog when shifting.
 

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Discussion Starter #3
oh yeah, I forgot about the MAF. How do turbo cars do it then?
 

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The WRX has a MAF and a BOV...but maybe it's not an actual MAF but it sure looks like it

so does the Mits GS-T and GSX ( i think)
 

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Hm, now that ya mention that, Afterhours, you do sound right. (FYI- Not trying to be an ass here...) I just know it can't be true, I don't know why, but I know that Craig and James have BOV's and an MAF. My car is being built so the SC spools up to 15psi quickly and then blows off down to 12psi, and my car is being built for reliability, so running rich is out of the question for me.

Anyone know the actual way a BOV works when using a calibrated MAF?

E1
 

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Doesnt the Zetec also use a MAF. I saw Seawulfs turbo setup, and he had a Pro-M MAF with a BOV. SO it should work properly.
 

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Discussion Starter #7
The streetflight kits use the stock maf. Maybe it's in the tuning. maybe the ECU sort of ignores the maf briefly every time the throttle is let off. or maybe it uses only the MAP during decel. (IIRC, cougars do have map sensors, right?)
 

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WRXs have a recirculating blow off valve. It sends the air back into the intake tract.
 
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we all have a MAF......and if you are boosting....you need a by-pass valve.


I should post a picture of the Godzilla Bov's i have....they are freaking huge!! I will post a pic of the raptor and Godzilla side by side!! Its pretty funny...

Attached pictures!!
 

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You don't NEED a bypass valve over a blow-off valve with a MAF but it is BETTER to route it back into the intake. Since doing the streetflight chip I have had a few problems(about 3 times so far) with stalling coming down from highway off ramps and shifting to neutral and letting it coast down.

When I was pushing 5-6 psi I had no problems with the HKS causing a stall or bad idle. The only time I stalled was when I was using a bypass valve as a blow-off valve and it was venting all the time except under boost. If you get a proper blow-off valve you won't have that problem. The car did have a smoother throttle response with the bypass, especially when you let off the gas in gear. Now the car kind of jerks when you let off the gas in gear.

A good tuner can tune around having a blow-off on a MAF. A lot of MAF cars have blow-off valves and live with the problems associated with them. A BOV is definitely more for show. That's why I got the BOV I have is cause I loved the noise it makes and I can live with the small problems. There is some concern wether the short rich condition between shifts could cause problems internally but it's mainly conjecture with no hard knowledge, as far as I know. Some even think that the rich condition can help the turbo keep spooled up between shifts, sort of a poor mans anti-lag.

So to summarize. BOV is cooler but has a few problems on MAF setups and bypass is better for overall smoother throttle delivery yet doesn't give you the satisfying noise.
 

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I have a turbo xs type s bov and it vents to the atmosphere. It will cause the car to stumble if you rev it at a stop and dip into boost and let it blow off. As far as standard driving it causes no problems. It sounds good too :)

video from late 02
swooooooosh
 

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Discussion Starter #12
Originally posted by: naynay
we all have a MAF......and if you are boosting....you need a by-pass valve.


I should post a picture of the Godzilla Bov's i have....they are freaking huge!! I will post a pic of the raptor and Godzilla side by side!! Its pretty funny...

Attached pictures!!
Damn that's huge; want some turbo to go with that BOV... ;)
 

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The normal stuttering step to a BOV verses a Bypass Valve on a MAF equipped car is the PCM does not know you lost said amount of air and therefore can cause a stumbling or drop in rpm.

This can be tuned out with a chip or even a tuning device like an S-AFC. (provided of course you send it a boost signal)
 

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Correct me if I am wrong.

But could you not relocate the MAF closer to the TB....with the BOV prior of the maf, so that the BOV vents before the MAF. This way the air being vented is not metered.
 

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Discussion Starter #15
I read in my turbo book that the farther the maf is from the filter the worse the throttle response. I'm guessing having the maf that far away would cause horrible throttle response.
 

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That makes sense.


I know with a recirculated BOV the sound is awesome when you have an open element filter. The BOV 'echo's at least on a turbo application that is.
 

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The only problem with having the BOV before the MAF means you have the MAF after the turbo. Some tuners don't like this and some do. Some say having the MAF after the turbo is harder to tune and I could agree with that. But all these things are the price we must pay for power.
 
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Originally posted by: Seawulf
The only problem with having the BOV before the MAF means you have the MAF after the turbo. Some tuners don't like this and some do. Some say having the MAF after the turbo is harder to tune and I could agree with that. But all these things are the price we must pay for power.





Interesting...........Time to hit the books on that one.
 

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sorry to butt in, but for my eclipse gst in order for me to vent out to the atmosphere without having problems i had to change my maf so it was after the BOV so it would read the proper readings... but then again i ripped out my stock huge nasty thing and bought a GM maf from a vette and a translator so it was easy to do and gives me the same tuning advantages as a S-AFC plus its actual readings before the intake manifold but after the BOV
 

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The air is meant to travel only one way through the MAF. If you have the BOV before the MAF the surge has to back flow through the MAF which damages it. Not only that but you would be adding even more "expected" airflow to the PCM by again flowing it through the MAF.

Having the MAF after the turbo is harder to tune because of the much hotter air charge flowing through the MAF.
Also they make MAF's specially designed to be used that way. (blow-through)

The reason some folks design a turbo setup with a blow-through MAF is a turbo is greatly affected by any intake restriction before it. This is why I would suggest an aftermarket MAF when using it before the turbo for the sole reason that it does not have the restrictive center bar design. The slightly bigger housing is a plus too, but 75mm is plenty.

Superchargers are not affected nearly as much. (Roots/screw style negligible)
 
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