GoFastBits (GFB) Atmospheric Blow Off Valve (BOV)

[docron]

Coming from the Abarth world a decade ago as a hobby build car, the GFB BOV was a great modification. In the Alfa 4C, there were no options for an atmospheric BOV. Called up my drug dealer Greg@GRP and asked if there were any BOV options for the M139. He suggested the GFB BOV… install is literally 10 minute swap (UNLESS you drop one of the bolts in the engine bay and have to jack of the car and remove the rear diffuser…ask me how i know! LOL)

I also have the Burger Motorsports (BMS) BOV plate and if youve been watching BMS JB4 youtube video, you do hear them mention the install of their BOV plate.

The concern(s) of an atmospheric BOV on our M139 i4, although theoretical and not yet proven, is that the OEM tune as well as the engine configuration might not like richer AFRs and is too sensitive to boost/gas variations with it being atmospheric and will probably throw some CELs or affect performance. I guess we’ll see.

For those who are not familiar with the Pros and Cons with an atmospheric BOV, here is chatgpt:

Atmospheric Blow-Off Valve (BOV)

Pros:

1. Sound Appeal:
   • Creates a distinctive “whoosh” sound when releasing pressure, popular among car enthusiasts.
2. Reduces Compressor Surge:
   • Helps prevent back pressure on the turbocharger when lifting off the throttle, extending turbo life.
3. Simple Venting Mechanism:
   • Vents excess boost pressure directly to the atmosphere, reducing complexity in some setups.
4. Improved Throttle Response (in some cases):
   • Reduces lag by quickly releasing pressure, allowing faster spool-up.

Cons:

1. Rich Fuel Conditions (in MAF-based systems):
   • Venting to the atmosphere can confuse Mass Air Flow (MAF) sensors, leading to rich air-fuel mixtures and stalling.
2. Potential Emissions Issues:
   • Not always emissions-compliant; may cause issues in regions with strict regulations.
3. Noise Complaints:
   • The loud “pssh” noise may be unwanted in residential or quiet areas.
4. Not Ideal for All ECU Setups:
   • Cars not tuned for atmospheric BOVs might run poorly unless properly calibrated.

Until someone cracks the m139 i4 ECU (Shinoo….JUBU….BMS…whomever) and does a proper ECU tune, i wanted something to maybe decrease the low end lag and improve throttle response and who doesnt want the old skool Tiel/HKS psssssssh right? The low end lag is horrible compared to my tuned 4C.

Install was easy.
1. Disconnect harness plug on OEM BOV.
2. Remove 3 bolts
3. Dislodge wire bundle mounting clip near BOV, you will need more clearance space to mount the GFB BOV. Just use a little flat screwdriver. See picture.
4. Orient the GFB BOV so bolt holes line up. There is only one orientation that will work and its easy to figure it out.
5. Use the 3 GFB supplied bolts to mount BOV.
6. Plug in supplied GFB wire harness adapter to reconnect BOV harness.
7. Relocate dislodged wire bundle mounting clip.
Done!

After a short 10 mile test drive, boost seems better while pushing. Sound is great. No CEL . Driving another 100 miles today to C&C and running around so will report back.

 

[Rayjoedef]

excellent report of findings Doc! Curious how/if throttle response is improved? Have been looking for throttle controller but none exist for Emira. I'm assuming an intake will assist with that.

 

[killjoy]

Been waiting for some one to do a review on these, thank you so much.
But why no video clip of the sound ?

 

[killjoy]

I also see you have the BMS blow off valve, will you be reviewing that as well, or comparing?

 

[F1 SML8R]

@docron Appreciate the write-up man. Fingers crossed all goes well today during your 100 mile drive. That should be more than enough to confirm if a CEL will come up given how tight these ECU's are.

At you convenience, can you also comment as to whether you played with the silver dial on top (the thing that looks like you can turn it with a coin)? If I recall correctly from the GFB website, it allows you to tune how much pressure vents from an air volume perspective which impacts the sound level of the "woosh". I'm guessing this setting might impact whether a CEL kicks in or not as well.

 

[docron]

Okay back from 100 miles of street and highway driving from 0-100mph, in all gears with varying degrees of push and throttle. Albeit only in touring since i am only 600 miles in.

Firstly, no CEL (so far).
Secondly, love the psssssh… so much fun. you can even hear the sound with the engine cover on, with the windows up and even through my sound deadening on the firewall..
Thirdly, throttle response seems better in the sense of maybe less turbo lag?

And tbh, I admit I didnt know that the coin slot on the top will adjust blow off. I did not adjust it at all, just left it as it came.

So far, so good.

 

[docron]

This is what chatgpt says about how an atmospheric BOV improves throttle response. Again, until someone does a proper ECU tune, one of my goals was to decrease turbo lag especially on the lower end of the powerband.

ChatGPT:
An atmospheric blow-off valve (BOV) can improve throttle response in turbocharged engines by quickly releasing excess pressure in the intake system when the throttle is suddenly closed (like during gear shifts or deceleration). Here’s how it works and how it helps:

What happens without a BOV:

• When the throttle plate closes suddenly (e.g., during shifting), the turbo is still spinning and compressing air.
• This compressed air hits the closed throttle and creates backpressure (a pressure spike).
• That backpressure slows down or stalls the turbo, a phenomenon known as compressor surge.

What an atmospheric BOV does:

• The BOV vents this excess pressure to the atmosphere (instead of recirculating it).
• This reduces compressor surge and allows the turbo to keep spinning more freely and maintain speed.

How it improves throttle response:

• Since the turbo hasn’t slowed down as much, it can rebuild boost pressure faster when the throttle reopens.
• This reduces turbo lag, meaning the engine can respond more quickly when you get back on the gas.

Summary:
An atmospheric BOV helps maintain turbo speed between throttle lifts, which in turn improves throttle response by reducing the time it takes to build boost when accelerating again.

 

[docron]

Regarding the BMS BOV plate, i dont know if i will test it or not. Would seem like a step back from the full GFB BOV.

Ironically, I was initially going to install the BMS plate first and test it a bit but i was like might as well do the GFB.

The BMS plate install is super easy. See pics.
What’s interesting is that even though OEM BOV is an AMG part, the valve part and mechanism is very plasticky and flimsy.

 

[F1 SML8R]

Great to hear and I wouldn't mess with the coin slot adjustment if all is well as is.

BTW, the car really is different once you get into Sport and Track mode. I was fortunate that I flew up to SF to buy my car and drove it back home. So, I managed to get through more than half the break-in just on the way home. Then it turned into either I or my wife taking my car on every trip to supermarket, Home Depot for house shit, and to the mother-in-law's to break this sucker in so I could hit track mode!

BTW, for anyone out in So cal, the real test will be next week:

Buttonwillow Circuit Track (New Track) CW 5/25/25

Golden Gate Lotus Club on Sunday, May 25, 2025 at Buttonwillow Raceway, Buttonwillow, CA - Note: This is the new Buttonwillow "Circuit" track, not the "Classic" track. Note that pricing for the Circuit track is more expensive because the track rental price is higher. You will find that othe...

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