[Tes]

Just curious, anyone here have an external blow off valve on the F87 N55? From searching on forums and FB groups, I couldn't really find an example. Cruising around with a buddy of mine that has a 1M with an external valve I kinda want one haha. My understanding is that the internal valve is located on the compressor housing and electronically actuated which has been a challenge on the N55.

[tenkies]

https://f87.bimmerpost.com/forums/sh....php?t=1691511

I have it on my car. Stock tune the sound is very subtle. BM3 stage 1 tune the sucker is noticeable.

[Tes]

Originally Posted by tenkies

https://f87.bimmerpost.com/forums/sh....php?t=1691511

I have it on my car. Stock tune the sound is very subtle. BM3 stage 1 tune the sucker is noticeable.

Awesome!! thank you so much Guess I searched the wrong word haha was searching blow off valve. I appreciate it.

[detroitm2]

whoooooooosh...

[CalAcacian]

Originally Posted by Tes

Awesome!! thank you so much Guess I searched the wrong word haha was searching blow off valve. I appreciate it.

They are similar, but technically different pieces achieving a similar goal. Both a diverter and a blow-off remove excess pressure from the intake tract when the throttle closes and the car is developing boost. If that air was not removed, there would be an increase in pressure between the impeller of the turbo and the closed throttle, the excess pressure would then force itself back out of the turbo the wrong direction. This is compressor surge, a chuffing sound of the pressure leaking back out through impeller. This will slow your turbo down (increasing lag when you get back on the throttle) and cause accelerated wear on your bearings.

What they do with the excess air determines which device it is.

A diverter valve reinjects that air into the intake track prior to the impeller. This allows you to take advantage of the work already done by the turbo charger to collect that air and put it right back into the intake tract. This leads to better throttle response and reduced turbo lag.

A blow-off simply vents that air to atmosphere (giving you the characteristic stu-stu-stu-stu or other noises based on the design of the vent pipe). A blow off, while mechanically simpler and arguably better sounding, is generally worse for performance for street and track driving. By giving up that excess air, you force the turbo charger to spool up longer when you get back on throttle to be in boost. In addition, this air has already passed by the MAF sensor, so the engine has calculated additional fuel for this air. If you leak it to the atmosphere, the engine will run rich when you get back on throttle, reducing power and increasing emissions.

In short, a blow-off will make your car slower, but sound cooler. You can upgrade the stock diverter to one which can seal slightly better and sound better, but you won't be getting the same sound as a blow-off.