MPR

Heard many different things about both types of bov's.

There are pros and cons to both.

Just thought I'd get some of your opinions and views on this. (For those of you who don't know the difference: recirculating puts the air back into the intake pipe before the turbo, external just dumps the air out in the open.)

PSSSSSsssssh!


Discuss:

RDub

what are the pros and cons?

bbarbulo

iTrader: (2)

the real pros and cons involve 2 things: emissions controls and MAF measurement of incoming intake air pre-turbo. if you dump that air to atmosphere, the MAF reading is incorrect and the engine runs rich (it metered more air than made it to the throttle body). also the bit about the environment... that part I don't really believe since PCV and EGR valves usually dump right into the intake manifold (post t-body on N/A cars going turbo), so it's unlikely that a charge pipe would be filled with nastyness. that being said, I've seen oily charge pipes from the PCV going pre-turbo.

akira

As far as our cars care, open atmosphere. theres no need to recirc a bov in a map system.

MPR

On my volvo 740 turbo, I removed the factory recirculating bov and installed an external bov. I also removed the restrictor in the vacuum line from the intake mani to the bov. This allows it to open instantly when you lift off the throttle. This engine also uses an AMM (air mass meter) which measures the mass of air entering the engine (located before the turbo) and adjusts the fuel injection system accordingly.

Now after going for several runs in the car with the setup like this, I found no issues at all with venting the air into the atmosphere rather than back in the the intake pipe before the turbo.

Also with the bov being way more responsive now, I found the turbo spools back up quicker as well.

bbarbulo

iTrader: (2)

ya, removing the restrictor will make the turbo spool up faster. but don't fool yourself into thinking the fuel injection is bang on. remember that the metered air didn't make it into the manifold.

I'm not all that up on volvos specifically, so maybe check out turbobricks website, if I recall they're all about the older volvos.

MPR

^^yeah. I'll check out that website.

I have an a/f ratio gauge I'm going to install with it's own wide band O2 so I can monitor roughly how she's running.

I'm hoping since the stock fuel pressure regulator is a rising rate (or FMU) meaning it increases fuel pressure with increasing boost levels, that I can up the boost 2psi or more to 10+psi and it will simply compensate with more fuel pressure. My cavalier with the turbo ran like this and had no issues.

As for the metered air not reaching the intake mani, I'm not too worried since it will only cause it to run rich momentarily.

SilverSleeper

By Ontario law, you must run a recirculating blow off valve.

MPR

How many external bov's have I heard on the street's? Actually, not many.

It doesn't make sense why that is law. It's only dumping air that has been compressed.

I'll just pretend I didn't heat this law...lol....