[sambonator]

Originally Posted by pat@forge

Increased heat is a byproduct of compression, as the air is discharged it will expand and cool. There will be a slight increase in heat but it will only be a fraction of what is seen in the charge pipes.

I think it picks up a lot of heat from the hot turbo compressors. We can do some calculations using PV=nRT, but I think we'll find that the pressure/volume changes don't have as much effect on temperature as the heat added by the hot compressors.

Originally Posted by pat@forge

Also, the volume of the discharged air is so slight it will be consumed in a revolution or two of the motor. So the air will be consumed in about .01 seconds give or take.

Most of the heat issues will probably be from the turbo compressors not being able to get cooled off by ambient air during hot air recirculation.

These are my theories, and will just be theories since I won't be able to test them .

[unagi1]

Originally Posted by sambonator

Through my testing I've really not noticed any difference turning the DV into a BOV, except sound. I was running them recirculating at first.

My theory is that this isn't going to be a difference you can feel. I believe now that venting the hot gasses will have a marginal effect on reducing engine temps, by allowing the engine to vent hot gasses rather than reingesting it. It may also reduce timing getting pulled when getting back on the gas immediately after shifts, by not allowing it to reingest the hot hair. I think this is why almost every turbocharged racing car uses blow off valves instead of diverter valves.

The reason for venting to atmosphere vs. recirc has more to do with how the ECU meters air coming into the engine rather than an attempt to lower combustion temps. EGR systems are more effective in doing this, and it's not for performance reasons but emissions.

I didn't see a mass air sensor on any of the engine diagrams, so am betting that this is a speed-density system (MAP) and that you can vent to atmosphere without affecting the engine's operation. In a mass air system (MAF) you need to keep the metered air recirculating in order for the engine to accurately measure the amount of fuel to inject. If some of this air mysteriously disappears from the equation, then under certain conditions the car will run rich. This might or might not cause problems (cat. converters, etc.) but is still not a good idea.

So, yeah...BMW didn't want to build a rally car so they decided to recirculate blow-off air

[Mr. 5]

It's not my style because of the BOV thing, but the way you did this is really clean.
Good work!

[karma8]

Will you be able to do a sound clip? I really want to hear how it would sound!

[Mr. 5]

Holy thread revival batman!

[M3 Eater]

Any one know if after market DV converted above would create the same boost holding capacity as a high end bov. How bout some boost logs ??

[David@Sonic MS]

how is it sound? any sound clip?

[Terrance28]

I've been saying this for a long time. Our turbos are really too small to benefit from the extra air being forced back into the intake, it will not help them spool any faster or better. So whether you vent it out or recirc it back it, it wouldn't matter with this car. I just feel a BOV will hold boost better when you start hitting 16+psi imho. And its not all about holding boost its also about how good it can release it too, without sending that charged air back to the turbos. Anyway very nice setup to the OP.

[M3 Eater]

I felt like my car didn't respond as well when I tried this with my stock DV's. Throttle response was sluggish in my opinion. If I didn't like the way my car drove then.... I prob wouldn't like it with my aftermarket DV's any better.

[techlogik]

Sound/video?

[forza1976]

You guys realize the OP posted this thread well over 2 and a half years ago...

[MF80]

Originally Posted by Mr. 5

Holy thread revival batman!

lol...

[Ghines1279]

why did he put filters on the place where air was coming out? You think he was worried about debris going back in some how?

[M3 Eater]

I am thinking about doing this now as I want to use the front recirculation inlet for my oil/air breather separator. I guess it would be cool to have a BOV sound but I need to get the pressure in my crank case down. I think the channel of flow through the cap of my breather is choked off a bit by a 1/8 hole.