Kool

I know that our BOV's do not release pressure into the atmosphere. I have read here that this is a good thing because it allows the system to maintain pressure as well as keeps the info that the barn door sends the DME accurate(correct air-flow calculations). But I was just wondering what the advantages are to venting the BOV to the atmosphere. When I watch WRC all those cars vent to the atmosphere. If that is in fact a disadvantage why have all of the teams decided to have the BOV vented that way. Does anyone have any idea. Danno?

Kool

Bump

ribs

If you run a vent-to-atmosphere BOV with a MAF or AFM (like our cars stock) metered system, you run into problems because metered air is purged from the system, making the ECU think the engine consumed more air than it actually did, making it run rich between gear shifts and after throttle lifts (I think you already knew this though). The only advantages I see with a vented BOV is that it can flow more air in very high boost/HP cars as it doesn't have to go back into the intake tube...this will help keep your turbo spooled and fight compressor surge better than a bypass valve that has to force all of its vented air through a 1" or so hole. If you have ever seen some of the higher end greddy, HKS, or other vented BOV's you will see the exhaust is much larger than the dinky one we have stock on our cars. I don't think using a stock or 993 TT bypass valve will cause any bottlenecks until you start talking about big turbo upgrades, in which case you may be better off with a monster BOV...but you will need to compensate for the richness if you vent it. The only other thing I see as an advantage is the cool sound..."vrrrroooooom...pssssshhhhhtttt!!!...vrrrroooom!". I plan to buy danno's MAP sensor upgrade once I sell my fuchs, and with it I will get some obnoxiously loud vented BOV as that has always been one of my favorite parts of modded turbo cars that I have always wanted - the sound...with danno's MAP thing air is no longer metered...it is calculated using pressure and temperature (P and T in PV=nRT) and then converted to meter signals, so it doesn't matter if you vent to atmosphere or not. HTH,

Danno

How about these threads?

<a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=18&t=002052" target="_blank">Installed a Apexi BOV and it works good.... </a>
<a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=18&t=002258" target="_blank">I can't vent into the atmosphere??? Car dies at idle </a>

Considering the only time a bypass/recirc/blow-off valve operates is during shifts and when you let up on the throttle, I'd rather spend my time and effort focusing on getting more from the car during the 'other' times. Namely when the gas is FLOORED!!! <img src="graemlins/xyxwave.gif" border="0" alt="[bigbye]" />

Olli Snellman

BOV helps turbo to spin between the shifts.Have you noticed how they change gears on those WRC cars.I have an opportunity to take a ride last year with finnish rally champion Marcus Grönholm (leader of WRC series at the moment).He drives that Peugeot 206 WRC.There is no need to use the clutch or release the gas pedal during the sifts, so the turbo is spinning with maxium revs all the time.Ofcourse they are not using that old AFM type systems.Quess what they are using?? Yes MAP.
I must say that ride was one of the best experiences i have ever had

Olli
'88 951

TheJonesBoy

Aside from BOV's, the rally cars also use exhaust manifold fuel injection to keep the turbo spinning. Yes, they inject fuel into the hot exhaust manifold. It explodes, and the pressure wave keeps the turbo spinning during shifting and engine braking. The sound is freaking awesome.

vvvRRROOOOMMMM.. &lt;BANG&gt; VROOOOMMM.. &lt;BANG&gt; &lt;BANG&gt;...

Kool

Thanks for all of the responses. I see your point Danno.

That exhaust manifold fuel injection is a pretty trick. I always thought that those flames were because the cars were running rich. Could you imagine a 951 with a exhaust manifold fuel injection system. That would be crazy as hell. I wonder if something like that is legal in GTS or something like that. I know there is absolutely no point to have it in a street car. I wonder what that did to the turbo life?


Those WRC cars are pretty impressive. What other tricks do they have?

Danno

I think the really trick one was the Lancia Delta-Integrale with both a supercharger AND a turbocharger in series with each other! <img src="graemlins/jumper.gif" border="0" alt="[jumper]" /> <img src="graemlins/jumper.gif" border="0" alt="[jumper]" /> <img src="graemlins/jumper.gif" border="0" alt="[jumper]" />

Olli Snellman

That Delta, which Danno mentioned was FAST.It was also too fast because it took life of Henri Toivonen,who was very good finnish rally driver (aren't they all ?) FIA changed rules quite soon after that crash.No more tube frames and also no more over 600 hp.Most WRC cars has now officially about 380 hp...

Olli
'88 951

Kool

Asupercharger and a turbo in line. I guess that the supercharger kept the system pressurized better in off throttle systems.

Redeye

You can also forget about turbo lag with that setup!

eugene

I understand that blowing off to the atmosphere creates a rich condition since previously metered air is being released.

I was wondering if it is significant enough to affect performance(at the track) and also create any negative condition in the combustion chamber. Such as fouling of plugs or wash off oil from the cylinder walls.

Thank you to all you out there for the contributions.