I was thinking out loud about turbos on race cars, and had an idea. Most turbo blowoff valves vent either to the environment or into the exhaust side of the turbo, effectively wasting that boost. why not vent the excess boost back into the intake side of the turbo, pressurizing the intake side but still letting some excess boost escape but still maintaining most of the boost so that when you get back to the throttle, the lag is reduced. granted, this might mean the blowoff valve would stay open for prolonged periods of time, but other than possibly wear on the spring holding the BOV closed during normal operation and potentially stressing the air inlet upstream of the turbo, I can't think of any problems with this sort of setup.
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Oct. 6, 2010 9:58 a.m. Slyp_Dawg Reader
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Oct. 6, 2010 10:06 a.m. RossD Dork
Diverter valves? Audi/VW/Porsches use them. When the throttle snaps shut the valve opens to allow the air to loop back from high pressure side of the compressor back to the low pressure side. It helps keep the turbo spinning, too. BOV let metered air out before combustion and can screw with AFR (and send un burnt fuel out the tail pipe=flames). I've never heard of a BOV that vents to the exhaust but I rarely know much.
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Oct. 6, 2010 10:07 a.m. Spinout007 Dork
I could be wrong but if I'm not mistaken a properly setup bov would only vent the excess pressure caused by the throttle plate shutting. Theoretically not causing a boost loss. Iirc the main reason for them is to prevent compressor surge and the turbulence of air not knowing which way to go. I could be wrong, and have been in the past.
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Oct. 6, 2010 10:11 a.m. Strizzo SuperDork
the old bmw F1 turbo motors put the throttle at the inlet of the turbo, thus eliminating the need for the BOV.
i've never seen a BOV that vented to the exhaust, most of them vent back to the inlet side of the turbo, which is needed to keep the "closed system" between the MAF and the O2 sensor. this also reduces lag like you theorized
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Oct. 6, 2010 10:12 a.m. Wonkothesane Reader
I've never heard of a BOV directing to the exhaust, that seems like a dangerous idea...
A properly designed system (i.e.: stock) will vent it back onto the turbo inlet duct, somewhere between the AFM (Air flow meter) and the inducer on the turbo. Because most modern cars use some sort of air metering system (AFM, MAF, etc), so you can't just "dump" that air to the outside world without negative affects such as excessively rich conditions when you let off the throttle and other emissions, MPG, and drive ability issues.
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Oct. 6, 2010 10:19 a.m. 1988RedT2 Reader
Slyp_Dawg wrote:
I was thinking out loud about turbos on race cars, and had an idea. Most turbo blowoff valves vent either to the environment or into the exhaust side of the turbo, effectively wasting that boost. why not vent the excess boost back into the intake side of the turbo, pressurizing the intake side but still letting some excess boost escape but still maintaining most of the boost so that when you get back to the throttle, the lag is reduced. granted, this might mean the blowoff valve would stay open for prolonged periods of time, but other than possibly wear on the spring holding the BOV closed during normal operation and potentially stressing the air inlet upstream of the turbo, I can't think of any problems with this sort of setup.
Problems? I can't think of any either! I'm running a TurboXS #RBV-H34 on my RX-7. The relief is piped back into the short intake plumbing just upstream from the compressor. http://turboxs.com/more_info.php?ID=7
I'm not running a MAF, so air metering wasn't a concern. Unlike most guys running turbos, I prefer "stealth mode" and a loud blow-off valve is the last thing I want. You can still hear it, though. Works great!
And I've never heard of a BOV dumping into the exhaust either, FWIW.
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Oct. 6, 2010 10:27 a.m. Raze Dork
I think you're confusing BOV with Wastegate...
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Oct. 6, 2010 11:14 a.m. Slyp_Dawg Reader
yeah, when I wrote that I got BOV and wastegate mixed up, went back and changed wastegate to BOV but didn't really proofread and take out the part saying the BOV vented to the exhaust. of course, it could have also been due to a flawed understanding of how the Corvette C6 Twin Turbo setup worked (looks like the stock quad-tips, but two of the tips are for the wastegate and two are for the exhaust)
anyway, the idea I had was centered around the idea of a lowered, box flared Hillman Imp, inspired heavily by the old DRM/Group 5 BMW 320 with the motivation to back up those looks and make use of all that aero, and of course a bumper-dump boom-hole, in the spirit of the old Bimmers, except at the bumper instead of the side skirts
