Exactly how important is the blow off valve when running a turbo? I want a turbo on my 8, but also make it a sleeper, and the blow off valve makes that PSSSH-noise every gearchange. Can it be removed or "forgotten" when installing a turbo or will I lose extra power?

 

could go with a bypass valve instead, most stock turbo'd cars do

 

^^^ You can get blow off valves which vent back into the inlet tract as opposed to venting to the atmosphere.

 

bov or recirc valves are inportant. if your going for a sleeper effect get the recirc, dont go without one though cause if you dont have one it will cause back surge in the turbo compressor which will dramatically reduce the life of the turbo, and have an effect on boost because it will take longer to reach boost or spool the turbo when your "backspinning" it between gears

 

all turbo cars have a turbo...bypass valve... pop-off valve... all the same but the stocks ones are normally really quiet so you don't hear the pssst. Usually stock ones are made out of plastic butterfly valves inside. Aftermarket ones have stiffer springs and metal valves making the air bypss the intake stream much more violently causing the noise you hear.

and no it does not matter if you route the air backinto the intake tract, the bov will be just as loud.

 

A blow off valve/Compressor surge valve isn't mandatory, especially under low boost. However, damage to the compressor (turbo) could result after prolonged running without a way to relieve the pressure building up between shifts, etc.

Routing the charge back into the intake pipes can silence a BOV/CSV readily. I've heard re-routed, er..I mean I 'haven't' heard Re-routed systems make much noise at all.

Course, I had a vent-to-atmosphere BOV which was inaudable too.

 

WTF???

I beg to differ.

On my S14 Silvia, I originally tried to go 'stealth' and had a BOV vent back into the inlet just before the throttle body.

Sounded stock as a rock quiet.......... and that was with 19psi being dumped by a aftermarket BOV plumbed back into the inlet.

I later changed this unit for a Blitz BOV which dumped straight into the atmosphere........... now that was f***ing loud!

 

I'm using an FM recirculating BOV on my Miata.
It is still quite audible, but it is considerably more quiet than a vented-to-atmosphere BOV.
Of course, the volume is directly proportional to the amount of air you are venting.
At 5 - 7 PSI, it is almost inaudible. At 14 (where the real fun begins) it is pretty hard to ignore.
On the RX-8, you are only going to run about 7 PSI max on the OEM fuel delivery system, so a recirc BOV will be very stealthy.

 

The stock bpv on my last car (Volvo) was rather loud after I upped the boost from 11 to 15psi, but it was nothing like a vta blowoff.

 

had a Eclipse and when I dumped into the intake track or to the atmosphere with a GReddy BOV it didn't matter at all. at 5psi or 19psi, the sound was the same. I guess it matters on the model also, I guess.....

 

i don't think u will need a BOV if the boost pressure ain't that strong... BOV is needed only when u r running high pressure OR if u want to show off...

 

that is a good question. everyone seems to have differing opinions on the subject. personally i want to supercharge the 8. i guess as far as the bov goes, how long do you want it to last? how long are you willing to wait for it to spool? are you willing to replace the engine when the vains get ingested and carve all kinds of pretty grooves through the engine and finally built up in your muffler? of course you might get lucky and the turbo will desinigrate on the exhaust side and save your engine!but why risk all that. just find a bov that is designed to be quiet.

 

"Need" is a bit subjective. You never "need" a BOV, though your turbo will suffer greatly if you don't have one and either run boost pressures over 7 PSI or (and more importantly), you operate the turbo under the surge limit which is almost a certainty if you size the turbo on the small-ish end for better response.

There were many turbo vehicles in years past that didn't have a relief valve of any type and operated at relatively high boost pressures (the Lebaron comes to mind).
They also didn't last very long...

The vanes don't disintegrate because of surge. It is the bearings that bite it.
Generally, the result is just a ton of smoke and no boost. Ask me how I know...

 

True.

 

stupid question is there bov on superchargers?

 

Can be added.

 

this si off topic but it is something to do with TC and SC.... TC uses exaust to spool it up... so there might be lag if the turbo is big enough... but SC is driven by "belt"(if i remember correctly) then does that mean boost is on the tap instantly when u give it gas?

 

Yes, more or less.

 

Well, there are several different types of superchargers, some of which could incorporate a BOV.
The centrifugal type (Paxton, Vortech, etc.) operates just like a turbo, only it is driven by a belt instead of a turbine. It continues to generate boost after the throttle is closed so a BOV would be useful.
The positive displacement and internally compressing SCs usually wont incorporate a BOV in the system because their supply of air is cut off when the throttle is closed since it is upstream. They stop compressing because there is nothing going in to compress.
However, on systems that are designed with a positive displacement TC before the throttle, a recirculation valve is incorporated to send the compressed air back to the SC inlet to reduce its drag.

An SC (except the centrifugal) is producing boost all of the time. However, it is doing so at a penalty of high parasitic loss. The net power will be higher as the RPMs climb. The centrifugal makes boost proportional to RPM, so it produces nearly no boost at low RPMs (at a lower parasitic loss).
The turbo produes boost independant of RPM - it is driven by flow and will respond to an increase in throttle at a rate proportional to RPM. At low RPMs, it will take a period of time (1/10s of a second) to develop full boost. At higher RPMs, there is no delay (lag) and the response is as fast, or faster, than an SC.

The issue for all forms of forced induction is the proper selection of the actual device employed. The sizing of the SC or TC will determine the RPM range where the application of power is most effective and the losses are minimized.