I have heard from people that you dont need bov's but then i hear from people that you do. I understand that compressor surge is bad, but how bad? Buick Grand Nationals and GMC Syclones didnt even come with a bov from the factory. My dads GN has 120,000 miles on the original turbo and he doesnt have a bov. So what is the deal? Right now i dont have one and i love how it sounds. If its not really bad for it, then i wont be getting one.

 

from what I have heard is that with out a bov. you spin the turbos backwards when you let off the gas. cause if you have 10 psi and close the throtle its got to go somewhere.

 

Syclones and Typhoons had Waste gates.. same concept.. different proceedure.

 

You beat me to it!

 

Wastegate: Used to control boost and shaft rpm by bypassing excess exaust when a determined boost level is reached.

BOV: Used when you let off the throttle to vent the air that is still building now that the throtle blades are closed. Without a bov you will put a lot of stress on your turbo berrings and your throttle blades.

Almost always a wastegate is needed, and a bov is optional. However, a bov is HIGHLY recomended to keep added stress out of the way.

 

A wastegate is totally different than a blow off valve. The wastegate just controls boost levels, it doesnt relieve pressure when you close the throttle plates.

Well I would agree with you that it would put extra stress on the turbo, but why dont factory turbo vehicles have bov's then?

 

Yeah, as he said, wastegates and blow-off valves are completely different in their function.

Part of the reason Sy/Ty's and GN's didn't come with BOV's is because they're automatics, and while they would still be beneficial while letting off the throttle real quick in those applications, they aren't slamming the throttle plate shut at every WOT shift like a manual car is. Many factory turbo cars came with BOV's... DSM's, Supra's, 3KGT's, WRX's, just off the top of my head.
Either way I'd always use one on a moderately+ driven street car, that's just me though.

 

What TwnTrboZ28 said WRT to definitions.

As far as being necessary… neither are. Wastegates are just a way of running a smaller, faster spooling turbine, but if you were willing to tolerate a slower spool things would be more efficient without.

As far as blow off valves go, manual or automatic, it would not open under load with a good driver, the only time it would see use would be if something got screwed up, a panic stop… it’s mostly an invention of the street/import crowd where most people drive and shift slightly worse then my grandmother, and have become popular because the ricers associate the sound with power. I would consider running one just in case or if the car has a tendency to blow hoses off, but I wouldn’t go out of my way to get one or spend real money on one.

As far as the turbo rotation reversing… those are just old wives tails. It may prevent forcing the turbo into surge, but again, properly driven and properly sized that shouldn’t be a problem.

 

83TA, why would it not open? Isn't it going to open during every shift? Or are you saying something to the effect of keeping the throttle open somewhat while shifting? (not WOT obviously)

 

He said they dont open under load, only when you let off the throttle. Both the BOV (release to atmosphere) or Bypass valve (reroutes back into the system) prevent compressor surge, but for some people its about performance (or perception of better performance) instead of protection. I've never had a setup with and without one to compare, so cant say I know if it really makes a difference or not. But the idea for some people is that the release of that pressure prevents the turbine from slowing down. I dont think it would ever go backwards, but that pressure would cause the turbine to slow down, and thats not helpfull considering that you're gonna shift into the next gear and build boost all over again. Relieve the pressure and the turbine keeps spinning, makes sense for a manual car. I dont think it matters as much for Autos since they have a stall converter (builds boost really fast anyway).

 

If you're throwing a fast shift you shouldn't really have time to close the throttle, just enough to start the RPM's dropping a little to match when the clutch reengages in a RR situation or not at all, just fast enough not to hit the limiter in a drag situation.

In neither case should the throttle close enough to open the blowoff.

 

ConFusing............Ahhh *Naturally aspried*

Just Joking.

 

Okay, I think I get what you'r saying now. Keep the throttle open alittle while shifting and the r's that the engine do drop aren't enough of a hazard or stress on the engine?

Is there a specific pressure bov's are set at to open? How do those work?

 

most BOVs are just a vaccume line from the intake- i know greddy makes them adjustable so you can fine tune it. when your making boost its closed then when you let off and the boost drops suddenly it makes it open. a stock turbo on a national or sy-ty is fine without a BOV but most of the time when guys go into the range of a te 63-1 they start to use them. it does make a pretty neat noise when i lift off the throttle with my turbonetics cheetah turbo in 20lbs of boost