I know the BOV does the "pushhhh!" noise when letting up on the accelerator after the turbo spools up but what exactly does the wastegate do? I've always thought of it as a BOV that is silent. I see all these VW's that are turbo'ed and hear the turbo spooling but when the car shifts, there is no sound. What is the difference or rather what does each do? Most turbo kits come with both so i think both are necessary for complete system install but i'd appreciate any answers.

 

BOV, releases air that is trapped in the charge piping, after the tb has been closed from lifting off hte gas pedal, but a wastegate regulates how much boost is allowed to reach the engine. When the turbo spools up it creates more boost then a car can handle, and the wastegate dumps the extra boost into the exhaust instead of to the engine.

 

The waste gate dumps excess exhaust pressure to slow the turbo. It dosent dump boost.

 

reason why the vw's bov you're talking about are so quiet is that they're probably recirculation valves. the loud bov's generally release pressure to the atmosphere. this generally isn't good to do on a car with a mass air flow sensor unless the bov is setup before the maf, which is hard to do in a correct setup since the maf needs to be before the turbo. if the car uses a map sensor you can generally release the air to the atmosphere.

the whole reason for a bov is simply to keep the pressure from returning to the turbo causing slowing, stopping, or worst of all reversing of the blades of the turbo.

as said above, a wastegate dumps exhaust to limit the speed of the turbo, which is what limits the amount of boost. loud wastegate setups dump the exhaust to the atmosphere but this supposedly causes bad o2 sensor readings if using a wbo2 and usually sounds like ***. its best to dump the exhaust in the exhaust piping and before the o2 sensor for best results.

 

how would it affect the o2 sensor? it only measures A/F ratios not volume.

 

u have a wastegate that dumps into the exhaust........seems like to much work, but the vw's run a diverter valve which is like a blow off valve. only thing with the diverter valves on vw's is if u turns it the other way it becomes very loud even though it doesnt bleed into the open air

 

some people have seen differences between the two setups. i'd personally want all the exhaust going to the sensor to be as accurate as possible... don't want to take any chances of running lean at all.

 

This is a little off topic, but why can you hear the turbos spooling in the vw's, etc? I've always wondered, even when they are taking off with normal acceleration you can hear the turbo. I don't get that at all on my car... maybe I should get a whistle tip.

 

That's cause those little 1.8 liter engines have little turbos that spool up at like 2000rpm.

 

back on topic...what is the ideal size for the wastegate (assuming that it is a t4 setup) to use. i see most guys are using the 38mm, but i have seen some as big as 50mm. what would be the most significant difference in using a larger wastegate as opposed too a smaller one?

 

it lets out more exhaust gas. bigger hole, better flow.. it'll help if ur exhaust housing is a bit smaller..

someone correct me if i'm wrong...

and 38mm is almost 100 dollars cheaper than the 40mm.. and the price sky rockets from there.

 

it is easier to control lower boost pressures with a larger wastegate from my understanding.....but essentially it just allows a larger volume of exhaust gas to bypass the turbine.

 

I bet if you had a stock exhaust you would hear it more, you probably don't hear the turbo because of the deep tone of your exhaust and muffler.

 

I hear mine all the time because I pull cold air from the cowl area (by windshield) via a 3.5" pipe.
I don't run a blow off valve at all. I've got 20,000mi on mine with no trouble fromt the turbo so untill I do I'm not spending the money.
I thought you'd hear yours Brad from pulling the air in the fenderwell area... Humm...
That .72mm turbo we have on the GN engine at the shop was sent to us.. and several others with a improper machiened housing and it never made a whistle sound. We got the correct housing and now it sounds like a tornado!
~Scott

 

The stock ones are very loud...VERY loud ^^

 

Another reason we can't hear ours spool up is the fact that we have 5 feet of piping between the heads and the turbo. DSM,s Civics, and VWs all have the turbo bolted to the exhaust manifold, with only a few inches of distance between the valves and the impellers. I can rev my car all day long in neutral and it won't build a bit of boost, however a SRT-4 blows off in reverse.