Could someone tell me the differences between a wastegate and a blow off valve.


Tnx


Juker008

 

Blow off valve vents pressurized air from the charge pipes whenever the throttle plate closes (when you let off the gas to shift a manual, for example). The thought behind this is that rather than the pressure being fed into the engine, it hits the [closed] throttle plate and basically "reverses" working against the turbocharger that's trying to cram even more air into the same space. Keeps the turbo spooled up for action in the next gear. There are tons of varities... these make the cool noises you hear when big boost turbo cars shift.

A wastegate is basically a valve that allows exhaust gases to bypass the turbocharger therefore regulating the speed at which the turbo spins and thus the boost pressure it's producing.

Here's a pic of my Integra motor:



The red circle contains the wastegate, the blue circle contains the blow-off valve (Turbonetics Deltagate Mark II and HKS Super Sequential, respectively, fwiw).

 

So a safe and easy way of saying it is a blowoff valve is for the intake side and the wastegate is for the exhaust side.

Now here is something that strikes me. Is it possible to run a high boost application w/o a wastegate. The way that I see it is the turbo will always be spooling HIGH, because there is no wastegate to allow the extra exhaust that is needed. But the blowoff valve would simply exhaust the extra boost that is generated by the HIGH spining turbo. Would this work? Is this effective? What are the down sides?


Ohhh Shit thats ur drag car. Man I am dieing to see that thing in action. What do u expect to have that thing run.

Oh by the way u need a driver .


Juker008

 

The wastegate is there to prevent overboost. It helps regulate the boost the turbo is producing by not allowing it to feed on more exhaust gases than you want it to. So if your target is 16psi of boost, once it starts to get close to that the wastegate opens to prevent the turbo from building more than 16psi of boost.

 

The turbo would never stop producing boost. You don't want this.

That car went 13.30 @ 106 at 10psi and was much faster at 17psi but I never took it to the track on that much boost. I do have a video of me racing a Ninja 750 laying around somwehere.

Need a driver my ass -- I'm down for a race whenever you are.

 

You took it to 17psi... hope your bottom-end is built because that's a LOT of boost. I am very aware that the B18C1 loves boost, but not THAT much boost

BTW, I have three pistons and four stock rods for that car if you want. Plus a intake cam-shaft.

 

Oh yeah.. JE forged pistons.

 

Thanks for the offers but that car is long gone. I bought it new in January of 1997, boosted it in early December. Ran 10psi max on the stock bottom end for about 20k miles and rebuilt it using JE 9:1's and Crower rods. Also had some L.A. Sleeves pressed in. It ran like an animal at 17psi, but it was somewhat of a bitch to tune since I was using the old pump & regulator setup + RC 310cc injectors. I regret not having taken it to the track at 17psi... I didn't have slicks (at the time they cost a FORTUNE) and it would shred the stock tires at 10psi... at 17 it was just out of hand. I was pulling 2.3 short times because it just refused to hook up. Dyno'd at 252hp and 198ft-lbs at 10psi. It was probably around 320/240'ish at 17psi.

I sold the motor and turbo setup in early 2000, swapped a stock B18C1 back in and traded the car for my previous 2000 TL. Ahhh the memories...

 

NO, these parts are not interchangeable, you couldn't have a BOV installed to do a wastegates job or vice versa.

downside? how about a turbo cramming 20+ psi of pressure into ur engine when the most it could handle is 8, now you tell me if there could be a downside to that. the more pressure you generate, the stronger your wastegate has to be otherwise it wont be able to withstand the force and the spring will blow out, causing overboost.

i use a GReddy Type-S BOV and the stock wastegate set to 18PSi max on the 2JZ

 

I'm running 20 psi in my gti right now!

 

my mechanic runs 32 pounds in his porsche.

 

The ability to run without a wastegate is possible, but requires sizing attention beyond what could rationally be done. Some turbo applications have turbos that can't keep up with the demand as the revs climb allowing the boost the trail off even with the wastegate closed.

But as a practical rule, you have to have a wastegate. There are two types, internal and external. It is generally thought of thought that external gates provided better control; which is true. But this is normally only for higher boost application. Most factory systems use and internal (integral) wastegate as it is less complex since it is part of the turbine housing. Most internal wastegates are fine to control boost levels up to 15 - 18 psi (what I ran on my Typhoon). The wastegate control does vary from manufacturers, some pull it open and others push it closed.

The BOV (Blow Off Valve) or sometimes called CBV (Compressor Bypass Valve) is there, as others have mentioned, to prevent compressor surge. Compressor surge is the action of when the throttle is closed, the air will try to equalize with the ambient pressure. The only way to go is back through the compressor. This causes the compressor wheel to slow down quickly and reverberate slowly damaging the bearing. Since the compressor slowed there is a greater delay in getting back into full boost when you get back on the throttle.

However, some older automatic turbo vehicles do not us a BOV as it wasn't as needed. Since an automatic shifts while your foot is still on the throttle, the throttle plate was still open. This allowed the engine to ingest the boost during a shift. The only time compressor surge occurred was when you get off the throttle quickly. The T-Type/GN and Syclone/Typhoon did not use a BOV and my old Typhoon made a nasty sound when you let off the gas especially with an open cone intake.