How effective are pop off valves at covering if the wastegate fails or if it's not ported enough? I know people will say port the WG and be done with it but let's say this is only a temporary solution.

How much boost can they vent off?

Anybody have experience with them. Thanks guys.

 

Correct me if I'm wrong but the BOV is to stop the shockwave from hitting the turbo and breaking it. The waste gate is used to control the amount of boost your turbo can spool up to.

I'm guessing you have the stock turbo to a series 5 and you want to run about 10 psi, if so your solution is to either use an external waste gate or port it.

 

Hes talking about a POP of valve, not a blow off valve.
That was taken off RX-7.com:
http://www.rx7.com/cgi-local/2catalog.cgi?cat=9&part=5

 

I wasnt referring to the BOV I was asking about a POV (pop off valve) totally different thing.

I did a search (should have done it in the first place) and I found my answer. I pop off valve should not be used as a way to control boost only as extra insurance. If a pop off valve goes off constantly it will kill the turbo.

Thanks anyways.

 

Just port your wastegate...

I have a Greddy Pop-off valve and it is effective at dumping boost and makes a really gross farting noise when doing it so you will know when to back off.

You really do not want to use the Pop-off valve to limit boost w/ any reqularity as it will cause the turbo to overspin and wear out your bearings and seals quickly- then you will have to take the turbo off for a rebuild as well as WG port.

Restrict the intake and/or exhaust until you can get the turbo off for the WG port.

Edit- Oh, I'm too slow to post...

 

It's a very expensive temporary solution compared to something as simple as porting the wastegate.
All of it...

 

This was such a good point, I thought I'd repeat it. Put some kind of restriction in the intake and/or exhaust. This will lower your boost levels!

 

A Pop-Off valve is a BOV. Both relieve pressure in the intake system after the turbo. A wastegate is in the exhaust stream. Its purpose is to bypass exhaust gases around the turbo.

edit:

After reading this again, if you're talking about an external wastegate you would need a custom exhaust manifold to mount it. As Nz stated a rather expensive solution.


Rob

 

An your power levels. Why bother with modifications to exhaust and intake if you're just going to restrict them? You might as well have left it stock.

Don't **** around with half-assed measures; sort out the wastegate. Big flap, big port.

 

you are wrong. they are totaly different....

a BOV opens under vac. to let the built up boost between the closed throttle plates and turbo out so it doesn't hit the throttle plates, bounce back to the turbo and try to spin it the other way.

a pop off vavle is like a fuse. if it's set at 12psi. it does nothing at all if you are running less then that. as soon as you hit 12psi it open and les ALL boost out. it's used as an emegery back up like a fuse.

if you are trying to use a pop off for limiting boost. it will just spool the turbo, hit 12psi. open. now at 0 psi. spool. hit 12psi. open. now at 0. etc. it won't hold 11 psi. it'll just keep jumping from 0 to 12psi and the car will run like crap.

 

If you want a temporary boost-limiting device, simply remove your FCD and let the stock ECU do its thing. Total cost: $0, total labor time: 30 seconds.

 

How bad are the effects or removing the FCD? From what I understand at fuel cut thefuel to the 2nd rotor is cut off. Anything else going on?

 

That's all that happens.

 

I have a greddy pop off valve, but i havnt installed it yet. im going to be using it as insurance too, i get massive creep sometimes, and i need to port my wastegate more. i dont see why it would hurt anything, except cause a very rich condition until the boost is back under the set pressure. ive heard it will cause some hesitation though, because of the rich condition.

 

It significantly overspeeds the turbo, because for a second it's pushing against nothing. This damages bearings. Repeated use will kill your turbo!

POV's should not be used to protect against boost creep. Sort out the wastegate!

 

So nothing bad happens when a t2 hits fuel cut? It would be cool if anybody could clarify. I mean it sounds like such a violent action on the engine. I myself have never experienced fuel cut.

 

So nothing bad happens when a t2 hits fuel cut? It would be cool if anybody could clarify. I mean it sounds like such a violent action on the engine. I myself have never experienced fuel cut.

The stock ECU will cut ALL fuel during overboost fuel cut, so it will not hurt anything. Same as the rev-limiter, it cuts all fuel.

I imagine a very leaky injector could leak enough to cause a lean condition (a little bit of fuel) instead of fuel cut. That would be bad...

Leaking injectors is such a common problem in our cars, I would definitely check them/professionally clean them before any performance work.

 

Fuel is only cut to the rear rotor.
A leaky injector dribbles only a tiny amount of fuel. Even it was ignited (unlikely), the amount of heat generated wouldn't even be close to that required for detonation to occur.

 

As mentioned above, it was a temporary solution until the WG port was complete. Yeah, it's going to lower power levels, but so is venting off boost in any fashion, whether through a pop-off, blow-off, or WG (ported or unported).

 

Thanks all for the replies. I am surprised there are no long term negative effects to fuel cut. Does this also apply to hitting fuel cut regularly?

 

once you hit it once you won't hit it again... because the car just stops. it's not like you can drive while hitting it.

you just won't be able to floor the car. because it's faster then you keep hitting fuel cut.

 

Adding a restriction to reduce boost to (say) 8psi will result in less power than if the wastegate could hold it at 8psi. This is because you're using engine power to overcome the restriction instead of drive the wheels.

POV's should never be used to control boost.

 

I don't think it's a good idea to hit fuel cut on a regular basis. Mazda designed this feature only as a safety mesure, not as a long-term feature. Among other issues, the engine is going to be out of balance if only the front rotor is firing, which is going to be hard on the bearings, if not other parts.

BTW, do you have some type of handicap that limits your control over your right foot? My brother is in the medical business, so I can probably recommend some physical therapists in your area if you are having trouble.

 

Thanks for the reply. Sometimes I do have a heavy foot. I am in the orthopedics business so I got that covered already . I'm administrative support for one of the biggest orthopedics firms in northern california.