ok, I asked about the restrictor plate in the exhaust the other day, and while it's a good idea, I'm still exploring other options to lower boost.

I did some searching and read up about the pop off valve and what I gathered is that you're supposed to set it above your max boost to serve as a last resort safety feature and not use it to control boost. why is this?

If my car can put out 12 psi and I use a pov to control or limit the boost to like 8-9, which means I'd be activating it quite often, what will this harm? I know the turbo will still be making more than that, but it would anyway regardless of the pov. Besides creeping, 12 should be okay for the stock turbo. Another thing I read is that you might run rich due to the air released by the pov that is still accounted for by the ecu. What is too rich and how bad is it?

Think about this.. the stock ecu will run a good mixture up to 8.6 psi.. if I have an FCD and a pov installed and set to 10, then as the boost rises to whatever, b/c of the FCD, the ecu will only account for 8.6 pounds of boost and the pop off valve will be constantly venting, letting only 10 pounds into the engine. The turbo could be making whatever, but the mixture would still be pretty good. In a sense, they are cancelling eachother out. Is this right?

In general, is there anything I'm missing here about the pov(about the operation)?

 

Yes it wiil. It will overspeed the turbo leading to bearing and/or seal failure. A POV should not be used to control boost. It should be used as a last resort safety feature only, and if you hear it "pop", you should get off the gas immediately.

 

doesn't work. it lets all the boost out when it opens. so it'll go 9-0-9-0-9-0-9-0 every 2 secs...

and you are letting air out that the ecu thinks is going into the engine.

 

okay.. didn't know it worked like that, glad I asked..

so if that's not an option, is there anyway I can restrict the intake more than the stock airbox does? Maybe a poorly made filter?

 

I'm almost certain stock is pretty damn restrictive. What kind of set up are you looking at that you can't control the boost? I'm assuming you have already ported the stock wastegate to the max the stock flap can go? If thats not working there are some places that can weld on a bigger flap.

 

Stock cars don't boost creep. If your car does, you've done something(s) to increase exhaust flow beyond the wastegate's capability. Either sort out your wastegate (port it or upgrade to S5), or undo some of those mods.

 

The restricted intake is a good option for lowering boost....
Its better than a restricted exhaust, since the turbo can still spool up quick...but it limits your max boost.
If you have the stock intake, and you feel that your car is making too much power (or having boost creep) you have two options.
1- Trade in your FC for a Honda.
2- Just cut a flat peice of thin plastic (like for crafts, etc), to the size of the air filter, and cut a few holes in it- then place it over the filter, in the airbox.
Maybe your wastegate or actuator is malfunctioning if you are getting lots of boost creep!

 

I don't know why boost creep keeps getting mentioned, let's say I don't have a problem with that.. let's say my car just puts out a solid 12 psi and I don't want it to be that high. Something like the plastic piece on top of the filter is the kind of idea I was looking for.. I just want to know if this will have any effects besides lowering boost and power. In other words, will restricting the stock airbox more hurt anything, that's all I want to know.

and good lord man! trade for a honda.. sick.. just plain sick..

 

Creep is being mentioned because the stock wastegate fully opens at 5.5-6psi. On S5 the factory boost controler keeps it closed to ~8psi. So any boost levels above these on stock turbo is boost creep - over running the stock wastegates flow.
Now, if you have a boost controller keeping it at 12psi, thats different. But you wouldn't be restricting everything to lower boost then; you would lower your boost controller setting.
So whats your set-up. No one can help you w/ out knowing that.

 

Because up until now, you haven't mentioed why you want to restrict your motor. This question is normally asked by people with boost creep. You’re the first person to ask how to restrict a car that doesn’t have this problem!
If you give us all the information at the beginning, you get the answers you want much sooner.

 

Wow, solid 12 psi... no boost creep there!!

Good idea to make up a sig, or tell us your setup.

There isn't really anything wrong with running 12psi if you have a computer to enhance fuel.. but (I'm assuming you MUST be running an FCD since you made no mention of having a Haltech or anything)
If you are running 12 psi I am assuming you must have a 3" exhaust system, but I'm suprised you are running totally stock intake?
Your car is most likely leaning out like crazy right now....
Something just doesn't add up here!

 

ok, slow down, this is getting way more complicated than it should be. I didn't want to start from the beginning or go into detail because this is a hypothetical situation as of now and I felt it would be irrelevant. All I wanted to know was if it was safe to restrict the stock airbox anymore than it already is.. that's all.

Secondly, I was under the impression that boost creep was any extra boost put out over what you normally run, e.g. if I were to run 12 psi on average than boost creeping would be when it spikes up to say 15. isn't this right?

Now from the beginning, and I'll make this as brief as possible... My car is an 88 TII that is more or less stock (besides a walbro and an aftermarket boost gauge). It runs about 5.5 psi now. I'm about to put on a full 3" racing beat exhaust which should(again hypotheticly) raise my boost up to around 12 psi. There's no doubt that my engine won't handle this now, so I need to take it down to like 9-10. I was hopeing to restrict the stock airbox more to accomplish this. On top of that I'm getting a POV which I will set to like 11-12 assuming that I usually max out at 10. This will of course eliminate the threat of what I thought was boost creep, as far as the engine goes.. the turbo on the other hand could be in trouble, but I figure it will be okay seeing as it's good for a bit more than my engine plus i'll know to get off the gas if the POV goes..

So does this clear everything up? I felt like I mentioned my car and the upcoming exhaust a hundred times and besides being redundant in my head, I just didn't think it was important to my general question.. which btw, I think I got my answer to.. "yes, it's okay to restrict the airbox more, but you'll lose power." I know this, it's just temporary..

 

A POV/BOV (I know, they're different) is NOT a boost control device. It is there to protect the turbo (a BOV) when you close the throttle, or open under emergency boost spike conditions (a POV). The only way to "properly" control boost is via the wastegate. If you don't want to modify the wastegate, you will have to put a restriction somewhere. The airbox is the best place for this restriction.

 

Yep- you can restrict the airbox.
You will also be hitting fuel cut with the 3"- do you have a FCD??
There is no need at all fir a POV unless you are running very high boost levels, and you are racing under full throttle all the time. Under those conditions, a control system faliure, such as the wastgate getting jammed or something, won't result in a 25 psi engine-go-boom!
It's a backup device only. That would be like using the emergency hand brake to stop the car all the time.

You MAY notice a slight dowturn in fuel economy with the restricted box... not sure though...

You can port the wastagate too- it'll help reduce creep to maybe 10 psi or less instead of 12-13....

Oh, and ANYTHING over 5.5 psi is creeping!!! (On the factory wastegate)
We all see a bit of that though...

 

thanks aaron and bam, that's all I wanted to know, but you don't think a POV is good idea for me.. I know not to use it as a boost controller as I learned earlier in this post, but if I were to get the boost down to a steady 9 or 10, then I thought a POV set at 12 would be a good idea, seeing as it's the 12 psi that I don't want my engine to see, then it would be a safety device, hopeing it wouldn't be going off often..

and I do have a RB FCD, but I'm a little reluctant to put it back on, because the last time I tried it, my car didn't start due to a blown ecu. I'm not sure if it was the FCD or something else I was doing..

 

Hmmm, care to explain how this works when the stock boost is set at 7.5psi?


-Ted

 

Sure Ted, the little "~ " wavy thing before the 8 indicates "about."