13bpower

Looks like it would be a great, cheap way to solve to boost spike problems that modified s4 T2's have.

[url]http://www.rx7.com/cgi-local/2catalog.cgi?cat=9&part=5[url]

Anyone have this? Should I get it?

BlackRx7

I think its a good idea but much $$, I'd rather just leave my wastegate open..

13bpower

Over 600 posts and I still cant get a link to work! Damn my incompetence!

Form what I have read people have problems with boost spike even when the waste gate is fully ported. Is this not true. I'm still learning here, so what am I missing?

NZConvertible

Pop-off valves are only used as a back-up safety device. They should never be used to control boost, because every time they operate they overspeed the turbo. This would quickly lead to bearing failure if it was always popping off.
S4's actually suffer from boost creep, not boost spikes. The only way to cure this is to make the wastegate flow more exhaust gas by porting it.

NZConvertible

If the wastegate's too small it'll still overboost. Plus it'll be very sluggish at low revs. Bad idea.

13bpower

Creep, Spike, I thought is was the same thing! What is the difference? Porting the wastgate... will that have me running safe with a intake, and a straight through turbo back exhaust? Would my boost be at 9-11#?

Rotary Dawg

Well if you had a ball bearing turbo then a pop-off valve would work wouldn't it?

Scott 89t2

think of a pop off vavle as a fuse...

it's incase a vac line pops off or breaks it goes off and you don't blow your engine.

it can't be used to control boost.

13bpower

Exactly what I was thinking. I am concerned with the boost going crazy for whatever reason any blowing my engine up.

So the pop off valve would prevent that from happening, correct?

Set boost at 10# and pop off valve at 12# to make sure my engine won't spontaneously explode.

Cheers!

ask jims5434 why u should have one

marcus219

http://www.rx7.com/cgi-local/2catalog.cgi?cat=9&part=5

Scott 89t2

as long as you never go over 10psi...
which you probably are. which is why you are trying to get it. but that's not what it's for...

it should never go off while driving.

13bpower

It should never go off when driving? Now I'm confused! When does it go off? What can I do to 'control' boost?

NZConvertible

Boost spike is when boost shoots past the set max point and then falls back to where it should be. On a graph it would look like a spike. It's caused by the boost control system not reacting quick enough to rapidly rising boost. Sometimes this can be a good thing, because it results in a more mid-range torque. Because it occurs at lower revs you don't run out of fuel.
Boost creep is when the boost rises to the set max and levels out, but then continues to rise as revs rise. It's caused by the wategate being too small to bypass enough exhaust gas to keep boost under control. With as ported S4 wastegate you should replace the flap with a bigger one so you can port it as big as possible. Those who port it only big enough for the stock flap still have problems, just not quite as bad. That wouldn't make any difference. BB turbos work exactly the same as plain-bearing ones.

Scott 89t2

if goes off incase something else breaks. so it is set higher then what the boost goes to. like a fuse I said. do you understand what a fuse does? do you blow fuses everyday while driving? no.

13bpower

I understand the fuse part, but wouldn't these 'things' break while driving?

Also the description on the link above is contradictory from what is being stated here. That is causing the confusion.

Turblown

iTrader: (12)

But don't those leak often?

BlackRx7

sorry but i'd rather have less boost respones at low rpms than a blown motor any day

NZConvertible

You don't understand. Holding your wastegate open will not have any effect on boost creep. It will still be too small. It will creep just as bad, but it'll have very poor boost response. Like I said, bad idea...

NZConvertible

From that link:

"Protect your motor from too much boost with the GReddy Pop Off Valve. A great safeguard against wastegate failure or boost creep, the pop off valve releases any boost above your desired limit and helps protects your motor from a costly rebuild. "

What they say is technically correct, but to install one of these to protect against boost creep is a bad idea. If your turbo has a problem with creep, then it will have that problem every time you want full boost, meaning you're relying on the POV to keep boost down. This will eventually kill your turbo, as I said above.
A wastegate is the proper way to control boost. You should do whatever it takes to keep boost down (wastegate mods, intake/exhaust restrictions, etc) under normal conditions, and can use a POV as insurance in case something goes wrong.

Turblown

iTrader: (12)

But don't pop off valve's leak boost???

13bpower

Thanks for the clarification NZ. Everything is clear now.

NZConvertible

Not until they reach your preset boost point. Unless it's broken...

rx7freddie

ok everyone on here seems like that know what there talkin about i was wondering if u have a turbo 2 getto tid and airbox still on it and when u try to push the car like high rpms it seems like it doesnt want u to go higher then 5 smothly . what coudl that be

Scott 89t2

well stock boost is 5psi on the 86-88 so....