Boost Creep

[b4black]

I have heard several people comment that they can get up to 10, 11, and even 12 psi by "keeping their foot into it". I was seeing this also. If I removed my exhaust and replaced the air box with a K&N cone, I could get up to 12+ psi with no problem. This isn't what is supposed to happen! The stock wastegate actuator should limit boost to 9 psi and no more. If it goes much higher, then the boost is "creeping up"

At 9 psi, the WG flapper opens and relieves exhaust pressure away from the turbine. If the hole is too small, then not enough pressure is relieved, and boost continues to rise. This is boost creep.

I am starting to think that this is a common problem. Or at least on all 82/83 cars, since in '82 the turbine was made smaller than previous years. The cure is to enlarge (port) the WG hole just a little. Unfortuanately this requires removing the turbocharger.

While higher boost is good, creeping boost is not reliable or consistent. A ported WG hole should give rock steady control, insuring the boost goes up to and not beyond where it is set.

 

[bill]

Is the boost really creeping?when you removed your exhaust and changed the air filter and the boost increased did it always run higher 12+ when you were getting on it or did it vary each time,one time 9 then 12 then 10 or was it always 12+.you see if it varys then i would say the wastegate is haveing a hard time controlling boost,but if it stays somewhat constant with the stuff removed and then with it all back on again it stays at lets say 9 psi constant then i would say theres nothing wrong with the boost control.buy removeing the exhaust and K&N filter you have just increased the vilocity at which the engine can now operate at regardless were the boost is adjusted at.for all we know the boost was set at 12psi but when the factory puts on the cat back exhaust and that joke of a air box which i bet removeing that alone would in crease boost a little.i don't know how any air can get though that hole.I'v seen four cylinder cars with a bigger air intake than that thing.just like if your secondaries don't open and your pulling just from the primaries your boost probabley won't even hit 9psi for the very simple reason that the engine can't breath.just as if you put a fourbarrel carb on once was a two and remove the exhaust manifolds and put headers and duals on a stock engine,it will get faster (with the proper jetting)even though nothing else has changed.I had a chevy 350 that i did this exact change over to and the car dropped half a second and i did nothing else to the engine.a turbo engine is know different.it goes to show how restricted the engines really are in these cars and proves that theres plenty more to come.In conclusion I think these cars are set higher then 7 to 9 psi stock it's just the restrictions on the engine don't let it get there.thats why we use bigger down pipes and ram air inductions.

 

[GNVAIR]

Hey Rich,
I was curious if the 81-83's used a waste gate solenoid to control boost like the 84-87 cars do. This can also be a problem. Another thing could be running the engine too lean at WOT.
If you decide to open up the wastegate hole, try calling ATR. They sell oversized incanel pucks for like $10@.
Just make sure not to open the hole up too much. I think .900 is where you want it to be.

 

[b4black]

bill,

I agree with most of what you're saying. I do think the intake/exhaust restrictions are controlling boost to an extent.

What I see when I go to WOT is the boost shoots up to 9, then slowly climbs from there. The WG is opening, but is not stopping the boost from rising, just slowing it down. With the air box and exhaust on, it will only go to maybe 10. With things uncapped, it will make it to 12, but this is inconsistent. (I thought I must have blown my actuator.)

So the intake/exhuast is the boost control, but it really should be the WG. When I switched to an adjustable actuator, the boost shoots to eight (or wherever it's set) and then creeps from there. I guess this wasn't a problem on stock engines, since they couldn't creep far above 9 and nobody would ever know it without a boost gauge.

Lee,

We don't have the soleniods like the SFI cars. I was hoping I could just open the hole as big as possible with the stock puck. Also flaring (bellmouthing) the inside. I also want to experiment with an in-line relief valve.

 

[fc227]

Rich

You may need to enlarge the waste gate hole that macthes up with the puck.

I had bad boost creep after the exhaust was modified. , The wastegate hole was only 1/2" diameter , I enlarged it to just under the size of the puck .

Problem solved .