re-rx7

Im still on stock actuator. Actually its a stock replacement from another 8 turbo. THere is not a gradual decrease in Boost pressure. Holds a strong 19-20 psi all the way up to 6k rpm and drops quickly. Like it was shutoff. I really need to find a gd BC and swap it in.

sparky

iTrader: (1)

Whether your car "runs great" is completely relative and subjective. Did you log boost? If so, please post the boost logs.

When you go WOT, at what RPM do you floor it? Floor it at 2500 in 3rd, or 4th and tell me exactly at what engine RPM the boost gauge hits 20 PSI.

sparky

iTrader: (1)

Incidentally, has your car been tuned for your mods and to run at 20+PSI ? You state that a boost leak test was run. Did you do that test yourself? Do you know what pressure level the test was run up to? It tested leak-free up to x PSI???

sparky

iTrader: (1)

So, I take it that you installed the used actuator yourself. Am I correct in so assuming? Why did you change actuators in the first place? If you did the WGA install, then do you recall if you pretensioned the spring, or if you just installed the actuator rod onto the flapper valve's pivot arm fully extended with no additional tension???

re-rx7

The stock one was bent from previors owner and frozen. Evolution dynamics here in dallas installed it. I tested it myself up to 23 psi. It held for 15+ sec. I will try the 2500 rpm punch today. Pre tension seems gd as the arm is firmly in place on flapper rod. NO play.

sparky

iTrader: (1)

Did the turbo exhibit the same 8 PSI drop in boost with the old actuator that it does now after you made the swap?

I am a little confused when you say that you tested the "new" actuator up to 23#. Did you test it with compressed air and a gauge up on the bench, or did you road test the actuator after installing it on the car?

re-rx7

The old actuator exhibited no boost at all. The arm was seized and the cotter pin had broken off into flapper rod. To solve we replace the hotside with an evo 8 hotside. Same thing. Compressed air and my boost gauge on dash. Soap and water. I have to use a portable tank since i dont have a compressor. Im still trying to locate a knwn wrkin mbc.

connor4200

im having the same issue havnt done a leak test yet but i will post a vid of mine in the next 12 hours or so

sparky

iTrader: (1)

Evolution Dynamics installed the actuator with zero preload. That is why boost tapers down to 10-12#. You determined by performing a BLT that the gate was staying closed, or "holding" until 23#. But, that is only an accurate indicator of IM pressure acting on the WGA's diaphragm. IM pressure does not take into account the dynamic force of exhaust pressure. That is, BLT's don't give an accurate and total picture of WGA function when the turbo is actually building boost.

It may be holding to 23# of intake pressure during a BLT but it is actually opening much earlier(10-12#). BLT's are a good static indicator of pressure on the intake side, however they are not an accurate indicator of seat cracking and lifting of the WG flapper valve because the BLT does not take into account the dynamic force of the exhaust pressure within the turbine housing at the flapper valve seat which is lifting the valve off its seat at a ratio of at least 2:1.

EDIT: furthermore, all variables need to be taken into consideration. For your test to even be a valid indicator of the pressure "seen" by the actuator's internal diaphragm, one has to make sure that the MBC is out of the loop. Otherwise it interferes by limiting pressure entering the WGA port.

sparky

iTrader: (1)

What you really want as a practical matter is to eliminate the boost taper so that you can essentially maintain your peak boost level at or near 20#, right?

To get to the bottom of the problem I would first off remove the MBC for the time being. Install a new piece of 4mm vacuum hose directly from the compressor j-pipe nipple to the port on the WGA cannister. Do a WOT run to establish at what spring pressure the actuator is currrntly set. Then we'll take it from there and start to adjust preload incrementally.

re-rx7

How do you adjust/preload the stock actuator? Un hook and pop the locking nut loose?

re-rx7

Will do this evening.

cazlow

iTrader: (3)

Have you not done a boost leak test? I didn't see anywhere in your posts where you had? You should start there before anything else.

FWIW.... I literally had the exact same issue. I'd hold full boost until 5.5-6k and it would drop to maybe 7-10psi til redline. The car would fall on its face and felt like a dog. My issue was the throttle body shaft seals. Replaced them with Mil.spec tbss and my problems were solved... Good luck.

re-rx7

Blt was done. No leaks.

sparky

iTrader: (1)

I'll post up a how to in about an hour when I get home.