Stock top mount, beefed up...

[sen2two]

Stock ECU, turbo, motor, ect... The dip in power is from boost dropping from 11psi to 6psi due to stock turbo and wastegate no being able to hold 11psi all the way to 7k rpm. The 226whp run has the most significant dip due to being in 4th gear. The boost went from 14psi down to 6psi.

But i have an upgraded Garrett internal wastegate on the way to hopefully remedy this problem.

[Max777]

Ok, a boost drop makes sense. Would installing a boost controller fix the problem? A garret wastegate, depending on price, doesn't sound like a bad idea.

11PSI? I have a 255lph pump, 750cc secondaries, and an RTEK 1.7 ecu... can I run 11psi then? My gague only goes up to like 6~8psi max right now.

[sen2two]

Originally Posted by Max777

Ok, a boost drop makes sense. Would installing a boost controller fix the problem? A garret wastegate, depending on price, doesn't sound like a bad idea.

11PSI? I have a 255lph pump, 750cc secondaries, and an RTEK 1.7 ecu... can I run 11psi then? My gague only goes up to like 6~8psi max right now.

A boost controller would make absolutely no difference at all. And given your upgrades surpass mine, you should be able to handle 11psi just fine. But to be safe, check it with a wideband to make sure your not leaning out or get some minor tuning done. an safc2 would be fine in your case...

[RETed]

NVM


-Ted

[sen2two]

OK



-Keith

[RETed]

My reply was assuming you were going to replace just the actuator, but when I reread what you wrote, it sounded like you were going to replace the entire turbo...right?


-Ted

[sen2two]

No, im going to replace just the actuator. From my own personal experience, i believe the wastegate is the enemy when refering to our stock turbos not holding boost up top. (along with the restrictive exhaust housing on the turbo. I also believe this is why S4 turbos do not have such a problem with holding boost with there larger less restrictive exhaust housing. all in theory of course) I could explain it my way, but below is from BNR, the turbo specialist refering to the stock Rx7 turbo.

quoted from BNR's website:

"Upgraded wastegate actuators are the best way to keep the boost level from falling off up in the top RPM. There are a few things that can contribute to this issue. The issue is backpressure between the turbine wheel and engine causing the pressure to push against the wastegate valve assembly. This opens the wastegate premature and causes you to lose boost pressure. The more you port the wastegate port, the worse the problem will be. The solution is a higher spring tension wastegate actuator upgrade. This is a quick and cheap way to generate a noticible power and torque gain in mid range RPM while holding boost up in the top of the RPM band. There are a few actuators to choose from and it depends on what boost level you are trying to run. From there we will help you decide which actuator is best for your application."

The one im using is very similar if not, one of the very ones they use. So hopefully it will work. If not lesson learned... Not that any of this has to do with the intercooler though.

[RETed]

Crap, I should've just left my reply then... :P

It all depends on what exactly is causing the boost drop?
If it's due to too small of a turbo, then the actuator isn't going to help.
IIRC, a "modified" WG actuator only changes the boost curve by changing the spring pretension to the wastegate actuator.
HKS used to sell these things, but with the advent of boost control technology, there was no sense offering them anymore.
(Electronic) boost controllers have gotten so good, that messing around with modified actuators is a waste of time.

If the wastegate is the culprit, then this can be confirmed by datalogging your boost levels.
Does the boost levels fluctuate at the top end?
If so, then a stronger spring might help.

Most of us do run EBC's, so it's easy to just adjust the EBC to see if this helps.

If the turbo is just too small, nothing you will do will help.
The actuator isn't going to help.
The EBC isn't going to help either.

There is a quick and dirty way to test this, but I warn you it's dangerous...
Disconnect the vaccum line to the WG actuator and see if this changes your boost levels.
If your boost still drops, you're just going way past the physical limits of the turbo itself.
Obvious dangers of overboosting apply here, so be very careful about how much you mash the gas pedal when trying this.


-Ted

[TitaniumTT]

Or, have someone watch the WG actuator while it's on the dyno. I have the same problem with boost levels falling off up top. I don't have a dip, but it does fall off. I suspect that the spring just isn't stong enough. So, next time on the dyno, someone will watch the vitals, someone will watch the duty cycle, and someone will watch the physical actuator to see if the EMAP is overpowering the WG and actuator and venting too much.

If it is, the search begins for a new actuator.

However, I suspect that with such a violent drop like that and then it coming back, it's something else.

[Max777]

Originally Posted by sen2two

A boost controller would make absolutely no difference at all. And given your upgrades surpass mine, you should be able to handle 11psi just fine. But to be safe, check it with a wideband to make sure your not leaning out or get some minor tuning done. an safc2 would be fine in your case...

Really? I thought that it holds the boost from opening the wastegate untill pressure reaches 11psi, therefore boost should not drop as much?

Or am i missing something here?

Have you tried using one to see what happens?

[TitaniumTT]

If you've got more EMAP than the MAP can hold, it will open the WG even with the spring.

[Max777]

so you're saying the exhaust manifold pressure will force the wastegate door open? I can see that happening, however, a boost controller SHOULD help a little bit. I am curious to see a dyno run with a 10psi setting on the boost controller, I am positive that the power curve would have a lot smaller dip than with just a stock WG/no restrictor in the pressure line.

I guess a BC is not the perfect solution, but it works well enough to merit its use.

EDIT: Anyway, you know a whole lot more about it, so enlighten me with your thoughts.

[Ender]

Yes, the exhaust manifold pressure can push past the wastegate, and it makes perfect sense that this problem is increased whenever you make your wastegate port larger (more surface area for the air to press against, yet the same actuator holding it back). A good EBC should be able to all but eliminate that problem since it will keep the pressure to the actuator low until it actually needs to start limiting boost.