Measuring stock exhaust restriction

[Multiades]

Originally Posted by twiceblown

okay, Chris, so with the #s you supplied for flapper and diaphragm area, i come up with:

flapper diameter / diaphragm diam / Flap Area / Diaphragm Area / Stock Actuator Spring Pressure / Turbine Housing PSI / Flap PSI / Diap PSI / Ideal Actuator Spring Pressure

34.00 57.00 1.41 3.96 7.00 30.00 42.23 27.70 10.67
38.00 57.00 1.76 3.96 7.00 30.00 52.76 27.70 13.33

You're missing something. The effective diameter of the flapper is actually less than the overall diameter. The flap may be 34mm, but the PORT is only 29-30mm. I was assuming flap diameter - 4mm (29mm=stock, 34mm=TRE, 38mm=bullseye).

[twiceblown]

You're right, Chris.
So, assuming -4mm for port size:

(15psi boost)
34mm flapper; Mani pressure: 32psi; Ideal spring: 8.86 PSI
38mm flapper; Mani pressure: 32psi; Ideal spring: 11.39 PSI

(22psi boost)
34mm flapper; mani pressure: 40psi; Ideal spring: 11.08 PSI
38mm flapper; mani pressure: 40psi; Ideal spring: 14.23 PSI

So, how are the guys like IPO, Jack T, and Monet actually boosting 30+PSI without huge amounts of exhaust energy being wasted through the wastegate port? Granted, i don't know what kind of actuators they're using, nor how much spring pressure they've increased by either preload or washers, but i can't imagine anything less than a huge amount of exhaust energy being wasted due to the "blow by".

[Multiades]

^Keep in mind you're talking about PEAK exhaust pressure. It's only that high around 7k.

That's why boost falls off so bad.

Originally Posted by twiceblown

So, how are the guys like IPO, Jack T, and Monet actually boosting 30+PSI without huge amounts of exhaust energy being wasted through the wastegate port? Granted, i don't know what kind of actuators they're using, nor how much spring pressure they've increased by either preload or washers, but i can't imagine anything less than a huge amount of exhaust energy being wasted due to the "blow by".

There is probably a large exhaust volume being bypassed at higher RPM, but there is also a larger exhaust SOURCE. Leaking 100cfm of exhaust might not be enough to drastically reduce boost at 6 or 7k, while it might at 4 or 5k.

I'm looking at this problem in part as a way to improve existing methods of boost control. External actuators don't NEED to be drastically inferior to externals, but they leave something to be desired in stock form.

Externals are superior in large part because they use very large diaphragms relative to the wastegate valve area (giving pneumatic leverage to overcome drastically higher spring preload), and because they apply boost pressure to CLOSE the valve until boost control is required. Externals are awesome, but the're expensive, bulky, and weren't designed into my setup (nothing against my headers and O2s, they rock).

-Chris

[FWombat]

Originally Posted by twiceblown

Also, FWombat, do you have data for the 3K and below range? I'm curious to see how much variation occurs in the lower RPMs that leads to such a decrease in boost threshold or increase spool with the 3" exhaust (we've all felt the changes). Currently, at 4K, stock pressure drop across the turbine is 11.5psi and the 3" is 11.25psi. So, from those #s, i wouldn't think that any turbo that would spool at 4K or below would see any difference in boost threshold (though the practicality of this obviously is different). Am i missing something?

I went back through my logs, but most of my pulls started in the 3-3.5 K range, so I probably didn't have consistent data below 4k RPMs. However, on the pulls that I didn't have lower-RPM data for, the difference between stock exhaust and the 3" exhaust was negligable until 3.5-4K RPMs.

I think the lower-RPM spool difference between exhausts is more about the exhaust having a smoother, less turbulent path that preserves velocity better.

Originally Posted by twiceblown

I think he said 15psi holding 13 to redline. With those increases in differntial pressures pre and post turbine, i'm guessing that his wastegate is being forced open causing the drop in boost pressure. a log of how the boost solenoid is doing could show that, couldn't it?

The tests were all at about 15 PSI peak dropping to around 13 PSI at redline. I held the boost solenoid at a constant duty cycle in order to get more consistent pressure measurements -- error correction in the boost control makes for a wavy pre-turbine pressure shape as the flapper opens and closes.

As the car gets into higher RPMS and the pre-turbine pressure rises, the WG flapper is absolutely being forced open, as evidenced by the falling boost pressure. I'll go into more detail in another post...

- Brian

[FWombat]

Originally Posted by doctorstupid

I know that TEC has dual port wastegate actuators. one nipple is used to hold it shut with boost before desired boost is reached, then the boost controller flips the ports so that port is no longer pressurized and pressurizes the other port which pushes the valve open. I do not know who makes them, and I've only had the pleasure of seeing them once, on a local 15G car.

Dual port wastegate actuators would be a HUGE help in overcoming the exhaust pressure exerted on the flappers. As boost ramps up, there would be more boost pressure available to help the actuator stay in the closed position, helping to overcome the rising pre-turbine pressure. Boost should be (kind of) proportional to the pre-turbine pressure so the two forces would negate each other to an extent.

I was thinking about cutting open a stock TD05 actuator to see if I could figure out a way to make it dual port, but I don't know if there's any way I could seal up the arm while still allowing it to move.

If we could figure out dual-port actuators, we woudn't even need to run super-strong springs to keep them shut. I really think it's the ideal solution...

[Multiades]

Originally Posted by FWombat

I was thinking about cutting open a stock TD05 actuator to see if I could figure out a way to make it dual port, but I don't know if there's any way I could seal up the arm while still allowing it to move.

If we could figure out dual-port actuators, we woudn't even need to run super-strong springs to keep them shut. I really think it's the ideal solution...

I agree. Unless the arm is already sealed on the stock flapper, there would be no easy way to do it.

It totally prevents the need for strong minimum wastegate pressure (high pressure springs).

That's why externals end up having better control. I wish there was an easy bolt-on actuator solution.

[Highboosted]

Originally Posted by Multiades

I agree. Unless the arm is already sealed on the stock flapper, there would be no easy way to do it.

It totally prevents the need for strong minimum wastegate pressure (high pressure springs).

That's why externals end up having better control. I wish there was an easy bolt-on actuator solution.

It can be resonably sealed, think about the Greddy type s BOV, yea it leaks a tiny bit, but does it affect how the car runs? Heck, I probly could hack a clone BOV so the rod that was the BOV piston attaches to the rod that operates the actuator. Anyone find more info on TEC's wastegates?

[twiceblown]

well, it would have to be sealed pretty good, or at least equal to the other side. Since the additional spring power would have to come from boost, the pressure within each actuator needs to be close.

maybe someone can find a flexible diaphragm made of similar material that can be adapted to the stock arm. On the TD04s at least, there's a washer and a cone that hold the spring and diaphragm in place. putting another diaphragm (i hate typing that word) between the actuator body and the washer would be easy. Connecting it to the arm, on the other hand, would not!

i just had a thought: since both actuators need to see similar pressures from boost, how about machining out a new one (or a hard seal made of brass) that plugs up the large hole. A little bit of grease on the arm, and you would definitely get a good seal without the need for a diaphragm (there's that word again!). The stock hole is about 1/4" and the arm is about 3/16", so make a sleeve that's got an OD of just a bit more than 1/4" and an ID just a bit less than 3/16". Then slap on a fitting and you're good to go. let me see what i can find at McMaster Carr.

[twiceblown]

now, do you regulate boost with a solenoid that switches pressure from each side of the diaphragm or by bleeding off pressure from the boosted side? You also need to make sure that the spring side does not see vacuum otherwise the flapper may open prior to positive manifold pressure. A check valve should do it, though.

[RobBeck]

Even though it sounds like a good idea, I think its just easier to run a heavier spring... unless you find yourself having to purchase an extremely heavy spring to fix the issue. What kind of pressures are you guys running to get this dropoff?

Rob