Mike Murcia

I see posts about updated wastegates, and how, even with an electronic boost controller blocking all boost signal to the wastegate, you can get increased performance by upgrading the WG. What is the reason here? I know that the stock WG starts to open and bleed boost at ~4 psi, but if you don't give it any boost signal until a set boost pressure (say 15psi), how can the wastegate be hindering performance? Unless the stock WG opens with exhaust pressure alone (no signal from the pressure port), I can't see the advantage to getting a new WG if you have a reliable boost controller. Any thoughts?

Danno

"how can the wastegate be hindering performance?"

That's because the wastegate opening is a dual-function of both diaphragm pressure and exhaust pressure. Even with zero pressure in the diaphragm, the valve can still be pushed open by exhaust-pressure, which increases with RPM.

Ideally, a boost-controller must sense both intake boost-pressure and exhaust-pressure and adjust the diaphragm pressure accordingly. This can only be done by an electronic controller that will bleed off diaphragm pressure as RPMs increase in order to compensate for the exhaust-pressure. Thus, the pressure on the valve will be held constant.

So here's what the stock-wastegate looks like with a simple manual controller:

Notice that the manual-controller only responds to incoming boost-pressure from the wastegate. The higher the boost, the more the controller opens in response. But it has no idea what the exhaust-pressure is, thus it's function is additive on top of the exhaust-pressure. In the upper-RPMs, notice that the exhaust-pressure by itself is more than necessary to open the wastegate, thus the dropping high-RPM boost.

Now if we were to shim the stock wastegate, or install an aftermarket one with stiffer spring, we can increase the amount of pressure needed to open the wastegate-spring, and we also lower the effect the exhaust-pressure has on the wastegate valve:

Notice that the manual boost-controller still responds the same way, only opening in relation to incoming boost-pressure. Even with a stiffer wastegate spring, the manual boost-controller will still allow too much pressure to enter the diaphragm and cause a high-RPM boost-drop due to increasing exhaust pressure. Several people have reported recently that even with their Tial wastegates , they were getting a high-RPM boost drop. The solution was to increase the spring-tension even more. Thus pushing further away the effect the exhaust-pressure has on the valve.

The optimal solution is to have a smart controller that measures the boost-curve and adjusts the pressure at the diaphragm to hold constant boost. This is an electronic controller with fuzzy-logic that can learn from previous runs. It will open up the wastegate initially to dump boost at the turbo's sweet-spot on the compressor map. Then as the turbo runs out of steam in the upper-RPMs and exhaust-pressure increases, it will actually dial back diaphragm pressure to zero to compensate:


Notice the effect this has at various RPMs. With a manual-controller, it will let through X-amount of boost to the diaphragm at both 4000rpm AND 6000rpm if incoming boost is 18psi and you really want 15psi. The effect of letting through constant pressure in response to the same boost-level, is that the upper-RPMs will see the wastegate opening too much. With an electronic controller, 18psi present at the inlet at 4000rpm will result in X-amount going to the diaphragm to open it, but that same 18psi at 6000rpm will have very little getting past the controller as it tries to clamp shut the wastegate in the upper-RPMs to preserve boost; it learned from the previous run if boost dropped.

pk951

With a tial wg and manaul boost controler you won't have a problem holding 15 psi or 18 psi, but by that time, the turbo could be out of it's effeceny range creating excessive heat in the charge.

Mike Murcia

Danno - excellent write up. Very imformative. So the only real advantage to getting a new (stiff spring) wastegate is if you do not have a fuzzy logic boost controller with a shimmed WG. Right?

Sam Lin

You need a dual port wastegate with an electronic boost controller for best results so the controller can force the wastegate open and closed as needed.

Sam

Danno

"Very imformative. So the only real advantage to getting a new (stiff spring) wastegate is if you do not have a fuzzy logic boost controller with a shimmed WG. Right?"

Nope, you always need a stiff spring, regardless if you've got a manual or electronic controller. If you look at the transition from the #1 to #2 pictures above, you'll see that in #1, even with zero input from the boost-controller, the exhaust pressure will push open the wasteate valve. In going to a shimmed spring in #2, you'll see that's there's sufficient tension to keep the wastegate valve shut even with exhaust-pressure (stiffer-rate spring even better).

"You need a dual port wastegate with an electronic boost controller for best results so the controller can force the wastegate open and closed as needed."

Yes, an electronic boost-controller is light-years ahead of a manual unit. BUT, dual-port vs. single-port is irrelevant. Take a look at this diagram of a Tial wastegate:

The only thing that ever closes the wastegate valve is the spring. There is never ever any extra force closing the valve other than the spring no matter how you hook up a manual or electronic boost-controller in either single- or dual-port mode.

The primary benefit of dual-port configuration is with the manual pressure-regulator valves in the #3 picture above. Since it always lets through pressure to the wastegate and cracks it open prematurely, you won't have boost-spikes. But max-boost will build slower. For the fastest turbo spool-up at the lowest RPM possible, you want to use a manual check-valve or electronic controller in single-port mode with a stiff spring. If you want 15psi with a Tial, then get the 1-bar spring. Running 18-psi, then use the 1.2-bar spring.

Sam Lin

Danno, with a dual port wastegate and EBC, my EBC is hooked up to both ports of the wastegate with dual solenoids, so if it's not clamping the wastegate shut with boost, it's holding it open with boost. That's the fastest spooling.

Sam

krickmann

Yes, doesn't the dual solenoid style EBC change the operation of the #3 diagram?

SehrSchnell

Okay..let's do some engineering here... If you you have dual port wastegate and the manifold pressure is applied to both sides of the diaphram, the pressure differential (plus the minor exaust pressure on the back of the valve) minus the spring force is what actually opens the wastegate. In a single port, it is purely the manifold pressure (not differential)(plus the minor exaust pressure on the back of the valve) vs the spring force that opens the valve. A dual port wastegate has the help of the boost on both sides of the diaphram to balance it's opening. Controlling the differential pressure is somewhat easier than a single port gate plus the required spring rate is lower.

87944turbo

I have been looking for an explanation of EBC vs. MBC for a while. Giving this thread a bump b/c its thorough and technical! Am I the only one that misses having more threads like this?

hally

i've set my boost control up like this, combining danno's diagrams #1 and #3.
My boost is pretty steady at 15psi all the way to 6300rpm. Maybe due to less exhaust pressure it is a little higher at lower rpm. Switched up to a 1 bar tial spring.

RK951

Hally,
Just curious but why do you need the reliaboost inline when you already have the MBC set at 15psi and a 1bar(~15psi) spring?

hally

Hi Rick,
I had the reliaboost lying around collecting dust and thought with the length of the signal hoses down to the wastegate i though i may as well put a check in there close to banjo bolt. Hard to say if it made any difference. What definitely did make a difference though was going from 0.8 -> 1 bar spring in the Tial, i was getting high rpm boost rolloff with the 0.8 bar spring.

RK951

Thanks Hally. I've sort of contemplated the same thing. It would be interesting to see a dyno run with and without the reliaboost inline.