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Rethinking The Wastegate - Synchronic Wastegates

Synapse Engineering Synchronic Wastegate

Aaron Bonk
Mar 19, 2007
0705_turp_01_z+wastegate_engineering+wastegate Photo 1/15   |   Rethinking The Wastegate - Synchronic Wastegates

You won't find the word "wastegate" in the dictionary. It's a bit troubling. Especially for us. This entire magazine is based off of a concept that, officially, doesn't exist-at least according to Webster. But for the most part, we all know what a wastegate is and what it does. It's possible Webster hasn't had time to do some updating in a while. Maybe we can help:

waste·gate ('wAst·'gAt), n. 1. An exhaust bypass valve employed by turbocharged engines used to control boost pressure by means of alternating exhaust gas flow either to or away from the turbine.

There. That wasn't so hard, was it? You can thank me later, Webster.

0705_turp_02_z+wastegate_engineering+engine Photo 2/15   |   We tested Synapse Engineering's new Synchronic wastegate on an Integra GSR engine. At 14 psi, the B18C1 produced 427 hp on Do It Dyno Performance Center's Dynojet. The car makes upwards of 630 hp, but there are two reasons we conducted our tests at low boost: first, traction limits on the dyno limits our accuracy, and second, 14 psi is about the maximum where the conventional wastegate used wouldn't produce creep.

Major breakthroughs in wastegate design and engineering have been few and far between as of late. Yes, valve and valve seat materials have been tested, changed and patented, diaphragms have been toughened up, and of course aesthetics have been played with, but the simple yet effective principles of the conventional actuator-type wastegate remain just that-simple and unchanged. But there are always those who have to go and make a simple thing more complex. And so is the case with the engineers at Synapse Engineering, the company responsible for redesigning the conventional wastegate.

The wastegate gets its name from the fact that it does its job by wasting a portion of the engine's exhaust gases. For a wastegate to work, all it has to do is bypass a determined amount of exhaust gas destined for the turbine to some other place. This, in turn, controls the turbine's shaft speed, which determines how much boost the engine sees. Since a turbo system is sort of self-feeding (the more boost that's made the more exhaust gases are made) both variables are regulated by manipulating just one, boost, through exhaust flow. The higher volume of gas the wastegate bypasses, the slower the turbine spins. The opposite is also true. There are a number of problems associated with the conventional wastegate design, but the biggest is that it wastes exhaust gas energy to do its job. Wasting something to get something isn't always the best way to get a job done, but it's unavoidable when dealing with wastegates. There's nothing we can do about that. At least not for now.

0705_turp_03_z+wastegate_engineering+diaphragm Photo 3/15   |   The Synchronic wastegate does not have a rubber diaphragm, so there's not much here that can wear out. At full valve lift, you can see the four individual chambers and surface areas of the wastegate. Each chamber is sealed off from the rest of the wastegate with o-rings and grease, both proprietary to Synapse.

But there are other problems inherent to traditional wastegates that can be fixed. One such problem has to do with valve lift, and is one that Synapse has actually improved upon with its Synchronic wastegate. A conventional wastegate valve begins opening much earlier than we'd actually like it to. This way, they do their job at, say, 20 psi by beginning to open at, say, 10 psi. Even though we don't want it to open at 10 psi, or tell it to open at 10 psi, it does anyways. If it didn't, we'd see more than 20 psi at the top. The point at which the valve initially opens is referred to as its cracking pressure-our 10psi point in this example. Cracking pressures for most external wastegates are generally about half of whatever maximum boost is. As soon as the valve is cracked open, exhaust gases that would otherwise continue to spool the turbine until maximum boost is reached are wasted. This will either make it take longer for the turbo to reach maximum boost or not let it reach that point at all. Either way it's bad for power curves and for performance.

Conventional wastegates aren't complex. The design consists of two separate housings, one of which houses the valve, which the exhaust gases flow past. The other side contains a spring that preloads itself against the valve to keep it closed. This is also the side that receives the boost pressure signal. A plate and rubber diaphragm are fitted beneath the spring and fixed to the top of the valve. The spring applies pressure to keep the valve closed, but when boost pressure exceeds spring pressure, the diaphragm and plate force the spring to compress and open the valve. A spring that, when compressed, exhibits 15 pounds of force will open the exhaust bypass valve once that amount of pressure is exerted onto the diaphragm ... sort of. The problem with conventional wastegates is that the rubber diaphragms stretch, can tear, and exhibit durometer changes as temperatures change. Pressure is wasted on stretching the diaphragm before the valve is even opened. This is bad for boost control. Besides the fact that rubber diaphragms eventually wear out, tear, get softer or harder, even in new condition they're designed to stretch. This means that boost pressure diverted into the wastegate must stretch the diaphragm before the valve can even begin to move. It makes for slow response time when it comes to boost control, and as temperatures change, it can actually respond differently to equal boost pressures. In other words, as temperatures rise, it can take longer to stretch the diaphragm and open the valve. And, at the very least, it's unpredictable. In the amount of time it takes the conventional wastegate to fully stretch the diaphragm and begin to crack the valve open, the Synchronic's valve is fully opened. This is because the Synchronic wastegate says goodbye to the rubber diaphragm. It says goodbye to the wastegate as we know it.

0705_turp_07_z+wastegate_engineering+opening Photo 7/15   |   Rethinking The Wastegate - Synchronic Wastegates

Now would be a good time to talk about just how far a wastegate's valve opens, and how that helps or hurts things. When a wastegate is unable to bypass a large enough volume of exhaust gases, excessive boost will occur. This is known as boost creep. The common fix is to fit a wastegate with a larger valve and exhaust opening to the turbo. While the larger valve fix works, it doesn't really get to the core of the problem, and in turn, it can actually create an entirely new problem. Large-valve wastegates will consistently regulate and prevent over-boost, but once boost is stabilized they tend to release too much exhaust gases and waste what could be used for additional turbine spin. More power lost here. The Synchronic wastegate uses a self-centering piston instead of a diaphragm. The piston reacts more quickly and also allows tuners to swap springs for different rates while keeping boost levels the same. This means you can adjust how fast the valve reacts per pound " of boost. The Synchronic wastegate's billet aluminum piston negates the need for a valveguide, and also allows the valve to spin. There are two benefits here: first, eliminating the valveguide ensures against any binding or sticking when the wastegate gets older and exhibits some corrosion, and second, it allows the valve to spin 360 degrees for even wear on the valve and seat. Conventional wastegate valves don't spin, so hot spots and wear usually build up in certain places, causing just a leak at best.

One feature that makes the Synchronic wastegate unique is its interchangeable valve seats. Synapse offers different sized seats, each effectively changing the wastegate's inlet diameter and ultimately the volume of air that will pass through it. This allows users to fine-tune even further, not having to compromise with what the existing diameter of the wastegate is. Altering the power curve is easy when seat sizes can be switched as flow characteristics for different sized engines and different sized turbines will require varying amounts of exhaust gas bypass. The wastegate includes various sized seats, including 39mm and 50mm ones, which means you won't have to pay for any upgrading as far as wastegates go when you turn up the boost significantly.

0705_turp_08_z+wastegate_engineering+opening Photo 8/15   |   Conventional wastegates exhibit very low valve lift. It's not necessarily the size of the opening, or the valve, but the valve's lack of lift that can cause creep. Unfortunately, the diaphragm design won't allow for valve lifts like the Synchronic wastegate does.

The Synchronic wastegate's valve housing is manufactured of 304 stainless steel, not 347 stainless steel or 254 alloy like most wastegates. Alloys like 347 and 254 have a high nickel content, which contributes to thermal expansion. The 304 alloy has a more balanced nickel and chromium level, which doesn't allow for such levels of thermal expansion and, in turn, helps fight off boost creep from warping and fatigue. The 347 and 254 alloys are stronger from a structural standpoint, but since the wastegate doesn't carry a structural load it doesn't matter here. The Synchronic's valve and valve seat are also rather unconventional in their materials. For example, 400 stainless steel was selected here instead of the more common Nitronic stainless steel alloy. The 400 alloy's high chromium content helps stabilize the valve's steel at high temperatures, unlike Nitronic alloys that are high in Nickel and allow for thermal expansion, resulting in valve sticking under extreme temperatures.

The Synchronic actuator consists of four varying-sized surface areas inside, not two equal ones like conventional wastegates have. As boost pressure is applied to a surface area, a force is applied and the spring compresses, thus lifting the valve. The Synchronic wastegate's varying surface areas and ports make for a number of different boost combinations that can be applied without the need for a controller. All that's required is splicing the lines together and routing them to a pressure source on the engine. This all controls how far up the valve moves, not just how many pounds of boost the turbo will produce. The conventional wastegate is also different in this respect. Rates can be changed by swapping springs but remain dependent on the amount of preload. Also, as spring rates increase here, and more boost is made, the diaphragm has to stretch more, resulting in a valve that doesn't lift as much and possible boost creep. This all determines when the wastegate will open and just how much boost the engine will see, so it's got to be right. With the Synchronic wastegate, users can adjust spring preload and spring rate interdependent of one another as well as control how the valve rises, and how high it rises, as boost climbs. This increases response time and wastegate flow characteristics and should be tailored for individual engines.

0705_turp_11_z+wastegate_engineering+valve_seat Photo 9/15   |   One of Synchronic's add-on valve seats. It's really easy to pop out existing seats once the wastegate's been warmed up and used. Just don't grab it while it's scolding hot.

So how does it work? We tested the Synchronic wastegate on an Integra GSR engine making around 430 hp at 14 psi. The B18C1 was fitted with a competitor's conventional wastegate that uses a 40mm valve. Pushing the engine past 14 psi created much more boost than we needed since the conventional wastegate's valve had minimal lift, which resulted in boost creep. In order to replicate the situation as best as we could after switching wastegates, we kept the GSR's boost level at 14 psi with the Synchronic wastegate installed. If we had " more time, we would have liked to have retuned the AEM engine management and cranked up the boost with the new wastegate. Instead, we performed some comparison tests at low boost and got ourselves comfortable with the new wastegate. Without any other changes, the Synchronic produced more torque and horsepower after 6500 rpm. We can attribute this to the fact that we were able to tailor the valve seat size that worked best for our combination. The Synchronic allowed us to relieve just the right amount of exhaust pressure to stabilize 14 psi. If we simply bolted on the biggest wastegate we could have found, we likely wouldn't have seen increases at the top end since too much exhaust gases would bypass the turbine. Sure, boost would have been controlled either way, but at the expense of lost exhaust gases that we could have used. And we know that the smaller wastegate wasn't working since boost creep was inevitable at higher pressures.

The variables of the Synchronic wastegate seem almost endless. Between valve seat diameter changes, spring preload and rate adjustments, and port/chamber configurations, there is a setting to suit just about any powerplant we've ever come across. Maybe now the word wastegate will finally be added to the dictionary.


Synapse Engineering
San Diego, CA 92121
By Aaron Bonk
342 Articles



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