Twin External Vs Single External Wastegates

I see a more people running twin external wastegates, and in fact a trader on here produces a twin wastegate turbo kit, BUT what is the advantage of twin waste gates over a single wastegate ?

Fully divided setup, wastegates/manifold/turbo will spool faster.

I see a more people running twin external wastegates, and in fact a trader on here produces a twin wastegate turbo kit, BUT what is the advantage of twin waste gates over a single wastegate ?

More dependable boost control when making serious power.

Think of the wastegate as a bleed valve. If the exhaust gas is too much for the wastegate, or if the wastegate is slow to react, then you will see a boost spike. 2 of them means that they won't need to work so quickly and the boost is easier to keep in check.

Fully divided setup, wastegates/manifold/turbo will spool faster.

Oooo does it do that too?

I see a more people running twin external wastegates, and in fact a trader on here produces a twin wastegate turbo kit, BUT what is the advantage of twin waste gates over a single wastegate ?

The below is as I understand it, so the theory may be wrong.. but here goes!

The logic applies when you are running a twin-scroll turbo and manifold.

The engine obviously has a specific firing order. In an open/single scroll manifold, some exhaust valves will be closing, when others are open/opening and expunging their gas into the manifold. These exhaust 'pulses' will, in a single scroll setup, interfere with one another and stop the flow of the manifold from being as smooth.

Firing Order: 1 - 5 - 3 - 6 - 2 - 4.

With a twin scroll arrangement, you separate the 123rd and 456th cylinder exhaust ports into two groups, thus the firing order of the engine means that the pulses of the exhaust gas do not interfere with one another. This pattern of separation also means that the timing of the pulses are equally staggered in each port bank, for one full cylinder firing cycle.

The idea of the twin waste gate setup, is to keep these two groups of cylinders separate until they reach the turbo housing/flange. With a single waste gate setup, you have to have both halves of the twin scroll manifold joined where they meet the waste gate...which will remove some of the positive effects of the twin scroll manifold.

In threory it makes a difference. The downside is: increased heat. More complication and less space to work. More to go wrong.

Personally I'm an advocate of the Twin scroll manifold, turbo, with one large HKS 60mm waste gate setup. Tried and tested by HKS themselves to ensure no boost creep, and in a test on supraforums by PHR(I think) the single waste gate HKS manifold out-performed the twin waste gate, all singing all dancing Full Race Model.

Great description from TheTurtleshead! That's just how I see it, too. But I would never really choose a twin wastegate set up myself, lots more weight swinging on a tubular manifold, and packaging it all around a steering column on a RHD car is going to compromise things. It would be nice if a commercial cast manifold existed to run twin modestly sized integral wastegate turbos like on the RB26 engines.

I agree with your sentiment about a decent cast manifold Chris (Wagner tuning do some lovely ones for audis with equal length runners), but two turbos are added weight and complexity that just aren't worth the minimal gains on a road car.

I went through all this research when deciding on my setup. Found a nice simple single turbo/wastegate setup on a cast unit for reliability. Remember this is aimed for 550bhp street car with everyday reliability from the setup.

Remember "KISS" lol

Tim

TB Developments

I'm always reading stuff about cast manifolds and reliability etc, I've been running twin gate tubular setups for years and I've never had an issue with cracking once, full boost at 2900rpm and close to 800bhp is not going to be beaten easily.

I agree to an extent Jamie, but I've also seen plenty of Greddy and HKS manifolds come up for sale over the years which have had repairs done, so it must happen at least occasionally. I would guess the likeliness of cracking increases over time from fatigue caused by weight, movement and heat.

If I were buying a premium tubular manifold, I wouldn't expect cracking for years. If I were Buying decent cast, I wouldn't expect it for probably the remaining life of the car.

Cracking of tubular manifolds is definitely related to the number of heat cycles.....

Ive had my hks repaired, i then built a horrid looking bracket to support the turbo from above and no not off the strut brace;)

Pics?

Pics?

Really? it does look crap but it is functional......i think.

come on lets see it in all its glory

Tim

TB Developments

Really? it does look crap but it is functional......i think.

Yup curious about the mounting points etc.

Ok,

Sorry bit confused here, how can a twin wastegate setup physically spool quicker then a single gate? When they are both closed on spool up?

I personally think if you have the correct size wastegate for your turbo i can't see any real benefit to the twin wastegates setup except it cost a lot more money, less room and more to go wrong for no real benefit.

Sorry bit confused here, how can a twin wastegate setup physically spool quicker then a single gate? When they are both closed on spool up?

I personally think if you have the correct size wastegate for your turbo i can't see any real benefit to the twin wastegates setup except it cost a lot more money, less room and more to go wrong for no real benefit.

It's not the wastegates that make it spool faster, its the twin separate systems that splits the cylinders. The only way to do that is to have 2 complete wastegate systems.

scotts correct here, the purpose of the twin scroll is to keep the pressure waves separate from the cylinders that are out of phase of each other, so if they merge for a single wastegate you are getting cross feeding, so you have to keep everything separate from the engine, through the turbo and wastegates so this is why you need 2. Once it gets from the discharge of the wastegate and the turbocharger turbine it doesn't matter anymore

Tim

TB Developments

....... through the turbo and wastegates so this is why you need 2......

Unless your divider in the wategate feed goes all the way to the valve on the single wastegate setup.

I'm always reading stuff about cast manifolds and reliability etc, I've been running twin gate tubular setups for years and I've never had an issue with cracking once, full boost at 2900rpm and close to 800bhp is not going to be beaten easily.

I was looking at your dyno plots and was aghast at how early you spool and what you make top end.

Before I disappeared for a while it was my goal to get the earliest spool I could at 600hp, and I tried a lot of systems, including ryan's mapping of the vvti system, and always a cast manifold as it made so much difference to throttle response and spool, but nothing comes close to touching your system, it's quite something.

I had a tubular manifold from boost logic, and it just turned to putty eventually, mind you, so did their 4" stainless exhaust. 4 years of use and it was like tissue paper.

John Bailey's new SRD build thread confirms everything you say about boostlogic products.

Agree with most of what is being said here, from a technical stand point that is regarding twin scroll and dual wastegates etc, this advantage is more noticeable on larger turbos, but if you run a smaller setup in the region of 550hp I very much doubt you see any real world gains, in fact if you are not careful with the newer turbos now available you may increase the chance of surge.

If I was looking for big power then Jamies setup is ideal, for 550hp a much smaller single scroll turbo on a cast manifold would be my choice, not only for cost but also for simplicity.

The problem with current cast manifolds for the 2JZ is they are all the log design. This is okay for quick spool, but otherwise the design is flawed, as they're restrictive and encourage high EGTs.

If only Wagner tuning made one for this engine.

http://www.wagner-tuning.uk/ekmps/shops/wagnertuningltd/images/audi-sport-quattro-evo-exhaust-manifold-[3]-38-p.jpg