Dual wastegate, advantage and disadvantage

[silvester_e4]

Im about to upgrade my headers and one of the mechanic in the shop suggesting that i should have 2 wastegate for the stock twin scroll turbo.
My questions are:
1. Is it recommended to have a dual wastegate for a twin scroll turbo?
2. What are the advantages and disadvatages of this kind of setup?

any suggestion/comments would be very much appriciated.

 

[evopwr]

Just copied a slab of text from the internetz:

dual gates are usually used in split scroll (aka divided) setups...the reason behind it is to keep the exhaust pulses of each separate from the other to maximize the pulse energy...when you take a divided setup and merge the sides together you are effectively making it an equal pressure manifold and no longer a true divided setup...the only way to use one gate w/ a divided setup would be to merge the two sides together and have it divided all the way up to the wg's actuator...ive seen one or two done properly...but most just opt for dual 38's or 44's for ballas

sometimes dual gates are used on a typical merge setup for better boost control...but nothing a 44mm or 60mm single gate shouldn't be able to handle

Advantage: less pressure drop, although insignificant in 99% cases
Disadvantage: $$, less room, $$

 

[dakiller]

If you want to take advantage of the twin scroll, you really need the 2 wastegates. Twin scroll has the advantage of having effectively 2 separate turbine wheel characteristics where one half is designed to spool up quick at low rpm/flow and the other is for the high rpm/flow power to keep it going through the top of the power band. It is nearly like having twin turbos all in one.

If you don't keep the sides completely separate then you won't be taking advantage of the twin scroll and you may as well just merge all the pipes.

 

[evopwr]

if the manifold is designed properly 1 wastegate is adequate for twinscroll. ie separate outlets for each 'scroll' which then merge at the wastegate.

 

[MDK87]

Isn't the point to keep the phased outlets seperate until it reaches the turbo? And the wastegate must come before the turbo...So then - "If you don't keep the sides completely separate then you won't be taking advantage of the twin scroll and you may as well just merge all the pipes. "

Is it really comparable to having twin turbos though? (I assume you mean sequential)
It's not like (4cyl example) you're only using two cylinders for low and then high RPM. At any RPM point, you're always using the gasses from 4 cylinders to drive the turbine.
Unless there is some way of tuning the runner lengths to get this effect?
Or is the turbine profile somehow manipulated to provide this characteristic?
All in all it just seems like a slightly more efficient way of running a single turbo.

 

[Rockabilly]

Isn't the point to keep the phased outlets seperate until it reaches the turbo? And the wastegate must come before the turbo...So then - "If you don't keep the sides completely separate then you won't be taking advantage of the twin scroll and you may as well just merge all the pipes. "

Is it really comparable to having twin turbos though? (I assume you mean sequential)
It's not like (4cyl example) you're only using two cylinders for low and then high RPM. At any RPM point, you're always using the gasses from 4 cylinders to drive the turbine.
Unless there is some way of tuning the runner lengths to get this effect?
Or is the turbine profile somehow manipulated to provide this characteristic?
All in all it just seems like a slightly more efficient way of running a single turbo.

One cylinder firing into one side of the twin scroll maintains it's velocity/force better than one cylinder blowing into a large single scroll funnel.

But the runners must alternate left/right, left/right to balance the force. The 2 merges need a wastegate runner coming off each.
If you branch the 2 wastegate runners together for 1 ext wastegate, the twin scroll housing gets balanced by the merge before the gate.
Twin scroll technically gets a better 60 footer & earlier spool for cornering etc.
PS: 2 independent wastegates will only balance 2 cylinders each. It won't balance the whole turbine & 4 cylinders at one time.
Cheers

 

[MDK87]

So does that mean a twin scroll vs single scroll (all other things being equal) will provide a more linear power delivery but ultimately provide a lesser peak HP value?
I guess the idea is that you'd just upsize the turbo to compensate for this and get as close to the best of both worlds as possible..

 

[Rockabilly]

So does that mean a twin scroll vs single scroll (all other things being equal) will provide a more linear power delivery but ultimately provide a lesser peak HP value?
I guess the idea is that you'd just upsize the turbo to compensate for this and get as close to the best of both worlds as possible..

Yes more linear, but like a Cyclone dual runner inlet, works earlier, but drops off up high.
They shoulda made a combination of both the above in & out. Torque like a diesel.
Cheers

 

[MDK87]

Good stuff Aldo

 

[4piknup]

But what if the wastegate pipes were seperate almost to the gate valve. Like siamesed. Then the gasses/pressurewaves have little chance of reversion and interfering with the other chambers.
Or you could have a tuned length on the gate merge so the reversion pulse has a extractor effect.

But, also consider this whole part of the system is under pressure and these gasses will have some inertia to them

 

[Rockabilly]

But what if the wastegate pipes were seperate almost to the gate valve. Like siamesed. Then the gasses/pressurewaves have little chance of reversion and interfering with the other chambers.
Or you could have a tuned length on the gate merge so the reversion pulse has a extractor effect.

But, also consider this whole part of the system is under pressure and these gasses will have some inertia to them

2x 32mm OD wastegate runners can be used to merge just before a 45mm ext wastegate door.
You're wasting a combination of the 2 runners through the volume of 45mm for waste velocity.
Cheers

 

[MDK87]

Or you could just vent through one tube if you're cheap like me and don't want to buy two wastegates. Although doing so will probably raise your minimum boost level.

 

[khubner1]

theres another thing you can do with a twin scroll and thats a trick boost threshold reduction system

i had read of an American tuning house experimenting with a massive twin scroll turbo on a 2jz engine. what they were doing was feeding all 6 cylinders into a single scroll of the turbo until a boost or manifold pressure was obtained at which point the second scroll opened up to allow a higher peak boost and turbine speed to maintain boost pressure. the desired result was bringing the turbo onto boost much much sooner than it otherwise would have.

i wish i could find the article for you guys as it would be a cool little thing to have in our cars allowing use to run larger turbos just like smaller ones

 

[4piknup]

V.interesting k

 

[GeoKez]

Saw a video somewhere not long ago about a car manufacture using something like that K. They had a twin scroll turbo that uses an actuator to open the second scroll when there was enough gasses, spools like a mofo. All 3d printed. Big $$. Might have seen it on 4g, not sure.

 

[GeoKez]

http://youtu.be/DNedUZxP8NU

 

[MDK87]

3D printed turbos... Never thought I'd see that. Mind = blown.

 

[Benzo4gT]

The cleaner pops in at 2:40 to mop up the drool :drool:

 

[4piknup]

3D printed turbos... Never thought I'd see that. Mind = blown.

Printed with the moving parts printed inside them...wtf.
I always say if someone put it together, I can pull it apart, fix and reassemble. Not this time

 

[4piknup]

There was another video from same guys explaining how they 3d print titanium and other metals. Awesome.