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Holset HX35 twin-scroll...two wastegates?

BrandonEchols

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Hey guys, been doing some research on turbo setups, and one the piqued my interest was the HX35.
This would be down the road a bit, but I want something that will reliably put down around 400hp, and be well within it's efficiency range, and have room to grow.
I'd rather run 15-20 psi to make this number than close to 30.
Looks like I can get a T3 or and T4 flange on the hotside also, and I'd definitely want to keep the twinscroll for the sake of spooling time (not sure if the T3 or T4 would be better for earlier spooling, anyone?)
Question is this: Would I need to run two wastegates for the twin-scroll aspect of this thing?
I was thinking I might use a DNP tubular manifold (I believe they are fully divided) with whatever flange I decide on, but those only have accommodations for one wastegate. I'd like use just one if possible, but I've heard some talk that one wastegate effectively renders the twin-scroll aspect worthless, which I definitely don't want.
I'm just looking for some ideas on how this would work...anyone?
 

boostedinaz

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Not a 100% needed. If you can get a manifold built with piping exiting each side of the mani and joining into a single pipe with the wastegate on it you could get away with a single WG. Probably not the easiest way to go since I don't think to many people have an off the shelf mani like that.

EDIT: It likes like DNP made one like I described.

dnpt4.jpg
 
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onesickcrx

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The picture above with one wastegate makes it not a true twin scroll, because the pulses are now combined. So there for you have a nice divided turbo and manifold that controls the boost together which means its just like having a regular manifold and turbo
 

BrandonEchols

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Quoting onesickcrx:
The picture above with one wastegate makes it not a true twin scroll, because the pulses are now combined. So there for you have a nice divided turbo and manifold that controls the boost together which means its just like having a regular manifold and turbo



Is that true even if they are divided all the way up until the wastegate?
I have a small understanding in the reading I've been doing, about what 'crosstalk' is...but if it's fully divided up until the wastegate actually attaches, is this still the case?
 
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4thStroke

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I believe that as long as the pair of runners if joined before the hotside, it's not a true twin scroll.

Twin scrolls can be tough to beat, but unless you have deep pockets, it can be tough to take that route.
 

cheekychimp

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Do you really need to go external waste gate if you are only hoping for 400 hp and 20 psi. The OEM Holset twin scroll turbo housings were not designed to be externally gated as far as I know. If you want to keep things simple and are prepared to do some' fabrication you could also consider one of these.

Quick Spool Valve

It requires a divided turbo housing but an undivided manifold. Essentially it allows you to have a 1.00 AR housing which spools like a .55 AR but loses nothing up top. I personally think it has a lot of advantages over a twin scroll setup especially in our cramped engine bay but it would require a modified downpipe as the valve will drop the turbo anything up to an inch lower which could affect O2 housing to down pipe and even intake pipe fitment.

I'm pretty sure at some point I will try this but I've got too much other stuff to finish first before I start changing the turbo setup again.

Paul.
 

boostedinaz

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Quoting onesickcrx:
The picture above with one wastegate makes it not a true twin scroll, because the pulses are now combined. So there for you have a nice divided turbo and manifold that controls the boost together which means its just like having a regular manifold and turbo



Good call, didn't even think about that. I doubt that the reversion from each little mini runner is much but two WGs would not have the issue at all.
 

Barnes

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I still don't see how one wastegate is a problem. If one major reason for a twin scroll is for spool, nothing will be going out the wastegate before you hit max boost. So as long as the manifold is divided up to the turbine housing inlet, it doesn't matter. After the gate opens, as long as the design isn't restrictive, I don't see why it would negate the effects of the twin scroll.
 

onesickcrx

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Quick example, if a four-cylinder engine's firing sequence is 1-3-4-2, cylinder 1 is ending its expansion stroke and opening its exhaust valves while cylinder 2 still has its exhaust valves open (while in its overlap period, where both the intake and exhaust valves are partially open at the same time). In a single-scroll or undivided manifold, the exhaust gas pressure pulse from cylinder 1 is therefore going to interfere with cylinder 2's ability to expel its exhaust gases, rather than delivering it undisturbed to the turbo's turbine the way a twin-scroll system allows.

The result of the superior scavenging effect from a twin-scroll design is better pressure distribution in the exhaust ports and more efficient delivery of exhaust gas energy to the turbocharger's turbine. This in turn allows greater valve overlap, resulting in an improved quality and quantity of the air charge entering each cylinder. In fact, with more valve overlap, the scavenging effect of the exhaust flow can literally draw more air in on the intake side while drawing out the last of the low-pressure exhaust gases, helping pack each cylinder with a denser and purer air charge. And as we all know, a denser and purer air charge means stronger combustion and more power, and more power is good!


If you have one wastegate it no longer has the ability to run only 2 cylinders threw each port of the Manifold / Turbo. You would be forcing the turbo to run all four and kill the benefits on twin scroll /ubbthreads/images/graemlins/wink.gif
 

belize1334

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By connecting the two scrolls to a single waste-gate you create a shared volume so they are not physically separate. But, the effect of this is going to be minimized if the connection is far from the collector. Imagine a hypothetical where each wg passage is like four feet long and then connects to a single gate. The linear distance between the collectors is now 8 feet and the exhaust pulses will be largely damped over this distance so you'd probably never notice the difference. On the other hand, if the passages are only 1" long then they join basically at the collectors and it acts like a single scroll. At a minimum, connecting to a single gate will never be worse than single scroll and at best it may approach the effectiveness of twin-scroll... but at the expense of having to mount the gate a long way from the collectors.

I say use two separate gates... do it once and do it right.
 
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BrandonEchols

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I definitely agree about doing it right the first time. Thats why I'm asking now, I wanna get all these things sorted before I start buying parts, etc. for this at some point.
I was actually wondering the same thing, so I'm glad paul threw it out there...do I need an external gate? I know some of the Holsets are made without the internal gate, but if I get one that has it...should I use it? Are there any measurable positive effects from using an external gate, other than being able to handle more boost pressure? Any gains by dumping to the atmosphere instead of back into the exhaust?

I actually may consider that valve...it looks very interesting...
 
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onesickcrx

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There are alot of turbos out there that will make 400hp around 20 pounds but, It mostly depends on your motor setup. Why not run like a Forced Performance mani and 30R so you can still grow and have great bottom end? Drop the twin scroll unless you looking to have spool of a 30 but top end of 35 or bigger
 

Barnes

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Quoting onesickcrx:
If you have one wastegate it no longer has the ability to run only 2 cylinders threw each port of the Manifold / Turbo. You would be forcing the turbo to run all four and kill the benefits on twin scroll /ubbthreads/images/graemlins/wink.gif



Is this the 'cross talk' that was previous mentioned?
 

belize1334

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I keep trying to find a metaphorical use for Token Ring in this analogy but I'm coming up empty handed.
 

turbowop

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Quoting belize1334:
I keep trying to find a metaphorical use for Token Ring in this analogy but I'm coming up empty handed.



Yeah, that won't work. Our manifolds are of a hierarchical star topology.
 

85tr

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Oct 21, 2006
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washington
Im gonna run a hx35, divided manifold with twin wastegates, the wastegate runners are still not done but i can tell you with a fully divided mani if you want to run a singe wastegate there is just not unuff room for you to make and place the collector you would need to keep the manifold fully divided .Here are some pics of my setup.
 
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