Well, after about 3 years, I'm starting to make progress again towards turbocharging this car. My question is for those with or who have built twin scroll or dual charger setups with multiple wastegates.
That is, would you recommend an exhaust pressure sensor for each wastegate to 1) ensure both gates are operating correctly/evenly and 2) prevent dangerous lean cylinder conditions from uneven gating of the exhaust?
Note: I do plan on running an EGT on each runner, which should also help diagnose issues with the gates.
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EGT on each runner is a good idea, but unless you have $600 just for EGT gauges, I wouldnt, 1 at the collector is plenty.
This is a different, I have never heard of an Exhaust Pressure Gauge.
Would this be to monitor back presure?
How does exhaust pressure affect the wastegates?
They run off intake vacuum my friend.
How would you have a lean cylinder?
Your fuel maps should be greater than what your actually producing, just incase of boost spikes.
BLTNBSTD (FKA Phil Lindsay) wrote:This is a different, I have never heard of an Exhaust Pressure Gauge.
Would this be to monitor back presure?
Yes. Delphi makes them, but I'm not sure what their pressure range or heat tolerances are (probably intended only for post Turbo or NA), so I'll have to look into that, I suppose
BLTNBSTD (FKA Phil Lindsay) wrote:
How does exhaust pressure affect the wastegates?
They run off intake vacuum my friend.
Correct...but if one gate's spring is stiffer than the other, more exhaust is expelled out one gate than the other, resulting in higher exhaust inertia required from one combination of cylinders (either 1&4 or 2&3) to spin the turbine, resulting in higher exhaust pressure for those cylinders. Or a worse case scenario, one gate fails and locks up (closed) resulting in one set of cylinders giving all of it's energy to the turbine, requiring the other set to gate all of the waste exhaust. This can also be applied for if a gate fails the opposite way where the gate stays wide open.
BLTNBSTD (FKA Phil Lindsay) wrote:
How would you have a lean cylinder?
Your fuel maps should be greater than what your actually producing, just incase of boost spikes.
Pretty much answered in my last response...If there is higher backpressure in one set of cylinders, those cylinders cannot ingest as much air in one stroke as the cylinders with less backpressure, and because no efi (short of probably a Motec) supports individual cylinder tuning, the VE map provides the same amount of fuel to each cylinder which can result in excessively lean and rich cylinders. An EGT on each runner would help to monitor this kind of condition...Besides, $600 is nothing compared to what the end cost of my header will probably be
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I wouldn't worry about the exhaust pressure sensor. I mean, are you really going to take apart the wastegate and shim the spring to make sure they open at EXACTLY the same time? If you one opens a little late, the extra gas will go into the other volute or turbo, no big deal. Like mentioned above, all of the injectors will always be squirting the same amount of fuel, so the worst case scenario would be that a couple of cylinders would see a slightly different burn duration due to different backpressure. And the dual EGT's is not a bad idea, they are not too expensive. These are 100 dollars complete per:
http://www.summitracing.com/parts/VDO-310953/
I just realized you posted at the same time as I did (literally). Haha.
wait so are you running two turbo chargers? thats quite different than running a twin scroll turbine housing. With the twin scroll the only thing you need to do differently for the whole setup is design the collector of the turbo manifold for a twin scroll, heck I'm sure they just sell the collector prefabbed. you can even run a twin scroll turbine with a normal manifold and just not get the full benefits of the exhaust pulse pairing.
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Leafy wrote:wait so are you running two turbo chargers? thats quite different than running a twin scroll turbine housing. With the twin scroll the only thing you need to do differently for the whole setup is design the collector of the turbo manifold for a twin scroll, heck I'm sure they just sell the collector prefabbed. you can even run a twin scroll turbine with a normal manifold and just not get the full benefits of the exhaust pulse pairing.
You find me a single header fabricator that pairs cylinders 1&4 and 2&3 together on an equal length single scroll manifold. It's much easier, simpler and cheaper to just pair 1&2 and 3&4 and the results would be no different if they
DID pair 1&4 and 2&3.
The turbo I'm using is a single s250 twin scroll with a 1.15 A/R (I'll be getting an s360 with a .91 A/R for track use) and I want the benefits of paired cylinders. I know I "can" run it as a single entry, but I don't want to, as I'm sure the response will be slow with those lazy A/R's (throttling the turbine housing, however, has certainly peaked my interest).
I only asked about the twin charged because some people here drive more than 4-bangers, and it's essentially the same concept as a true twin scroll setup, requiring two wastegates to control two separate sets of exhaust pulses.
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Fair enough. I was just trying to get clarification and then started rambling. I cannot wait to see this thing finished, BG S360's are huge.
1994 Saturn SL2 Home Coming Edition: backup car
2002 Chevy Cavalier LS Sport Coupe: In a Junk Yard
1995 Mazda Miata R-package Class=STR
Sponsored by:
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WPI SAE Risk and Sustainability Management Officer
Sadly, you would be one of the very few running the twin scroll setup, so your question would probably be better answered on a place like honda-tech. I've seen some back pressure setups and it seems pretty simple, this place sells a very simple designed kit.
http://fcsfab.com/products.html
s366 is a good sized turbo, I did a twin scroll with a 366 on a 200ser with mvs38mm wastegates. Whats your goals with your car and this is on a 2.4 right?
R.I.P. Brian Klocke, you will never be forgotten
Thanks for the link Fetter.
Yeah, it's a 2.4. The turbo is an s360 (60mm) though, not an s366 (66mm). It has a slightly smaller exhaust wheel which puts it about halfway between an s256 and the s366 on the turbine side. The initial goal with the s360 is to just tune it around 1 bar and see what she'll do (looking for 400whp+). I'm not sure how far I want to take it passed that with 10.7:1 compression though...I have considered e85, but haven't seen any local pumps with it, yet, and if it remains a track turbo, I might just end up running c16.
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BLTNBSTD (FKA Phil Lindsay) wrote:
How does exhaust pressure affect the wastegates?
They run off intake vacuum my friend.
A couple of clarifications:
Exhaust pressure affects wastegate operation via the force it presents to the face of the wastegate valve. It is a very active factor in wastegate behavior.
One of the other factors is, of course, manifold pressure, or more specifically, boost pressure. Vacuum itself is not a factor, for the engine is not in vacuum condition when the wastegate is in operation, it is in the boosted condition.
To the OP: A common method of wastegating twin-scroll turbine sections is to use a single wastegate that utilizes a 2 into 1 merge, with each leg leading to one cylinder pair. It's simple and effective.
Bill Hahn Jr.
Hahn RaceCraft
World's Quickest and Fastest Street J-Bodies
Turbocharging GM FWD's since 1988
www.turbosystem.com
oh, and looking for a modest 300-350 whp from the s250 for a fun street turbo. Both turbos have the same vband discharge and the vband discharge mounting locations are very close (less than 1/4"), which should make for an easy/quick swap.
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Whalesac wrote:
You find me a single header fabricator that pairs cylinders 1&4 and 2&3 together on an equal length single scroll manifold. It's much easier, simpler and cheaper to just pair 1&2 and 3&4 and the results would be no different if they DID pair 1&4 and 2&3.
Not entirely true. Pairing 1&4 and 2&3 results in even pulse timing, which will improve flow (pulse, null, pulse, null). The 1&2 and 3&4 pairing approach creates an odd-firing pulse pattern (pulse, pulse, null, null) due to cylinders adjacent to one another in the firing order paired together.
The former scenario is superior to the latter.
Bill Hahn Jr.
Hahn RaceCraft
World's Quickest and Fastest Street J-Bodies
Turbocharging GM FWD's since 1988
www.turbosystem.com
Bill Hahn Jr. wrote:BLTNBSTD (FKA Phil Lindsay) wrote:
How does exhaust pressure affect the wastegates?
They run off intake vacuum my friend.
A couple of clarifications:
Exhaust pressure affects wastegate operation via the force it presents to the face of the wastegate valve. It is a very active factor in wastegate behavior.
One of the other factors is, of course, manifold pressure, or more specifically, boost pressure. Vacuum itself is not a factor, for the engine is not in vacuum condition when the wastegate is in operation, it is in the boosted condition.
To the OP: A common method of wastegating twin-scroll turbine sections is to use a single wastegate that utilizes a 2 into 1 merge, with each leg leading to one cylinder pair. It's simple and effective.
I considered this. Shouldn't they remain separated all the way up to the face of the valve, though.
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In a perfect world, yes. But in practical operation, it's a very minor distinction. If I understand your interpretation, you are concerned that any common tract between the two separated pairs of cylinders will degrade twin-scroll intended operation. Am I correct?
Bill Hahn Jr.
Hahn RaceCraft
World's Quickest and Fastest Street J-Bodies
Turbocharging GM FWD's since 1988
www.turbosystem.com
Bill Hahn Jr. wrote:Whalesac wrote:
You find me a single header fabricator that pairs cylinders 1&4 and 2&3 together on an equal length single scroll manifold. It's much easier, simpler and cheaper to just pair 1&2 and 3&4 and the results would be no different if they DID pair 1&4 and 2&3.
Not entirely true. Pairing 1&4 and 2&3 results in even pulse timing, which will improve flow (pulse, null, pulse, null). The 1&2 and 3&4 pairing approach creates an odd-firing pulse pattern (pulse, pulse, null, null) due to cylinders adjacent to one another in the firing order paired together.
The former scenario is superior to the latter.
I said in a single merge (i.e. single scroll) a header designer rarely builds 1&4 and 2&3 adjacent to one another so that you can just cut off the flange and put in your own merge to separate the cylinders. You are basically reinforcing what I already said.
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Bill Hahn Jr. wrote:In a perfect world, yes. But in practical operation, it's a very minor distinction. If I understand your interpretation, you are concerned that any common tract between the two separated pairs of cylinders will degrade twin-scroll intended operation. Am I correct?
In short, yes. I understand that it doesn't need to be "perfect," but I want to cut out reversion as much as possible.
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Whalesac wrote:Bill Hahn Jr. wrote:Whalesac wrote:
You find me a single header fabricator that pairs cylinders 1&4 and 2&3 together on an equal length single scroll manifold. It's much easier, simpler and cheaper to just pair 1&2 and 3&4 and the results would be no different if they DID pair 1&4 and 2&3.
Not entirely true. Pairing 1&4 and 2&3 results in even pulse timing, which will improve flow (pulse, null, pulse, null). The 1&2 and 3&4 pairing approach creates an odd-firing pulse pattern (pulse, pulse, null, null) due to cylinders adjacent to one another in the firing order paired together.
The former scenario is superior to the latter.
I said in a single merge (i.e. single scroll) a header designer rarely builds 1&4 and 2&3 adjacent to one another so that you can just cut off the flange and put in your own merge to separate the cylinders. You are basically reinforcing what I already said.
Which is what I thought I accounted for when I said design the collector. I didnt think I alluded that it would be as easy as taking a normal turbo manifold and just hacking the collector off and welding in a new one.
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Sponsored by:
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Whalesac wrote:Bill Hahn Jr. wrote:In a perfect world, yes. But in practical operation, it's a very minor distinction. If I understand your interpretation, you are concerned that any common tract between the two separated pairs of cylinders will degrade twin-scroll intended operation. Am I correct?
In short, yes. I understand that it doesn't need to be "perfect," but I want to cut out reversion as much as possible.
OK. Let's delve a bit deeper into this.
What is your impression of how a twin-scroll (divided volute) turbine section is designed to operate, i. e.: What is its desired functionality or improvement over a single scroll, and how does it achieve that desired functionality?
Bill Hahn Jr.
Hahn RaceCraft
World's Quickest and Fastest Street J-Bodies
Turbocharging GM FWD's since 1988
www.turbosystem.com
Whalesac wrote:Bill Hahn Jr. wrote:Whalesac wrote:
You find me a single header fabricator that pairs cylinders 1&4 and 2&3 together on an equal length single scroll manifold. It's much easier, simpler and cheaper to just pair 1&2 and 3&4 and the results would be no different if they DID pair 1&4 and 2&3.
Not entirely true. Pairing 1&4 and 2&3 results in even pulse timing, which will improve flow (pulse, null, pulse, null). The 1&2 and 3&4 pairing approach creates an odd-firing pulse pattern (pulse, pulse, null, null) due to cylinders adjacent to one another in the firing order paired together.
The former scenario is superior to the latter.
I said in a single merge (i.e. single scroll) a header designer rarely builds 1&4 and 2&3 adjacent to one another so that you can just cut off the flange and put in your own merge to separate the cylinders. You are basically reinforcing what I already said.
Well, no...I am taking exception with what you said. The specific part I am taking exception with is highlighted in green above. There IS a difference, and my explanation expounded on why this difference exists.
Bill Hahn Jr.
Hahn RaceCraft
World's Quickest and Fastest Street J-Bodies
Turbocharging GM FWD's since 1988
www.turbosystem.com
Excuse, me but I didn't renew my Premuim Membership, so I cannot edit my posts any longer, lol!
In the instance of the cylinder pairing, I was of the impression you were referring to a dual-scroll manifold, as that's the topic here. I now see you were not However, I am still taking at least
some exception, for we then enter the realm of the rotational firing collector, which improves manifold operation.
Bill Hahn Jr.
Hahn RaceCraft
World's Quickest and Fastest Street J-Bodies
Turbocharging GM FWD's since 1988
www.turbosystem.com
Bill Hahn Jr. wrote:Whalesac wrote:Bill Hahn Jr. wrote:In a perfect world, yes. But in practical operation, it's a very minor distinction. If I understand your interpretation, you are concerned that any common tract between the two separated pairs of cylinders will degrade twin-scroll intended operation. Am I correct?
In short, yes. I understand that it doesn't need to be "perfect," but I want to cut out reversion as much as possible.
OK. Let's delve a bit deeper into this.
What is your impression of how a twin-scroll (divided volute) turbine section is designed to operate, i. e.: What is its desired functionality or improvement over a single scroll, and how does it achieve that desired functionality?
Exhaust pulse is expelled out the exhaust valve, travels down the runner, passes through the collector and then applies a torque/energy on the exhaust wheel. With a portion of the exhaust traveling past the wheel, some remains in the manifold and sends a pulse back towards the valve. Depending on the RPM, load, size and aero of wheel and length of runner this reflected pulse energy can vary greatly. A single scroll fires a pulse from the next cylinder in the firing order, which increases interference with the reflected pulse. I twin scroll will still have this, but the rate of interference is halved because the next interference pulse is every other fired cylinder, which results in faster transience and spool characteristics. With increased load and increased pulse energy, the pulses can eventually induce reversion when pressure builds up in the exhaust manifold.
This is my understanding of a twin scroll...now correct me, like I know you like to do
Oh and BTW, mods are free to lock this thread whenever they feel like it. I believe my original question was already answered.
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Nah, I don't set out to "correct" you, hehe! I tend to clarify information and expound upon discussions for the benefit of all those who may read these threads. I just like to teach. Most readers enjoy this information sharing.
I will give you credit for going out to do some research before you replied to my post...fully 25 minutes elapsed there. Not bad! All too many times, folks just spout off when upon to discuss, instead of going to seek some quality information to share. Well done!
So, to the subject matter: Everything technical you've said in this latest post is very true, and also feeds well into why we should pair the cylinders accordingly for even pulses in a twin-scroll. You chose a good source.
There is another reason why the twin scroll will improve turbo response, and it involves turbine wheel geometry and the tendency of exhaust gases to seek the lowest pressure region of the wheel and housing as they exit the turbocharger. This means that during early spooling behavior, the gases all tend to move towards the small diameter portion of the wheel, as it is nearest the low pressure of the turbine outlet. This wheel region has a much lower polar moment of inertia. This lower moment (shorter lever) does not apply as much leverage to the wheel as the larger diameter turbine blades can. However, until we have developed some significant exhaust pressure, exhaust gas energy is not applied to these larger diameter blades effectively.
When we force half of the engine's exhaust pulses to impinge upon the larger diameter portion of the turbine wheel using a divided volute (twin-scroll), the stronger leverage afforded accelerates the wheel faster, and Voila! Faster spool.
However, and here's the real rub, the "Gotcha" moment...twin scroll turbines, as they feed each half of the engine's pulses into very different flowing sections of the turbocharger, actually will develop different exhaust pressure signatures, even at full boost. It is for this reason that a common wastegate tract can actually assist in helping to equalize this pressure difference.
Does the common tract degrade the twin-scroll's faster-boosting intention? No. This aspect is more about gas volume flow being directed at the higher-leverage portion of the turbine wheel, and that's not affected by the common tract...exhaust gas flow is not lost from the side feeding this portion of the wheel, for the other cylinders are pushing just as much exhaust flow into their side, thus blocking any actual loss of gas from the primary side.
They are interesting animals, these twin scrolls!
Bill Hahn Jr.
Hahn RaceCraft
World's Quickest and Fastest Street J-Bodies
Turbocharging GM FWD's since 1988
www.turbosystem.com
