Compound boost not as expected

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Big Al
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Re: Compound boost not as expected

Post by Big Al » Tue Jul 10, 2018 5:15 pm

Don't measure backpressure is my advice for all of you. It clouds your brainpower with irrelevant data. If the static backpressure is higher or lower then your boost doesn't say anything at all actually, one have to measure the dynamic backpressure at the exhaustvalve with high speed logging to truly know.
There are so many components that can make the static back become (much) higher without ever causing negative impact on the engine ...
A quick example is that Garretts exhaust housings always gives higher static backpressure then other brands because of how they have formed them inside. A second example is that VNT turbos make higher static boost then conventional turbos too ...

About compound. A well built compound engine is ALWAYS better then a single turbo setup. Enough said ;)

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Re: Compound boost not as expected

Post by englertracing » Tue Jul 10, 2018 7:29 pm

craigory wrote:
Tue Jul 10, 2018 5:04 pm
Was the lancia not a parallel type system? Not actually compound?
Turbo then a supercharger with a bypass

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Re: Compound boost not as expected

Post by englertracing » Wed Jul 11, 2018 2:33 am

this guy is doing compound
https://youtu.be/uYy5A-s5myI
https://www.youtube.com/watch?v=wMN6wGQOvBk

http://www.hilmersson-racing.com/manta-fakta/

actually i think he might be running a bypass...

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Re: Compound boost not as expected

Post by TimIacobucci » Wed Jul 11, 2018 3:45 pm

Big Al wrote:
Tue Jul 10, 2018 5:15 pm
Don't measure backpressure is my advice for all of you. It clouds your brainpower with irrelevant data. If the static backpressure is higher or lower then your boost doesn't say anything at all actually, one have to measure the dynamic backpressure at the exhaustvalve with high speed logging to truly know.
I agree that pressure at the valve at overlap is key here, hence all the focus on na exhaust header design for effective scavenging but I cannot see how the static backpressure measurement is meaningless.

There are 2 big important corollarys to a large difference in backpressure in a turbo engine. (I am essentially assessing the blower + engine as a system to itself simply seen as a larger na engine to the turbo for the this argument). That is power and detonation resistance. There are good examples of the same turbo engine with the same turbine wheel and cam, using a different turbine housings. The larger housing will always produce less backpressure and more power for the same boost. The same setup will generally allow more timing on the same fuel and boost as well.
Big Al wrote:
Tue Jul 10, 2018 5:15 pm
There are so many components that can make the static back become (much) higher without ever causing negative impact on the engine ...
A quick example is that Garretts exhaust housings always gives higher static backpressure then other brands because of how they have formed them inside. A second example is that VNT turbos make higher static boost then conventional turbos too ...

About compound. A well built compound engine is ALWAYS better then a single turbo setup. Enough said ;)
Are you saying that vnt has high static boost vs static backpressure to conventional turbines? I would argue this is an excellent example of how important a lower backpressure is, the entire development and design of variable turbines is to gain the higher efficiency of a bigger turbine without the laggy drawback of it. As for the Garrett design what is different about it? Turbine housing or turbine wheel or what? Which age/generation garretts are you referring to? I cannot imagine a scenario where a higher static backpressure is not an indication of increased restriction.

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Re: Compound boost not as expected

Post by Big Al » Wed Jul 11, 2018 5:08 pm

The problem with measuring the static backpressure is that there are so many errors with the reading. People just say "as long as the static backpressure is lower then the boost you are fine", and that is some rule of thumb that so so wrong ...
Are you having a twinentry turbo+exhaust manifold?
Are you having a Log or a tubular exhaust manifold?
Do you have a 2v or 4v head?
Do you have a small turbine and large exhaust housing or vice versa?
Are your WG near or far from the exhaust valve?
Are your reading near of far from the exhaust valve?
Are your reading placed in a small or big cross sectional?
Are your pressure reading near the WG?
What angle into the manifold are the reading?
Does your head have a low reverse flow reading?
How much overlap does your cams have?
How much boost do you have?
Are you having a Garret turbo? If not what turbo and what size of exhaust housing do you have? (differs between housings bigger is not always better)
Does your turbo have VNT?
and so on ...
Things that change the reading.
I have seen a good real time example of static backpressures on same engine on dyno that did have double the static backpressure vs boost ,against a dyno pull that had static pressure under boost, the dyno with double the static backpressure had better spool and higher HP. Both times was same boost and on same engine, the difference on this A-B-A test was only a exhaust housing.
So I say don't measure. It doesn't say anything.

If you want to measure backpressure and have a reading that is useful then you have to measure at the downpipe and NOT before the turbine. Here are a place that you definitely don't want higher pressure.

I'm saying that a VNT exhaust side on the turbo has higher static backpressure then a conventional setup exhust side turbo. And we know that VNT is not that bad at all ;)
We have to remember that we WANT high pressure at the turbine (but not at the exhaust valve)... that's what drives the turbo :)

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Re: Compound boost not as expected

Post by TimIacobucci » Wed Jul 11, 2018 5:38 pm

This is interesting. Lots to respond to here.

Which vnt are you talking about? Most holset stuff I've seen is higher closed (obviously) but full open usually effectively hugh and very efficient at higher rpm.

What was the setup that gained hp on a smaller housing?

I could see if the housing was just too big for the combo and couldn't spool it effectively before you were out of the effective range of the cam/headflow ect. Smaller is always going to make more torque because it spools faster, unless it's soo small it's choking before torque peak.

I agree all those factors you listed are important but generally a b a comparison the less backpressure the better the engine runs. I would say the biggest factor is cam overlap and operating range. A high overlap high rpm cam is not going to play nice at 2x backpressure. Likewise a low rpm small overlap cam will be relatively indifferent to it and not gain as much from a less restrictive turbine.

The idea here is when viewed as an entire system you could begin to cam and treat the turbo system more like na when you get into a favorable pressure differential across the open intake and exhaust valves.

You are absolutely correct about a turbo manifold being a chaotic mess to measure. Usually the area after the runners have merged and before the turbine starts to reduce is the general standard. It also requires some amount of damping to get a usable signal as you will still see lots of pulsing in a fast log. Not much unlike an unfiltered or undamped map signal but you can run the engine off that signal with SD.

I don't see how uncertainty in using and interpreting the measurement makes it worthless. If anything I see that as a sign it needs to be studied more to grasp the full nature of the measurement as part of the entire system and how the different factors you listed interact. I do agree this entire twincharge design theory needs to be actually tested and measured much more to get a handle on it and not to assume anything from any one measurement.

The thing is there is evidence from multiple setups that with twincharging a higher static boost vs backpressure leads to
higher detonation resistance. I mean just conceptually do you think a turbo sized to make a good amount of boost at low rpm and the required tight turbine and high drive pressure will not dramatically reduce its allowable ignition advance at high boost levels?

Surely there is something to it and backpressure is a least a piece of that puzzle.


If you agree compounding is effective and worthwhile how do you theorize its advantages working? I am not questioning your understanding to argue against you, it just seems you have different experiences and information / opinions I would like to understand better.

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Re: Compound boost not as expected

Post by TimIacobucci » Wed Jul 11, 2018 5:42 pm

This is interesting. Lots to respond to here.

Which vnt are you talking about? Most holset stuff I've seen backpressure is higher closed (obviously) but full open the turbine is usually effectively huge and very efficient at higher rpm.

What was the setup that gained hp on a smaller housing?

I could see if the housing was just too big for the combo and couldn't spool it effectively before you were out of the effective range of the cam/headflow ect. Smaller is always going to make more torque because it spools faster, unless it's soo small it's choking before torque peak.

I agree all those factors you listed are important but generally a b a comparison the less backpressure the better the engine runs. I would say the biggest factor is cam overlap and operating range. A high overlap high rpm cam is not going to play nice at 2x backpressure. Likewise a low rpm small overlap cam will be relatively indifferent to it and not gain as much from a less restrictive turbine.

My understanding here is when viewed as an entire system you could begin to cam and treat the turbo system more like na when you get into a favorable pressure differential across the open intake and exhaust valves.

You are absolutely correct about a turbo manifold being a chaotic mess to measure. Usually the area after the runners have merged and before the turbine starts to reduce is the general standard. It also requires some amount of damping to get a usable signal as you will still see lots of pulsing in a fast log. Not much unlike an unfiltered or undamped map signal but you can run the engine off that signal with SD.

I don't see how uncertainty in using and interpreting the measurement makes it worthless. If anything I see that as a sign it needs to be studied more to grasp the full nature of the measurement as part of the entire system and how the different factors you listed interact. I do agree this entire twincharge design theory needs to be actually tested and measured much more to get a handle on it and not to assume anything from any one measurement.

The thing is there is evidence from multiple setups that with twincharging a higher static boost vs backpressure leads to
higher detonation resistance. I mean just conceptually do you think a turbo sized to make a good amount of boost at low rpm and the required tight turbine and high drive pressure will not dramatically reduce its allowable ignition advance at high boost levels?

Surely there is something to it and backpressure is a least a piece of that puzzle.


If you agree compounding is effective and worthwhile how do you theorize its advantages working? I am not questioning your understanding to argue against you, it just seems you have different experiences and information / opinions I would like to understand better myself.

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Re: Compound boost not as expected

Post by Big Al » Wed Jul 11, 2018 7:05 pm

Talking mostly about Garrett VNT, Holset's VGT is a completely diffrent design and have not that higher static pressure (of what I know).

The one with the smaller housing made more HP. But it was not much (the turbo compressor was at maximum flow at both runs). The difference was the heat, The smaller housing made more heat in the exhaust manifold in spoolup so at max HP there was less heat loss because of that. And that made the HP difference.

So true about the cam overlap, this makes a huge difference how much backpressure the engine can take before you have HP loss. Another thing that is important on my engine but not often used in other ones is a really small throat in the head after the exhaust valve. This makes a good "reverse flow restriction". Other things that I personally witnessed is how hard your exhaust valve springs are. Too weak and you are loosing HP because the valve doesn't close properly on high backpressure.

When you say twincharge do you mean supercharger+turbo or two turbos?

"I mean just conceptually do you think a turbo sized to make a good amount of boost at low rpm and the required tight turbine and high drive pressure will not dramatically reduce its allowable ignition advance at high boost levels? "
I don't like to talk ignition advance , in my mind you always try to build your engine so that the advance is as little as possible ... zero ignition is the holy grail.
I say it depends on the turbo. Take mine for example I have a 64mm turbine exducer on my 500hp turbo and a modified 0.48 housing. My turbo spools better and makes more HP then almost all of the other 500hp engines that people built and tuned of same engine model. And this on a bone stock engine with log manifold , stock cams , stock intake and so on :)
A big turbine and small housing always flows more from the dynamic pressure then the opposite combo. So a higher static back pressure reading on the big turbine combo doesn't really say that much because It still is less restrictive at higher rpm then the small turbine is dynamically.

I have much knowledge in compounding on two turbos (and soon 3 too) but not that much on a supercharger+turbo setup. So I have to know on what setup you want answers.

I have a friend that works as a turbo builder in a small turbo company , this company is building a tripple turbo ~600hp 2L engine as we speak and hopefully they are going to dyno this car this weekend. This setup is really advanced double small twinscrollturbos in parallel and a big twinentry one after (i think it was without wastegate) in series. The small turbos waste into one port of the twinentry of the big one. This makes the spool 300rpm (tested in another setup) faster then if you wasted the normal way in a compound setup.

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Re: Compound boost not as expected

Post by TimIacobucci » Wed Jul 11, 2018 7:51 pm

That compound setup sounds extremely interesting. I would love to see pictures or details on the results.

Your setup sounds potent and I agree with you on big turbine small housing vs small turbine big housing, the bigger wheel has a greater area and torque to apply to get work done, I think getting the best flow over the largest turbine wheel is the most effective if you can find / build a turbo that way.

What exactly is your 500hp engine?

I meant more timing as in closest to optimal timing for peak torque and not being knock limited.

I was referring to compounding as twincharging super + turbo but I am curious how much difference you see between compounding turbos stages and compounding super + turbo.

If the goal is response I don't think even small twinscroll turbos can compete with a positive displacement blower.

I also understand what you are saying about port sizing and flow but I am generally talking about being able to build the head and cam more like a hot na setup. Taking advantage of high rpm cams and the port size and flow to suit them.

A blower only car is practicality impossible to over cam, it just ends up blowing more raw fuel and good intake charge into the exhaust. Not great for fuel consumption but nice if you are trying to motivate a large turbo downstream.

The 2.3 from the this thread in stock form is maybe not the best example but it does respond well to porting.

Image

I doubt this setup would be happy with backpressure 2:1

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Re: Compound boost not as expected

Post by craigory » Wed Jul 11, 2018 10:03 pm

Just so were on the same page.. Flow path is-

Air filter > (recirc outlet) > h1c turbo compressor > water to air IC > m62 charger > air to air FMIC > (recirc inlet) > throttle body.

Recirc bypass is a modified vacuum operated external wastegate..

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Re: Compound boost not as expected

Post by englertracing » Thu Jul 12, 2018 2:30 am

the m62 does NOT feature internal compression right?

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Re: Compound boost not as expected

Post by TimIacobucci » Thu Jul 12, 2018 3:36 am

No, it's a roots design. It just traps a certain volume of air and shoves it out the other side and the compression happens at the outlet.

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Re: Compound boost not as expected

Post by Big Al » Thu Jul 12, 2018 10:16 am

TimIacobucci wrote:
Wed Jul 11, 2018 7:51 pm
That compound setup sounds extremely interesting. I would love to see pictures or details on the results.
I'll share after dyno :)

What exactly is your 500hp engine?
It is a Cosworth YB, so it's a better version lima ;)

"I was referring to compounding as twincharging super + turbo but I am curious how much difference you see between compounding turbos stages and compounding super + turbo."
Quite a lot actually, A supercharger+turbo is more often built as a NA "with higher density intake". So the setup differs a lot in what parts you choose for that.

"If the goal is response I don't think even small twinscroll turbos can compete with a positive displacement blower. "
I cant say if it is that way or not (because my poor experience with that setup), but I can say that a well built turbo+turbo compund system have almost no lag at all. Like you could build your blow off so that it blows off the air between the turbos and build the WG system as I mentioned before.

"A blower only car is practicality impossible to over cam, it just ends up blowing more raw fuel and good intake charge into the exhaust. Not great for fuel consumption but nice if you are trying to motivate a large turbo downstream."
This is what I think one of the biggest differences between super+turbo and turbo+turbo setup, a turbo+turbo setup you don't really want to overcam I'ts better to make the boost higher to make same massflow from that missing airflow on a "smaller cam"

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Re: Compound boost not as expected

Post by n2xlr8n » Thu Jul 12, 2018 10:33 am

TimIacobucci wrote:
Wed Jul 11, 2018 7:51 pm

Image

I doubt this setup would be happy with backpressure 2:1
Jon does beautiful work.
He who is in me is greater than he who is in the world.

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Re: Compound boost not as expected

Post by TimIacobucci » Sat Jul 14, 2018 2:30 pm

Big Al wrote:
Thu Jul 12, 2018 10:16 am
This is what I think one of the biggest differences between super+turbo and turbo+turbo setup, a turbo+turbo setup you don't really want to overcam I'ts better to make the boost higher to make same massflow from that missing airflow on a "smaller cam"
I find this very interesting and I think there is allot to be discussed and learned about this subject.

Kevin Jewer said this, here,
https://www.yellowbullet.com/forum/show ... 1?page=119 post #1181 depending how you that shows up in your browser.
I did post previously that a drop in back pressure ratio from about 1.5:1 to about 0.6:1 was worth 5% VE at the same boost. It's nice, but not a huge advantage IMO. There is also the improvement in pumping loss, but however I try to calculate that, it's also a pretty small difference. So I don't worry about it as much as I used to.
There's allot to be said about both these things. Firstly making up mass flow in turbo boost is very relative to operating range and use. His converter stalls to 6500 rpm for instance. To discount aggressive high rpm camming is assuming allot about the setup.

At the same time in that thread he does I believe essentially focus on trying to optimize overall system efficiency by optimizing the best use of the turbos. Trying to get them both working at happy efficient areas of the compressor with the best turbine sizing for his engine size and operating range.

So I would say he seems to think getting the turbo(s) spun up and doing efficient useful work seems more important than overall engine VE and backpressure to boost ratio. However he does measure and has actually quantified one example as having a 5% difference which is more specific than anything else I have come across.

That is nothing to take lightly, especially in cam selection. If you have an engine built with the ability to spin more rpm reliabily you have way more flexibility in gearing, sometimes (most times) the gear selection is limited. If you CAN cam the engine higher and you don't because you are just planning on boosting it harder at a lower rpm you are leaving allot on the table vs a setup that uses rpm + more boost.

The noteworthy thing here is aside from the drive power to turn the blower there is little tradeoff in this regard twincharged, if the engine can rev and you can cam the hell out of it, why would you not with a favorable boost/backpressure ratio and it's corresponding VE advantages?

Even in a compound turbo setup if you don't mind giving up some response, again another compromise you are not making twincharged, you can obviously achieve 1:1 or better and take advantage of it. Kevin talks about comparing few other compound setups he's involved with in that thread as well. Some with boost higher than backpressure.

I guess for twincharging the question is how high in the rpm is the blower still efficient and how much power is required to drive it vs leaning on the turbo harder up top to make up the mass flow?

This answer seems relative to the blower and turbo sizing to the engine.

Another question is when/ if the blower "check valve" effect keeping boost higher than backpressure and allowing higher VE and aggressive camming outweighs its parasitic drag to power it.

My theory is with a good sized efficient blower and engine built to rev and cammed for it there should be a benefit to maintaining at least some amount of compounding after the turbo vs bypassing it entirely.

I don't think this is usually how twincharging is executed most times though and leads to inaccurate conclusions about its usefulness. Running a stock smallish blower at higher rpm on a small stock or turbo type cam twincharged, then comparing it to the same setup with just a good turbo system without the blower is not giving the system a fair test. Lots of people do only this then falsely conclude more power turbo only, twincharging is a waste of time.

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