Compound boost.

[Jaden]

Originally Posted by CSG Mike

There's some monkey math going on here...

I'm getting really tired of blanket statements like this with no backing it up.

Point out the monkey math or STFU...

Jaden

p.s. I have no problem showing my work. This can get a bit confusing when looking at diesels because they are trying to go beyond the limits of a single turbo's PR. That's why I said it's a slightly different concept but the same rules apply.

In a diesel compound turbo setup because you're running higher total boost levels, you can get a primary turbo that has a 1200hp limit if you want the airflow to make 1200hp. This is because you can run 40psi of boost in the primary and 25 in the secondary to make a total boost of ~151psi or 15 psi in the secondary for a total boost of ~109psi but either way there you can go by the upper limit of the capability of the primary and don't have to worry about the airflow at the pr you are running as much.

40 psi at sea level would be a P/R of 3.77 = (40+14.7)*.069. 25 psi at sea level a P/R of 2.73 = (25+14.7)*.069 for a total P/R of 10.29= 2.73*3.77 because you multiply the P/Rs. 10.29 times 14.7 (atmospheric at sea level) is 151. 15 psi is a P/R at sea level of ~2 for a total P/R of 7.54 multiply by 14.7 for total boost of ~109

You run 151 psi in a gas car and it's going boom. so you're dealing with lower PRs which means you have to be aware of the air flow at the pr you'll be running for that primary.

If you want to run 70-80 lbs a minute and 750hp with a total boost of 45 psi, you need a turbo or s/c that has a 70-80lb/min airflow at a pr of 2.0 or less if you want to get any benefit out of it. If wtf-86 was running a GTX3076R like the other guy was running it only puts out 45-50lbs/min at 2.0 PR. so you aren't going to get more than 500 hp at 45 psi if your secondary runs at 10psi which in his case with the pos disp. s/c, was likely the case.

look at the compressor map of a GTX3076R (attached)the absolute maximum lbs/min it can provide at a P/R of 2.0 is 55.at 10hp/lbs/min that's a max hp of 550, which I believe is right about where WTF-86 maxed out. Here's the reason you can't run more than a 2.0 p/r on the primary in this case. The secondary is running a ~1.65 P/R. That gives you a total P/R of 3.3 which is ~47psi at sea level(BTW, all of these calcs change slightly the higher in elevation you go where atmospheric pressures change). If you run a larger pulley on the S/C to get lower boost from the S/C so that you have a higher P/R on the turbo, you end up defeating the purpose by losing out on the low end torque provided by more S/C.

With a bigger turbo, say a t88 which pushes out 80lbs/min at a pr of 2.0 you'll no longer have the bottle neck at the primary turbo and at 45 psi you'll be able to make 800hp if the car can breathe that much air at 45 psi.

Now look at the compressor map of a T88. It's closer to 80+lbs/min at a P/R of 2.0. It would allow for closer to 800hp at that P/R at a decent efficiency.

There's no fucking monkey math here.

[Dipstik-sportech]

All of those twin charged 86s posted use a positive displacement supercharger not a centrifugal style.

[Jaden]

Originally Posted by Dipstik-sportech

All of those twin charged 86s posted use a positive displacement supercharger not a centrifugal style.

They also used them as secondaries, but this thread is meant to discuss all aspects of compound boosting.

Multiple turbos, turbo s/c, s/c turbo, or even s/c-s/c....

hmmm. nothing stopping someone from using a centrifugal s/c into a pos. disp. s/c for a totally linear gain.... well, except for expense and that you're robbing more power from the engine to turn the two S/Cs.

Jaden

[CSG Mike]

The monkey math is in the part where you think 500hp at 3800rpm is possible. That's nearly 700 lb/ft of torque.

There are no existing components for the FA20 that can even handle that sort of stress.

I'll be more than happy to eat my words and buy a few rounds if you execute this to completion.

[Jaden]

Originally Posted by CSG Mike

The monkey math is in the part where you think 500hp at 3800rpm is possible. That's nearly 700 lb/ft of torque.

There are no existing components for the FA20 that can even handle that sort of stress.

I'll be more than happy to eat my words and buy a few rounds if you execute this to completion.

I said you'd have the air flow to make that much power not that you'd make that much power, what's more important is the torque curve, not the power. at 13 psi and 45 lbs/minute at 3500 rpm, even if the engine can't ingest all that air at that rpm, your torque curve is going to be monstrously better than a single turbo that's capable of 700+ hp. That's the whole point of compound boost, increasing the low end torque and getting a flatter torque curve and more linear power gain. Again, that's why I linked to the dsm that was running 8's at only 600hp.

He's able to do that because of the monstrous torque curve that compound boost gives you.

Plus it's going to make a hell of a lot more power at 3500rpm at 13 psi with 45lbs/min available than at 7 psi with 30lbs/min available.

Jaden

[CSG Mike]

I don't even know why you keep bringing up psi when you're already measuring the air by mass... psi is irrelevant, relatively speaking, if you know how much air mass is going into the engine.

I'd be curious to know how you plan on cooling this level of compression.

[Jaden]

Originally Posted by CSG Mike

I don't even know why you keep bringing up psi when you're already measuring the air by mass... psi is irrelevant, relatively speaking, if you know how much air mass is going into the engine.

I'd be curious to know how you plan on cooling this level of compression.

I'm not putting 45 psi into the engine, that was just a level to throw out there to illustrate the likely problem that wtf86 was running into...lol... I'm not trying to make 800hp...lol If wtf86 was running the GTX3076r at 35 or 45 psi it can't provide any more than 50-55 lbs a minute at a p/r of 2.0 which is what it would have to run at in a compound boost setup with a pos disp s/c running at 10psi. At 45 psi a fa20 should be able to ingest 82 lbs a minute so his problem was likely too small a primary turbo.

Ok let me explain it for you... You CANNOT solely look at airflow. that is NOT the most important thing.

An engine's displacement provides a certain amount of room for fuel and air to fit into it.

After that you have restrictions. You have restrictions from the intake manifold, you have restrictions from the heads and you have restrictions from the exhaust.

The final amount of fuel/air that the engine can fit is based on all of these things.

You need a fuel air ratio that won't result in detonation and destroy the engine.

The more oxygen you can fit in the cylinder the more fuel you can fit and the more power you can make.

Here is what FI allows. It compresses the air to allow you to fit more oxygen and therefore add more fuel to the cylinder without using more cylinders or bigger cylinders. So you are increasing the effective displacement of the engine. at a p/r of 2.0, you are doubling the effective displacement of the engine.

Air flow is the amount of air that a given compressor can flow at a given boost level which is shown in the compressor map (in respect to what we are discussing). There are actual other contexts of discussing airflow when talking about what the heads flow or exhaust flows etc, but those are in relation to how much air the ENGINE can flow, compressor maps only show what the FI system is capable of flowing and providing to the engine.

The amount of power you can generate is solely based on the air flow. (The air flow that the ENGINE can accept, not the air flow that the turbo can provide).

HOWEVER, the amount of air you can fit into the cylinder is solely based on effective displacement. You increase the effective displacement by increasing boost. Increasing the boost, increases the effective displacement.

You can't just throw a Vortech v3- Si trim S/C on a 2.0 liter engine and expect to make 700 hp at 7 or 9 psi of boost because the displacement doesn't allow that much air flow at 7 or 9 psi of boost regardless of how much the s/c can provide. Same thing with a turbo. You can't throw a t-88 and expect the engine to take in 65 lbs of air a minute running at 8 psi of boost. You need higher levels of boost to increase the effective displacement so that the engine can ingest that amount of air.

You have to look at both airflow AND boost to make the power you want on an engine. This is especially true on a lower displacement engine because you need higher boost levels to swallow the airflow compared to a larger displacement engine.

That's why an LSX can make 700hp at 9 psi of boost with a larger turbo or two medium sized turbos where a 2 liter engine needs 35 psi of boost to make the same power. let's take a closer look at these Real World figures to determine why that is.

a 6.2 liter lsx that makes 700 at 9 psi of boost. 9 psi at sea level is a p/r of 1.63. So you are fitting ~63% more air than the engine/heads/exhaust does alone.
If you start out with 425... guess what? multiply that by 1.63 and you get 695 or so...


a 2.0 liter fa20 that makes 700 at 35 psi of boost(that might be a bit generous). 35 psi at sea level is a p/r of 3.42. It is therefore ingesting ~242% more air than the engine/heads/exhaust does alone.
If you start out with 200... guess what? multiply that by 3.42 and you get 689 or so... Amazing, the real world results that people have seen mete up with the math almost perfectly.


The smaller engine has to make up for more than 3 times as little displacement and there are other factors that make it easier to make power in a larger displacement motor like speed of air charge freer flowing heads etc... so that you have to make up for a little bit more.

But this idea that FI system airflow is the be all end all of hp generation is insane and shows a basic lack of understanding of how boost functions.

I mean understanding that we are trying to change the effective displacement of the engine with boost is absolutely CRITICAL to effective FI management and power generation.

It's really simple. The smaller the displacement, the higher the boost necessary to make the same amount of power by being able to flow more air INTO the engine.

Understanding this concept is critical to choosing the right FI systems and even MORE critical in understanding how to deploy compound boost systems.

You need the right airflow for your power goals from the FI system, but you need the right boost levels for your displacement to be able to FIT that much air in the engine.

Jaden

[Jaden]

With all of the above in mind, there are two things to look at. Restriction at the primary FI system and restriction at the engine.

The problem that arises with restriction at the primary FI system is that it isn't flowing enough air, so you get to a level of boost where you aren't going to generate any more power because you aren't providing the necessary air flow FROM the FI system. In a compound boost setup, you can increase the boost of the secondary and REALLY increase your overall boost, but you aren't increasing the air flow, so your primary is restricting the power generation.

The problem that arises at restriction at the engine is that all the airflow from the turbo in the world isn't going to fit into the engine without INCREASING the boost level and therefore increasing the effective displacement of the engine.

There are other ways you can also decrease engine air flow restriction, with higher lift or duration or decreased exhaust restriction(insert increased exhaust size like a 3.5" exhaust), but in reference to FI systems the easiest way is to increase boost levels, although sometimes a combination of both best suits the desired outcome.

Jaden

[Jaden]

That's the other beauty of compound charge setups. When you choose the right systems, they are running at their peak efficiency ranges.

The secondary doesn't care that it's compressing air at twice the density of ambient. As far as its concerned, it's just ambient. It compresses it at a ratio of 1.6 or whatever the ratio it's compressing it at. It's efficiency at that pressure ratio is the same regardless of what the ambient (as far as it's concerned it IS ambient) is.

In the version I'm now considering as a test mule, probably an SCi trim Vortech (not Si as I was using in the example I don't want THAT much flow) feeding into a works carb turbo, I would simply use the front mount intercooler for the charge from the vortech (which will be running at a very efficient level for that S/C) and the liquid to air intercooler that comes with the works turbo. It might be subject to heatsoak because of the way the intercooler and interchanger would have to be mounted in front of each other, but there are ways around that too.

Jaden

[CSG Mike]

Originally Posted by Jaden

I'm not putting 45 psi into the engine, that was just a level to throw out there to illustrate the likely problem that wtf86 was running into...lol... I'm not trying to make 800hp...lol If wtf86 was running the GTX3076r at 35 or 45 psi it can't provide any more than 50-55 lbs a minute at a p/r of 2.0 which is what it would have to run at in a compound boost setup with a pos disp s/c running at 10psi. At 45 psi a fa20 should be able to ingest 82 lbs a minute so his problem was likely too small a primary turbo.

Ok let me explain it for you... You CANNOT solely look at airflow. that is NOT the most important thing.

An engine's displacement provides a certain amount of room for fuel and air to fit into it.

After that you have restrictions. You have restrictions from the intake manifold, you have restrictions from the heads and you have restrictions from the exhaust.

The final amount of fuel/air that the engine can fit is based on all of these things.

You need a fuel air ratio that won't result in detonation and destroy the engine.

The more oxygen you can fit in the cylinder the more fuel you can fit and the more power you can make.

Here is what FI allows. It compresses the air to allow you to fit more oxygen and therefore add more fuel to the cylinder without using more cylinders or bigger cylinders. So you are increasing the effective displacement of the engine. at a p/r of 2.0, you are doubling the effective displacement of the engine.

Air flow is the amount of air that a given compressor can flow at a given boost level which is shown in the compressor map (in respect to what we are discussing). There are actual other contexts of discussing airflow when talking about what the heads flow or exhaust flows etc, but those are in relation to how much air the ENGINE can flow, compressor maps only show what the FI system is capable of flowing and providing to the engine.

The amount of power you can generate is solely based on the air flow. (The air flow that the ENGINE can accept, not the air flow that the turbo can provide).

HOWEVER, the amount of air you can fit into the cylinder is solely based on effective displacement. You increase the effective displacement by increasing boost. Increasing the boost, increases the effective displacement.

You can't just throw a Vortech v3- Si trim S/C on a 2.0 liter engine and expect to make 700 hp at 7 or 9 psi of boost because the displacement doesn't allow that much air flow at 7 or 9 psi of boost regardless of how much the s/c can provide. Same thing with a turbo. You can't throw a t-88 and expect the engine to take in 65 lbs of air a minute running at 8 psi of boost. You need higher levels of boost to increase the effective displacement so that the engine can ingest that amount of air.

You have to look at both airflow AND boost to make the power you want on an engine. This is especially true on a lower displacement engine because you need higher boost levels to swallow the airflow compared to a larger displacement engine.

That's why an LSX can make 700hp at 9 psi of boost with a larger turbo or two medium sized turbos where a 2 liter engine needs 35 psi of boost to make the same power. let's take a closer look at these Real World figures to determine why that is.

a 6.2 liter lsx that makes 700 at 9 psi of boost. 9 psi at sea level is a p/r of 1.63. So you are fitting ~63% more air than the engine/heads/exhaust does alone.
If you start out with 425... guess what? multiply that by 1.63 and you get 695 or so...


a 2.0 liter fa20 that makes 700 at 35 psi of boost(that might be a bit generous). 35 psi at sea level is a p/r of 3.42. It is therefore ingesting ~242% more air than the engine/heads/exhaust does alone.
If you start out with 200... guess what? multiply that by 3.42 and you get 689 or so... Amazing, the real world results that people have seen mete up with the math almost perfectly.


The smaller engine has to make up for more than 3 times as little displacement and there are other factors that make it easier to make power in a larger displacement motor like speed of air charge freer flowing heads etc... so that you have to make up for a little bit more.

But this idea that FI system airflow is the be all end all of hp generation is insane and shows a basic lack of understanding of how boost functions.

I mean understanding that we are trying to change the effective displacement of the engine with boost is absolutely CRITICAL to effective FI management and power generation.

It's really simple. The smaller the displacement, the higher the boost necessary to make the same amount of power by being able to flow more air INTO the engine.

Understanding this concept is critical to choosing the right FI systems and even MORE critical in understanding how to deploy compound boost systems.

You need the right airflow for your power goals from the FI system, but you need the right boost levels for your displacement to be able to FIT that much air in the engine.

Jaden

One day, you'll realize that this whole post is monkey math.

I recommend you revisit high school chemistry and study some gas law. Then, take some upper division collegiate level fluid dynamics courses, and then some graduate level courses on combustion, and you'll see why what you posted is math that "conveniently fits" but is actually completely incorrect.

Hint: In your pursuit to match up psi with relative output, you've completely forgotten about heat. I ask again: how do you plan on cooling this level of compression?

Hint #2: PSI is meaningless. Since we're thinking strictly theoreticals, YES, I can, in fact, come up with a theoretical scenario where a 2.0 liter displacement engine CAN make 700 horsepower, at 7 psi.

Have you *actually* ever boosted a car to a significant level of power before?

[EAGLE5]

LOL.

[Spartarus]

Ok, you learned to look at a compressor map, swallowed a blue pill, and woke up in the matrix.

You don't know kung fu.

Stop.

Yes, compound boost is an interesting topic, but you need to be doing more learning and less declaring.

[FRS Justin]

here is some useless info but interesting


Here are the ten most powerful ones on the market today :
2015 Mercedes-Benz GLA 45 AMG / CLA 45 AMG
Mercedes-AMG developed a 2.0L turbo which currently is the most powerful series-production four-cylinder engine in the world. Available in the GLA 45 AMG and the CLA 45 AMG, its output is rated at 355 hp and 332 lb-ft of torque.
2016 Volvo XC90
Volvo's 2.0L turbo and supercharged four-cylinder engine is part their new Drive-E powertrain family. In the 2016 Volvo XC90, it develops 316 hp and 295 lb-ft of torque.
2015 Ford Mustang
Ford offers a new four-cylinder 2.3L EcoBoost turbocharged engine which has been specifically tuned for the 2015 Mustang to produce 310 hp and 320 lb-ft of torque.
2015 Subaru WRX STI
For the 2015 WRX STI, Subaru has the highest-displacement four-cylinder engine in this list, a 2.5L turbo that produces 305 hp and 290 lb-ft of torque.
2015 Mitsubishi Lancer Evolution
The 2015 Mitsubishi Lancer Evolution has a 2.0L turbo engine with an output of 291 hp and 300 lb-ft of torque.
2015 Audi S3
Audi's most potent turbocharged four-cylinder 2.0L engine is included in the 2015 S3, producing 290 hp and 280 lb-ft of torque.
2015 Kia Optima
The 2015 Kia Optima has a four-cylinder 2.0L turbo engine with an output of 274 hp and 269 lb-ft of torque.
2015 Cadillac ATS / CTS
In the 2015 Cadillac ATS, GM's turbocharged 2.0L four-cylinder engine produces 272 hp and 295 lb-ft of torque.
2015 Subaru WRX
The 2015 Subaru WRX boasts a turbo 2.0L four-cylinder engine that produces 268 hp and 258 lb-ft of torque.
2015 Ford Focus ST
An EcoBoost turbocharged 2.0L four-cylinder engine is included in the 2015 Ford Focus ST, which develops 252 hp and 270 lb-ft of torque


Look at number 2 Volvo its a compound s/c and turbo, kinda cool a manufacture is trying it but the numbers aren't close to 500hp tho

[EAGLE5]

https://s-media-cache-ak0.pinimg.com...fe015fe1ca.jpg