RedLine Tech/Turbo Facts

[Demon_C5]

Is there a place one can go to research and gain an understanding on the inner-workings of the RedLine? More specifically, how the ECU relates to the turbo/boost, regulating or increasing boost, safe boost levels with stock turbo, stock power ratings of turbo, airflow restrictions of the stock system, etc.

I'd like to get the skinny on the RedLine from the ground up, since this is my first turbo equipped vehicle. I see a few things on vendor sites and here on the forum that seem contradictory, and would like to seperate fact from fiction.

Thanks!

[Bogie]

Originally Posted by Demon_C5

Is there a place one can go to research and gain an understanding on the inner-workings of the RedLine?

If you find it, let me know.

Here's the compressor map:


You can get bits a pieces form the Solstice Book, and some of the interviews with the designers.

[|V3nom|]

what does that graph even mean, im so confused by it .

[Griz]

Originally Posted by |V3nom|

what does that graph even mean, im so confused by it .

Translation: The more you mash the pedal, the faster you go the volume of fuel is inversely proportionate to the time spent with the pedal mashed to the floor.

[Bogie]

Originally Posted by |V3nom|

what does that graph even mean, im so confused by it .

Horizontal line (x axis) is the volumetric flow. The volume of air moving through the turbo.

Vertical Line (y axis) is the pressure, normalized to ambient. Number on the left is from the chart. Number on the right is psi (what you see on the boost gauge)

1.0 = 0
1.4 = 5.9
1.8 = 11.8
2.2 = 17.6
2.6 = 23.5
2.8 = 26.5

The middle of the chart identifies the efficiency at each respective flow and psi.

The chart also shows the redline for the impeller, which occurs at 183500 rpm. If you look at the psi for redline, it's between 2.6 and 2.8, which means you redline the turbo between 23.5 and 26.5. Stock design is "up to" 20.

[SCVanguard]

I was going to start asking about this as well. Now that I've seen graphs for our little turbo compared to some upgraded ones that run much more boost, I just have to ask...can the engine take the extra psi? What other things do you need to change in order to run the bigger turbos?

[|V3nom|]

so does the chart show that you get the most airflow or something around 150000 rpms?

[Demon_C5]

I wasn't thinking quite that specific, but something along the lines of what I had mentioned would be nice.

I take it nobody really knows though?

[Bogie]

Originally Posted by |V3nom|

so does the chart show that you get the most airflow or something around 150000 rpms?

I was using the impeller RPM as an example of where the turbo redlines.

For the engine itself, you have to work the numbers from a displacement and valve overlap standpoint.

We have a 2 Liter (122 cid) engine. Without any valve overlap and assuming we move air equal to displacement over the four stroke cycle, then air flow is determined by engine RPM:

2000RPM = 70.6 cfm
5000RPM = 176.5 cfm
6000RPM = 212 cfm

Our turbo chart measures flow in meters per second instead of cfm. Converting, we get:

2000RPM = 70.6 cfm = 0.033 m3/s
5000RPM = 176.5 cfm = 0.083 m3/s
6000RPM = 212 cfm = 0.1 m3/s

The 73% efficiency section of the chart occurs for flow of between .08 to .12 m3/s.

At first glance it would appear the meat of the SKY RPM range falls below the peak efficiency range of the turbo. This is where VVT valve overlap comes in. The numbers above assume the flow is equal to what the displacement can handle on each stroke cycle. By overlapping the valves, additional air is pushed through, moving the operating region further to the right than reflected in the calculations above, which gives the turbo the flow rate it needs for optimal performance.

When running near engine redline of 6300, the engine is working at a flow rate for optimal flow to the turbo, so there might not be any overlap. Most overlap occurs for low RPM, which is where the additional flow is needed to keep the turbo running efficiently.


cid = cubic inches of displacement
cfm = cubic feet per minute
m3/s = cubic meters per second

[|V3nom|]

ive given up trying to understand it hurts my head lol. dont try to explain it, i really dont need to know it and i dont want to put the effort to figure it out, mainly due to me being lazy :P.

[SKYMAN-CT]

Originally Posted by Bogie

I was using the impeller RPM as an example of where the turbo redlines.

For the engine itself, you have to work the numbers from a displacement and valve overlap standpoint.

We have a 2 Liter (122 cid) engine. Without any valve overlap and assuming we move air equal to displacement over the four stroke cycle, then air flow is determined by engine RPM:

2000RPM = 70.6 cfm
5000RPM = 176.5 cfm
6000RPM = 212 cfm

Our turbo chart measures flow in meters per second instead of cfm. Converting, we get:

2000RPM = 70.6 cfm = 0.033 m3/s
5000RPM = 176.5 cfm = 0.083 m3/s
6000RPM = 212 cfm = 0.1 m3/s

The 73% efficiency section of the chart occurs for flow of between .08 to .12 m3/s.

At first glance it would appear the meat of the SKY RPM range falls below the peak efficiency range of the turbo. This is where VVT valve overlap comes in. The numbers above assume the flow is equal to what the displacement can handle on each stroke cycle. By overlapping the valves, additional air is pushed through, moving the operating region further to the right than reflected in the calculations above, which gives the turbo the flow rate it needs for optimal performance.

When running near engine redline of 6300, the engine is working at a flow rate for optimal flow to the turbo, so there might not be any overlap. Most overlap occurs for low RPM, which is where the additional flow is needed to keep the turbo running efficiently.


cid = cubic inches of displacement
cfm = cubic feet per minute
m3/s = cubic meters per second

Great job Bogie,

Now I remember why I learned all the math and conversions back in engineering school?

[R3DLIN3]

What I find most interesting is that I am running 23-25 psi @ .7 efficiency, and peak efficiency is .73 for this turbo. Some here have claimed that running 23-25 psi on the stock turbo is very inefficient boost, yet this chart clearly shows only a 2-3% reduction from lower boost efficiency.

[Bogie]

I've boiled it down to RPM and PSI, along with what looks like the prime operating zone, which I've highlighted with a green oval. The idea is to have the RPM lines cross the psi lines at the optimal location in the middle of the chart.

The RPM lines are based on "basic" flow not accounting for valve overlap. The actual operating lines will move to the right, so I suspect our turbo operates closer to the green oval than the RPM lines suggest. I'm not sure by how much because I don't know how much flow occurs on the valve overlap at each RPM.

The horizontal lines are psi lines; I'm showing operating lines at 12, 18, 23, and 25 psi.

The stock system is designed to operate "not to exceed" 20 psi. It looks like you can stretch it to 23 psi OK, but the 25 psi line is above the turbo redline (the top most line on the original graph) at all flow rates except the area above the optimum zone. If you're running 25psi on a regular basis, you are playing in a dangerous region at the turbo design limit.

Caveat: I'm playing with straight engineering numbers. The reality of the Borg Warner in our vehicles might not be fully reflected in the chart. I'm assuming a 14.7 psi ambient. The flow numbers are based on what goes through the engine. There will be fluctuations between the turbo and the intake, which I don't know how to account for or model. So use this information to gather a general idea of what's going on. When it comes to actually tuning a vehicle, you'll probably need a good dose of reality (which always tends to destroy the pretty engineering numbers) before you can get it right. And I'll leave discussion of that technical reality to the folks who actually do this for living.

[RedHeaded RedLine]

Originally Posted by Bogie

I've boiled it down to RPM and PSI, along with what looks like the prime operating zone, which I've highlighted with a green oval.

Hubby gets it. - I like the pretty colors... use more colors. -J