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Discussion Starter #1 (Edited)
I would like to know more about how turbo boost is applied to our 1.5L engine. So I have a few questions.

1. Do the instruments that plug into the OBD port give you a real time readout of boost?

2. Is the boost constant at a given rpm. For example always at the 18.5 limit at 3000 rpm, or does the system only supply to max boost when accelerating and back off when cruising at highway speeds.

3. At what rpm (under acceleration?) does the boost reach the 18.5 limit?

Of course we don't 'need to know' the answer, but I am curious.
 

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1) Yes, it's real-time, subject to the polling interval of your OBD gadget and the accuracy of the numbers reported by the sensor.

2) You have it correct; when there's not much requested load on the engine, there will be no boost, irregardless of the current RPM. Steady cruise at normal highway speeds on level ground will never have any boost.

3) Don't know the answer to that one, but I expect it's not much; it's a tiny turbo and a tiny engine. Shouldn't need a ridiculous amount of exhaust flow to reach max potential. Certainly you don't have to be at redline or anything.
 

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Turbo boost is related to engine load (air flow into the engine) as more air in equals more exhaust out. More exhaust pressure/volume will normally cause more spin in the turbo which equals more boost pressure. But, there is some control of the boost by something called a "waste gate" that can limit the boost. This can be directly controlled mechanically or can be controlled by the engine management computer. So, you can't have boost without sufficient exhaust flow/pressure but you can limit the boost and control it. So, at a given speed you can have a great amount of variation in exhaust flow/turbo boost depending on how much exhaust is flowing out of the engine. A simple example of this would be how much air/exhaust would be flowing at 3000 RPM if you were 1) Going up a steep hill with your foot to the floor, 2) driving at a steady speed on a flat road, or 3) going down a steep downhill with the throttle closed. In each of these situations the boost would be very different. In #3 and maybe in #2 you would have little and likely no boost whatsoever.

Read more here: https://en.wikipedia.org/wiki/Turbocharger
 

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Max torque of 179 ft.-lb. is reached at 2000 rpm and maintained all the way to 5000 rpm.
Max HP of 190 achieved at 5600 rpm.
I deduce that the maximum turbo boost is reached at 2000 rpm and is carried all the way thru to 5000 rpm.
 

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I use the ScanGauge II (Linear Logic) OBD-II reader, $170. Have it set to display engine coolant temp, tranny fluid temp, boost and loop (open/ closed). Honda says max boost is set at 16.5 psi.
 

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I think the 16.5psi may be misleading. I think it's 16.5psi increase over the incoming charge to the compressor. So if normally it's at -12psi of vacuum., then with 16.5psi boost, you get +4.5psi above atmospheric. That's at least what I'm seeing when I have a bluetooth adapter plugged in. Found that interesting. Most of the time, the turbo is producing boost, but overall MAP is still showing a vacuum.
 

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I think the 16.5psi may be misleading. I think it's 16.5psi increase over the incoming charge to the compressor. So if normally it's at -12psi of vacuum., then with 16.5psi boost, you get +4.5psi above atmospheric. That's at least what I'm seeing when I have a bluetooth adapter plugged in. Found that interesting. Most of the time, the turbo is producing boost, but overall MAP is still showing a vacuum.
Wow really? That?s really conservative no? Turbo upgrade?
 

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I use the ScanGauge II (Linear Logic) OBD-II reader, $170. Have it set to display engine coolant temp, tranny fluid temp, boost and loop (open/ closed). Honda says max boost is set at 16.5 psi.
Is 16.5 something you've observed with your ScanGuage, or a (likely typo) from the spec sheet? (I ask because the 10th-gen Civic is listed at 16.5, and one of the design points for the CR-V turbo was increased boost. (And other Honda sources place the '17 CR-V at the expected 18.5 psi)
 

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Discussion Starter #11
I am still uncertain why a constant cruise speed of 3000 rpm does not produce the same amount of exhaust gases as an engine accelerating through 3000 rpm. Wouldn't the amount of gas be (3000/4 * 1.5L) 1125 Liters/Minute in both cases? I can see why a closed throttle would result in less exhaust gas and engine braking as the engine decelerated through 3000 rpm.

So wouldn't the available boost be about the same when cruising vs accelerating? Is the waste gate being manipulated to reduce the boost when cruising in our CR-V to reduce fuel consumption?

I have ordered a bluetooth OBD-II device. I will be making some observations in the coming weeks using the Torque Android app.

I hope to find out if that 18.5 (or 16.5) psi maximum boost number is absolute or a delta above the 14.7 psi at normalized sea level for a total of about 31.2 (or 29.2) psi. And the rpm where we first see maximum boost.
 

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Boost is load depended not RPM. If you free rev the motor in Park does it make boost? The answer should be very little to none. More load--> more gas --> more exhaust thermal energy --> boost

If you are cruising you won't see max boost. Wouldn't make any sense since your MPG would go down the drain. But if you are accelerating and applying load than that is when boost will apply. how much boost depends on engine load, rpm speed, a few other factors (i.e. ignition timing, etc etc)


FYI hondata already has all the dyno number and boost number on their website. From the looks of it boost is just under 14.3 psi around 3250rpm, peak torque is around 4400-4500 in stock form and about 180 @ 6500 to the ground. See link below.

https://www.hondata.com/flashpro-2017-crv
 

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I am still uncertain why a constant cruise speed of 3000 rpm does not produce the same amount of exhaust gases as an engine accelerating through 3000 rpm. Wouldn't the amount of gas be (3000/4 * 1.5L) 1125 Liters/Minute in both cases? I can see why a closed throttle would result in less exhaust gas and engine braking as the engine decelerated through 3000 rpm.

So wouldn't the available boost be about the same when cruising vs accelerating? Is the waste gate being manipulated to reduce the boost when cruising in our CR-V to reduce fuel consumption?

I have ordered a bluetooth OBD-II device. I will be making some observations in the coming weeks using the Torque Android app.

I hope to find out if that 18.5 (or 16.5) psi maximum boost number is absolute or a delta above the 14.7 psi at normalized sea level for a total of about 31.2 (or 29.2) psi. And the rpm where we first see maximum boost.
Reading your reply I can see you may not understand how an internal combustion engine works. First, you can only compress what air you allow into the engine. This is the purpose of the throttle plate. The amount of power you make is determined by the pressure in the cylinder. At a given speed that pressure can change greatly depending on engine load. Engine load refers to how hard the engine is working to maintain a certain speed. Again consider a vehicle running a stead speed on a level road to the same vehicle going down a steep hill with the throttle closed or up a steep hill with the throttle fully opened. In each case the amount of air going into the cylinder is different. If you add more air to a given space it will compress more and produce more pressure and power. (and more exhaust to spin your turbocharger) Less air will make the pressure in the cylinder lower and produce less power. Anything that comes in the intake valve has to go out the exhaust. The more air you put into that cylinder the more you have coming out waiting for a chance to spin up that turbo supercharger.
 

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Discussion Starter #16
I think you are right again, hans471+. I am here to learn.
 
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