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Discussion Starter #1
so I've recently turbocharged by d16y8 with Go-Autoworks' street kit with the Garrett t3 60 .48 a/r
while it's obvious why I gained power from boost pressure, what I don't understand is why it feels like there is so much more torque in the vacuum/lower throttle range. e.g. if I hold the throttle at 10inHg (which is light throttle, at least in my car) I can definitely tell that there is a lot more torque and my car speeds up much faster than before. I can hear the turbo spooling, or rather maintaining a constant rate, but my vacuum/boost gauge says 10inHg so I know I'm still in the vacuum parts of my maps. So why is there all this torque even when the turbo isn't forcing air into the engine? what is different? I know it cant just be the tune because then so many people would go out an get their naturally aspirated cars tuned for this torque gain (its significant) so I know it has something to do with the turbos effect on the air that the engine is sucking in. Any ideas?
 

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There is this weird notion that a turbo somehow decreases throttle response, but its total BS. With a well sized turbo as soon as you start to touch the throttle the turbo is starting to spin and pump air. So even when youre at low throttle and the pressure drop across the throttle is is still below atmospheric, you still have positive pressure before the throttle and are flowing more than you would be NA.
In other words, throttle response (depending on your definition of the term) is actually improved!

This is one of the only legitimate issues with turbos when road racing. Its not that throttle response is hurt, its that the power can come on even with a small amount of throttle.
With an NA car, you can hold the throttle at one point through a long corner and youre torque does not change much (especially if RPM is constant), but when turbocharged you can experience partial throttle boost, where the turbo starts spooling without the throttle position is held constant.
 

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Discussion Starter #5
There is this weird notion that a turbo somehow decreases throttle response, but its total BS. With a well sized turbo as soon as you start to touch the throttle the turbo is starting to spin and pump air. So even when youre at low throttle and the pressure drop across the throttle is is still below atmospheric, you still have positive pressure before the throttle and are flowing more than you would be NA.
In other words, throttle response (depending on your definition of the term) is actually improved!

This is one of the only legitimate issues with turbos when road racing. Its not that throttle response is hurt, its that the power can come on even with a small amount of throttle.
With an NA car, you can hold the throttle at one point through a long corner and youre torque does not change much (especially if RPM is constant), but when turbocharged you can experience partial throttle boost, where the turbo starts spooling without the throttle position is held constant.
Thats exactly what i was looking for! So essentially, more air is being flowed through the intake at 10inHg with the turbo than there would be at 10inHg without the turbo (or any throttle position for that matter). I guess it's almost the inverse of poor throttle response in that although there is a lag to the total power available at any given throttle position, the current power (at any throttle position) is going to be higher than it would be on an na motor, correct?
 

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Discussion Starter #6
an issue i have about the increased flow of air enabling more torque in the vacuum range is this: how do tuners tune part throttle (mostly in the vacuum range) if the amount of air is increasing? and why do people advise others to "keep out of boost" when running on a basemap when even in the vacuum ranges the fuel requirement will be higher (which is because of the higher torque, correct?)? even the tuning programs seem in need of more info from the engine i.e. the map sensor reads the manifold air pressure but the flow is dependent upon throttle position/longevity as well as turbo size. So i guess my main question is how tuners can so easily tune part throttle when the flow of air is always changing despite what any gauge/sensor says (disregarding maf sensors, as most hondas that i know of do not have these).
 

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That is not what full tilt said.

First do not relate amount of air to pressure, boost cfm or anything else other than mass air flow or your thinking will be wrong.

the amount of air flowing through any point the engine is pretty much the same in that the amount that goes into the air cleaner is what comes out the exhaust pipe plus the fuel as well of course.

If the turbo is pumping rather than just idling along, it will pump air into the charge pipe until it reaches a pressure where the power of the hot side is in balance with the power required by the cold side to pump that mass of air at that pressure.

The throttle plate controls the amount of air flowing into the inlet manifold. At a set throttle position, more boost equals more airflow into the engine AND less vacuum in the manifold. To maintain equal vacuum in the manifold AFTER the throttle when under boost in the charge pipe BEFORE the throttle, you need to close the throttle more to maintain constant mass air flow. This results to very close to the same manifold vacuum and fuel flow requirement to make the same power to maintain a constant cruise speed.

Tuners may change this by playing with spark and fuel to give more power at the same vacuum, but they can alsoi do that on an NA engine. How much they can gain depends on the factory tune and how well it was optimised to those factors.

The factory has to consider many things other than power and economy only in your use environment.

They need to consider things like emissions, extremely cold or hot environment, durability, reliability, simplicity of operation poor fuel quality, stable idle as A/C and alternator and P/S kick in, smoot quiet operation and throttle response and I am sure several other things that you tuner can neglect to some extent.
 

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lol.

Simply put. The motor sucks in air right. On NA it sucks as hard as it can to get the air in. power is lose due to some of that.

Turbo is spinning because motor is running. It it now pushing air in while the car is sucking. So the car is working less.

Now real world test.
Pull a waging with some weight in it. Kinda hard but you can do it.
Now have someone push on the other end while your pulling. Very easy right/.
Now boost would be using a truck to push the waging.
 

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I don't buy the reduced pumping losses argument with a turbo. In fact I think the opposite.

The engine still has to pull the vacuum in the IM so that pumping has to occur to the same extent for the same MAP.

The engine has to pump harder on the exhaust stroke to force all exhaust through the restriction of the turbo. At light throttle there is not that much exhaust gas so it is fairly easy to pump through the turbine scroll nozzle, but it still does exist.

A turbo is not an over unity device. ie it cannot pump out more energy than it takes to drive it.
 

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Discussion Starter #11
patprimmer, i think i almost understand. Amount of air is related to mass air flow, pressure is measured after the throttle, and boost cfm is the cubic feet of air moved by the turbo, correct? You said that the throttle plate controls the amount of air going into the inlet manifold (and thus the engine). So if i held the throttle open at a certain position (and held it there) more and more air would be flowing into the engine because of the turbocharger. If i wanted to keep the amount of air flowing into the engine constant, then i would have to slowly (or at whichever rate) close the throttle plate. So i guess manifold pressure (as measured by my vacuum/boost gauge) is not a measurement of throttle position, correct?

I think it's time for me to reread all 26 pages of rrussell's thread lol

airflow, pressure, cfm, throttle...lol i'll get there, i hope i'm not asking unintelligent questions!
 

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patprimmer, i think i almost understand. Amount of air is related to mass air flow, pressure is measured after the throttle well certainly MAP is measured after the throttle plate, and boost cfm is the cubic feet of air moved by the turbo You don't quite grasp this yet. Boost is measure in PSI. CFM is not a realistic measure as the mass of air in the same number of cubic feet changes with both pressure and temperature, correct? You said that the throttle plate controls the amount of air going into the inlet manifold (and thus the engine). So if i held the throttle open at a certain position (and held it there) more and more air would be flowing into the engine because of the turbocharger Kinda. The turbo will always try to balance out both wheels. They are on a common shaft so must turn at the same speed. If the hot side is producing more power than the cold side absorbs, the turbo will spool up. if it is producing less, the turbo will spool down. As the turbo changes speed it will likely change boost and you will need to change throttle position to maintain a constant MAP. The whole situation is dynamic. The time taken for the turbo speed to become enough to reach significant boost is the lag time. The turbo always trying to reach a speed where the two wheels are in equilibrium (fancy word that kinda means in balance) and that is what makes turbo cars harder to drive on a winding track. You need to keep readjusting throttle to maintain steady power and the changes in power have both a time delay and tend to be at an exponential rate (another fancy word that kinda means it's a snowball effect). If i wanted to keep the amount of air flowing into the engine constant, then i would have to slowly (or at whichever rate) close the throttle plate. So i guess manifold pressure (as measured by my vacuum/boost gauge) is not a measurement of throttle position, correct? Correct

I think it's time for me to reread all 26 pages of rrussell's thread lol

rrussel is well worth reading and re reading until you really get what he is saying

airflow, pressure, cfm, throttle...lol i'll get there, i hope i'm not asking unintelligent questions!

Combined gas law - Wikipedia, the free encyclopedia

These say that in a gas, temperature, pressure and volume are intimately related.

Example

in a bicycle pump blocked of at the tyre connection end.

You draw the handle out. This increases the volume and the one way valve (washer) allows everything to equalise as air flows in so you have a set volume of air at near enough to ambient temperature and pressure.

You push the handle in. The volume decreases, but both temperature and pressure increase. That is why the pump gets hot as you pump up a tyre

Also if you open the valve on a bottle of LPG, the gas gets cold and it's volume increases almost infinitely as you release it from the pressurised bottle.
 

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Discussion Starter #15
Ok that all makes sense to me now, thank you for clearing that up! And feel free to use the big words lol I understand their meanings.
Acid Beaver, thats because the turbo is supplying more air than what is normally taken in by the engine, correct?
And I whole heartedly agree that the turbo does not supply free energy,work, or power. I had a big arguement at work because a guy was telling me that this group in california made a 100percent efficient generator and I told him that only the Carnot engine is 100 percent efficient and exists only in theory. Thermodynamics ftw lol Turbos do not create or generate free power, they just utilize an engines waste exhaust to enable the engine to ingest more air.
 

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I don't buy the reduced pumping losses argument with a turbo. In fact I think the opposite.

The engine still has to pull the vacuum in the IM so that pumping has to occur to the same extent for the same MAP.

The engine has to pump harder on the exhaust stroke to force all exhaust through the restriction of the turbo. At light throttle there is not that much exhaust gas so it is fairly easy to pump through the turbine scroll nozzle, but it still does exist.

A turbo is not an over unity device. ie it cannot pump out more energy than it takes to drive it.
Agreed.

All else being equal, the only way turbocharging will improve BSFC is with engine downsizing.... to a point.
 

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Yeah.

Smaller engines are more efficient because there are generally less friction and pumping losses for the same power output. The issue is when you go too small, and the ECU has to enrich every time you want to accelerate.

D15/16's are small enough as it is, so I wouldn't reduce their displacement at all. However, with something larger, especially V6/V8 engines, reducing engine size will improve efficiency, and turbocharging will allow the engine to recover the power lost.

The RDX with its turbo I4 engine is an example of a downsized turbocharged engine that doesn't really work. Whenever you want to accelerate, even if you're using cruise control, it will spool the turbo and add fuel to protect the engine. Part of this is the DBW calibration, but even so, the engine is a little too small for an SUV on the highway.
 

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Discussion Starter #20
Ok that's what I was thinking. Now would turbocharging an engine, a d16 for example, would it have a better BSFC than say a larger engine of comparable output? It would make sense if it did based on what I've read.
 
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