Turbo sizing article(by me)

[nissanfanatic]

http://www.automotiveforums.com/vbul...=108747&page=7

The last post on the page. Tell me if you find any mistakes or should I say anything correct. I used this method to size the turbocharger on my car. It works!

[SaabJohan]

From a fast look I can tell you that your calculations of the temperature rise is incorrect. I think I have posted how to calculate that earlier.

Also note that it's common that there is a small pressure drop in the compressor inlet (due to the air filter and so on), this + pressure loss in the intercooler and tubing results in a slightly higher compression ratio than one might think.

When calculating flow though the engine one can start with the engine output, an engine typically requires somewhere around 3.5 to 4 kg air per kWh.

Using volumetric efficiency can be somewhat difficult to calculate with if one doesn't have any measured data. Typically VE is around 70 to 100% for a modern four valve engine, but racing engines can be have VE's of over 130%.

[Zgringo]

Originally Posted by SaabJohan

From a fast look I can tell you that your calculations of the temperature rise is incorrect. I think I have posted how to calculate that earlier.

Also note that it's common that there is a small pressure drop in the compressor inlet (due to the air filter and so on), this + pressure loss in the intercooler and tubing results in a slightly higher compression ratio than one might think.

When calculating flow though the engine one can start with the engine output, an engine typically requires somewhere around 3.5 to 4 kg air per kWh.

Using volumetric efficiency can be somewhat difficult to calculate with if one doesn't have any measured data. Typically VE is around 70 to 100% for a modern four valve engine, but racing engines can be have VE's of over 130%.

Very good, I'm impressed to see someone has there ducks in a row.

Albert

[454Casull]

Originally Posted by SaabJohan

From a fast look I can tell you that your calculations of the temperature rise is incorrect. I think I have posted how to calculate that earlier.

Also note that it's common that there is a small pressure drop in the compressor inlet (due to the air filter and so on), this + pressure loss in the intercooler and tubing results in a slightly higher compression ratio than one might think.

When calculating flow though the engine one can start with the engine output, an engine typically requires somewhere around 3.5 to 4 kg air per kWh.

Using volumetric efficiency can be somewhat difficult to calculate with if one doesn't have any measured data. Typically VE is around 70 to 100% for a modern four valve engine, but racing engines can be have VE's of over 130%.

Not to nitpick or anything, but kWh is a unit of energy, not power (I assume by "output" you meant "power").

[duplox]

So, if 'power' is not energy... what is power? There is a direct conversion for kWh to HP. If anything, horsepower is the less sensical representation of 'power'. Torque(turning power) times RPM divided by 5252... who cares? Just give me a torque vs rpm graph.

[nissanfanatic]

Originally Posted by SaabJohan

Also note that it's common that there is a small pressure drop in the compressor inlet (due to the air filter and so on), this + pressure loss in the intercooler and tubing results in a slightly higher compression ratio than one might think.

That is usually about 1-2psi combined correct? Considering most people who actually go through with this will have a high flow filter.

Originally Posted by SaabJohan

When calculating flow though the engine one can start with the engine output, an engine typically requires somewhere around 3.5 to 4 kg air per kWh.

Roughly 10hp to every 1lb/min of airflow. Now do you calculate horsepower before the turbocharger is installed by multiplying existing output (in HP) by the pressure ratio? I used that method and it matched up with the 400m mph calculator.

Originally Posted by SaabJohan

Using volumetric efficiency can be somewhat difficult to calculate with if one doesn't have any measured data. Typically VE is around 70 to 100% for a modern four valve engine, but racing engines can be have VE's of over 130%.

Could you possibly measure this by output converted to airflow? Like my 146CID theoretically flows 16.2lb/min at 5600rpm where it makes 155hp. Now do 16.2/15.5 and get 1.04. So there is a VE of 96%? Please point me in the right direction if I am wrong. Thanks.

[BeEfCaKe]

Originally Posted by duplox

So, if 'power' is not energy... what is power? There is a direct conversion for kWh to HP. If anything, horsepower is the less sensical representation of 'power'. Torque(turning power) times RPM divided by 5252... who cares? Just give me a torque vs rpm graph.

Power is NOT energy.. Energy(Joules -->J) is obtained by integrating power(Watts--> W --> J/s).
kWh is a unit of ENERGY as you can see, because it too is in Joules.

[duplox]

My bad, there is a conversion for kW to hp, not kwh... damn h. thanks for the clarification

[SaabJohan]

To get a good indication of VE from engine power since we doesn't know the efficiency of the engine. We should however be able to estimate it with data on fuel flow and air fuel ratio (if the engine have been runned in a dyno earlier this data are typically known or can be calculated). Fuel from can be calculated from the injector size and the time they are open (it can also be corrected further for a more exact result).

The pressure losses seen over the intercooler and the air filter can vary, but in general they shouldn't be that high.

When estimating the power of a forced induction engine compared to the same engine without forced induction you must calculate the difference in density as seen in the intake manifold. So simply divide the absolute pressure with the absolute pressure as seen in the NA version (typically 1 bar), this can then be corrected by calculating the effect of the temperature rise caused by the compressor. If the intercooler is considered good enough this part can be skipped.

[nissanfanatic]

Thanks.