[wildcat]

I had my smog done again.  Apparently hadn't paid much attention 2 years ago, just glad it passed but noted with surprise the numbers I got on a 140k + car.  So

I'd like to share them for comparison.  This is an original Cabriolet Cali-car sold in Woodlands Hills back in '93.

 

 

                          %Co2    %O2            HC   (PPM)                            CO%                   NO (PPM)    

Test        RPM    Meas    Meas      Max   Ave  Meas             Max    Ave   Meas       Max   Ave  Meas

15 mph   1746   14.68    3.72         86    23      9                 0.50    0.08  0.01        697   194   211

25 mph   1480   14.70    2.01         51    14      8                 0.48    0.06  0.01        724   166   244 

 

Didn't do anything to the car figuring if it needed some assistance I'd take care of it... so the air filter had a few thousand miles,

the spark plugs NKG's which I'm really fond of had more, rotor, distributor etc. same.

 

I was impressed to say the least. Its always nice when they pass but this was a pleasant surprise.

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[ds968]

I'm surprised at the results every time I smog check my 968s  ( both are over 125 K miles now ) although I should't be ; these cars run so clean you'd have to deliberately try to make them fail... heck, short of removing the catalytic converter you can neglect just about everything else and still pass it seems..     

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[wildcat]

Nice huh? And I probably wouldn't have paid any attention only I noticed the tech ran the test twice and I wondered why... couldn't believe it I suppose.

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[flash]

lol - the lab had to run my tests twice when i was getting the supercharger kit certified.  it ran so clean they thought it had to be wrong.

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[968Syncro]

One of the big reasons is the variocam.    The valve timing can be optimized for low emissions at low RPM without compromising performance at high RPM.

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[wildcat]

With computerized fuel injection and a supercharger installed, I would argue that your system is not pumping more air into the chamber only faster, so your emissions would be the same.

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[flash]

it definitely adds more air.

 

http://ateupwithmotor.com/terms-technolo...rcharging/

 

http://auto.howstuffworks.com/supercharger.htm

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[Kim]

a fixed cylinder volume filled more (or perhaps completely) due to a higher positive pressure air source above atmospheric = a higher total volume of air/cylinder fill. I don't know that the cylinder could be filled "faster" under postive supercharger pressure vs under a vacuum by decompression because the piston speed is fixed whether there is a supercharger or not (hence the fill time is fixed) but the addition of positive pressure from a supercharger would ensure that it is filled more.

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[flash]

eloquently put

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[Kim]

My internal knowledge level had exceeded storage capacity. Not necessarily meaning that I know a lot; perhaps only that I have limited capacity to store even trivial quantities of info.  In any event, I just needed to get rid of something that I knew I would not need need tomorrow. Sometimes it is good to be inebriated by the exuberance of your own verbosity.

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[flash]

lol - i have been saying for a while now that i don't want to learn anything new, because it meant that something old was going to fall out.

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[wildcat]

Right, and if you put the car on a dyno and set it for 25 mph, using my car for an example, would run at 1480 rpm.  Put the same car with a supercharger on the dyno and run it  at 1480 rpm and your speed would register 25 mph.  It is a static test, and the mechanics; how many revolutions required to drive the car at 25 mph.  The variable that the supercharger introduces is rate of acceleration due to increased air flow , which causes the engine to accelerate faster.  In layman's terms.

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[flash]

the variable that the supercharger introduces is the amount of work the engine can do, due to the increased air and fuel.  increased acceleration is a result of the increased work.  when you add air and fuel, you get more power.  however, the combustion of that mixture is controlled by the computer, and so depending on how it is mapped, the emissions can be different.  this is why it took me a year and a half, and some special maps, to get the emissions right, so that the kit would pass the tests.

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[wildcat]

I should have included the statement "all else being equal",  modifying the maps makes all the difference in how the computer handles the air / fuel ratio and subsequently as you claimed "definitely more air".  

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[Bulti]

A supercharger is a compressor, so it packs the air molecules closer together when entering the combustion chamber at each intake stroke. So definitely more air goes into the engine, no matter how you put it.

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[flash]

yup, and if you put in more air, without altering the maps, you change the mixture, and therefore the emissions readings

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[wildcat]

That really depends on how much boost the supercharger or turbocharger provides. Naturally aspirated, the engine sucks in the air,  the supercharger/turbo pushes the air, but by how much... that depends on the design of the system.  A waste-gate will limit the amount going in but can be calibrated to allow as much air as the naturally aspirated would but more quickly. Compression does not imply more air.

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[flash]

not at all.  lean the mix out by adding any boost at all, without adding fuel, and the readings go wonky.  i went through this extensively when tuning the supercharger kit.  you would be amazed at how little boost it takes to put the readings out of range.  it was interesting though to see that the increase percentage in power is almost exactly the increase percentage in fuel delivery.  makes sense if you think about it.

 

and compression does mean more air.  you are taking the air and making it more dense, which means more air takes up the same space.  by definition, that means that the same stroke of the engine will now be filled with more air.  the speed increase is irrelevant.  it's the increase in volume that adds power.

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[wildcat]

A jet engine is a big compressor that increases the velocity of air,  you don't get more air.  The Bernoulli principle as expressed with water is that for a given pressure in a pipe of x-dimensions when constricted by a smaller pipe increases the velocity of water which does not mean more water, just faster.

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[flash]

i think you need to study how a compressor, and specifically a supercharger or turbocharger works.  it increases air PRESSURE.  the increase in velocity is a byproduct, but not what is responsible for the increase in power.

 

the application of bernoili's principle here is incorrect.  if you followed that principle, the pressure would DECREASE as it accelerated, but it does not.  in INCREASES.

 

as for a jet engine, while it has a big compressor, that is not what makes the engine work.  it is spraying the fuel at the compressed (read more dense) air, and igniting it with sparks, and then feeding all of that through a nozzle, that produces the thrust.  the law to be used here is newton's third.   by the way, in a jet engine, after it passes the first fan, the air actually SLOWS DOWN when it hits the compressor.  it only speeds up as a result of the turbine and nozzle at the end.

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