air flow

Post by **180sx** » Mon May 12, 2003 5:05 am

ok a question since ia m puting in a new engine into my 240sx (ka24de)i am thinking about changing the headers enlarging the exhaust pipe removing the cat and y splitting it so i can have 2 mufflers also the orifginal intake will be removed a new one will have enlarged intake pipe that is also y splited after the air sensor and will have 2 k&n filter heads on it. so far i had this replies what do u thinkwould this be:a) waist of money and no gainb) good idea do it up c) won't be worth the moneyd) waist of money and waist of torck

Post by **AZhitman** » Mon May 12, 2003 5:05 am

Insufficient backpressure SOUNDS like a good idea. However, a loss of torque can result, and the 240 is desperately lacking already.

I'd ask this in the 240sx KA forum - There are several guys there running hot rod KA's, learn from their mistakes and successes.

Post by **lessthanjakejohn** » Mon May 12, 2003 5:05 am

Yes, well I am not exactly sure what you are talking about. Try drawing something up with paint or something. Just don't go with to big of pipe since it will increase back pressure since the air will flow slower and the loss of airflow speed will not suck in air as well.

For the intake your be better off buying someone's used Injen Cai or Ram. Less to mess with and it provides the best gain.

AZ, he'd want to try the all motor section.

Also, does anyone know the ideal airflow speed for an exhaust system?

Post by **Q45tech** » Mon May 12, 2003 5:05 am

The greatest restrictions in an engine are the intake and exhaust valves. The farther away you are from these restrictions the less any changes you make will be meaningful improvements.

Measure the existing restrictions: TB, MAF, air filter, air box, air input with a manometer.

Post by **Eswift** » Mon May 12, 2003 5:05 am

but dennis, we dont all have pocket digital manometers...

*great stocking stuffer for engineers

on the serious side, i tend to agree with dennis here. The best option would be to model the whole system and run an array of finite element simulations, but not all of us have free access to ansys and adams on a cray.

i can tell you, without any finite element analsyis, just common sense, that 2 mufflers in parallel on a NA KA block is excessive.

Post by **Q45tech** » Mon May 12, 2003 5:05 am

When you reduce the designed in backpressure, you upset the reflected wave in the headers which helps suck out exhaust and creates a vacuum adding to the atmospheric pressure during overlap.

The whole system is designed around the cams so changing a minor part may not do much good.

Contrary to common wisdom: Changing anything after the cats won't decrease low rpm torque.............as there is no backpressure at low rpms.

Manometer are cheap less than $59 retail:http://www.dwyer-inst.com/htdo...0.cfm

Post by **Eswift** » Mon May 12, 2003 5:05 am

exactly my point dennis, you would think someone would have thrown one in a stocking for me by now...

mmm reflected waves in the headers....gotta learn adams this summer.

Post by **Q45tech** » Mon May 12, 2003 5:05 am

I had very unscientific ideas until I started measuring things.

There is a reason that all flow bench experts use 28" H20 [negative 1 psi] as the world standard in evaluating heads......95% of the time that is the actual vacuum drawn by the TOTAL intake system out thru MAF, Filter air inlet.

Must be the way all the design formula interact....valve curtain area, valve diamter to head pocket, runner taper, runner length, plenum volume to maintain a Helmholtz resonance, ideal TB diameter/ MAF throat for low vs high response, MAF calibration, etc and so forth.

Assumming that all STREET engines need a 6.6% restriction [1.0 psi= 28" H20] tells you how extremely hard it will be to get much improvement.

http://www.superflow.com/suppo...e.htm"Engines tend to peak when the maximum velocity through the valve at the maximum point in the intake cycle is about 550 to 600 feet per second. At greater velocities, the power drops. The engine will keep getting more and more power until it reaches the point where the "Mach" is 0.55, and then the power drops. You have to increase the airflow, and reduce the Mach number, in order to get power at a higher speed. Mach is ratio of air speed to the speed of sound, about 1080 feet per second at sea level."http://www.superflow.com/suppo...q.htm

http://www.tractorsport.com/wwwboard.html

Seee the fallacy in measuring just one part of the system:http://www.bmw-m.net/techdata/e36intflow.htm240 CFM>380 CFM @6"........... stock with MAF screens vs no screen Cone yet no power increase because 240 cfm = 288 HP .................as you lower the restriction you must lower the differential vacuum to compensate..........the things you don't change [valve diameter] are always the worse restriction........what is the smallest diameter path.........working with large diameters....ie air filters, Mafs, TB produces the least results.

http://www.bolhuijo.com/airflowtest/htt ... om....html

Post by **Q45tech** » Mon May 12, 2003 5:05 am

http://www.cpdl.kettering.edu/rcp.ppt

The above may not link depending on bowser: copy and pasteShows you how to see the turbulence in something like a MAF or a TB.

http://neptune.spacebears.com/....html

Post by **miteymax86** » Mon May 12, 2003 5:05 am

Do I need to state again that Dennis is my hero? I just did.

air flow

air flow

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