Very Technical Question

[MX-3 Ricer]

I'm thinking about building an custom forced induction intake for my car. But I need to know how many CFM of air runs through the engine @ 1000 and 5000rpms on a stock setup.

[tk1138]

Well, there are a lot of things to be carefull of, you should probably investigate the FI forum for advice/ things to watch out for,but anyway... <BR>The formula for Ideal Air Volume per time rate of a four stroke engine will be<BR>Engine Displacement*Frequency*1/2<BR>1597cc*1000RPM*1/2=798.5L/min=210CFM<P>1597*5000RPM*1/2=4000L/Min=1054CFM<P>Now this is IDEAL with no restrictions going in mind you, so the actual numbers are lower, but this is an order of magnitude approximation. To get more accurate numbers you'll probably need to use a flowbench, or if you can find the corilary of MAF potential to air volume/time you can use that and test it yourself. Also Vol/time will depend greatly on the load.<P>Maximum Boost is a book that's strongly recomended to those undergoing FI projects.<P>Good luck

[David Coleman]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by tk1138:<BR><STRONG>Well, there are a lot of things to be carefull of, you should probably investigate the FI forum for advice/ things to watch out for,but anyway... <BR>The formula for Ideal Air Volume per time rate of a four stroke engine will be<BR>Engine Displacement*Frequency*1/2<BR>1597cc*1000RPM*1/2=798.5L/min=210CFM<P>1597*5000RPM*1/2=4000L/Min=1054CFM<P>Now this is IDEAL with no restrictions going in mind you, so the actual numbers are lower, but this is an order of magnitude approximation. To get more accurate numbers you'll probably need to use a flowbench, or if you can find the corilary of MAF potential to air volume/time you can use that and test it yourself. Also Vol/time will depend greatly on the load.<P>Maximum Boost is a book that's strongly recomended to those undergoing FI projects.<P>Good luck</STRONG><HR></BLOCKQUOTE><P>Those numbers are incorrect, because your formula is wrong.<P>cfm = [RPM * Ev * 0.5 * cid]/1728<P>So it should flow around 25CFM @ 1000RPM, and 132CFM @ 5000RPM.

[maldo]

If you upgrade to the FC3S MAF, it is capable of 220cfm. This is your biggest restriction.

[David Coleman]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by tk1138:<BR><STRONG><BR>blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah <I>but this is an order of magnitude approximation.</I> blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah <BR></STRONG><HR></BLOCKQUOTE><P>Note: You were off by an order of magnitude

[ProtegeSTS]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by maldo:<BR><STRONG>If you upgrade to the FC3S MAF, it is capable of 220cfm. This is your biggest restriction.</STRONG><HR></BLOCKQUOTE><P>Not with low boost applications...from Randy's page:<P>8) Will the RX-7 flowmeter add performance to by 6psi Sebring supercharger or Greddy turbo? <P>I don't know. I don't own a boosted car. Only a Dyno can tell you for sure but I suspect that a 6psi system will not see much gains from the flowmeter interchange. When I had the flowmeter bench tested it flowed 165 CFM at 10 inches water and 300 CFM at 28 inches water. The 10 and 28 inches are flowbench *standards* for NA and boosted respectivly. (The standards are generalizations so YMMV). A 6 psi boosted 1.6 will suck 300 CFM at the flowmeter at 7200 rpm (source = Norm Garrett at 2/1999 tech day) so the flowmeter is sized adequately for small boost levels. More boost, displacement, or rpm will definatly require something larger. <P> <A HREF="http://members.aol.com/solomiata/airflowmtr.html" TARGET=_blank>http://members.aol.com/solomiata/airflowmtr.html</A>

[tk1138]

Please educate me Dave! I thought it was high, but couldn't see where the error was.<BR> <BR>What is this variable Ev?<P>Thanks

[David Coleman]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by tk1138:<BR><STRONG>Please educate me Dave! I thought it was high, but couldn't see where the error was.<BR> <BR>What is this variable Ev?<P>Thanks</STRONG><HR></BLOCKQUOTE><P>Volumetric Effeciency. Usually ~90-95% at peak torque for modern 4 valve pentroof heads.

[tk1138]

I see my error now, I used Liters to Gallons insted of Liters to Feet. Oops & Thanks.<BR>1L=3.786Gal, 1L=1000cc<BR>1L=.0353ft^3

[MX-3 Ricer]

WOW thanks for the input guys. Soon I'll be on my way to building a new consept insted of supercharging or using a turbo. It will be forced by high power fans and a intercooler will not be needed since there is no heat from the fan. I'm gona get some sheet aluninum and build a custom intake that will hold 2 120mm fans each capable of moveing 200cfm that should induce around a consistant flow of 400cfm. I'll put up a post of my results when its done. Thanks Guys.

[tk1138]

Not to discurage you, but this concept has been done before. Some people use marine blower units for this effect, and frequently wind up throwing a blade off the fans shaft when the engine is at high RPMs, not to say it can't be safely done, but beware of this type.<P>The reason that this isn't popular is that it's MUCH less efficient than super or turbocharging. If you give your fans a constant power source they'll be doing a lot of work at low engine RPM, and might even create drag at high RPM. Both super and turbo chargers provide a 'realtivly' proprtional air mass per unit time to engine speed. They increase power, but (generally) decrease efficiency.<P>The last major thing to say about this is that compressing air creates most of the heat that an IC removes. Whenever an impeller is providing boost, it's doing work by compressing air. This compresion causes the air to emit heat to reduce it's internal energy... LeChatlier....<P>Be REALLY carefull about sucking stuff into your intake. And get it dynoed if you think it works.<P>You might be able to find stuff using the search feature with the key words 'electric turbo', electronic turbo', 'marine blower'<P>Good luck