CFM Continued...

[Todd....!!]

With what you say in mind, then WHY does a STOCK 426 Hemi SONGLE intake
runner flow about 300 cfm each, from the factory??

Just wonderin...

I have heard that you want your cfm to be about 30% MORE than what is
theoretically required, due to our nonprefect world operating
environment and all...

Thanks for your formula's and input in this subject, it's
enlightening...

Todd....!!

---------



Greg Hermann wrote:
> 
> >Thanks to Ken, Todd & Gary for your answers regarding CFM.  Perhaps I didnít
> >ask the question correctly.   A stock TPI runs out of flow about 4800 rpm on
> >a stock 350 ci engine.  Iím looking for an EFI intake system for my twin
> >turbo 434 ci engine.
> >
> >The guy putting the turbos together said that the stock TPI is a good choice
> >because it will give me something really important for a fun to drive street
> >car, great throttle response and low end torque.
> >
> 
> How fast are you planning to turn the engine? Say for a 434, 5400 will be it?
> 
> Then, the engine will be trying to breathe in 434 x 5400 x 0.5 x 1/1728 ,
> or 678 cfm at the highest speed you will be turning it. The runners to each
> cylinder will be wanting to flow 1/8 of this much, or about 85 cfm each.
> 
> The trick is to size everything in the flow path so that you do not have
> excessive pressure drop at any one point in the path at the amount of flow
> the engine wants to draw in. What the guy talking to you is missing is that
> with a pressurized intake--the pressure drop in the runners is proportional
> to the density of the air flowing through them!
> 
> Of course--you will also have proportionally more pressure you can afford
> to lose with the turbo motor, So whatever will work well with the same size
> and speed range  NA motor is pretty close for a turbo motor. Going maybe a
> fuzz BIGGER than what you would use for a similar size/speed NA motor will
> tend to lower backpressure from the turbo on the motor, and lower EGT's
> some.
> 
> Going any smaller than what you would run on an NA 434 would hurt
> performance some, and durability more.
> 
> Flow on the inlet side of the turbos will be the amount of air the engine
> breathes times the manifold density ratio--a LOT more cfm. Everything on
> the inlet side of the turbos should be sized accordingly, and also to have
> VERY low pressure losses at this design flow The amount of back pressure
> which the turbo(s) will put on the engine to make a given amount of boost
> is EXTREMELY sensitive to losses in the inlet tract to the turbos!.
> 
> Regards, Greg