Air flow for 700bhp
 

Do any of you technical guy's know how to work out how much air flow is roughly need through a 20B to make 700bhp? I need to make up an air filter box of some sort for my build and want to work out he surface area of filter I need. 700bhp is well over an above what I expect to make so gives me some safety margin.

Appreciate any help that can be offered.

Thanks
Lee

Contact Howard Coleman as he's really good with turbo compressor maps.

rotary airflow for 700 SAE rotary rwhp is 1344 CFM/93 pounds per minute.

same for 2 rotor or 3 rotor...

HTH

Howard

Hi Howard, thanks for the reply. That will be very useful. I was actually referring to flywheel power. So if we said say 600bhp wheels is that flow rate roughly linear? I.e I can divide it down?

Cheers
Lee

For flywheel power: about 80lbs/min for a 700 BHP rotary of typical thermal/mechanical efficiency. (What that might translate into apparent RWHP is going to be dependent upon a number of other factors and assumptions, which are not necessarily linearly scaled.)

i fired up the engine simulator, and i learned what we should have already known.

the given lbs/min figures are both about right, i used 82lbs/min or 1200cfm, which is enough airflow for 600hp.

the part we should have known, of course is that the HP depends on airflow, but also BSFC, and the various frictions and losses in the system (everything from the water pump, transmission, mufflers, etc)

for instance the test engine is a 7.4L Chevy big block with a supercharger. it makes 632hp@6000rpm, and 1206cfm of airflow. if i switch it to turbos, at the same 1206cfm, it makes 710hp because you no longer need to spin the supercharger.

similarly going from the 632hp/1206cfm of airflow on gasoline and switching to methanol, we then make 716hp using only 1183cfm. (methanol + turbo is 786hp and 1182cfm)

so 82lbs/min +/- efficiency.... will get you the hp you want. which we already knew

i should point out too that the V8, makes big HP swings with these small changes because its a giant engine that is inefficient. so when we change a variable, like the supercharger, we are changing something from terrible to decent, and that is a big deal. the rotary, being smaller, and from an airflow standpoint, vastly better, would probably show smaller swings.

on that note the 7.4L v8 at 700hp is only making 96hp/L, which is nothing to get excited about. the 2.3 Ecoboost is rated at 350hp, which is 152hp/L. if you double the rotaries displacement, like we do for sizing a turbo, its about 4L, and at 600hp, you're also at 150hp/L, its enough you need to be careful tuning it, but in 2016, the automakers sell stuff with this much hp/L and still offer warranties...

Roots blowers are very energy inefficient. Centrifugal compressors (exhaust and belt driven) actually compress the air by throwing it into a curved wall, Roots blowers just sort of cram more air at the engine than it can take. It's like you're putting paper in a box, and you have a choice of folding it neatly or wadding it up and showing it in with a block of wood.

Then there are screw blowers with ARE compressors because of their taper, which are more efficient. On high powered drag engines it can take 1000 less HP to drive a screw blower than a Roots blower.

What car is this 20B going in? If in an FD you'll be happy wrapping some sort of chicken fencing material in front of the turbo…
yes it's that tight.

Yes it is tight! Still want a filter though planning on making a box to mount remotely.
Cheers
Lee