Does anybody know what an EA82 (be it carb, spfi, mpfi, turbo) has for a CFM rating on a stock engine? Just curious. Doing my forced induction math, and It would be nice to see a figure. I'm guessing less than or equal to 150cfm on the n/a models.

For just a straight-up calculation (not worrying about manifold vacuum or blow by, etc.)

 

1cu.ft. = 28,300cc

 

In 360 degrees of rotation, 2 cylinders are filled (900cc)

 

Engine max speed (being generous) is 8000rpm

total displacement in 1 minute = 8000x900 = 7,200,000cc

7,200,000/28,300 = 254cfm

 

More realistically,

Max speed is 6,500rpm

total displacement = 5,850,000

CFM = 206

 

With pressure drops through the intake, it's probably closer to 175CFM at the intake, I'd guess. (At least for an N/A engine)

The above formula looks reasonable, but normally a "volumetric efficiency" value is added to compensate for the ability to actually fill the cylinder. A VE of around 0.85 (85%) should be about right.

An interesting discussion... bringing out the engineers. I'm by no means an automotive engineer but I pulled Marks handbook and they state 85% as the low end for "high output aircraft engines at rated speeds". Would this put a 4 banger a little lower, say 80%?

 

The above formula looks reasonable, but normally a "volumetric efficiency" value is added to compensate for the ability to actually fill the cylinder. A VE of around 0.85 (85%) should be about right.

I knew there'd be some kind of losses when you try to suck air past filters, valves, and other restrictions - I just have no idea how much they'd be.

 

Doing a little searching with google, it seems like most of the links use values in the 80-85% range for volumetric efficiency, at least for a n/a engine.

Volumetric efficiency varies greatly over the RPM range, and is roughly proportional to the engines torque curve. From what I've seen of the EA82/EA82T curve the VE falls off sharply in the top end, I'd say 65% to 70% would be a better guess at redline.

 

Gary

Volumetric efficiency varies greatly over the RPM range, and is roughly proportional to the engines torque curve. From what I've seen of the EA82/EA82T curve the VE falls off sharply in the top end, I'd say 65% to 70% would be a better guess at redline.

 

Gary

Yee HA!!! I love stuff like this.

 

All_talk is essentially correct, but... this is assuming stock cam timing. the engine has a higher potential VE than the 65-70% if tuned to do so. BTW, VE at idle is horrible, lower than the 65-70%. So everything is relative to how the engine is set up.