JonOfScio Posted August 17, 2005 Share Posted August 17, 2005 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. Link to comment Share on other sites More sharing options...
stephenw22 Posted August 17, 2005 Share Posted August 17, 2005 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) Link to comment Share on other sites More sharing options...
NorthWet Posted August 17, 2005 Share Posted August 17, 2005 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. Link to comment Share on other sites More sharing options...
dpoppeli Posted August 17, 2005 Share Posted August 17, 2005 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. Link to comment Share on other sites More sharing options...
stephenw22 Posted August 17, 2005 Share Posted August 17, 2005 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. Link to comment Share on other sites More sharing options...
All_talk Posted August 17, 2005 Share Posted August 17, 2005 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 Link to comment Share on other sites More sharing options...
NorthWet Posted August 17, 2005 Share Posted August 17, 2005 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. Link to comment Share on other sites More sharing options...
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