rocketbob

rocketbob

Well Known Member
My son and I are working on building a flow bench to do some porting and polishing on cylinders and to explore making the induction system a bit more efficient.

Does anyone know if there are any technical documents that list the air requirements in PPH for Lycomings?

I know I can calculate this assuming 100% volummetric efficiency but I'd really like to know what the real-world VE numbers are. But since the fuel flow numbers are widely known (in PPH) I'm wondering if I can just assume a 12.5:1 ratio and get the air required.
 
Last edited:
rocketbob said:
My son and I are working on building a flow bench to do some porting and polishing on cylinders and to explore making the induction system a bit more efficient.

Does anyone know if there are any technical documents that list the air requirements in PPH for Lycomings?

I know I can calculate this assuming 100% volummetric efficiency but I'd really like to know what the real-world VE numbers are. But since the fuel flow numbers are widely known (in PPH) I'm wondering if I can just assume a 12.5:1 ratio and get the air required.
Click to expand...

Years ago, I was taught 15:1 or even 16:1. But I don't know if that's correct or not.

I'd expect the the highest airflow might not occur at full power due to using fuel flow for cooling. But it might occur near there with leaning. And it might depend on the carb or FI used. Maybe ask that company what to expect....

Dave
 
I think LyCon might have that info, or Airflow Performance.

You might try checking with them.
 
The best way is to just use the standard stoichiometric calculation at 14.7 to 1 mixture and .076 lb per cubic foot air weight. This is what we use to calculate the throttle bodies we build for our fuel injection systems. Allan...:D
 
Bob,

You might try Monte (?) Barrett at Barrett engines. He has, in the past, commented on how conventional calculations aren't exactly right in the real world, how "summer engines" test differently than "winter engines". It has to do with air flow past the intake valves, and its dependency on air temperature (speed of sound changes with air temperature).

It's complicated.
 
Volumetric efficiency...

... is unlikely to exceed 100% at the low speeds our aircraft engines turn, Bob, and probably is less.

Some naturally aspirated auto racing engines can actually reach 120 - 125% volumetric efficiency but they have to turn 8000 - 9000 RPM and use pretty sophisticated assymetrical camshaft profiles that require roller cams. For those engines, practically speaking, air flow is almost continuous. Mass flow inertia affects can be wonderful when the block is strong enough, the mainbearing webs are strong enough, the rods are strong enough, the crankshaft is strong enough and supported by five main bearings, there isn't any propeller intertia, etc. I never attempted to figure out the effective CR and BMEP in one of my Super Late Model engines, but 600 HP and 475 ft-lbs of torque (on the dyno) was a lot from a small block Chevy in 1981.

I admire your intellectual curiousity and look forward to seeing what you can learn with a flow bench.

Larry Tompkins
N544WB RV-6A
W52 Battle Ground, WA
 
Hi Bob

Has anyone tried a supercharger on a Lycoming? Just a thought. BTW the carb is working out just fine on Miss Sandy. See you at OSH;)
 
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