Sid,
I can't answer that. My pipes are not add-on tips as seen on one of the vendor' web pages. They cannot be removed for verification testing.
Mine were sqeezed into an oval, and holes drilled in a pattern on the flattened bottom, then each hole was bent back a bit by inserting a rod (think screw driver) in the hole and pulling the handle in the downstream direction.
The T-18 makes a respectable 174 MPH @ WOT 4000 DA 2650 RPM on a 125 HP O-290.
Comparing my T-18 to Marilyn's RV-4 isn't apples-to-apples: she has a 160 HP O-320 with a unmuffled crossover system, no Piccolo. It has the exact same sound as the Youtube recordings (sweet!). The T-18 is softer but has 90% the engine displacement and only 78% of the power. I would expect it to be quieter.
Trying a Piccolo pipe tip on my Turbo Rotary powered RV-8 did get a 2.2 DBa reduction. Readings are taken at my face while at cruise speed @ 4000 MSL. It was 116.8 now 114.6. Still too loud, but a 3 DB decrease is half the sound pressure, so 2.2 DB is not insignificant. I suppose these on-going sound level tests will be at different altitudes and speeds over time, I just keep the meter in the foot well, and test whenever I think of it.
I calculated the area and number of holes to replace the lost exit area caused by squeezing the tip.
I only have 6.3 flight hours on the RV-8 sofar, and no wheel pants or leg fairings, so speed testing...NOT. however, I have attained 183 MPH TAS at 4000 MSL, @ 31" MP, not bad.
Why 4000 MSL instead of the accepted 8000 that VANs uses?
Because it is just outside the 3000 MSL lid of class B over the airport, in the area with a 5000 MSL lid. It's easy to get to and easy to stay in. As I get more flight time and assure reliability, I will go farther afield so I can get up to 8000 MSL and beyond...
