Muffler pressure on a Saito 80 measured at the field late today was 13 column inches (+/-1”) of water. At first blush four-stroke pressure seems to be stronger than two stroke pressure at idle to mid rpm. More test time is needed to be sure. An ST 90 two stroke with standard old style muffler measured 7 1/4” to 8” at full rpm and the pressure at idle was zero. The ST pressure was much less than that seen on other two strokes. The transition on the ST was reported to be marginal to bad.

Saito 80 =13”
ST 90 = 7 1/2”
OS 50 = 12”
Royal w standard muffler = 12”
Royal w Macs muffler = 15” to 17”

Bill