Originally Posted by
drac1
That's the muffler I bought for my GT33 and I don't think it was designed for the OS in particular, but I decided to give it a go.
Have you tried the 20.5 X 10? That's the prop I'm gong to try. I'm thinking it should give around the same RPM as the 19.5 X 11.5?
I'm getting that RPM with a 20.5 X 10 on my 185cdi, so if the 33 can get close to it using that muffler, it should be OK.
Scott, I've run the apc narrow blade 20.5x10 on the CDI/ GT33/ pipe combo. The gasoline I use is Avgas mixed with a good racing synthetic at 50:1. I got 7200 max rpm, an rpm number we don't hardly ever need or use. I also tried the 21x10 apc and rpm dropped off to around 6700 which was bunch. The engine just didn't sound happy.
One thing to keep in mind is the type of gas one uses will make a difference in maximum output. The same gasoline mix as above is what I generally use on the 33 turning the 20x10.5 Narrow. I get about 7400 on that set-up.
I ran premium auto gas a couple years ago (same oil and ratio) just because and got about 7800 rpm for the 20x10.5. I decided I really hated the stench of auto gas and didn't need the extra power so I went back to Avgas ever since and have no plan to change, ever again.