90 hp mac prop size question

[khallups]

I have a 90hp Mac on a old benson. It has a 50x26 prop on it that needs to be replaced. I have access to a 50x22 prop and was wondering how it will preform on this Mac. I believe it to be a cruise prop but I need the power prop to get off a short runway at field elevation of 1919. Any opinions?

[gyromike]

Too small with too little pitch. You need a Tennessee Props 52x26 for a 90 Mac.

[Gyro28866]

I think you would turn tooooo many rpm, lean the engine and burn it up!
I am flyin a 50 -28 Tenn Prop on my 90 Mac
And of course the carb needs to be jetted corectly, also.
Call Rick Whittridge, (GoGoGadget)

[dabkb2]

Is it a Tennessee prop? If so then they might be able to change the pitch.

[khallups]

I thought it would be to small, No isn't a tennessee prop.
Thanks guys.

[Gyro28866]

Kelly
I fly a 90 Mac, on my 72 Mac, last summer. I had a ding on my Tennessee Prop and was going to sent it to the factory and have it repaired. I put a St. Croix prop on it. This was an old school mac prop. On my first flight, as it turns out. I suspect, I was turning more rpm and this allowed the engine to run lean for the way the carb was jetted. I went from normal temps of 380 to over 600 in a matter of about 15 seconds. I melted a piston and siezed the engine.
So, if you change the prop diameter and pitch to something else, make sure you are jetted properly, so you do not lean the engine.
Here's a pic of the piston.

[helicopter ed]

I have a 90hp Mac on a old benson. It has a 50x26 prop on it that needs to be replaced. I have access to a 50x22 prop and was wondering how it will preform on this Mac. I believe it to be a cruise prop but I need the power prop to get off a short runway at field elevation of 1919. Any opinions?

Normal prop on 90 Mac is 52" X 26 pitch. the 50" X 22 is a good climb prop but not an ideal cruise prop. If u stick close to the airport as most Mac guys do, the 50" X 22 is A-Ok. Thx for asking, helicopter ed