when

**bubbasmacks** · 01-04-2008, 10:14 PM

When to use reduction??? If I have a prop set at 15 degrees and it will allow the engine to run at 3600 rpms, If I added a reduction of 2-1 with same prop just adjusted to 30 degrees. would or would not the prop have the same amount of push? I have asked this question to an airplane site and noone could tell me a good answer. I know some v8 run a reduction on big boats, I thought it was because the engine turned to many rpms. I have a 0540 DD which is 300 hp and it turns the prop like it should so I am lost to see why a v8 with same hp needs reductions if it turns the right amount of rpm .Torque perhaps? Any one with a college degree in making stuff work help me out.

The reason I need to know is I have an a4032 engine which is 4 cylinder 32cid and only 6hp it sounds and looks like a big engine just not enough.

**josh_2562** · 01-04-2008, 10:55 PM

I'm not the best one for this ? but I'll try lol. with auto engine they make there power around 5000rpms. if you run a auto engine you can only run the engine up to 3000rpms. when they go with a gear box it allow the engine to run up to it peak hp but keep the prop speed down to 3000 and below. if you can adjust your prop you should set the pitch so that the engine only spins up to about 2950rpms.they say props push less when spun over 3000rpms.

the airplane engines where made to spin props so they make there hp around 3000rpms

what prop are you running on your boat

hope I helped a little