I just bought a set of 26 Hydros and they have diffuser rings on them. I will be trying them on a staight bottom 35 Fountain any thoughts????

Are you having any problems getting on plane now? I made the decision to have them removed from the P5Xs. Won't know until spring if this was a good decision. But I wasn't having any issues on planing even with shorties.

Not at all.

I'm running a P5X on a imco 2"shortie. No diffuser and can't get on a plane with 5 people and a full tank. HP500 with Whipple and AFR heads so I have plenty of power. I will be adding a diffuser this spring as that was recommended by a number of people in the industry. We'll see what happens.

I may have to add the diffuser ring, but I had to try to see if I could pick up any more speed. I never have more than just another person in the boat, so hopefully should be good.

NOT ALWAYS but, 5 blade propelllers don't typically require diffuser rings. the reason is, the amount of blade area can typically load hard enough to get the boat up and on plane. If you really struggle to get on plane with the diff's removed on 5 blade props, concider reversing the prop rotation as a quick test. This will affect boat attitude under way however so test cautiously. Otherwise, you "X" dimention is probably questionable.

I still don't understand ultra high X's to obtain 1-3 if the overall usability is compromised.

What exactly is the purpose of a diffuser ring and what does it look like on the prop?

Diffusers are the extention of the exhaust tube aft the prop blades. The intention is to "diffuse" the exhaust gases away from the high pressure side of the blades prventing slip, cavitation, and blow out. They can be any length, straight or flaired.

They can affect boat attitude and of course planing ability

Thanks for the info. I thought that was the explanation, but wasn't sure. If you have straight thru the hull exhaust with no captains call, then the diffuser would not have an effect on the prop?

Yes and no. Pressure differentials between the ambiant air and exhaust tube can pull some air through the exhaust passages and create some issues. If the passage is securely sealed, you are correct.