yes they are XR's

Ill try to get a picture of an IMCO cavitation plate tomorrow night.

hmmmmm

So what's the difference between the XR and XZ drives - why would one choose one over the other?

Here is a picture of an IMCO cavitation plate that is supplied with their 2" shortie.

Yes, I do have those... and now I know what they are.

I was able to squeeze 100mph out of mine under perfect conditions. And I have seen on the Eliminator site a 28 w/496 HO's showing 101mph - Powerboats NW is a dealer that claims his 28's with 496 HO's do between 101 and 105mph....but I'm not sure how he has those rigged.

My sense is there are a several items that can cause the variations like how they are propped, if they have extension boxes, how much load they have, what their xDim is, etc... I think it would be safe to say that a current 28 with 496 HO's should run somewhere between high 90's and low 100's.

I have xr's with 1.36, stamped on the side though i will make sure, they could be 1.35.....I am running 30P Bravos and have seen best of 93, though mine is the older tall deck boat. I am going to change the spark plugs (should be good for 300 RPM) they haven't been done in awhile and then maybe go to the 32's.... I tired them once and i was at 92 but my rpm was lacking....didn't think about the plugs till another buddy with a 496 mag ho was prop testing and couldn't get the rpms up, he hadn't changed the plugs in awhile, he did then boat gained the rpms and more mphs, plus was finally able to turn the bigger prop....

from my understanding the XZ was only made for a few years, the XR is what they make now. The difference was something in how the gears were cut..I think....Also i was told the xr can handle 500 hp as that is what they put behind the Hp525...Not sure why you would told only 425 on your xr's maybe it the lower gears, but not sure. If the gears are what make the diffence you can just change them....

Todd Where Are You? He Has The Same Boat I Belive He Is Running 5 Blades.