HPBCANADA.COM

Further to my wanted add for a new lower, I thought I'd post up the differences on my boat between a coned OX66 lower against an HPDI unit. First difference I noticed is the HPDI unit is lighter, by 8lbs to be precise. I know the gear ratio difference will be there, (1:81 vs 1:75), we'll see if the motor notices. The skeg is substantially larger on the Hpdi and has a built-in torque tab that looks to be larger and likely more effective than the riveted-on Bob's unit I have. Overall length (tip of bullet to rear of casing) is 20" on OX66 and 17 1/8" on HPDI, a difference of 2 7/8". Propshaft is 1" higher on HPDI relative to mounting surface. Lighter and a lower overall centre of gravity, albeit small, is at least a step in the right direction. I'll add as I find out. Hopefully will have the HPDI unit on for next weekend.

interesting that the HPDI is "shorter".. you get to lower your motor a little bit.

The big thing is... How good was the cone/tamer job on the OX case? I think that the biiig skeg(which I like btw) might slow things down a bit. Regardless... After this case.. I'm done with OX cases.

The job was pretty decent, I'd say an 8.5 outta 10. I'll take some sq. inch measurements of the skeg and find the difference in surface area, and do the same with the difference in length of the case, I bet it's close.

I'm thinking the thickness.

Ahh yes, the thickness... I'll measure it and see, front,middle, and the tab and see what's up.

Mitchie is all about girth...

Mitchies a yard sale. Poeple don't need skegs

Did some preliminary testing today with an HPDI lower. It had five exhaust relief holes in each side, and slightly modified water intakes. I found the results interesting.
Pros of HPDI unit...
1) Higher top speed, 81.7 vs a previous best of 80.5.
2) Handling improved, turning at any speed was far more positive, also tended to chinewalk less.
3) A factory finish on case is WAY better than painted and epoxied. (and paint again, and again...)
4) Overall seems to be a tougher unit, the bearing carrier is retained better IMO.
Cons of HPDI unit...
1) Killed holeshot, I think because of many factors, higher gear ratio (1:75 vs 1:81, 3.5%), exhaust relief may have taken away some low end punch, and caused less exhaust gasses around prop at below planing speeds. This could likely be mitigated with larger relief holes in prop, an over-hub may not have noticed at all.
2) Considerably less bow lift. It would still carry the bow fine, but required quite a bit more positive trim to do it.
3) Less water psi at same transom height as my Bob's coned OX66 lower, there is a mod for the HPDI unit that would likely fix that.

how much did your rpm change with the new ratio ?