Is there a general rule of thumb for how much pitch to drop when going from 1.5 to 1.36 gears. If I run a labbed 30 now what should I try with a imco shorty 1.36

28

mathematically, 1.5 ratio with a 30 pitch prop is equivalent to a 1.36 with a 27 pitch prop. you said your running a lab 30 but is it labbed with a recipe that adds pitch or lower pitch also there is a slip factor to take into consideration. generally a higher pitch prop will have a higher slip percentage, so if the gear ratio change results in a lower slip percentage you will need to go even lower in pitch.
this is based on the power of the engine remaining constant and not having the torque greatly affected by ratio change.
Ex. 1.5 ratio 30 pitch 5500 rpm 16% slip 88 mph
1.36 27 5500 16% 88 mph
1.36 26 5500 13% 88 mph

88mph? Let me grab my flux capacitor and delorean. I'll be right back.

On a serious note, I've done a back to back comparison on a twin engine deep V hull with 1.36 and 24 bravos and the same boat 1.5 and 26s. It actually ran alittle better with the 24s and 1.36.

Cruised 59 at 4,000 while with the 26s it was 56 at 4000 the top ends were 73 at 5000 with the 24s and 72 with the 26s. Was surprised how much better the boat liked the smaller props and 1.36.


So as said above you're going to be somewhere between a 26 to 28p prop depending on slip and rpm. If you have room to gain rpm with your engine setup then the smaller prop should give you some better acceleration if you can turn Afew more r's. I heard a rumor bblades does prop test program (in my best Brett voice)

The boat may be a little lazy pulling out with the 1.36 vs 1.5

I run 1.36 and the cat is definitely not lazy out of the hole . I see the op has a 25' Daytona so our boats are similar . My bud with 25' Daytona and 1.5 ran a 28 while I run a labbed 26 on mine .

1.5 to 1.36 is right about 3" in pitch with the identical props.

[QUOTE=the deep;4187916]I run 1.36 and the cat is definitely not lazy out of the hole . I see the op has a 25' Daytona so our boats are similar . My bud with 25' Daytona and 1.5 ran a 28 while I run a labbed 26 on mine .

That's where the May comes in, having no clue as to what he's running for power, he may or may not have an issue.

650hp with plans to increase

Changing gear ratio changes the torque multiplier, at some point with big power you run out of pitch and have no choice but to change ratio.