bbladesprops

Use WOT rpm at a trim level that provides the best running attitude and speed for the hull. Use the best water conditions and add trim till the boat is safe, stable the speed rises. If the speed begins to fall and rpm is rising, you are over trimmed and WOT rpm would be back at the best speed.

Knowing this rpm and the propeller being used in conjunction with the hull design allows us to use experience to determine what tweaks or what other propeller configurations to go to in order to obtain the best solution for the user.

Know how to ask the right questions and actually hearing the customers desires is key.

Your over propped if you are below the recomended rpm range when trimmed as described above. Different props have different personalities which can sometimes make it feel over propped.

Griff

WOT at full trim for your max speed

Even at 1/4 trim, you are still in the wot range for your engine.

monstaaa

prop shaft level with the bottom of the boat is the fastest . providing there is no hook or rocker in the bottom of your boat. for the timing , typicaly carbed b.b's run about 34 degrees +or-, and if your concerned of detonation , install a pyrometer/e.g.t gauge. depending on the prop, number of blades, diameter, rake, cup each will differ in operation.
i usually test props in a triangle formation as to go with, across and against the current and wind , then total the 3 and get the final number for planeing,cruise,and top end, keeping track the whole time of rpm and speed. i also level the boat on land prior to testing,then the drive while the boat is level using an acurate level 4 foot long as to make sure that i am as close to absolute parellel as possible, and then mark the indicator panel with vinyl tape to indicate exactl neutral.
using these methods of operation have led me to accurate decisions in prop selection. nothing beats patience and thoroughness.

good luck.

bcfountain

thanks all.i have O2 sensors in my risers to a air/fuel gage.it really only tells me if i am fat or lean.would this gage tell me if i have detonation?

oldandtired

My 22zx Donzi has a 502 MPI, stock except for a pair of CMI tube tops. It weighs in at 3900 dry. It runs around 75-77mph spinning a 27" Mirage. I think that your boat, being 500 lbs lighter and having way more power, should run much faster. I also think that you should be able to spin that 28 to near redline. Your mileage is definitely in the "sucks" category. I do think that your timing is a bit conservative. I initially set my timing with a gun to 34 but decided to revert to my crummy ways. I got out on the water and tweaked and ran until I found the fastest setting and then backed off a hair. I have never bothered to check where I even left it and haven't had any problems. I also don't have a blower so I have a lot more margin before detonation. Also, check your mixture. Rich is safe but can cost a lot of gas and power when you go too far.

Rene

oldandtired

Get a five wire (wideband). They are available for around $300 nowadays and can tell you exactly where you are.

Rene

monstaaa

nothing can replace a pyro/ e.g.t .

i ran a 27 kryptonit4e w/ h.p 500 and bravo 1 1.50 with a lab 28 x 14 1/2 prop. 85 mph. single step.4800 lb.


staight bottoms will run bout 7 -10 slower.

due to the weight difference , maybe 3 slower or even equal at best.

bcfountain

i am thinging the same thing.the speed just does not sound right.did the 500sc and the 525sc have 750 carbs?do you think i do not have enough?i am running a 1050 domanator.i can jet up to 99 sguared,and pick up 1-2 mph,but is a pain driving in the docks,just cannot get ride of the rollong idle.it gives all sytoms of being to fat,but why the mph gain?i am going to try the timming and turn it up to 32 and see what goes.i know i have a older hull,but fill i should see a good 80.thanks all.brad

Griff

No such thing as a 500sc.

525sc's use a 1050 dominator with 98 jets squared. 454ci, 7.5cr, 177 blower @5.5lbs of boost.

Jetting should not affect idle at all. The idle mixture does not change with jet sizes. It is a completely different circuit in the carb.

monstaaa

agreed,,,,,,, with griff.

bump it to 34 .

check you plugs, should be a cocoa brown, but i bet yours will be a little towards white.
remember fat wont hurt. its better than lean when you have a blower.