Good spotting Dave. Missed that completely.

Just did some number crunching.

With a 1.65 gear.

28" prop 73 mph @ 5100 = 11% good
28" prop 73 mph @ 5200 = 13% still ok, but some to be had
30" prop 73 mph @ 5100 = 17%
30" prop 73 mph @ 5200 = 18%

With a 1.5 gear.

28" prop 73 mph @ 5100 = 19%
28" prop 73 mph @ 5200 = 21%:eek:
30" prop 73 mph @ 5100 = 24%:eek::eek:
30" prop 73 mph @ 5200 = 26%:eek::eek::eek:

If you guys both run 1.5 gears, you need to get your boats dialed in + I'm not trying to be a smartazz or rude here, but honestly if running 1.5, whoever labbed your prop, did a bad job with those high slip numbers.

If you run 1.65 gears, you still have some speed left on the table.

On engines reving to 5000-5200 the norm would be to run 25" true pitch for the 70-73 mph speeds, with 1.5 gears.

I'm sure that they're running 1.65 ratios! Just an FYI, my Formula 292 SR-1 has a prop slip of 11% with stock Hydromotive QIV's A fastec hull IMO should have better slip numbers than a non-stepped formula hull.

Pretty sure that the 312's all came with 1.65 drives.

Run a duct from the engine hatch intake directly to your air intake and seal it off so you only take in cold air for the engines. Add a can of octane booster also.


You will pick up some hp there.

Next give Bblades a call.

Wannabe

And don't get any big splashes in that duct.:eek:

1) Lose as much weight as you can (especially fuel).
2) Weight you can't lose, move as far rearward as you can.
3) If you have a freshwater tank, drain it (they are usually far forward).
4) Roll up two towels and prop your engine hatch open with them - one to the left of center, and the other to the right of center. This will induce far more airflow into the engine compartment than any sort of quickie ductwork.
5) Make sure your throttle plates are opening ALL the way when the sticks are pushed forward (cable adjustment is often leaving a little bit there).
6) Forget the octane booster, unless it is incredibly hot outside - octane will not give you more power unless your motor is already retarding the timing to prevent knock.
7) We assume you know to raise your tabs all the way up out of the path of water. You may even want to temporarily take them off of the boat for the weight savings and potential tiny bit of hydrodynamic drag they may add.
8) We also assume you know how to trim your boat. Familiarize yourself with trim settings and watch the GPS.
9) Make sure your drives are properly toed in. Drives that are toed out add drag and give up speed.
10) Make sure your hull is clean. Waxing and rubbing magic salve on it really doesn't do much, but you can try a coat of good silicone based wax for a 2 minute micro-advantage.

11) You can experiment with a 2 degree bump in base timing. On back to back runs, don't touch your trim settings, and try it. Sometimes if your timing is conservative, you can pick up 5 hp or so. Other times, it pushes you into spark knock and your retard pulls timing out anyhow.

That's about it, aside from modifications or perhaps running exotic heavily oxygenated race fuels that are expensive and must be flushed from the tanks if any remains (although I presume you'd run it about dry and refill with pump gas after your face-off).

I've seen NuTec Special 4 add more than 25 horsepower to a 700hp motor with nothing but fattening up the jetting. I've seen it add 5 hp to a racebike (with similar fattening up the fuel setting). It's not what you want to run, though, since it will turn rubber to goo if you leave it in the system. VP Q16 is a similar fuel that does NOT attack your fuel system, and delivers 60% of the boost of Nutec S4. It's cheaper than the Nutec as well (NuTec S4/S5 was $15/gallon back in 2003).

I'm just rambling though - there's no way that it's worth the cost and hassle of spiking your tank with that stuff. You'd have to start with an empty tank, and put in at least 20 gallons of this stuff. Then you'd need to run it almost out and fill the tanks full up with straight gas and then run about 5 gallons of straight gas back thru the system...

MC

If your exhaust are the cast iron manifolds, swap them for some cast aluminum 496 take-offs. The 496's should flow a little better and they will save you a ton of weight. You should be able to find 2 sets pretty cheap...cheaper than good props.

As for props, find a marina that will loan props (with c'card down payment) and spend a calm weekday with a gps and a notebook and see if can find some faster props.

Keep equal number of people in your boats as your buddy has so he doesn't say you beat him that way. But, make sure they are petite lightweight hotties - less total weight and bragging rights all in one!

call me I can help

Gear ratio in my bravo's are 1.65 on Formula 312's
Yup- same speed on GPS,, dead same..

1.65 is the gear Ratio and they were done by Bret at B-blades.. so you would think he's the best to do the job..
I've asked a couple times about that as well,, slipseems high.
Maybe time for 5-blade props