Props and rpm

[balthaus]

Thanks for the input everyone.
My trans ratio is in my signature but it is 1.52:1

[balthaus]

Finally got back to the boat and the spare props are, in fact, 17 x 19. The Michigan Marine widget says the boat should achieve 40 mph.
Still need to check that 4 barrels are opening up and dumping fuel

[Fastjeff]

Don't put them on! I had a similar boat with the same engines and 15 pitch was enough (made 3,900 rpms WOT). That 19 pitch is WAY too much.

Jeff

[balthaus]

Fastjeff
It is not so much that I want to put them on.
I don't know what the current props are so I am assuming that the current props are the same as the spares.
I will likely go with your set up at a later date.
Thanks again

[balthaus]

Fastjeff
Would you say that your 17 x 15 props were best suited for fuel economy, speed or power?
With fuel in Louisville just below $4 gal, I would want to lean towards economy.
Thanks

[Fastjeff]

The 15 pitch props are excellent for economy and a bit so for speed (motors only make 3,900 rpms). That said, the boat explodes out of the water with them, and will retain plane all day long at 2,000 rpms (including making a full lock, 360 degree circle with a full load onboard). My usual cruise was 2,500 rpms/ 18 to 20 mph/ 8.5 to 9 gph.

Jeff

[balthaus]

Fastjeff
As I said previously I am not sure what props are on the boat now....like a dummy I did not check before putting her in...but, assuming ( yes I know..dangerous) that the current props and the spares are the same.
In your opinion can I still run the boat at reduced RPM until I can either get new props, the ones I have re-worked (if possible) or at least get the boat pulled to check the current prop size.

Thanks

[Fastjeff]

You can run them, but be damn careful planning off--if the motors are working hard and straining, don't go any further.

Jeff

PS: They may stall now and then in gear, at idle speed. Mine (four blade 17 x 15s) tended to do that--sort of like starting off your car in 2nd gear. With those 19s, that's like starting off in 3rd!

[Tranquilo]

I'm tuning my engine up with extra firepower to get my single 318 with a 14x10 prop to work efficiently.

It wasn't getting above 2300 rpm initially but since changing out the plugs, wires, electronic distributor (pertronix 2) - the boat gets moving to about 3250 rpm. The rep told me that replacing the stock coil with the hotter one designed for the system will give me a little more of a boost at that range.

I reset the ignition point with a pressure gauge (got it to 85psi peak) and the torque difference is noticeable. If my new coil adds a few hundred RPM, cool. Really, I just want to be able to run effectively at 3000 (I am guessing that it is the top end of the sustainable cruising speed)

It was suggested that after adding the hotter ignition, I may want to go with a slightly wider gap on hotter plugs.

We'll see if I don't blow myself up with this round of edits before doing that

I'll do a test of the fuel efficiency with a 5 gallon can once I'm in open, flat water.

[jmonday]

I can say with my new distributor and super cool NOT the flame thrower coil my boat does not run as good. I think you will like the flame thrower.