9.9 carburetor vs. 15hp carb test results with GPS

[iwombat]

Re: 9.9 carburetor vs. 15hp carb test results with GPS

I don't think anyone is arguing that the bigger throated carb won't get some kind of better performance. However the question is always posed "Will it make a 15hp?". There's enough differences between the later model 9.9s and 15s to indicate that it will not. But, we still have only anecdote, innuendo, and hunches to go on.

So far, nobody has offered any evidence that it is EXACTLY equal to an out-of-the-box 15hp.

I welcome the results of the experiment.

 

[Sandhammaren05]

Re: 9.9 carburetor vs. 15hp carb test results with GPS

The increase in acceleration and top end is a lot more dramatic when you put a 35 carburetor on a 20 or 25. See the related posts on this website where the experiment was carried out.

Exhaust tube differences on later model 9.9s, 15s might matter. Exhaust megaphones on 20s, 25s, 30s, and 35s are the same for a given year.

I SCREWED UP ON THE INFO SO TAKE NOTE.......................

Actually the outboard used was a 15 hp motor so the exhaust tube has been taken out of the equation.
So this was a reverse test. A 15 with a 9.9 carb.

In my opinion with the hole shot and top end speed of all the outboards (including both 30 hp motors) 3 mph is all your gonna get with a lot better hole shot and pick up speed regardless of the exhaust tube.

Maybe the experts can figure out what this new info means if anything since all I can do is guess.

 

[Sandhammaren05]

Re: 9.9 carburetor vs. 15hp carb test results with GPS

According to Crouch (see Dave Gerr's 'Propeller Handbook'), top speed goes as the square root of shaft horsepower to weight. The predicted fractional speed increase going from 10 to 15 hp would then be 1.22. 17 mph times 1.22 is about 20.8 mph. That's slightly above the reported fractional speed increase. RPM isn't stated, so with the 15 he might be able to turn a bit more pitch and pick up the rest of the speed. Sounds to me like it's in the right ballpark. Or?

In July I'll run a (Pro-Tech stainless) 11" pitch prop on a rebuilt 1981 Evinrude 15, on a log of a 13' fiberglass boat weighing 330 lb. dry. On a 15' Allison 'bass boat' weighing close to 300 lb., the 11" prop pushed the boat 22 mph with scored pistons while overheating, water intake at powerhead was stopped up with disintegrated rubber grommet. I expect to get about 25 mph on either boat. Will let you know.

So, bottom line was not much of an improvement in HP, but a big improvement in torque. Good to know.