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Tim Topping and I were talking this morning on this topic. The rules allow for the Bridgeport motor to be ported to the SST 60 specifications. But, the SST 60 is an engine designed for a tunnel boat, not a V hull. There is more drag in the water with the V hull compared to the tunnel at top speed. The tunnel requires less horsepower to go faster , so the more RPM you can turn the better.
It was not unusual for a SST 60 tunnel to run 8000 to 8500 rpm. Because of the power ban the motor is likely only making approximately 60 hp at that rpm.
There is a big advantage to having a dyno especially when your building something between a fishing motor spec and a SST 60.
Here’s a 2017 post from the top SST 60 engine builder:
Mike Wienandt
Team Member
Aug 2017
“Was reading one of the other posts, The engine has a bad harmonic vibration that you must avoid to prevent damage of the engine. 4000-4300 it shakes so bad it screws up the fuel in the float bowl and the engine will run lean. Also at 8000, DON'T GO THERE. Run best up to 7600-7700. Everyone that I have seem go to 8000 will stick pistons.”
It is important to know the power ban of your motor.....what rpm does it reach max hp , how many rpm does it maintain that hp and how quickly does the hp decrease after. Porting can really affect performance. You may only be developing max hp for 500 rpm and then the hp drops off rapidly.
Some engines will hold their max hp for over 1000 rpm. Those are normally the best ones.
Drivers with a lot of racing seat time and experience notice the differences right away. It’s difficult to make the correct prop selection when you don’t know exactly what you motor is capable of doing. Most don’t have enough different props to test. It gets expensive when you guess wrong in your prop purchase.
As a suggestion....first you want to find out the maximum rpm your motor will turn. If you run a 20 x 12 prop similar to your race props only less pitch. The motor should run out of rpm before you run full throttle for a long period of time. Your not concerned about top speed only rpm. The prop should also have strong acceleration. You want to know how that feels.
Now put a 25 x 12 ish prop on. It will make the motor work harder. See how many rpm you can pull and the mph. Most times you find a sweet spot in the rpm range where the motor has more power thru that rpm range and performs better. That is likely the rpm range where your motor makes the most power.
If the boat is a lake runner you run more pitch. A raceboat needs acceleration so it will run less pitch.
You may find you run best at 7000 running 24 pitch. Most T850 raceboats are not turning 8000 rpm. That explains why the motors are lasting.
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