Offshoreonly.com - twin motors

Offshoreonly.com (https://www.offshoreonly.com/forums/)

- General Q & A (https://www.offshoreonly.com/forums/general-q-20/)

- - twin motors (https://www.offshoreonly.com/forums/general-q/69016-twin-motors.html)

I have a 1987 27 mirage with twin 350 motors,and has sterling exhaust .The boat will do about 60 mph. I want to put 383 strokers kits in the boat. Is this worth the time and money. Will there be a big performance gain. What kind of rpm should the 350 motors be running, and will gain any rpm with the stroker kit? Thanks for the help in going faster!!!!

Welcome to the board!
If your engines are the stock 260's, normal RPM operating range is 4200-4600. You can safely prop it to go near 5000, but I would not exceed that with that engine/valvetrain.
You are going to have to do a lot more work to the engines' top end if you are going to add in a stroker kit.
Worked-over Vortec heads are going to be a minimum, or World Products will be needed to get the engines to flow. CompCams and Isky both have great grinds for your camshafts (I would think roller if you intend to run consistently at high RPM's).
You can stay with the Thunderbolt IV ignition, but I would go with the 350 mag cast iron intake, or the Edelbrock Performer RPM if you stay with the Q-Jet.
If you're going Holley, you have many more choices with manifolds.

In nutshell, all you're really going to be able to use to make a pair of good strokers are your blocks, carbs, ignitions, and exhausts.:) Is it all worth it? It all comes down to how long you intend to keep this boat.
Jim

My $.02

Is it time for a rebuild anyway? Were you reading an article about putting a 400 crank in a 350 and getting that "perfect" bore/stroke ratio?

I thought about the same thing and I agree that it depends on how long you are going to keep the boat. Building 383s out of your 250s is going to get expensive. I would think that you'd be almost as happy (your wallet sure will be) with a proper rebuild of your 350s. A good engine builder / machine shop can eek a few extra hp out of your 350 relatively inexpensively. I'd have it dynoed and tuned before re installing so you don't have to deal with tuning. The spend the $$$ you save on props.

Now, if you have deep pockets and really want 383s then let's supercharge them. Think about a couple of blown 383s in your 27. Loads of fun for the Captian. Brown stains in shorts for the passengers.