Marinette Boat Forum

..."One guy couldn't win a football game by himself,"

No, but "Megatron" comes close!

Agreed on the larger engine--propped properly--can get better gas mileage than a smaller one, especially if the boat is underpowered.

Jeff

Joe-
Agree with your point about volumetric efficiency.  A smaller engine that is not balanced e.g. intake flow, exhaust flow and low compression,  will not run efficiently.  A well balanced large engine e.g. intake and exhaust flow is equal, will run more efficiently.

The 318 is a poorly balanced engine that does not take advantage of it’s mechanical efficiency.  It is a mechanically balanced engine in the bore e.g. stroke and bore are almost equivalent.  However, it loses power due to low compression, poorly ported heads and intake manifold.  This is the reason so much additional power can be created by simply changing the heads and intake manifold geometry.  After these changes, the modified engine will be more efficient.  The fuel atomization will be better and combustion will be more efficient due to higher pressure.

The magic is in the balance of flow volume, power (compression) and mechanical efficiency.  The 318 makes a solid platform for 300+ horsepower with fuel efficiency.

...."
The 318 is a poorly balanced engine "

Millions of satisfied auto owners might not agree.

Jeff

Fastjeff wrote:...."
The 318 is a poorly balanced engine "

Millions of satisfied auto owners might not agree.

Jeff

Anything can be made better, some were made better. That being said,......... the only person who would not agree is that dude still driving around that stock Diplomat he bought off the showroom floor in 1980 with a 318, .......... with 300,000 miles on it. Then there's the guy who bought the Cuda in 1970, with the 440 six pack , yea I'm the Cuda guy. Your right though, it is hard to beat the reliability of a Chrysler engine.

Right on. A larger engine--with the proper prop (more pitch)--will give better gas mileage at cruising speed. Seen this many times (in comparative boat tests with different engine options) I don't doubt it. At WOT throttle, of course, the larger engine eats more fuel, but that is not the normal mode of boat operation, especially with a Marinette.

A bit of data to back this up: My FloScan tells me that it takes about 2 GPH for a 360 to run at 2,500 rpms--in neutral! It takes considerately more gas to turn 3,500 rpms, again in neutral. So, propping the motor to turn only 2,500 for cruising (vs. 3,500) saves gas from this factor alone. Of course, the motors can't be lugging at this rpm or all bets are off. Since the butterflies on the carbs of my 32 footer are barely open enough to admit a pencil at this speed, this is not the case in THIS instance.

Jeff

Rebuilt my 318's (well i let the experts do it) with Scat Enterprises 392 strokers under your approach. 80 hours all is well. Burns the same amount of fuel at 3,000rpm but way more torque so it picked up speed. Installed roller rockers as well. Larger carbs were needed 750 cfm's. Custom cams, increases lift and duration a bit maintained 9 to 1 compression. They run great! Builder says 350 hp each. Stock props 16 x 15, 1x 1.52 transmissions. Machinist says 318's are easy to stroke because there were no clearance issues.

Okay, now you need way more pitch on those props. That will give you more mpg without hindering the way she jumps onto plane.

Jeff

Hey Jeff! The next time she comes out for bottom paint, i will look into different props. Will be de-winterizing on March 25th. Come on spring and not spring snow storms.

Why did it require the larger carb if it uses the same amount of fuel? Or is that for full throttle?

Well i did not check my flowscan meters at wot. Spring is coming. At 3000rpm it was at 19gph.
I will right down all the numbers and post soon.