Although size is one of the differentiating factors we looked at in our engine comparison, there are other general questions you should ask when making an engine purchase. How do you plan to use your boat? How important is speed? Offshore fishing? Cruising? Sightseeing along the ICW? Where do you use your boat? In high humidity? Will it need to be winterized? Are parts and services readily available? How much of a fanatic are you about keeping your engine room clean? And perhaps most important, how many hours will you run your boat annually?

When it comes to comparing the engines themselves, things become even more complex. Even in a straightforward comparison like this one, where the numbers supposedly speak for themselves, there are things to keep in mind. Look at the weather, load, and sea conditions under which we conducted each test. They're similar but not identical, and that could affect performance.

And of course, the engines are anything but identical. The premium version of the Marine Power 454 EFI we tested uses electronically controlled port fuel injection to produce 370 hp, compared to the standard version that uses electronically controlled throttle-body fuel injection and puts out 340 hp. As you can see in our performance chart, the 454 Premium produced surprisingly good fuel economy. At a best cruise of 3500 rpm, this T-320 turned just over 30 mph, producing a maximum range of 291 miles. Not surprisingly, particularly given this engine's comparatively light weight (965 pounds dry), this package produced the fastest top speed, although at 36.7 mph it barely edged out the Cats. Being a V-8, it was obviously the widest (32.1") engine of the three, although its modest length (47.9") and height (32") left adequate space for maintenance and repair. And with a total suggested list price of $138,119, this boat was easily the most affordable of the three.

Weighing just 1,307 pounds dry, the Yanmar 6LY-UTE diesel squeezes 315 hp from just 316 cubic inches (5.2 liters). Measuring 52" including marine gear, it's relatively long, but being just 28" wide, this engine left almost enough room for a third engine. It produced the lowest top speed (34.9 mph), the best maximum on-plane range (412 miles), and the highest cruising speed (32.5 mph at 3000 rpm). Compared to other diesels in general and the Caterpillar 3116TA in particular, this is a fairly high-winding engine, generating its maximum horsepower at 3300 rpm. Our test boat actually turned 3400 rpm, which means it was slightly underpropped. With these engines the boat costs $184,649.

Although the Caterpillar 3116 was the longest (57.5") of the three engines, it was also the narrowest (27.9"), so there was plenty of room to perform maintenance and repair duties. Despite being the heaviest (1,500 pounds dry) of the three, the 3116 managed to beat the Yanmar in top speed by more than 1 mph and nearly nosed out the Marine Power. At 2500 rpm, this engine turned in a higher cruise speed (34.7 mph) than the Yanmar with slightly less range. At a list price of $186,729, the Cat-powered boat is virtually identical to the Yanmar version, although with the weakening dollar, you should check with your dealer for the latest price.

MORE POWER, SAME WEIGHT

Diesel engine builders keep pulling more horsepower from the same blocks. So while weight remains the same, power and performance go up.

That's the case for both diesels we tested in the Luhrs T-320. Caterpillar offers a 350-hp 3116 and a 420-hp 3126 that are indistinguishable from the 300-hp model we tested. That means the weight-to-horsepower ratio goes from 5.0 lbs/hp to 4.3 lbs/hp or better.

Yanmar introduced a new 350-hp version of the 6LY-UTE called the 6LY-STE. Ratios are 4.2 lbs/hp and 3.7 lbs/hp, respectively.

This review/article originally appeared in Power & Motoryacht Magazine, January 1995 and is written by Captain Jim Gorant. For more great powerboat reviews, visit their website and subscribe at: https://www.powerandmotoryacht.com/uncategorized/subscribe-power-motoryacht