Sep 25

Sep 25 Project Honda BF 150: The K24 Outboard Revs Up

When I think of how the idea of tuning the Honda BF 150 started, it was after spending so much time working on our outboard articles last year. On top of that research, we conducted a comprehensive survey that helped us gain valuable insight into outboard buyers shopping in the 150 - 300 HP range. That range of power represents a huge segment of the outboard engine industry, and is extremely competitive. There were a few things that really stood out in the feedback we received from the articles, and the data we collected from the survey. Consumers are more concerned with the weight of the engine than almost anything else. Brand loyalty wasn’t as important as I would’ve guessed, and although there is a divide in the preference for the type of engine (2 stroke vs 4 stroke), more and more consumers are less concerned about the engine configuration, as long as the engine is light and powerful.

Since we are focused on performance boats, there is a bit of a chasm in that world. On the one hand you have true performance products from Mercury Racing, which are fantastic offerings in the 250, 300 and 400 range; and on the other hand, you have a large segment of hardcore performance boaters looking to replace their lightweight 2 stroke engines. Many small boats struggle to handle the weight of the newer, larger offerings in the 250 HP plus range. Not only that, if you are repowering, and re-rigging, you will be looking at spending quite a bit of money. Jumping from a light 200 or 225 would mean you may be looking at a new 250 that weighs 100 Lbs more. You may need to change your setback, and jack plate, buy new props and change the setup quite a bit Add new gauges, and this means a full repower and applicable changes could run you well north of $25,000 for a single.

What attracts me to the smaller 150 - 175 HP 4 cylinder engines is that they utilize new technology, and are quite a bit lighter than the big blocks. If these smaller engines could make just 10% or 20% more power than stock, with simple modifications, it would be perfect for performance boaters that have smaller single engine boats, and make repowering way easier. Plus, it makes sense economically. Based on research, there is massive demand for a light performance orientated 225 HP engine.

Mercury 150 ProXS 4.jpg — Lighter

Mercury is catching on, with the introduction of the 150 ProXS. It will be the best 150 on the market based on price, power, and weight. It makes 163 HP. If it only made a little more.

Mercury and Yamaha probably have the most exciting engines in this category, the Mercury 150 3.0L four stroke, and the Yamaha 2.8L SHO engines are good engines in general. If they had a few performance modifications, could they be great? I think so. But what else is out there? If the Evinrude G2 2.7L was lighter, and had a better gear ratio, it would be game over for stock engines in this range, they are better than everything else other than those two big factors. Suzuki makes good engines, but they are heavy, and geared for tugboats. Honda, same issue as Suzuki. But, the one advantage Honda has in the BF 150 is that it uses a version of their automotive K24 engine.

On the street, the K24 engine is very capable, and has many years of performance parts development behind it. Not only that, the K24 is in some of the most popular Honda cars, they have made millions of them, they are extremely proven. Heavily modified versions that make huge horsepower use the stock crankshaft and they can hold up to extreme abuse. So, with a serious inventory of parts, and deep knowledge of the engine, there is a serious advantage for aftermarket potential with the BF 150.

4 Piston Racing is known for their cylinder heads and race engines. Impeccable work and dedication to racing make them standout.

After quite a bit of research, I got in touch with Luke Wilson at 4 Piston Racing, the leader in performance Honda cylinder heads and race engines. Luke and his partner Josh, along with their team at 4 Piston Racing, have an incredible reputation for their quality of work and dedication to racing. Luckily, Luke is also an avid boater, and very interested in fast boats; so he connected immediately with the idea. Luke is extremely confident in this engine and how it could perform on the water with the right modifications.

Honda Project BF150-4piston.jpg — K24

Luke and Josh from 4 Piston Racing, working on the outboard version of an engine they know extremely well. Their cylinder heads and race engines are legendary. They’ve built k24 based engines capable of 500 HP, naturally aspirated.

As it happened, I met with Honda at the Miami Boat Show in 2017, and told them about what we were working on. Needless to say, they were very interested in what we were doing. After quite a few meetings, Honda ended up wanting to use a prototype of the engine for marketing purposes. The marketing potential is really significant, in fact, I believe this could help Honda speak to a whole new consumer, and really move their brand out of the shadows. Honda is planning to show it in their booth at SEMA in October.

Prototypes are one thing, we have a lot more work to do for a version to test. The stock gearcase won’t work, and it will have to lose some weight still. Having said that, there is serious potential here, and our project goals are really ambitious. We will keep you updated as we go, and look to do some real world testing in the near future.

A few details about the engine:

The block is sleeved with coated Ramey Racing sleeves. Large bore pistons from Wiseco. Saenz Performance connecting rods. ECU by MoTec. And, a custom 4 Piston Racing cylinder head for this application. We plan on changing the gear ratio from 2.14:1, to 1.75:1, or 1.86:1, plus add low water pickup, and an appropriate nose cone.