Affect on Performance of Reducing Power and Power Stroke Design

Optimizing the performance of Boston Whaler boats
conch
Posts: 169
Joined: Sat Oct 17, 2015 8:43 am
Location: Florida Keys,Hawaii,Mississippi

Affect on Performance of Reducing Power and Power Stroke Design

Postby conch » Wed May 11, 2022 8:18 pm

Moving down approximately 40% in horsepower [and] switching to four-stroke-power-cycle engine from a two-stroke-stroke-power-cycle engine may not result in the same performance.

jimh
Posts: 10184
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: Affect on Performance of Reducing Power and Power Stroke Design

Postby jimh » Thu May 12, 2022 9:15 am

Performance is always a function of power and weight. If weight is constant and power is reduced by a factor of 0.6 of original power, then boat speed will reduce by a factor of 0.6^0.5 or 0.77.

When outboard engines were first introduced using four-stroke-power-cycle designs, there was proper concern that those engines might not provide a range of engine speeds with useful power (known as power band) that was as wide as the power band of two-stroke-power-cycle engines. Over time, manufacturers of four-stroke-power-cycle engines improved the power band of their engines by various methods. The reality of the present new outboard engine market is that four-stroke-power-cycle engine completely dominate the new engine market, and there are no longer any new two-stroke-power-cycle engines available to buy.

There are many four-stroke-power-cycle engines available now that have a very wide RPM range at which they can deliver good power and acceleration. Were this not true, then there would still be a demand for two-stroke-power-cycle engines. That lack of demand for new two-stroke-power-cycle engines caused the last major manufacturers of them, Mercury and Evinrude, to stop making them. There are no more OptiMax or E-TEC engines being made.

See

Requiem for the Two-stroke-power-cycle Outboard Engine
https://continuouswave.com/forum/viewtopic.php?f=4&t=6245&p=36592

Even more significant in the demise of two-stroke-power-cycle engines was the timing of the two announcements. Mercury ceased making two-stroke-power-cycle engines in 2018, leaving the ENTIRE market for them to Evinrude to have exclusively. Despite having the market for two-stroke-power-cycle engines all to themselves, Evinrude ceased production of them in 2020.

dtmackey
Posts: 662
Joined: Thu Sep 28, 2017 9:29 pm

Re: Affect on Performance of Reducing Power and Power Stroke Design

Postby dtmackey » Thu May 12, 2022 4:39 pm

jimh wrote: The reality of the present new outboard engine market is that four-stroke-power-cycle engine completely dominate the new engine market, and there are no longer any new two-stroke-power-cycle engines available to buy.


You are speaking of the U.S. market as two strokes are still manufactured today and available in other countries.

D-

jimh
Posts: 10184
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: Affect on Performance of Reducing Power and Power Stroke Design

Postby jimh » Thu May 12, 2022 5:13 pm

dtmackey wrote:You are speaking of the U.S. market as two strokes are still manufactured today and available in other countries.
Europe has the same emission regulations as the USA or even more stringent regulations. I don't think Mercury is making OptiMax engines for export to other countries. There is so much demand for their four-stroke-power-cycle engines that supply is constrained by production capacity.

Evinrude or Johnson engine are not being made at all, except for some spare parts for warranty replacements. Suzuki and Honda don't make two-stroke-power-cycle engines. Maybe Tohatsu or Yamaha make a few smaller two-stroke-power-cycle engines, but they aren't available in the USA.

I doubt there are any two-stroke-power-cycle engines with power ratings above 75-HP available in other countries, and, even if there were, exactly how you'd get one back to the USA is problematic.

dtmackey
Posts: 662
Joined: Thu Sep 28, 2017 9:29 pm

Re: Affect on Performance of Reducing Power and Power Stroke Design

Postby dtmackey » Thu May 12, 2022 5:31 pm

jimh wrote:I doubt there are any two-stroke-power-cycle engines with power ratings above 75-HP available in other countries, and, even if there were, exactly how you'd get one back to the USA is problematic.


Yamaha is still building and selling them with power ratings of 3-HP to 200-HP in some areas of the world. I just wanted to clarify on the statement that two strokes are no longer built.

D-

jimh
Posts: 10184
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: Affect on Performance of Reducing Power and Power Stroke Design

Postby jimh » Thu May 12, 2022 5:45 pm

dtmackey wrote:I just wanted to clarify on the statement that two strokes are no longer built.
That is not exactly what I said. What I said was:

--Evinrude is not making any two-stroke-power-cycle engines for sale as new engines; they might make a few for warranty replacement.

--Mercury is in a similar situation. I think they are still making replacement OptiMax power heads, but not new OptiMax engines for sale at retail.

I would not be surprised of Tohatsu or Yamaha were still making smaller two-stroke-power-cycle engines to sell into non-USA, non-European markets, but that does not really have an effect on the USA market.

Maybe new two-stroke-power-cycle engines are still popular in Indonesia or India or Africa or somewhere else, but they really are off the market in the USA now.

I am quite happy with the two-stroke-power-cycle direct-injection ultra-low-emission 225-HP engine I have on my boat, but I am a realist. If shopping for a new outboard engine in the USA now, the only choice is four-stroke-power-cycle. To throw out old bromides that want to dismiss all four-stroke-power-cycle engines as lacking the power of two-stroke-power-cycle engines is just that: out of date information no longer applicable.

Thanks to enhanced engine designs with refinements like variable valve timing, multiple intake and exhaust valves per cylinder, large displacement, tuned intake runners, computer control, and so on, the four-stroke-power-cycle engines are satisfying boaters quite nicely with their power output.

Even with the market all to their own, Evinrude was unable to grow their market share against four-stroke-power-cycle competitors. That is the reality of the new outboard engine market in the USA. Evinrude folded and have moved on. Exactly what they have moved on to is still unknown, but they were the last outboard engine manufacturer to make two-stroke-power-cycle engines able to be sold in the USA, Canada, and Europe, and they have stopped making them.