How to identify Mercury 2+2 engines

[laserguy]

I looked recently at a nicely maintained classic Montauk with a Mercury 115 (1988 or 1989). I remembered reading a "very thorough" discussion about the merits of this engine on ContinuousWave , but I realized I did not know how to identify one, if I wished to avoid it.

Is [the 2+2 configuration used in] all Mercury four-cylinder engines in 100 to 125-HP range from 1980 until 2000? Or from 1970's? Or except with Optimax?

What about Mariner-branded engine of 100 to 125-HP?

Was [2+2 used w ith] only some engines of 100 to 125-HP?

Or, is there some other permutation [for use of 2+2 configuration]?

This is not a request to discuss merits or lack thereof! That's already been flogged thoroughly.

Also, I passed on the boat. The owner said the engine sounded "funny", but he still wanted top dollar. Funny is not what I'm looking for, at least in a engine.

[jimh]

I don't think there are any four-cylinder OptiMax engines. The OptiMax was either a three-cylinder configuration, which was half of a V6 block, or a V6 block in two displacement ranges. Since an engine using the 2+2 method needs four cylinders, I feel confidant no OptiMax engines used the 2+2 method.

I believe the four-cylinder two-stroke-power-cycle engines were the only application of the 2+2 method. The displacement was 1.848-liter or 113-cubic-inch. I see them listed in a 2005 catalogue, but only in the specifications sections. They did not get a single page or mention in the catalogue material inside. These engines were rated at 115-HP or 125-HP, as far as I know.

The EPA phased-in their reduced emission standards for recreational outboard engines (and personal watercraft engines) over a nine-year period, beginning in 1998 and going to 2006. The emission standard provided for fleet averaging of emission, so it was possible for an outboard engine maker to sell some nonconforming engines that themselves did not meet the standard, as long as the total sales mix of engines complied. Because these four-cylinder 1.848-liter 2+2 engines were never able to meet the EPA standards for reduced exhaust gas emission standards, the sale of them in the USA was probably very limited by 2005.

There were some 100-HP-rated outboard engines, but they might have been just the three-cylinder 90-HP engine that was rated at 100-HP under a different rating system. This has occurred with some other engines; the same engine is sold in the USA as a 90-HP and in Europe as a 100-HP. I suspect that you might find this with the Mariner brand, which was more often seen overseas than in the USA.

[laserguy]

Thanks for the clarity on the phase-in of EPA regs as a fleet target, as opposed to a target at the engine level. Did not know that.

I knew the Opti's did not have a carb, but wasn't sure what size they came in.

According no NADA Guides, there was only a 4 stroke 115 in 2006 model year, which I understand was the end of all CARB non-compliant sales in the US. Interestingly, as you had noted, there was a 2 stroke 115 in 2005 as well as a 4 stroke 115 AND an Optimax 115!

[jimh]

Here is a bit more about EPA regulations:

What emissions standards apply to spark-ignition (gasoline) marine engines?

We also have several sets of standards for gasoline marine engines. For these engines we distinguish between:
• Outboards and personal watercraft
• Sterndrive and inboard engines
• Gasoline auxiliary engines

Outboards and Personal Watercraft Exhaust Standards

The outboard and personal watercraft exhaust standards phase in over nine years from 1998 to 2006. Because it is an averaging standard (See footnote below) manufacturers are typically offering a mix of new and old technology throughout the phase-in period. The standard is based on a curve function that is intended to represent the relationship between rated power and brake-specific emissions. In addition, California has two additional tiers of atandards that are more stringent than the EPA standards (see http://www.arb.ca.gov).

[Footnote: This means that emission credits may be earned for engines certified below the emission standard. These credits may be used to sell engines certified above the standard provided that, on average, the engines meet the emission standard.

Here is a table that shows the limits of exhaust gas emissions by year during the phase-in period:

From Table 11, Page 8, Overview of EPA's Emission Standards for Marine Engines

Table11smaller.png (30.02 KiB) Viewed 7744 times

[laserguy]

Per online calculator: 1.34 horsepower in 1 kilowatt.

So 4.3 kW is roughly 5.7 hp.

Using 2006 limits, I ran the calculation for ">4.3kW" category of HC+NOx permittable emissions. The answer was 81.2 g/kW-hr. So the ceiling for any engine is 81 g/kW-hr from the chart. For 6 hp and above, it then changes based on power output. Note the standard is in terms of work, not power: kW (hp) for 1 hour of operation.

Ran calc for 2006 200hp model and got 45.2 g/kW-hr.
If I did the math correctly, the emissions per hp declines with rising horsepower. So that 200hp engine can emit 6748 grams per hour of operation in total.

4 hp can emit 324 grams per hour of operation in total.

NB. My math is subject to correction.

[jimh]

I posted the table to show how the regulated exhaust gas emission limits were phased-in. You can just look at the coefficient multipliers for the various years. For example

1998 = 0.917
2006 = 0.250

So, roughly speaking, outboard engine regulated emissions had to reduce from 0.917-of-something-per-HP to about 0.250-of-something-per-HP over the nine years. To go to 0.25 from 0.91 is a reduction of 0.667. Expressed as a percentage that is about a 70-percent reduction. So the outboard engine makers had nine years to figure out how to reduce exhaust gas emission by 70-percent, again, roughly speaking. (I am sure there is more to it than this crude analysis, but my figures show the trend line.}

For the 2+2 approach used by Mercury a 70-percent reduction in emissions may have been a hurdle that could not be overcome. Since the method of suppressing combustion in the two unused cylinders at low speed was just to make the fuel:air mixture too lean to be combustible, it is likely that some of the hydrocarbons in the unburnt fuel were going out in the exhaust and being counted as exhaust emissions.

Note that the EPA allowed credits to be earned and applied, but in the case of Mercury they already had several noncompliant engines (like VERADO) which needed those credits to permit them to be sold. This probably further doomed the 2+2 to be an end-of-life product.

In comparison, the really very highly regarded and generally outstanding three-cylinder 90-HP engine of similar vintage, but without any sort of displacement on demand, was probably still in production for a while. I know at one point there were died-in-the-wool advocates of two-stroke-power-cycle engines that were recommending and encouraging purchase of the 90-HP engine before it went off the market, a sort of stock-up-now approach to evading the effect of the EPA. The surprise was the 90-HP was still on the market, probably propped up with emission credits, even after its demise was forecasted by the pundits.

[laserguy]

Thanks. That was very educational.

Presumably, I imagine loop charged engines could hold on longer because less unburnt fuel goes out with each exhaust stroke (one of the goals of loop charging). The inline 3 cylinders from Mercury (and OMC and Yamaha) are regarded as sweet engines, compared to the inline 4 cylinders and V-4's due to intrinsic balance problems, I believe.

What the last model year of the 90-HP Mercury?

[david s]

As a point of reference, a Mercury Marine catalog titled "Mercury Outboards Effective October 2008" lists the 90-HP in-line three-cylinder two-stroke-power-cycle engine being available at that time. The only carbureted and "classic" two-stroke-power-cycle engines listed in the publication are the 150-HP EFI V6 along with the 90-HP, 65-HP Jet, and 50-HP--the three latter motors are in-line three-cylinder models.

Additional information shown is "© MERCURY MARINE. Published 10/08. Printed in U.S.A."

Others may be able to confirm the final year of production and availability for the Mercury 90-HP three-cylinder two-stroke-power-cycle engine for the U.S.A. market, but the 2008 to 2009 time frame has to be getting close. At that point there's also a question regarding whether these engines were available on the consumer market or for commercial operators only.

[jimh]

From the information reported in the c.2008 brochure, it seems reasonable to infer the 2+2 115-HP and 125-HP engines were no longer being offered for sale at that time.