![90 horsepower mercury motor 90 horsepower mercury motor](https://p.globalsources.com/IMAGES/PDT/BIG/998/B1025689998.jpg)
In contrast, in a two-stroke the combustion of the fuel-air mixture takes place every stroke that the piston travels towards the crankshaft, from the top dead centre (TDC) to the bottom dead centre (BDC) this is called a power stroke. Four-stroke engines have one stroke dedicated to the induction of the fuel-air mixture into the cylinder, a second stroke to compress the fuel-air mixture and ignite it, a third stroke to allow the burning gases to drive the piston back down the cylinder (the power stroke) and a fourth stroke to expel (exhaust) the burned gases from the combustion chamber. The four-stroke engine has one power stroke for every four strokes of the piston – i.e. Our trio of 4-stroke engines were the Honda BF90, Mercury 90EFI and the Suzuki DF90.įor those who are still a little confused as to the difference between a 4-stroke and a 2-stroke, the simplest way to describe them is: The direct injection 2-strokes were the new Evinrude ETEC 90 HO and the Mercury 90 OptiMax. All four are in-line three-cylinder engines with triple carburettors. The four 2-stroke carburetted engines were the Mercury 90, Parsun T90, Tohatsu M90A and the Yamaha 90A. In the case of some of the engines, such as Mercury, we also cross checked with their own SmartCraft gauges in an effort to ensure that our figures were as accurate as possible. The tests were performed with just two people aboard a new Huntsman 525 CSB500, using a Lowrance fuel flow system and GPS. I realise that only makes nine, but the tenth, the Tohatsu 90 TLDI, wasn’t available for our test. The line-up has certainly changed, and now comprises a trio of 4-strokes, four 2-strokes and two direct injected 2-stroke engines. Well, times have certainly changed and today we are presented with ten 90hp offerings, although one, the Honda 90, has just been superseded by the Honda 100hp. carburetted engines as there was no such thing as a direct injected 2-stroke at that time. It was back in 1996 that we last ran a head-to-head comparison on 90hp outboards and at that time had only five, comprising four 2-strokes and one 4-stroke. The results proved both interesting and predictable. We took one boat to two different locations and spent a whole lot of time to put together a comprehensive fuel and performance data comparison on nine different 90hp outboards.