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  Evinrude G2: Effect of Rated Horsepower on Performance Considering No Displacement Change

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Author Topic:   Evinrude G2: Effect of Rated Horsepower on Performance Considering No Displacement Change
peteinsf posted 04-17-2015 02:00 PM ET (US)   Profile for peteinsf  
With the displacement and everything else seeming to be equal across the Evinrude G2 line, can it be assumed that the only real performance difference in the G2 models would be at or near WOT?


jimh posted 04-17-2015 03:12 PM ET (US)     Profile for jimh  Send Email to jimh     
The recently introduced Evinrude E-TEC 74-degree V6 engines are all using the same 3.4-liter displacement. They are not all identical in their mechanical features. Engines with 25-inch and 30-inch shaft lengths have power steering, and engines with 20-inch shaft lengths may not. There is a 300-HP model designated as the R.A.V.E model (for Rotax Adjustable Valve Exhaust) which has a significantly different power head design.

There may be a difference in weight from the power steering pump added weight that might affect performance. The R.A.V.E. model is likely to have quite different performance due to the adjusting of the exhaust valve port opening across the engine speed range.

For models that are not the R.A.V.E. and all have power steering, there is a range of rated horsepower from 200 to 300. The variation in rated horsepower is presumed to be due to variations in the firmware contained in the engine management module, which controls the combustion chamber. I have not seen any published data that shows the horsepower or torque at the propeller shaft as a function of engine speed for different models according to horsepower rating. I presume that the models near the 300-HP end of the ratings will be given more fuel and produce more power compared to the models at the 200-HP end of the rating band.

The engine speed range is specified to be the same for all these models, with the maximum engine speed given as 6,000-RPM. This seems to suggest that the difference in power must be spread across more of the engine speed range than just the last few hundred RPM at full throttle. This may be in contrast to some engines in which an added 50-HP is obtained by letting the engine accelerate to higher crankshaft rotational speeds, sometimes as much as an extra 500-RPM or more, than similar models of lower rated horsepower.

It may he helpful to understand that horsepower is a term that defines the rate at which a force is applied. It may be possible to have two engines that are operating at a certain crankshaft rotational speed, say 4,000-RPM, which is not their maximum speed. At 4,000-RPM crankshaft rotational speed, one engine may be programmed to use more fuel in the cylinders than another. By using more fuel in the cylinder, a combustion that produces more release of energy from the greater fuel volume is created. The greater energy is translated into a greater force pushing the piston down in the cylinder, and this produces more torque. The engine burning more fuel and producing more torque, will produce more horsepower at that crankshaft rotational speed than a similar engine that is running at the same crankshaft speed but has less fuel in its combustion chambers, therefore producing a less powerful force in the cylinder. The rate of rotation is the same, but the force available from each rotation may be greater in one engine than another. In this way, the engine rated for more power may produce more power all across the engine speed range compared to an engine of similar design but limited in its power by the control of the amount of fuel.

When you move the throttle lever of a modern engine, you are really giving the engine an electronic signal that tells the engine controller how much power you would like to develop

This notion that two engines of the same displacement could produce different power across a range of crankshaft speeds is not a new concept. In the 1960's I recall my teen-aged brother and his friends tinkered with cars. They would remove a two-barrel carburetor from an engine and bolt on a four-barrel carburetor. The four-barrel carburetor allowed more fuel to be sucked into the combustion chamber. More fuel was burned in each combustion cycle. More horsepower was produced. The displacement of the engine block stayed the same.

In terms of moving a boat, the top speed is going to be a function of horsepower. An engine with 300-HP will make a boat go faster than an engine of 200-HP. Let us say that the difference in speed will be 10-MPH. Where you will notice the difference in horsepower? Most likely you will notice the difference in horsepower the most when you open the throttle to wide-open or full throttle.

Don SSDD posted 04-18-2015 02:39 PM ET (US)     Profile for Don SSDD    
More fuel to the same cubic inch block may only mean more power across the rpm range, so it will be quicker but the top speed may be the same. It may have a higher top speed, but only if you use that additional HP & torque to run a higher rpm, run a lower ratio gear, and a bigger prop. You may not be able to get a higher redline.

You could buy a Chevy 327 with 250, 300, 340, 360, 365, and 375 HP. Same bore and stroke, but different cams, intakes, carbs, exhaust manifolds. Same thing is happening with a G2, but with sensors and a computer, maybe some different mechanical parts too. Modern engines usually have a much wider power band, rpm wise, even though rated at the same hp.


peteinsf posted 04-19-2015 02:04 PM ET (US)     Profile for peteinsf    
My thinking was:

Same boat, same prop, same weight, and same displacement = "same energy in" at any given RPM.

= RPM = Speed

I would think it would run too lean if they messed too much limiting fuel since there no intake valves to restrict the air.

elvis posted 04-19-2015 02:29 PM ET (US)     Profile for elvis  Send Email to elvis     
Anyone on this forum purchased one? Would love to hear an owner's evaluation.

I didn't see any at the charleston, sc boat show a few months back.

seahorse posted 04-19-2015 07:57 PM ET (US)     Profile for seahorse    

I would think it would run too lean if they messed too much limiting fuel since there no intake valves to restrict the air.

E-TECs use rotating throttle plates to regulate the air flow into the cylinders

jimh posted 04-21-2015 05:06 PM ET (US)     Profile for jimh  Send Email to jimh     
Engine crankshaft rotational speed is not a measure of horsepower. Horsepower is a rate of work done. You can spin an engine rated for 300-HP at 5,000-RPM with no load on it, and it is not making 300-HP.

If you have two engines with similar displacement, and one makes 300-HP while the other makes 200-HP, you can turn a higher pitch, larger diameter propeller with the 300-HP engine than you can with the 200-HP engine, even though at full throttle the engine crankshaft rotational speed will be the same. It takes more torque to turn the higher pitch propeller.

onlyawhaler posted 04-22-2015 03:37 PM ET (US)     Profile for onlyawhaler  Send Email to onlyawhaler     
A good overview on all Evinrude G2 engines and specifically on the 300-HP models is presented a recording by Boat Test by Captain Steve--worth a look


Freddy posted 04-22-2015 07:57 PM ET (US)     Profile for Freddy  Send Email to Freddy     
I like this video by Boat Test, also. Plus you can see an old Whaler.
jimh posted 04-24-2015 10:07 AM ET (US)     Profile for jimh  Send Email to jimh     
First PETEINSF posits:

I would think [an E-TEC engine] would run too lean if [its designers] messed too much limiting fuel since there [are] no intake valves to restrict the air.

To which SEAHORSE replies:

E-TECs use rotating throttle plates to regulate the air flow into the cylinders

The definition of throttle is "to choke or strangle." That is what a throttle does--it chokes off the air. A secondary meaning of throttle is "to regulate and especially to reduce the speed of (as an engine) by such means."

The concept of choking off the air to an engine is intrinsic in the use of the word throttle.

A further problem: there ARE intake valves; they are just called ports instead of valves. The intake port of a two-cycle engine controls the flow of the intake charge into the cylinder.

In addition, there are reed valves in the air path that open and close, controlling the path of air into the cylinder. The suggestion that there are no valves to restrict the air flow into the combustion chamber of an E-TEC 74-degree V6 engine is not correct.

The sealing off of the air flow by the throttle is so good that there has to be an idle air bypass path to let some air into the engine at minimum throttle. Control of the air flow is not a big problem in an E-TEC engine.

[I made a mistake in attribution of my quoted material, which I have corrected. My apologies to the person to whom I mistakenly attributed that comment.--jimh]

Peter posted 04-25-2015 08:43 AM ET (US)     Profile for Peter  Send Email to Peter     
On a 2-stroke, the piston sliding past and covering up the intake port is essentially the same as a gate valve. Functionally, it is the same as the intake valve in a 4-stroke as they both open and close during the combustion cycle to allow air into the combustion chamber and then allow that air to be compressed. The difference is that the 4-stroke valve requires more mechanical components to facilitate the opening and closing with a benefit that such arrangement has some degree of freedom regarding the timing of the close-open-close events.

This video provides a reasonable visual comparison of the valve action in both motor types.

Both 2 and 4-strokes use throttle plates to regulate the air flowing into their respective intake ports.

jimh posted 04-25-2015 12:32 PM ET (US)     Profile for jimh  Send Email to jimh     
Peter--Thanks for the further explanation of how a two-cycle engine regulates the flow of air. This odd notion being put forth that an E-TEC cannot regulate the flow of air seems unsupported by the actual facts. Thanks for making that clearer. As far as I can see, and as far as I know, there is no difference between a two-cycle engine and a four-cycle engine in terms of how the flow of air into the combustion chamber is controlled or throttled or regulated.
peteinsf posted 05-04-2015 09:53 AM ET (US)     Profile for peteinsf    

My thought was that a 4 stroke engine (with the same block) could have a variety of cam shafts that would allow designers to tune the mechanics and timing of fuel and air flow,

The premise of my post was if all the mechanical parts in a G2 are identical (100%) how would you limit the HP at below WOT.

I would think it would need more differences than just software. My point was if the intake and exhaust ports and heads are the same size (across G2 models) the motor would put out that save HP and torque at a given RPM (let's say 2500)...

If correct, people who want loads of torque but don't care about WOT performance the 200HP motor might still be a good deal.

Love to see a torque chart of all the G2 (and vs the 200HO+ e-techs)

(my first job out of high school was repairing OMC sailboat motors, I replaced 100's of water pumps, the 9.9 was the big model)

Maybe I need a factory tour!


jimh posted 05-05-2015 08:18 AM ET (US)     Profile for jimh  Send Email to jimh     
A poppet valve in the intake path of a four-cycle engine using cams will be open the same amount of time (in terms of percentage of the piston cycle) at all engine speeds, which is exactly the same as the ports of two-cycle engine. Until recently, four-cycle engines used fixed timing on the cams. In outboard four-cycle engines the Honda V-TEC models introduced some cam timing enhancements in c.2003. The use of cam timing in four-cycle outboard engines has been adopted by many manufacturers, but it is by no means universal--Mercury does not use it--and often is used only in engines in the top end of the horsepower range or in special versions of engines.


My thought was that a 4 stroke engine (with the same block) could have a variety of cam shafts that would allow designers to tune the mechanics and timing of fuel and air flow...

A two-cycle-power-stroke engine has the same possibilities, that is, a change can be made mechanically to the engine in some manner but not affect the displacement. The engine can be tuned by adjustment of the location and dimension of the ports. Mechanically tweaking the ports of a two-cycle engine has been done forever by mechanics hoping to improve or modify performance. It is just the same as someone putting in "a hot camshaft" into an engine with poppet valves.

Not mentioned so far, the Evinrude E-TEC and E-TEC G2 use direct fuel injection into the combustion chamber, which is a significant improvement in creating improved fuel economy, reduced emissions, and better performance. The use of direct-injection is now becoming more common in automobile four-cycle engines, but remains unknown in marine four-cycle outboard engines. With direct-injection the amount of fuel delivered to a cylinder combustion chamber can be very precisely controlled by electronic means.

I really don't understand why there is resistance to the notion that a two-cycle engine of a particular displacement could be tuned to deliver different amounts of horsepower and torque. No one seems to have any resistance to the notion a four-cycle engine could be tuned to different power ratings. Why believe that this is not possible with a two-cycle engine?

Power comes from fuel. Burn more fuel, get more power.

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