Kawasaki FX 651 V

[Skippydiesel]

Kawasaki FX 651 V has two siblings, the 691 & the 730

All three share the same engine capacity 626 cc (44.3 cu in), Compression 8.2:1, Stroke 78X76mm, weight, oil capacity, however manage deliver different outputs at the same 3600 RPM;

651
Maximum Power
20.5 hp (15.3 kW) at 3,600 RPM
Maximum Torque
39.0 ft-lbs (52.9 N·m) at 2,200 RPM

691
Maximum Power
22.0 hp (16.4 kW) at 3,600 RPM
Maximum Torque
39.3 ft-lbs (53.2 N·m) at 2,200 RPM

730
Maximum Power
23.5 hp (17.5 kW) at 3,600 RPM
Maximum Torque
39.7 ft-lbs (53.8 N·m) at 2,400 RPM

While hp goes up by 3, Torque (the ability to do work) is only slightly increased by 0.9 Nm at a higher rpm, taking the Torque climb from 1400 rpm down to 1200 rpm .

# How is this achieved ?
# Is there any real benefit (other than psychological) in the higher hp engine(s)?

 

[ILENGINE]

Can be done with different carb jetting, or other carb changes, or changes in ignition. Let me describe another series of engine that I am more familiar with. The Kohler CV18-20-22 The CV18 has a screw in the carb that limits the throttle butterfly to open ony 50%. You still get 3600 rpm but don't have full throttle use. The CV20 removes that screw to allow full throttle response. The CV22 has spark advance to vary the spark timing for power increase. All 3 engines use the same block.

 

[Skippydiesel]

Thanks Ilengine.

I am aware that B&S have a restriction in some of their carburettor/inlet manifold (extra large gasket) as a method of derating the engine.

I thought my Kwaka might have something similar and or a diffrent crankshaft profile.

Can't imagine timing would be a common choice but then your butterfly restrictor screw sounds pretty improbable - I guess most operators would just replace the screw with a shorter one and get the full hp --- tooooo easy!

 

[ILENGINE]

Can't imagine timing would be a common choice but then your butterfly restrictor screw sounds pretty improbable - I guess most operators would just replace the screw with a shorter one and get the full hp --- tooooo easy!

Didn't have to replace the screw just remove it The catch is you also had to reset te static governor setting and if the engine had a sudden unplanned disassembly it also voided the warranty if removed.

We referred to that as the $130 screw because that was the difference in price between the 18 and 20 hp engines.

And Honda used the same block concept on multiple HP engines also.

 

[Skippydiesel]

"The catch is you also had to reset te static governor setting"

Please explain - I would have thought the governor would have maintained/restricted the engine to the same rpm????

 

[ILENGINE]

"The catch is you also had to reset te static governor setting"

Please explain - I would have thought the governor would have maintained/restricted the engine to the same rpm????

The screw limited the throttle butterfly to only open halfway. So the governor was set for the throttle butterfly to only open 50% not the full straight open 100%. And if not reset the governor couldn't take advantage of the full movement of the throttle butterfly plate since the governor gear itself would limit movement to 50%

 

[Skippydiesel]

You have the advantage on me - I don't follow.
Why have a screw limiter, when the governor achieves the same 50% limit on rpm?
In my limited understanding, most governors work on engine rpm - not power, ergo a power increase (more fuel) does not change the governed engine speed.??

 

[ILENGINE]

Skippy correct. But here is the thing. Engine rpm is maintained by the governor at a set speed. As the engine load increases causes a drop in engine rpm. The governor spring overcomes that rpm drop to return the engine to the set rpm. Now as the engine load keeps increasing it keeps opening the throttle plate further until it hits the stop. And any load above that point results in an rpm drop. So with no stop in place it will allow the throttle plate to open further therefore allowing the engine to handle more load before rpm drop.

 

[Skippydiesel]

Thanks - that I understand.

So, in your engine example, Kohler CV18-20-22, the removal of the screw/butterfly stop, will allow the engine to deliver more power/torque under load (rpm dropping) it should not change the governed set speed (unless further modification done).
It would seem that purchasing the lower cost engine is a good move, if you want more power, just remove the limiting screw and vwala!

I wonder what mechanism limits my Kwaka engine hp ??

 

[ILENGINE]

Skippy, Correct. Briggs uses a restrictor plate in the intake to do the same things on some of there engines. Start your engine and go to full throttle with no load, and the throttle plate will be closed down to the point that is it just slightly wider than the idle position. Load resulting in rpm drop is what leads to the throttle opening.

The other truth is most people will never notice the difference between 18 and 20 hp. Good example is look at the hp on current lawnmowers. 42 inch deck riders with 18-26 hp engines. And years ago that would of been a 10-12 hp engine on that mower.