What's the Deal with Mower Horsepower?

Close up of mower engine

With over ten different zero turn mower brands in New Zealand, and around five different engine types, it’s easy to start by looking at horsepower. But these days horsepower is a very confusing and ambiguous measure of not only power, but how that power translates onto your lawn being cut.

A Bit about Horsepower (hp)

Horsepower as the name suggests is a measure of power. It hails back to the 18th century and was originally used to compare the power of draft horses to the new fad called the steam engine.

The mechanical horsepower / imperial horsepower is the equivalent power to 746 watts. It is typically only used in the mechanical world – people would look at you rather funny if you told them your microwave was 1.5hp!

Which mower is right for your property? Find out everything you need to know before you start. Get your free guide now.

Engine Horsepower Ratings - Here’s Where It Gets Tricky.

There’s a heap of engine brands out there – but for now we’re going to stick with two comparisons – Briggs & Stratton and Kawasaki.

We could get very technical with power curves and other technical rating information, but for now let’s compare the basic specifications two particular engines - Briggs & Stratton 44T9 Commercial Series and Kawasaki FR651 Series Engines – both very common engines found on zero turn mowers.

Right off the bat, you can see that both engines have a lot of similarities;

ModelBriggs & Stratton CS 44T9Kawasaki FR 651
Engine Displacement (cc)724726
Number of Cylinders22
Engine ConfigurationVertical ShaftVertical Shaft
OHV (Overhead Valve)YesYes
Weight (kg)3840kg
Bore (in)3.13.1
Stroke (in)2.93.0
Oil Capacity (L)1.982.1
Warranty2 Years3 Years

Aside from Kawasaki having a better warranty (and the heavier weight is a good sign), there’s not a lot of difference… but what’s missing?

ModelBriggs & Stratton CS 44T9Kawasaki FR 651
Horsepower (hp) at 3,600 rpm2521.5
Rating SystemSAEJ1940SAEJ1995

Now – that’s a huge difference! The salesman selling the mower with the Briggs & Stratton is definitely going to have an easier job selling his machine with 3.5hp 'more' than the zero turn mower with the Kawasaki engine. That’s because…

You Don’t Hear Anyone Talking about the SAE Rating!

The reason for the above supposed discrepancy is entirely due to the different engine rating. That could be covered in an different article – but you can see what this means for the consumer who doesn’t understand engine technicalities like the engineers at Kawasaki or Briggs & Stratton.

What Effect does Horsepower Have on the Lawn anyway?

This is a very broad statement – but in reality, as long as a zero-turn mower has sufficient horsepower for its size, it’s not going to make a hang of a heap of difference.

You could slap a 28-30hp engine onto a residential zero turn like a BOB-CAT CRZ or a Ferris IS Series machine, and here’s what’ll happen;

  • It’ll drive the same speed – (transaxles are limited anyway)
  • It’ll mow with a similar blade tip speed (If it did go faster the spindles would wear faster or even blow up)


  • It’ll be Louder
  • It’ll be heavier
  • It’ll be off-balance.

Here’s the low down on Horsepower when buying a mower;

  1. Consider the Mower Quality first
  2. Then Prioritise the engine’s quality/brand over its power
  3. Check the Horsepower rating if you’re comparing.

The reality is, no manufacturer is going to put an under-powered machine on the market, it’d be the quickest way to lose sales.

So, put your priority on getting a good quality engine on a good quality machine – and don’t get hung up on horsepower!

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