How does CCs affect blade power and torque?

[Boomer49]

I pulled this from online because it uses less words than I would. Maybe it will clarify things. "When it comes to measuring power output for a lawnmower engine, torque is often a more accurate measurement than horsepower. Let me explain why:

1. Torque vs. Horsepower:
   • Horsepower (HP): Traditionally, lawn mower power was measured in horsepower. One horsepower is equal to 33,000 foot-pounds per minute. However, horsepower only calculates the overall work the engine can produce.
   • Torque: Torque, on the other hand, measures the rotational force produced by the engine. Specifically, it quantifies the power involved in turning the mower’s rotary blades. When you mow the lawn, the blades rotate and twist to cut the grass. The amount of power used for this action is known as torque1.
2. Why Torque Matters for Lawn Mowers:
   • Rotary Blades: When the mower’s blades are turned on, you’re witnessing an example of torque. Torque is essential for spinning the blades and allowing them to cut through grass.
   • Bogging Down: Lawn mowers with higher torque are less likely to get bogged down when cutting thick or long grass. More torque means more force delivered to the blade, making it easier to handle challenging conditions.
   • Gross Torque: Walk-behind lawn mowers typically have a power rating expressed in gross torque, not gross horsepower. This emphasizes the engine’s capability to turn the blade effectively1.
3. Choosing the Right Torque:
   • Consider your specific needs:
     • Yard Size: If you have a small, flat yard that you mow regularly, a mower with 4.50 to 5.50 ft-lbs of torque should suffice.
     • Grass Thickness: For larger yards with tall or thick grass, opt for a mower with more torque.
   • Longevity: The torque you choose directly affects the mower’s ability to complete the job and improve the motor’s lifespan. While torque alone isn’t the sole consideration, it’s essential when selecting a lawn mower. In summary, while horsepower remains crucial for riding lawn mowers, push lawn mower owners often prioritize torque. So, when evaluating lawnmower power, keep torque in mind—it’s the force that keeps those blades spinning

 

[RevB]

I want to get a mower engine and swap onto my little 21" 140cc Craftsman. I let my yard get way too high and went to mow it, but it was barely able to handle it, and I had to push it 2ft, backtrack 3, then go forward slowly.

Anyway, I was looking at a new mower, but they're all 150 or 170 or 163 cc (for the well rated ones. There's several 200ish cc ones for outrageous money, or with like 2 stars.

So, I'm curious. How much does engine CC actually do? Will I notice a difference between my 140cc and a 150? What about 163 or 170? Where would I need to go to buy a bigger engine that I could just swap onto the mower?

You dont want a mower for that. Something like a DR push string trimmer.

 

[navydad2022]

I have a question,my mower is a 22 craftsman B&S engine rated to run at 3500 RPMs but l have my mine running at 3370 would this hurt my mower

 

[closecut]

That's what I am planning to do. I'm letting the grass lift up a bit because it was pretty wet the other day when I mowed (no choice on that).

Does HP do anything? StarTech said it was torque. Is HP a better way to measure power output than torque?

HP is rpm X torque.HP is more important than torque itself,because torque is only one part of the equation.I have seen a 1/16 hp electric motor pull concrete anchors out of the floor,but it was geared like a clock motor...very slow.
Most (but not all) small mowers are rated at 3600 rpm,so hp should be a fair comparison of the motors.Check the specs,including the torque and RPM at rated HP.
You can convert torque to horsepower by multiplying the torque rating by RPMs of the mower and dividing by 5,250. Now you can compare horsepower to horsepower.
A 21 inch mower should be almost unstoppable with a 5 hp motor,from my personal experience.

 

[closecut]

I have a question,my mower is a 22 craftsman B&S engine rated to run at 3500 RPMs but l have my mine running at 3370 would this hurt my mower

To get the max hp,it must be run at the specified speed.The fan for cooling is part of the equation,and most air cooled engines run cooler at rated speed than slower speed because of higher oil pressure,more air flow.
At the speed you are running,it should not have a big effect,unless you are "lugging" the motor under heavy load.
You are losing about 1 hp/
How are you checking the rpm?

 

[ILENGINE]

I have a question,my mower is a 22 craftsman B&S engine rated to run at 3500 RPMs but l have my mine running at 3370 would this hurt my mower

By my calculations you have a blade tip speed of 19,400 fpm which is slightly above the maximum allowed under safety standards of 19,000 fpm

To get the max hp,it must be run at the specified speed.The fan for cooling is part of the equation,and most air cooled engines run cooler at rated speed than slower speed because of higher oil pressure,more air flow.
At the speed you are running,it should not have a big effect,unless you are "lugging" the motor under heavy load.
You are losing about 1 hp/
How are you checking the rpm?

True but in the case of a rotary mower blade tip speed requirements will override max engine rpm, so even if the engine is rated at 3500 rpm blade tip requirements can drop that below max like with the example of the 22 inch mower then max engine rpm would be closer to 3300.

 

[Chuckers]

I have a question,my mower is a 22 craftsman B&S engine rated to run at 3500 RPMs but l have my mine running at 3370 would this hurt my mower

I'm not a mod - but hijacking a thread does 2 things...

1. It's unfair to the OP because it takes steam away from his thread.

2. It's unfair to yourself because you will get more eyes on your specific question (even if it is related to OP) and therefore get more answers.

Thus, please start your own thread if you have a question.

 

[callwill]

Find an old push mower that still runs. Set wheels for tallest cutting height. push down on the handle and get those front wheels way off the ground. Push it slowly into your over growth. Mow for a while and rake up the cuttings. Keep moving on area by area. Go back over it until you can mow with all 4 wheels on the ground.
Start mowing with your good mower.

 

[Little Fish]

My take on mowing wet grass..Dont.
Takes so much power and it always looks like $hit .
Everyone thinks they "have to" mow that wet stuff. You'd be better off waiting a day or two ,letting it dry off and even if it grows more and get better results.. Its easier to mow 6" dry grass than it is to mow 4" wet grass.
JMO..

My yard is a swamp. It hasn't rained for 3 days and there's still standing water...

 

[Little Fish]

Bigger is always better. HP means nothing. you want as much torque as you can get. Torque is what does the work. think of it like a race car an engine builder will maybe tell you what the HP is but well never tell you what the Torque is and where it comes in and hits it's peak. the twisting is what gets you down the road or in this case is what spins the blade. about 25-20 years ago there was a "war" in the lawn mower world that manufactures were inflating the HP on the engines more the what it was so someone stepped in and say hey stop doing that and now they list the CC and the "Peak" torque. so in a nut shell get the biggest you can get and Oh I personally would never buy any CRAPSman power equipment. if your looking to replace an engine on a machine look at the Predator engine from Harbor freight they are cheap and really pretty powerful. you tube search project farm this dude tests everything I think you will probably find an engine test in his vast vault of video's and he explains why he tests and what he's testing and it's affect. super smart dude!

I love PF!

Thanks for the advice. That's exactly what I needed.