How much horsepower do busses have?

In today’s blog post, we will answer the following question: How much horsepower do busses have? We will explain in detail the importance of engine power and how to maintain it for a longer lifespan. 

How much horsepower do busses have?

School buses can have from 235 up to 450 horsepower, depending on the engine. The most common brands of Skoolie engines are Cummins, Caterpillar and International Navistar. Each bus engine brand has its own specific criteria, and we review them in the table below:

Bus Engine Brand	International Navistar	Cummins	Caterpillar (CAT)
Engine	MaxxForce DT (DT466)	5.9L Cummins 24 valve(became the 6.7L in 2007)	CAT C7(Discontinued in 2009)
Horsepower	Up to 300 hp @ 2,200 rpm	235 – 325 HP @ 2,900 rpm	Up to 300 hp @ 2200 rpm
Torque	Up to 860 lb-ft @ 1,300 rpm	460 – 610 lb-ft @ 1,600 rpm	Up to 925 lbs-ft torque @ 2000 rpm
B50 Engine Life	550,000 miles	350,000 miles	450,000 miles

Horsepower – why it matters for school buses

A school bus’ engine power is measured in horsepower. Horsepower is the objective measure that calculates the mechanical work done by an internal combustion engine. The name of the measure was coined by a Scottish engineer named James Watt. 

According to Watt’s measurements, one horsepower equals 33,000 pound-feet of work per minute. Watt’s measurement was neither absolute nor the most accurate for calculating power, but it was not intended to calculate engine power in general.

In general, this measurement indicates the operability of a vehicle. It refers to how much force is produced per second, this force is what a vehicle uses to accelerate, so more horsepower gives faster acceleration.

So how much horsepower do you need for a school bus? How much horsepower you actually need depends on the weight of the bus and the speed you need. This answer is related to your lifestyle and daily activities, however, for an average Skoolie driver, less than 350 horsepower is sufficient. A larger amount is only needed if it is a heavier school bus or if it is necessary to accelerate faster.

A school bus usually can’t go faster than 65 mph, as most of them have built-in speed control. Do not forget that, essentially, a Skoolie is an (old) converted school bus. Still, if you manage (or ask a mechanic) to deactivate the speed limiter to your Skoolie, it can go as fast as any RV.

How much torque do busses have?

As seen in the table above, school buses can have between 460 up to 925 lbs-ft torque, again, depending on the engine type. But why does torque matter?

Torque is the energy developed by a heat engine, it produces a force that is transmitted to the connecting rod and the crankshaft. The reciprocating movement of the pistons is thus transformed into a circular movement; which is called torque or torque.

Inside the engine, the combustion gases generate a pressure inside the cylinders that pushes the pistons with a certain downward force that is transmitted towards the crankshaft, making it rotate due to the generated torque.

 A practical example to understand can be seen in the pedals of a bicycle; where the motor would be the person pedalling, and the motor torque, in that case, the pressure or force exerted on the pedals.

Optimal engine operation should be kept in the green band; specifically in the area marked with a letter E. At this point, we observe that the RPM will be between 1100 and 1400, with this, we will obtain torque, horsepower and optimal fuel performance. 

Each engine has its own operating ranges and we must know them in order to obtain fuel efficiency without sacrificing power and torque.

Once this concept is explained, we can deduce why a diesel bus engine has an outstanding drag capacity and how knowing the torque and power it provides will help us choose an engine according to our needs.

How does a school bus engine work?

A school bus diesel engine works by igniting (igniting) the fuel by being injected with a high-pressure spray into a combustion chamber (or pre-chamber, in the case of indirect injection) containing air at a temperature higher than the self-combustion temperature, with no need for a spark. 

The main components of a fuel system include the following:

•  Tank: It is the tank for the fuel of your bus.
• Fuel filter: Attaches to both ends of fuel pumps to separate impurities, ensuring optimum engine performance.
• Fuel pump: Its main function is to extract the fuel from the tank and pump it to the internal combustion engine.
• Fuel injectors: It is an electronic valve that opens and closes at regular intervals to deliver the correct amount of fuel to the engine.

How exactly does the fuel system of a school bus work?

As you already know, the fuel is stored in a special tank that is filled from the outside through a small hole that is sealed with a lid. Before being converted into energy, this fluid must first pass through a pump.

The fuel pump is what physically pumps this fluid and allows it to travel through metal lines. In this way, the fuel can reach the filter, where any impurities or dirt is removed before it enters the engine.

This last component is very important, therefore it is necessary to keep it clean. It is the only way to ensure that your Skoolie’s engine works properly and has a long service life.

As the fuel flows, the final conditions to provide complete combustion is atomization and spray pattern. The former is achieved as a result of injection pressure, due in part to the diameter of the holes in the injector. On the other hand, the space, angle and number of holes in the injector tip will determine the spray pattern.

Is a diesel engine better for a bus?

Historically, diesel engines have long been considered more enduring than their gasoline counterparts. One of the reasons for this is that a diesel engine runs slower than a gasoline vehicle. In addition, until the 1980s, diesel vehicles benefited from a simpler design, which promoted high reliability.

Later, however, these engines were made more complex. They are now equipped with turbo and high-pressure injectors. These additions have improved the performance of each car, but also undermined their reliability: these parts are now responsible for many breakdowns.

Today’s diesel vehicles no longer correspond to the opinion still anchored in many minds, who consider that this type of fuel is synonymous with an indestructible engine.

But if the diesel models have seen their robustness decline in recent decades, they remain on average more enduring than the petrol versions. If thermal engines (diesel as gasoline) would have a similar lifespan, a diesel model would travel on average 16,000 miles per year, compared to 9,300 annually for gasoline. 

In terms of mileage, the average lifespan of diesel would therefore be 155,000 miles, compared to 60,000 miles less for gasoline.

The bottom line

We hope we managed to make it clear what horsepower and torque are and why it matters for a bus. We also hope that you have understood how a bus engine works and how to properly maintain it.

If you do have other questions about this topic, please let us know!

FAQ on How much horsepower do busses have?

How fast does a Skoolie go?​​

A Skoolie usually can’t go faster than 65 mph, as most of them have built-in speed control. Do not forget that, essentially, a Skoolie is an (old) converted school bus. Still, if you manage (or ask a mechanic) to deactivate the speed limiter to your Skoolie, it can go as fast as any RV.

Do school buses get good gas mileage?

Yes, school buses get good gas mileage. A Skollie can get an average of 10 miles per gallon, which is pretty good for a bus. 

How long do diesel school bus engines last?

Diesel school bus engines last 15 to 20 years or 250,000 miles if properly maintained and treated with care. In rare cases, the Skoolie engines will not even get to seven years, as the causes of wear and breakdowns are plenty. 

Are bus engines turbocharged?

Yes, most of the bus engines made in the past few decades are turbocharged.  On buses, the engine is generally installed at the rear, lying down on the left side to free up space in front of the rear door, or upright, which allows better access for maintenance. There are also mid-engined buses and there are older buses that are not turbocharged.

References

• Quick Answer: How Much Horsepower Do Buses Have? – Ecommerce
• Torque — and Why it Matters for School Buses
• How do diesel engines work? – Explain that Stuff