The DuroMax XP20HP is a 500cc, single-cylinder, 4-stroke OHV gasoline engine designed for equipment that uses a horizontal 1-inch shaft. It has a 1.35-gallon fuel tank, recoil starting, forced-air cooling, and a maximum torque rating of 22.87 ft-lb at 2,500 rpm. DuroMax lists applications such as go-karts, pressure washers, mobile carwashes, log splitters, roto-tillers, and water or trash transfer pumps.
One specification deserves particular attention for U.S. buyers: the XP20HP is EPA certified, but DuroMax currently lists it as not CARB certified and not 50-state emissions compliant. That means emissions requirements should be checked before purchasing, especially if the engine will be used in California or another application requiring broader emissions certification.
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DuroMax XP20HP Specifications
| Specification | DuroMax XP20HP |
|---|---|
| Engine Type | 4-Stroke OHV |
| Displacement | 500 cc |
| Fuel Type | Unleaded gasoline, 87+ octane, up to 10% ethanol |
| Fuel Tank Capacity | 1.35 gallons |
| Starting System | Recoil start |
| Cooling | Forced air |
| Maximum Engine Speed | 4,000 rpm |
| Maximum Torque | 22.87 ft-lb (31 N·m) @ 2,500 rpm |
| Bore | 94 mm |
| Stroke | 72 mm |
| Shaft Orientation | Horizontal |
| Shaft Diameter | 1 inch |
| Shaft Length | 3.535 inches |
| Keyway | 1/4 inch |
| Shaft Rotation | Counter-clockwise |
| Shaft End | 3/8 in., 24 UNF-2B, drilled and tapped |
| Shaft Center to Base | 5.26 inches |
| Fuel Delivery | Carburetor |
| Lubrication | Splash |
| Oil Capacity | 40.5 fl oz (1.2 L) |
| Recommended Oil | SAE 10W-30 |
| Cylinder Sleeve | Cast iron |
| Bearing | Stainless steel ball bearing |
| Average Runtime | Approximately 2 hours |
| Dimensions | 19 × 17 × 19 inches |
| Weight | 77 lb |
| EPA Certified | Yes |
| CARB Certified | No |
| 50-State Emissions Compliance | No |
| Warranty | 3 years |
What to Check Before Buying the XP20HP
If you are buying the XP20HP as a replacement engine, displacement and shaft diameter are only part of the compatibility equation.
The engine uses a horizontal 1-inch shaft that is 3.535 inches long and has a 1/4-inch keyway. The shaft rotates counter-clockwise, and DuroMax specifies a 5.26-inch distance from the center of the shaft to the base.
Those measurements can determine whether the engine will physically fit your equipment. Before ordering, compare the XP20HP with your existing engine’s shaft length, shaft rotation, mounting arrangement, shaft height, and required operating speed.
The emissions specification also matters. The XP20HP is EPA certified, but DuroMax currently lists it as not CARB certified and not 50-state emissions compliant. If your project requires CARB certification or 50-state compliance, verify the requirements before purchasing.
The starting system is another consideration. The XP20HP is recoil-start only. If you specifically want electric starting, DuroMax also offers the XP20HPE, a related 500cc model with the same 1-inch shaft size and both recoil and electric starting.
Design and Build
500cc 4-Stroke OHV Engine
The XP20HP uses a 500cc 4-stroke OHV design and is positioned by DuroMax as its largest and most powerful single-cylinder engine.
The combination of displacement and horizontal-shaft layout makes it suitable for equipment that needs a replacement utility engine rather than a complete power unit with an integrated generator, pump, or transmission.
DuroMax lists a 94 mm bore and 72 mm stroke, with maximum torque of 22.87 ft-lb at 2,500 rpm.
Cast-Iron Cylinder Sleeve
The XP20HP uses a cast-iron cylinder sleeve. This is a useful construction detail when comparing utility engines, particularly for buyers looking at replacement motors intended for repeated use.
However, the presence of a cast-iron sleeve should not be treated as proof of a specific service life. Actual durability depends on load, maintenance, operating conditions, storage, and how the engine is installed.
Forced-Air Cooling
The engine uses forced-air cooling rather than a liquid-cooling system.
For an exposed horizontal-shaft application, this keeps the cooling system relatively straightforward because there is no radiator, coolant pump, or coolant circuit to maintain. The engine should still be installed and operated according to the manufacturer’s instructions, with sufficient airflow around the engine.
Recoil Starting
The XP20HP uses a recoil starter.
That means there is no starter battery or electric starter motor to maintain, but starting requires manually pulling the recoil handle. For equipment that is used occasionally or in locations where maintaining a battery is inconvenient, this can be a practical configuration.
If push-button starting is important, the XP20HPE is the related 500cc alternative with electric and recoil starting.
Fuel Tank and Runtime
The XP20HP has a 1.35-gallon gasoline tank. DuroMax lists an average runtime of approximately two hours.
That figure should be treated as an estimate rather than a guaranteed operating time. Actual fuel consumption will vary according to the equipment being powered, operating load, engine condition, and other operating conditions.
For longer jobs, the tank size can reduce the frequency of refueling, but fuel consumption should still be considered when matching the engine to a particular application.
The XP20HP uses a carburetor and is specified for unleaded gasoline of at least 87 octane with no more than 10% ethanol according to the service specifications.
Where the DuroMax XP20HP Makes Sense
Go-Karts
The horizontal 1-inch shaft makes the XP20HP relevant to certain go-kart builds.
However, the engine should not be purchased solely because it has a 1-inch shaft. The mounting arrangement, shaft length, shaft rotation, drivetrain, clutch or torque converter, and available frame space all need to match the intended build.
Pressure Washers
DuroMax specifically lists pressure washers among the applications for the XP20HP.
For a replacement project, compare the original engine’s mounting pattern, shaft specifications, operating speed, and power requirements before installing the XP20HP.
Mobile Carwashes
DuroMax also lists trailer-mounted mobile carwashes among the intended applications.
For this type of equipment, the engine needs to be matched to the pump and drive system. Shaft compatibility and operating speed are particularly important because the engine is only one part of the complete system.
Log Splitters
The XP20HP is also listed for log splitters.
Whether it is an appropriate replacement depends on the original engine specifications and the hydraulic system being used. Check the mounting arrangement and shaft configuration rather than assuming that any 500cc engine will be a direct replacement.
Roto-Tillers and Cultivators
DuroMax lists roto-tillers and cultivators as additional applications.
For these machines, physical fitment and shaft alignment matter just as much as engine displacement. Confirm the original engine’s dimensions and shaft requirements before ordering.
Water and Trash Transfer Pumps
Water and trash transfer pumps are another listed application.
Before installation, confirm the pump’s required engine speed, shaft rotation, mounting dimensions, and shaft configuration. A mismatch in any of these areas can make an otherwise suitable engine incompatible with the equipment.
Maintenance and Service
Regular maintenance is important for any small gasoline engine, and the XP20HP manual provides specific procedures and specifications.
Engine Oil
The XP20HP has an oil capacity of 40.5 fluid ounces, or approximately 1.2 liters. DuroMax recommends SAE 10W-30.
The engine should be filled with the correct amount of oil before its first operation. Do not assume the engine contains the required operating oil when it arrives.
Air Filter
The service manual identifies the air-filter element as a paper filter and states that it is not reusable.
Inspect the filter according to the manufacturer’s maintenance schedule, particularly when the engine is operated in dusty environments.
Spark Plug
The service specifications list a spark plug gap of approximately 0.027–0.031 inches, or 0.7–0.8 mm.
Check the current XP20HP manual before servicing the spark plug because correct gap and plug specifications are important for starting and engine operation.
Fuel Storage
Old gasoline can cause starting and fuel-system problems.
For storage longer than 30 days, follow the fuel-storage procedure in the XP20HP manual instead of simply leaving untreated gasoline in the tank.
The manufacturer provides separate procedures for short-term and longer-term storage, including draining fuel and preparing the engine for extended storage.
High-Altitude Operation
High-altitude operation requires additional attention because the engine’s carburetor is calibrated for a particular operating range.
DuroMax’s service information provides high-altitude guidance and warns about using a modified carburetor at lower elevations. If you operate the XP20HP at significant elevation, follow the manufacturer’s instructions rather than installing a jet or carburetor modification without verifying the correct configuration.
DuroMax XP20HP Pros and Cons
Pros
- 500cc 4-stroke OHV design.
- Horizontal 1-inch shaft.
- 22.87 ft-lb of maximum torque at 2,500 rpm.
- 1.35-gallon fuel tank.
- Recoil starting without a starter battery.
- Cast-iron cylinder sleeve.
- Stainless steel ball bearing.
- 3-year manufacturer warranty.
- Designed for several types of utility equipment.
Cons
- Recoil start only; there is no electric starter on the XP20HP.
- The engine weighs 77 pounds.
- It is not CARB certified.
- DuroMax lists it as not 50-state emissions compliant.
- Compatibility depends on the exact equipment and mounting configuration.
- A replacement installation may require additional components or adjustments depending on the original engine.
XP20HP vs. XP20HPE
The XP20HP and XP20HPE are closely related 500cc DuroMax engines, but their starting systems differ.
The XP20HP uses recoil starting only. The XP20HPE adds electric starting while retaining recoil starting.
Both models use a 500cc 4-stroke OHV engine, horizontal 1-inch shaft, 94 mm bore, 72 mm stroke, and the same listed maximum torque of 22.87 ft-lb at 2,500 rpm.
The XP20HP is listed at 77 pounds, while the XP20HPE is listed at 83 pounds. The XP20HPE also has larger listed dimensions because of its electric-start configuration.
If your equipment already has a suitable battery system and electric starting is important, the XP20HPE is worth comparing. If you specifically want a recoil-start engine, the XP20HP provides the simpler configuration.
Warranty and Support
DuroMax currently lists a 3-year warranty for the XP20HP.
The manufacturer also states that its U.S.-based support teams can assist with troubleshooting and diagnosis and that it maintains service centers across the country.
Warranty coverage can depend on the circumstances of a claim, so it is worth reviewing the current warranty terms and exclusions before purchase.
Frequently Asked Questions
Is the DuroMax XP20HP a 500cc engine?
Yes. The XP20HP is a 500cc, single-cylinder, 4-stroke OHV gasoline engine with a horizontal shaft. DuroMax lists a 94 mm bore and 72 mm stroke, along with maximum torque of 22.87 ft-lb at 2,500 rpm.
Does the DuroMax XP20HP have electric start?
No. The XP20HP is recoil-start only. The XP20HPE is the related 500cc model that adds electric starting while retaining recoil starting.
Is the DuroMax XP20HP CARB compliant?
No. DuroMax currently lists the XP20HP as EPA certified but not CARB certified and not 50-state emissions compliant. If your application requires CARB certification or 50-state compliance, verify the requirements before purchasing.
What size shaft does the XP20HP use?
The XP20HP has a horizontal 1-inch-diameter shaft that is 3.535 inches long and uses a 1/4-inch keyway. The shaft rotates counter-clockwise, and DuroMax lists a 3/8-inch, 24 UNF-2B drilled-and-tapped shaft end.
How much oil does the DuroMax XP20HP take?
The XP20HP has an oil capacity of 40.5 fluid ounces, or approximately 1.2 liters. DuroMax recommends SAE 10W-30 and specifies splash lubrication.
How much does the DuroMax XP20HP weigh?
DuroMax lists the XP20HP at 77 pounds. The XP20HPE electric-start version is listed at 83 pounds.
How long will the XP20HP run on a full tank?
DuroMax lists an average gasoline runtime of approximately two hours. Actual runtime can vary depending on the equipment being powered, operating load, engine condition, and operating conditions.
Final Verdict on the DuroMax XP20HP
The DuroMax XP20HP is a substantial horizontal-shaft utility engine built around a 500cc 4-stroke OHV design, a 1-inch shaft, recoil starting, and 22.87 ft-lb of maximum torque.
Its specifications make it relevant for equipment such as pressure washers, log splitters, tillers, go-karts, mobile carwashes, and transfer pumps, provided the mounting and shaft requirements match.
The most important points to check before buying are the shaft dimensions, rotation, mounting measurements, starting method, fuel requirements, and emissions status. The XP20HP is EPA certified, but it is not CARB certified and is not listed as 50-state emissions compliant.
For buyers who specifically need electric starting, the XP20HPE is the related 500cc alternative. For buyers who need a recoil-start horizontal-shaft engine, the XP20HP offers a straightforward configuration with a 1-inch shaft and a 3-year manufacturer warranty.