Overview#
The Generac SG040 is a 40 kW standby natural gas and LP vapor generator set built on Generac's 5.4-liter naturally aspirated V8 spark-ignited engine. Rated at 50 kVA standby and 45 kVA prime at 60 Hz, the SG040 represents an older platform in Generac's SG-Series lineup — the V8 engine architecture and Digital H control system distinguish it from the current inline-4 and Power Zone Pro equipped units at 35 kW and 45 kW.
The 5.4L V8 uses a carburetor and downflow secondary fuel regulator (versus the electronic fuel injection on the current 4.5L inline-4), with a required natural gas supply pressure of 8–14 in WC. Standard equipment includes the Digital H dual 4×20 display control panel with Modbus protocol, RS-232/485 communications, NFPA 110 Level 1 compliance, and isochronous governor control. A factory-installed radiator supports 50°C (122°F) ambient operation. UL 2200 and CSA 22.2 listed.
Technical Specifications#
Power Ratings (60 Hz, 1800 rpm)
| Rating | kW | kVA |
|---|---|---|
| Standby | 40 | 50 |
| Prime | 36 | 45 |
Engine — Generac 5.4L V8 SI
| Parameter | Value |
|---|---|
| Displacement | 5.4 L (329.5 in³) |
| Configuration | V8 |
| Aspiration | Naturally aspirated |
| Compression ratio | 9.0:1 |
| Rated speed | 1,800 rpm |
| Emissions | EPA Certified Stationary Emergency |
| Oil capacity | 6 qt (5.7 L) |
| Fuel type | Natural gas, propane vapor |
| Fuel inlet pressure (NG) | 8–14 in WC (2.0–3.5 kPa) |
Fuel Consumption — Natural Gas (standby rating)
| Load | Consumption |
|---|---|
| 25% | 263 scfh |
| 50% | 451 scfh |
| 75% | 609 scfh |
| 100% | 752 scfh |
Physical (Open Set)
| Dimension | Value |
|---|---|
| Length | 76.0 in (1,930 mm) |
| Width | 37.4 in (950 mm) |
| Height | 46.3 in (1,176 mm) |
| Dry weight | 2,256 lbs (1,023 kg) |
Level 1 acoustic enclosure: 112.5 × 38.0 × 49.5 in, steel 2,776 lbs.
Control System — Digital H
Digital H dual 4×20 display panel provides isochronous governor control, 3-phase digital voltage regulation, 7-day programmable exerciser, Modbus protocol with RS-232/485, date/time-stamped fault history, and NFPA 110 Level 1 and Level 2 compliance. Note: this is an earlier control generation than the Power Zone Pro used on current SG-Series units — remote communications capabilities are more limited.
Our Service Experience#
The SG040's V8 engine platform requires attention to a 8-plug spark plug service at 1,000-hour intervals — this is an easy interval to defer but noticeably affects running quality on natural gas. The carbureted fuel system (versus electronic injection on current models) is sensitive to fuel quality and supply pressure variation; we check inlet pressure and carb adjustment at every annual service. The higher fuel consumption of the V8 platform (752 scfh at full load vs 446 scfh on the 35 kW inline-4) should be factored into gas meter sizing for any new installation. Buyers evaluating this unit vs. the SG045 should note that the SG045 uses the current 4.5L inline-4 with Power Zone Pro — a significant control system upgrade.
Frequently Asked Questions#
How does the SG040 differ from the SG035 and SG045? The SG040 uses a 5.4L V8 engine and Digital H control panel — an older platform. The SG035 and SG045 both use the current 4.5L inline-4 with Power Zone Pro controller. The SG040 is a legacy design; buyers prioritizing control system features or lower fuel consumption may prefer the SG045.
What is the fuel consumption of the SG040? At full standby load, the SG040 consumes 752 scfh of natural gas. This is notably higher than the SG045's 554 scfh at 45 kW, reflecting the V8 engine's lower efficiency relative to the turbocharged inline-4 used on later models.
What control communications does the SG040 support? Digital H control provides Modbus protocol with RS-232 and RS-485 serial interfaces, 16-channel remote trending at 0.2 ms resolution, and predictive maintenance algorithms. No built-in Ethernet or TCP/IP — an external communications module is required for network-based monitoring.
What fuel pressure does the SG040 require? Natural gas supply pressure of 8–14 in WC at the generator inlet. This is a higher minimum than the current 4.5L inline-4 platform (5 in WC minimum). Verify gas meter and regulator capacity before installation.
Is the SG040 still supported by Generac? The SG040 is a legacy product. Parts are generally available through Generac's industrial dealer network, but the V8 engine platform and Digital H control have been superseded by current designs. For new installations, the SG045 is the recommended alternative.
