1990 Honda Prelude Si Engine: B21A1 2.1L DOHC Inline-Four

The 1990 Honda Prelude Si (North American market) is equipped with Honda’s B21A1 engine—a 2.1-liter, DOHC, 16-valve inline-four producing about 140 hp and 135 lb-ft of torque. This marked an upgrade from the 2.0-liter DOHC used in earlier third-generation Si models, offering slightly more displacement and power along with Honda’s PGM-FI electronic fuel injection.

The Engine at a Glance

For the 1990 model year in the U.S. and Canada, the Si trim moved to the B21A1. It’s part of Honda’s unique B20A/B21A family designed specifically for the third-generation Prelude (1988–1991), notable for its slanted mounting angle and crisp DOHC character. The 2.1-liter was sold in both Si and Si 4WS (four-wheel steering) variants.

Key Specifications

The following list outlines the core technical details enthusiasts and owners typically want to know about the 1990 Prelude Si’s powerplant.

• Engine code: B21A1
• Configuration: Inline-4, DOHC, 16 valves (PGM-FI fuel injection)
• Displacement: 2,056 cc (2.1 liters)
• Bore x stroke: 83.0 mm x 95.0 mm
• Output (factory ratings): approx. 140 hp @ 5,800 rpm; 135 lb-ft @ 5,000 rpm
• Compression ratio: about 9.4:1
• Timing: Belt-driven camshafts
• Notable design: Slanted mounting (approx. 18 degrees) unique to this Prelude generation

Taken together, these specs delivered a rev-happy, tractable engine that paired well with the Prelude’s balanced chassis and, when equipped, its innovative four-wheel steering system.

How to Verify Your Engine

While the 1990 Si should have the B21A1, production changes or swaps over the decades mean it’s wise to confirm what’s in your car. The following steps help you verify the engine code and configuration.

1. Check the engine stamp: Look for the “B21A1” stamping on the engine block (typically on a machined pad near the transmission side of the block).
2. Review the under-hood emissions/vehicle information label: Factory labels usually list the engine family and applicable emissions specs.
3. Cross-reference the VIN and build data: Dealer records, factory service manuals, or reputable online databases can confirm the original equipment for your VIN.
4. Inspect visual cues: The DOHC valve cover and intake layout are distinguishing features from the SOHC base-model engines.

Confirming these details ensures you have the correct baseline for ordering parts, planning maintenance, or evaluating performance upgrades.

Context and Model-Year Nuances

From 1988–1989, the U.S.-market “2.0Si” carried the B20A5 (2.0L DOHC). For 1990–1991, the Si badge moved to the 2.1L B21A1. Base “S” models in 1990–1991 used a SOHC 2.0L (B20A3). While trim names and offerings could vary by market, the North American 1990 Si is tied to the B21A1. If you’re outside North America, verify local specifications, as regional naming and engines sometimes differed.

Known Quirks and Maintenance Notes

Owners and technicians should be aware of a few engine-specific considerations with the B21A1.

• FRM cylinder liners: The B21A1 used fiber-reinforced metal cylinder walls, which can complicate rebuilds and contribute to higher oil consumption as mileage climbs.
• Service implications: Standard honing techniques and piston ring choices may not be compatible with FRM; machine shops need the correct abrasives or may resleeve to conventional iron.
• Timing belt maintenance: As with most belt-driven DOHC Hondas, timely belt and water pump replacement is critical to avoid engine damage.
• Parts sourcing: Many components remain available through aftermarket and specialist suppliers, but verifying B21A1-specific fitment is important.

With proper maintenance and attention to its FRM-specific needs, the B21A1 can remain a reliable and distinctive engine in the third-gen Prelude.

Bottom Line

If your car is a North American 1990 Honda Prelude Si, it should have the B21A1 2.1L DOHC inline-four, factory-rated around 140 hp, paired to either a 5-speed manual or 4-speed automatic, with optional four-wheel steering on the Si 4WS.

Summary

The 1990 Honda Prelude Si is powered by Honda’s B21A1—a 2.1-liter, DOHC, 16-valve inline-four delivering roughly 140 hp and 135 lb-ft. It’s a unique, slant-mounted engine from the B20A/B21A family, notable for PGM-FI and FRM liners. Earlier 2.0Si models (1988–1989) used the smaller B20A5, but the 1990 Si upgraded to the B21A1 in North America. Verify your engine code on the block and under-hood labels to be certain, especially on older vehicles where swaps are common.

What cars have a B20A engine?

B20A, B20A1

• 1985–1987.03 Honda Prelude Non-U.S.
• 1985.06–1987.04 Honda Accord Non-U.S.
• 1985.06–1987.04 Honda Vigor Non-U.S.

What engine does the Prelude si have?

The Prelude’s Si engine varied across generations, including the 3rd-gen’s 2.1L B21A1 (140 hp) and 4th-gen’s 2.3L H23A1 (160 hp). The high-performance, signature engine for the later 4th and 5th generations was the 2.2L H22A VTEC engine, known for its significant power.
 
3rd Generation (1990-1991) 

• Engine: 2.1L B21A1
• Power: 140 horsepower
• Key Feature: This was a dual overhead cam engine and a more powerful option for the “Sport Injected” (Si) model.

4th Generation (1992-1996) 

• Engine: 2.3L H23A1
• Power: Approximately 160 horsepower
• Key Feature: This generation saw the introduction of the H-series engine.

5th Generation (1997-2001) 

• Engine: 2.2L H22A1/A4 VTEC engine
• Power: Around 200-217 horsepower, depending on the market
• Key Feature: This became the Prelude’s signature high-performance engine, featuring Variable Valve Timing and Lift Electronic Control (VTEC).

H-Series Engine 

• The H22 engine is considered the Prelude’s performance pinnacle, with the highest torque of any Honda four-cylinder engine in its time.

Did the Prelude si have VTEC?

This Prelude is powered by an H22 DOHC VTEC engine which was only offered in Japan. The engine starts right away, idles smoothly, and accelerates well with VTEC engaging as it should. The 5 speed manual transmission shifts correctly and the clutch does not slip.

Which Prelude has H22?

H22A. Found in the Japanese 4th gen 1992-1996 Prelude Si VTEC (2WS BB4 & 4WS BB1). It produces 200 PS (147 kW; 197 hp) @ 6,800 rpm & 161.5 ft⋅lbf (219 N⋅m) @ 5,500 rpm and comes with a black valve cover.