Honda K20A2 Engine Guide
The Honda K-Series is one of the most beloved engine series in the JDM space. While the Honda crowd is often not taken seriously in many enthusiast circles, the K-Series is an excellent example of why they should be. The K-series was Honda’s 4-cylinder flagship replacement for the equally touted B-series. The preceding K-Series boasted significant advantages over the B-series, including larger displacement and higher-flow cylinder heads.
The K20 consists of nine distinct variants which all vary slightly in terms of construction and power delivery characteristics. One of the crowned jewels of the K20 line is the K20A2, which features the highest compression ratio and redline of the entire K20 lineup outside of the JDM-only high-performance K20A.
The K20A2 is also favored above other K20 variants due to its valvetrain. Where other K20 variants, like the K20A3, use a VTEC-E valvetrain that is seen less favorably, the K20A2 employs a true DOHC i-VTEC system that is known and loved in the Honda community.
In this article, we’ll cover the K20A2 in detail, discussing its specifications, applications, and mod potential.
Honda K20A2 Engine Specifications
|Displacement||1,996 cc (121.8 cu in)|
|Bore x Stroke||86.0mm x 85.9mm|
|Weight||Long Block: 275lbs|
|Horsepower||197-200 hp @ 7,400 rpm|
|Torque (lb-ft)||139-142 lb-ft @ 5,900-6,000 rpm|
As you can see from the above figures, the K20A2 has very impressive N/A power and torque figures for a 2.0L 4-cylinder engine.
Honda 2.0L KA20A2 Applications
- 2001–2006 Honda Civic Type R (EDM)
- 2002–2004 Acura RSX Type S
- 2002–2004 Honda Integra Type R (AUDM/NZDM)
Honda K20A2 vs K20A3 Differences
It is pretty much undisputed that the K20A2 is the better engine of the two despite having similar construction. Both the A2 and A3 share the same displacement, bore/stroke, and valves. However, the two K20 variants do differ in a few key ways that make the K20A2 the more desirable motor. The two main differences between the two are the cylinder heads and VTEC systems.
K20A2 vs K20A3 Compression
One of the differences between the K20A2 vs K20A3 that makes the biggest performance difference is the A2’s higher compression ratio. The A2 features higher compression pistons, which bumps compression to 11.0:1 over the A3’s compression ratio of 9.8:1. Among other factors, the A2’s higher compression ratio gives it a higher specific output than the A3 at 100hp/L.
K20A2 vs K20A3 VTEC Differences
The K20A2 also features a different and more advanced i-VTEC system than the K20A3. The K20A3’s VTEC-E system only has VTEC on the intake side of the valvetrain. In fact, the K20A3’s VTEC-E system lacks high-RPM cam profiles entirely. Instead, the VTEC-E system effectively forces the K20A3 to act as a 12-valve engine, not allowing one of the intake valves to open entirely until a set RPM is reached.
In comparison, the K20A2 uses a i-VTEC system that closely resembles earlier DOHC VTEC systems found on B-series engines. The K20A2 features three intake cam lobes. Two outer lobes are the K20A2’s low-RPM profiles which optimize low-RPM performance and fuel efficiency. A central lobe is the high-RPM race cam profile which initiates at 5,800 RPM and optimizes high-RPM power and performance. Additionally, the K20A2 utilizes a VTC mechanism which is a gear on the end of the intake cam that adjusts intake and exhaust timing overlap automatically.
The result of the difference in VTEC systems between the two engines is felt in high-RPM driving. The K20A2 will deliver the classic VTEC “pinned to your seat” boost of power at high RPMs. While you’ll feel a difference in performance at 5,000 rpm in the K20A3, it won’t be as noticeable.
Stock Honda K20A2 Engine Performance
From the factory, the K20A2 boasts some pretty impressive power figures for a tiny N/A 2.0L 4-cylinder. In comparison, the Toyota 1JZ-GE which has 0.5L more displacement and two more cylinders develops three less horsepower. That is a testament to the KA20A2’s unparalleled efficiency at the time.
In addition to being efficient, the K20A2 is also light. In practical terms, that helped in terms of the power to weight ratios of the vehicle equipped with the K20A2. For example, the 2004 Acura RSX Type-S which utilized the A2 has a weight-to-power ratio of 13.6lbs/hp. That beats the 17.4lbs/hp weight to power ratio of the notoriously light Nissan 240SX.
Since the K20A2 utilizes what members of the Honda community call “real VTEC” or true i-VTEC system, the A2 has interesting power delivery characteristics. As we covered earlier, the A2 has two primary cam profiles. At low RPMs, the K20A2 actually has comparable, if not less, low-end performance than the K20A3. The A2 truly comes alive once the 5,800 rpm threshold is reached. For that reason, it is better to really ring out the gears to extract maximum performance from the A2.
Honda K20A2 Engine Upgrades
All of the engines in the Honda K-series are known for their unparalleled reliability. In fact, if you are shooting for a “mild” horsepower figure from your K20A2 (300-350whp), most K-series enthusiasts will tell you that you won’t have to crack open the engine at all.
The most common high-horsepower modification for the K20A2 is a turbocharger kit. In stock form, the K20A2 is the perfect candidate for forced induction. With that being said, higher boost loads will require internal upgrades. Since the K20A2 has such a high compression ratio, lower compression forged pistons are often recommended. This will reduce the internal forces that the engine experiences.
In general, most people consider the K20A2’s stock internal hardware pretty solid. For example, with most people agree that the factory PRB intake and exhaust cams are the best options until ludicrously high horsepower figures.
While there is far more information floating around about high horsepower KA20A2 turbo builds, there is also a good number of people who aim for high KA20A2 horsepower while remaining naturally aspirated. With that being said, forced induction is far more cost-effective when aiming for high power figures.
Honda K20A2 Turbo
Forced induction is a very popular modification on the Honda K-series and the K20A2 in particular. A lot of RSX Type-S owners opt to turbocharge their cars with a prepackaged turbo kit that comes with all of the necessary components. As we stated earlier, the K20A2 is an extremely resilient engine that can handle over 100+ more horsepower than stock with no significant internal upgrades.
Despite its overall strength, many experienced K20A2 turbo enthusiasts still advocate for reinforcing the K20A2’s bottom end, upgrading the fueling system, replacing the timing chain assembly, refreshing the valve springs, and upgrading the factory head gasket. These precautions further bolster a 300-350 turbocharged K20A2 against high internal forces introduced by forced induction.
Once you reach the 350-400 horsepower, more extensive modifications are required. At this point, it is a good idea to have a machine shop resurface the cylinder head, the block, and bore 0.25mm over. This is also the point where you’ll need to upgrade to forged internals. Buy a new crankshaft, forged rods, OEM rod & main bearings, and forged low compression pistons (0.5mm over).
The 400-horsepower threshold is also when you should consider sleeving your K20A2’s block. This will reduce the amount of internal wear that your K20A2 experiences and act as an additional level of reinforcement.
An upgraded fueling system is also necessary for high horsepower K20A2 builds. The primary components that should be upgraded include the factory fuel pump, injectors, fuel lines, and fuel rail. For 400+ horsepower, you’ll need an AEM 340lph fuel pump (minimum), 1000cc injectors, -8AN supply fuel lines, -6AN return fuel lines, and a high flow fuel rail.
K20A2 Turbo Supporting Modifications
Since all Honda’s equipped with the KA20A2 from the factory are front-wheel drive, it is important to consider how you’ll be putting the power down. Most enthusiasts with high-horsepower turbo KA20A2 Hondas will agree that it is difficult to transfer beyond 350 horsepower to the pavement. The extra power will also unquestionably cause more strain to a number of different parts that would benefit from an upgrade.
While it is generally stated that the RSX Type-S factory axles are capable of withstanding upwards of 500 hp, power levels beyond that can cause axle warp. Traction bars are a potential solution to bolster the axles against the frame while also preventing wheel hop. For K20A2 drag builds, sticky and wide tires are a necessity. Without them, you’ll spin all of your power away.
With a higher horsepower figure comes more strain on the transmission. The factory-equipped 6-speed found in the RSX Type-S is a good transmission but should be upgraded with the introduction of high boost. One of the most commonly cited transmission upgrades for the K20A2 is PPG straight cut gears. Straight-cut gears do not produce any axial load, meaning that they can handle much more abuse. In addition to the gears themselves, you’ll also need to upgrade your clutch. Of course, your clutch choice will be entirely dependent on the horsepower figure that you are aiming to produce.
Most Common Honda K20A2 Engine Problems
A few common problems with the Honda K20A2 engine include:
- Front Main Crankshaft Seal Oil Leak
- Exhaust Cam Lobe Galling
- Excessive Engine Vibration
Throughout the rest of this article, we will discuss the above K20A2 inline-4 engine problems. It’s important to add a few quick notes, though. These are a few of the most common issues, which doesn’t necessarily mean they’re common in the true sense of the definition. Instead, when things do go wrong these are a few of the most common issues.
The Honda K20A2 engine does deliver very good reliability overall. That is especially true for a K20A2 that hasn’t been modified. That said, the K20A2 is a 20+ year old engine. Reliability isn’t just about mileage, age and proper maintenance are important factors too. Ultimately, keep that in mind since older engines can require a bit more TLC and repairs.
1) K20A2 Front Main Seal Oil Leak
Over time, K20 front main seals go bad and begin leaking oil from the timing chain cover area. It’s typically not something that instantly turns into a drastic leak. Rather, the rubber seal develops small cracks that allow minor drips of oil to leak. Left alone the leak will gradually get worse. K20 main seal oil leaks typically manifest near the 120,000 mile mark. Some last the life of the engine while others may be less lucky and experience K20 seal leaks earlier than 100,000 miles. Age and poor oil change history may cause problems to pop up sooner.
Visible leaks are the most obvious symptom and typically the only noticeable one. Again, the K20 front main seal lies behind the timing cover so look for signs of leaks in that area. If the leak is bad enough you may notice you’re topping off on oil more often than normal. Though, you’ll likely notice drops of oil on the ground before it gets that bad.
Luckily, a K20A2 front main seal leak is relatively easy and cheap to repair, especially if you have some DIY experience. The seal itself only costs around $10-40. For the non-DIY crowd, the damage to your wallet still isn’t too bad. Of course, labor costs vary across the world and some of it depends on your year and model Honda or Acura. That said, $200-400 is a reasonable estimate for front main seal replacement at a repair shop.
2) K20A2 Exhaust Camshaft Lobe Galling / Pitting
While camshaft lobe galling is more common on the K20A3, it is still a frequently reported issue on the K20A2 as well. Camshafts, also known as cams, sit in the cylinder head and are tasked with opening and closing the K20 intake and exhaust valves. The cam lobes are responsible for controlling intake and exhaust valve lift. Due to their frequent actuation and rotation, they tend to wear or pit over time. Cam lobe galling typically occurs after 100,000 miles, but can occur earlier due to poor engine oil maintenance or using oil that is too thin.
The symptoms are pretty minor, so it’s possible K20’s are driving around without even knowing they have an issue. Loss of power usually occurs gradually as this isn’t a problem that pops out of nowhere. Rather, power loss occurs over time as the excess friction continues to wear down the K20’s lobes. The most noticeable symptom is likely a clicking/tapping noise from the valve cover area. You can actually hear the noises from the friction if it’s bad enough.
Galling normally requires the K20 exhaust camshaft to be replaced entirely. The repair is pretty labor-intensive so it’s one of the pricier repairs out of the common K20 issues. Honda K20 exhaust cams can typically be had for a couple of hundred dollars. Not too bad for the DIY crew. If you end up at a repair shop with these issues expect to pay somewhere around $800-1300. It’s on the pricey side, but fortunately, that’s about as bad as it gets for the K20.
3) Honda K20A2 Excessive Engine Vibrations
There are a few basic maintenance items that can cause K20 engine vibration and rough running. Consider the basics first like spark plugs, ignition coils, dirty throttle body, etc. If none of the basics are responsible for the vibrations then motor mounts should be one of the top items on the checklist. This likely isn’t fair to even consider a problem.
Engine mounts are responsible for carrying the weight of the engine and partially absorbing bumps, corners, etc. K20 engine mounts are more of a standard maintenance item. They’re parts that wear down over time. However, engine mounts are common culprits of engine vibrations that may be overlooked.
The K20 mounts are pretty inexpensive and can usually be found for under $100 for both. You’ll need the right tools for the job, but it’s a pretty basic DIY otherwise. At repair shops expect to pay somewhere in the ballpark of $200-400 for replacement.
Honda K20A2 Engine Guide Summary
The Honda K20A2 variant is a fan favorite in the Honda community among multiple other K-series variants. In addition to having a higher compression ratio, the K20A2 has the more traditional DOHC i-VTEC valvetrain that Honda enthusiasts know and love. Objectively, the K20A2 is a very efficient and highly strung engine. In stock form, it retains a very high specific output at 100hp/L and does so reliably.
While the K20A2 performs well in stock form, most enthusiasts opt to go the route of forced induction. That is mainly due to the K20A2’s very strong factory construction which is able to handle around 350 horsepower in stock trim. While the A2 can be daily driven reliably at the 300+ horsepower mark running low-moderate boost, a reinforced bottom end and fueling upgrades are a wise decision from a reliability standpoint.
It is unlikely that a K20A2 will experience any truly serious or costly reliability faults. Most of the time, K20 reliability is inversely proportional to high power figures. The three most common K20A2 engine issues are a leaky front main seal, exhaust camshaft lobe galling, and excessive engine vibrations; none of which are truly common. The good news is that should your K20A2 experience any of these issues, repairs are often cheap and relatively easy to perform.
For more Honda K-series content, check out our 3 Most Common Honda K20 Engine Problems guide. As always, safe driving!