Guide to tuning and performance parts on the K20 engine from Honda

"Honda K series 2.0 Tuning"

The engine is very free revving, hitting around 8000rpm at the redline.

The K20 replaced the popular B20 series, and we've seen them fitted to a number of sporty cars, including the Arial Atom.

The short intake manifold optimises power, and the variable timing control and VTEC helps create an engine which has two very distinct personalities.

Some K20 engines were turbocharged, thanks to lower compression and a revised piston, crank and new engine timing! The redline is generally lower on the turbocharged versions for obvious reasons.

We rely on our visitors to pass on tips and tell us about their projects and what worked on their car, and this article is the culmination of the feedback we have received. First let us look at the history and specs of this engine and then consider which tuning modifications work best on it.

History of the K20 Engine

The K20A production run from 2001–2011. The K20Z was 2005-2015 and the K20C is stilll in production today.

Such was the success of this block it has been revised and tweaked and was released with power upto 306bhp from the factory, with plenty of leeway and room for the tuner to make more and many reporting the blocks are safe to 400hp (but your mileage will vary depending on the block and version you have, the R versions are much better built).

K20A JDM only (The VTEC comes in at 6000 rpm)

The Spec R engine had a lighter flywheel, high compression pistons, stiffer valve springs and longer camshaft durations. The cylinder heads were also ported and polished and these special engines were hand tooled at the factory. They show the potential of the other engines if you take your time tuning and setting them up.

• 2001–2006 Honda Civic Type R
  11.5:1 212 hp @ 8000 RPM 149 lbft@ 7000 RPM
• 2001–2006 Honda Integra Type R
  11.5:1 217 hp @ 8000 RPM 152 lbft@ 7000 RPM
• 2002–2008 Honda Accord Euro R
  11.5:1 217 hp @ 8000 RPM 152 lbft@ 6000 RPM
• 2007–2011 Honda Civic Type R
  11.7:1 221 hp @ 8000 RPM 159 lbft@ 6100 RPM (VTEC 5800)

K20A1

There was technically no A1 version - essentially it's still a K20A3 but a lower spec compression to handle the turbo!

Typically a twin scroll Mitsubishi TD04HL-15T turbocharger is fitted with 13.5psi of boost.

• 2001–2006 Honda Stream
  9.7:1 156 hp @ 6500 RPM 139 lbft@ 4000 RPM
• 2001–2006 Honda Stream
  9.8:1 158 hp @ 6500 RPM 140 lbft@ 4000 RPM

K20A2 (The VTEC comes in at 5800rpm)

• 2001–2006 Honda Civic Type R
  11.0:1 200 hp @ 7400 RPM 139 lbft@ 5900 RPM
• 2002–2004 Acura RSX Type S
  11.0:1 200 hp @ 7400 RPM 142 lbft@ 6000 RPM
• 2002–2004 Honda Integra Type R
  11.0:1 200 hp @ 7400 RPM 142 lbft@ 6000 RPM

K20A3 (The VTEC comes in at 2300rpm)

• 2002–2006 Acura RSX
  9.8:1 160 hp @ 6500 RPM 141 lbft@
• 4000 RPM
• 2002–2005 Honda Civic Si
  9.8:1 160 hp @ 6500 RPM 132 lbft@ 4000 RPM
• 2002–2005 Honda Civic SiR
  9.8:1 160 hp @ 6500 RPM 132 lbft@ 4000 RPM
• 2002–2005 Honda Civic Type
  S 9.8:1 160 hp @ 6500 RPM 132 lbft@ 4000 RPM
• 2003–2006 Honda Civic 2.0 i-VTEC
  9.8:1 155 hp @ 6500 RPM 131 lbft@ 5000 RPM

K20A4

• 2002–2006 Honda CR-V
  9.8:1 150 hp @ 6500 RPM 140 lbft@ 4000 RPM
• 2003–2007 Honda Accord
  158 hp @ 6500 RPM 140 lbft@ 4000 RPM

K20A6 (The VTEC comes in at 2500rpm)

• 2003–2006 Honda Accord
  9.8:1 155 hp @ 6500 RPM 140 lbft@ 4000 RPM
• 2003–2006 Honda Accord
  9.8:1 155 hp @ 6500 RPM 140 lbft@ 4000 RPM

K20A9

• 2004-2007 Honda FR-V
  9.8:1 150hp @6500 Rpm 142 lbft @4000 RPM

K20Z

• K2Z1
  2005–2006 Acura RSX Type-S
  11.0:1 210 hp 143 lb⋅ft @ 6200 RPM 8100 RPM
  2005–2006 Honda Integra Type S
  11.0:1 210 hp @ 7800 RPM 143 lb⋅ft @ 6200 RPM 8100 RPM
• K20Z2
  2006–2011 Acura CSX
  9.8:1 153 hp @ 6000 RPM 139 lb⋅ft @ 4500 RPM 6800 RPM
  2006–2011 Honda Civic
  9.8:1 153 hp @ 6000 RPM 139 lb⋅ft @ 4500 RPM 6800 RPM
  2006–2015 Honda Accord
  9.8:1 153 hp @ 6000 RPM 139 lb⋅ft @ 4500 RPM 6800 RPM
  2006–2010 Honda Civic 2.0 S / S-L
  9.8:1 153 hp @ 6000 RPM 139 lb⋅ft @ 4500 RPM 6800 RPM
• K20Z3
  2006–2011 Honda Civic Si
  11.0:1 197 hp 139 lb⋅ft 8000 RPM
  2007–2010 Acura CSX Type-S
  11.0:1 197 hp 139 lb⋅ft 8000 RPM
• K20Z4
  2007–2010 Honda Civic Type R
  11.0:1 201 hp @ 7800 RPM 142 lb⋅ft @ 6800 RPM 8000 RPM

K20C

• K20C1
  2015–present Honda Civic Type R
  9.8:1 306 hp @ 6500 RPM 295 lb⋅ft @ 2500 RPM
• K20C2
  2016–present Honda Civic LX
  10.8:1 158 hp @ 6500 RPM 138 lb⋅ft @ 4200 RPM
  2016–present United States Formula 4 Championship 10.8:1 158 hp @ 6500 RPM 138 lb⋅ft @ 4200 RPM
• K20C3
  2016–present Honda Avancier
  10.8:1 272 hp @ 6500 RPM 273 lb⋅ft @ 4200 RPM
• K20C4
  2018–present Honda Accord
  9.8:1 252 hp @ 6500 RPM 273 lb⋅ft @ 1500-4000 RPM
  2018–present Acura RDX
  9.8:1 272 hp @ 6500 RPM 280 lb⋅ft @ 1600-4500 RPM

We have a separate tuning guide for the K24 here

What are the most effective K20 tuning parts

The best modifications on an engine are in our opinion the ones that give the best value for money.

We won't be swayed by popular K20 modifications, they need to be cost effective.

Significant gains can be made from camshaft upgrades. Altering the camshaft profile alters the intake and exhaust durations on the engine and can dramatically change the bhp and power output.

There is a mod called the K FRANK, where you fit an Accord 2.4 bottom end with a type R head on the top. This will give you a lot more torque but you will need to lower your rev limit.

The K20Z4 was related to an S2000 engine so dropping in the crank from the S2000 would give good power gains (research your engine and donor engines carefully before doing this).

A stock K20 can usually cope with around 400hp before internal strengthening is required but we've heard of some K20A3 blocks breaking rods at 340hp.

Head swaps are popular mods, for example putting the K20A head and cam profile on the K20A2 to benefit from the cam durations and timing.

The Spec R K20 engine was fitted with a lighter flywheel and boasted high compression pistons, stiffer valve springs and longer camshaft durations.

The cylinder heads were also ported and polished and these special engines were hand tooled at the factory to very tight tolerances.

They show the potential of the other engines if you take your time tuning and setting them up focusing on these areas first.

Fast road cams commonly bump the performance across the rev range, you may lose a little bottom end power but high end rpm power will be lifted.

With the VTEC engines you can potentially force the VTEC to cut in at lower RPM, effectively giving you more low end power and better pickup as the sacrifice of economy.

This saves the effort of sourcing and fitting a fast road cam and may suit your K20 tuning needs more suitably.

Competition cams, bump the high end rpm power band but as a result the car will not idle smoothly and low end power nearly always suffers.

For a road car must carefully try to optimize your power band to your driving style.

Interestingly it's worth noting that the K20A3 VTEC only works on the intake but on the K20A2 it operates intake and exhaust.

You can think of the K20A3 as a 12 valve engine under 2200rpm and over this threshold the additional 4 valves are used thanks to the additional cam lobes.

I'd be amazed if you find a Competition camshaft is a pleasure to live with when on the daily commute.

Each engine responds better to mild camshaft durations so set your engine up on a rolling road.

The engine timing and injectors and fuel pump also have a large bearing on the torque gains you'll achieve.

Altering valve durations can alter the torque band and on most engines the exhaust and intake durations do not need to match, although most cams and tuners use matched pairs there are some advantages to extending the intake or exhaust durations.

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Modifying to Stage 1:

 Drilled & smoothed airbox, Sports exhaust manifold, Panel air filters, Remaps/piggy back ECU, Fast road camshaft, Intake headers, altering VTEC timing.

Modifying to Stage 2:

 induction kit, Ported and polished head, fuel pump upgrades, high flow fuel injectors, Fast road cam, Sports catalyst & performance exhaust.

Modifying to Stage 3:

 Twin charging conversions, Competition cam, Crank and Piston upgrades to alter compression, Internal engine upgrades (head flowing porting/bigger valves), Adding or Upgrading forced induction (turbo/supercharger), Engine balancing & blueprinting.

ECU flashing should help to release the full potential of all the upgrades you've done to your K20 and this is typically achieved with a Hondata or Apexi ECU.

It will usually give around 30% more power on turbocharged vehicles and 15% on NASP engines, but you mileage will vary depending on the upgrades you've done and the condition of your engine.

It is vital to any engine modification project to feed more fuel and air into the K20 engine

Air Intake manifolds transmit the air from the filter and allow it to be fed into the engine cylinders with fuel for the squish phase.

The K20 intakes are short and allow for very high velocity air flow, unless you are making large power gains there is little gain to be had by trying to improve the intakes on most K20 engines.

The shape and flow rate of the Air Intake manifolds can make a big difference to to fuel mixing and power on the K20.

It's not uncommon that air intake manifolds are in dire need of aftermarket tuning parts, although a few makers provide reasonably good air intake manifolds.

Fitting big valve kits, carrying out port matching and head flowing will also lift torque, and importantly will give you raising the torque increase on other parts.

K20 turbo upgrades - which are best?

The more air to get into an engine, the more fuel it can burn and uprating the induction with a turbocharger upgrade makes massive power gains.

NASP engines need quite a lot of work when you add a turbo, so we have a separate guide to help you take into account the pros and cons of going this route on your K20

If your motor is already turbocharged, tuning parts are giving better power gains and we find turbo engines are made with harder and stronger components.

Here are some turbo conversions on the K20 blocks, with injector sizes and verified dyno readings all quoting wheel horse power!

Bear in mind some of these engines were extensively modified so these are not the only parts added.

• 400hp GT3076  RC 750cc injectors
• 338hp Mitsubishi T517Z(greddy) RC 750cc injectors
• 590hp GT4094r twin scroll  1200cc PTE
• 600hp GT4094r Inline Pro 1000cc
• 340hp precision 60 trim  precision 1000cc
• 275hp td05/td06 RC 750cc injectors

Stock K20's can reportedly handle upto 25-30psi of boost providing the tuning is spot on!

It really is all about getting the timing, fuel and boost if you add it just right, or you'll end up with flat spots or engine failure.

Expect around 360 wheel hp for 10psi of boost on the K20.

We did see a stock K20Z1 reach 620hp with a GT35R, AFI sidewinder manifold and 1000RX injectors managed by the APex N1! This was quite an impressive achievement, and shows how good the K20Z1 block is.

However you will find an engine has weakspots so discover these limitations and fit better pistons and crank to cope with the power.

It's not unheard of mechanics spending a loads of money on turbo upgrades on the K20 only to watch the engine literally blow up when it's used on the roads.

Large upgraded turbos commonly experience low end lag, and small turbos spool up really quickly but do not have the peak rpm torque gains.

We are pleased that the range of turbochargers is always evolving and we commonly find variable vane turbochargers, where the vane profile is altered according to speed to lower lag and increase top end performance.

Twin scroll turbochargers divert the exhaust gases into a couple of channels and flow these at differently profiled vanes in the turbocharger. They also improve the scavenging effect of the engine.

It is common that there is a limit in the air flow sensor AFM/MAF on these engines when a lot more air is being pulled into the engine.

You'll see that 4 bar air sensors coping with quite large power gains, whereas the OEM air sensor limited bhp and torque at a much lower level.

Adding a supercharger or additional turbo will make large bhp gains, although more complex to configure. We have a twincharger bhp adding guide if you want to read more.

Fuelling

Don't overlook the need to boost the fuel system when you are increasing the bhp - it makes the car more thirsty.  We strongly recommend you to over specify your injector capacity.

As a rule of thumb add 20% capacity when buying an injector, helps cope with injector deterioration and allows you some spare capacity should the engine need more fuel.

The OEM injectors on the K20 are typically rated to 310cc output so are not far from their limits on the more powerful engines.

The most popular K20 injectors we've found people using are....

• RC 750cc injectors
• PTE 1200cc
• Inline Pro 1000cc
• Precision 1000cc

K20 Exhaust

You only need to to replace your exhaust if your current exhaust is actually creating a restriction.

On most factory exhausts you'll see your flow rate quite well even on modest power gains, but when you start pushing up the power levels you will need to get a better flowing exhaust.

Note that with the widest exhaust you can source this will slow up the exhaust flow rate - the best for power gains are usually between 1.5 to 2.5 inches. It is the shape and material more than the bore size.

Typically exhaust restrictions can be located the catalyst and filters installed, so adding a better flowing performance alternative will help avoid this restriction.

Weak spots Issues & problem areas on the K20

The K20 engines are generally reliable and solid as long as they are regularly serviced and maintained.

Regular oil changes are vital on the K20, especially when tuned and will help extend the life and reliability of the engine. The camshaft is usually the first thing to show up problems when the wrong grade of oil is used.

The front crankshaft oil seal is prone to weep a little oil.

A rough idle can be caused by a dirty throttle body or faulty idle control valve.

Engine mounts frequently fail and you'll notice engine vibrations more when this happens but it is not a cause for concern.

For more information on Tuning your Honda engine please join us in our friendly forum where you can discuss K20 tuning options in more detail with our K20 owners. It would also be worth reading our unbiased Honda tuning articles to get a full grasp of the benefits and drawbacks of each modification.

Please help us improve these tips by sending us your feedback in the comments box below.

We love to hear what our visitors have got up to and which parts work best for them on each model of car. Comments are used to improve the accuracy of these articles which are continually updated.

This article was written by Waynne Smith on TorqueCars, and I appreciate your feedback and suggestions. This entry was filed under Acura, Honda. You can leave a response below or join TorqueCars forum to discuss this article and car modification in detail with our members.

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