Honda K-Series Pre-Tuning Checklist
Everything you need to know before dyno tuning your Honda K-Series.
7 Things You Should Know Before Tuning Your Honda K series
1. The Biggest Bank For The Buck
The best bang for the buck modifications on a naturally aspirated k series are RBC intake manifold, 3 inch cold air intake, race header, and 3 inch exhaust. If you have a TSX (K24A2 motor) doing an RBC intake manifold on that engine will lose a lot of midrange torque if you’re keeping the 25 degree variable timing gear in place. I’ve actually seen better overall power band with the stock intake manifold, if you don't plan on switch over to the 50 degree VTC gear found on the K20/a2/z3 engines.
2. Whats Next After Bolt On Modifications?
A drop in camshaft is next after bolt on parts. On a stock engine doing a drop in aftermarket cam, you’ll see approximately 10-15 horsepower. We have found that the 06+ TSX cams to be 100% OEM reliable and drop in (no valve train change needed), and give 5-10 ft-lb torque and 5-10 whp increase in power. Any aftermarket cam in the k series engine has the potential for increased timing chain tensioner failure to occur. The timing chain tensioner is unfortunately one of the pitfalls of the K-series motors. We have found that once you drop in a non-OEM cam in a K-series engine, you open up a can of worms for unreliability. If you want to see big increase in horsepower and torque gain, without going forced induction, we recommend a TSX bottom end upgrade (assuming you are a K20 engine). If you don't change anything else (keeping the same intake, intake manifold, header, exhaust), we have seen 30-40 horsepower and torque gains. So you'll have a broader more usable power band, typically torque is 180-200 ft/lbs, and typical horsepower is 240-250, if everything else remains the same. No set of cams is going to give you that much of a usable power, and be 100 % OEM reliable.
3. Forced Induction (Supercharging)
There are numerous ways to go about forced induction on a k series engine. Supercharging is the most reliable route, but wont produce maximum horsepower. The most common kits on the market are the CT engineering “roots” style kit that gives instant response, and the Kraftwerks “centrifugal” style Rotrex kit that builds maximum power/boost towards redline. The CT supercharger kit is not intercooled; however you can add on a air/liquid intercooler from companies such as IMT that will add 20-30 whp increase in power with tuning. The KW kit is intercoolered with an air/air intercooler. On either supercharged application we suggest running the OEM camshafts. We have found the OEM cam profiles to be the best in these applications. If more power is desired from either kit, we suggest using e85 fuel. It will give an increase of 30-50 whp once tuned at the same boost level. In addition to running the supercharger kit, you will need to upgrade the OEM clutch. Competition stage 2 or 3 clutch kits work great for the supercharger kit power levels, and provide great drivability. Lastly, upgrading the header and exhaust are highly recommended. A race header like the skunk2 alpha and full race 3” exhaust will provide the best power and sound quality.
4. Forced Induction (Turbocharging)
Turbocharging the k series will give you maximum power potential, with the down side of reducing reliability. Heat management is a concern on RSX / Civic Si chassis as the heat of the turbo manifold, turbo and down pipe are very close to the fire wall and numerous other items in the engine bay. Depending on how efficient the turbo kit used is 400-500 whp on 93 octane is very reliable without upgrading the internals (and proper tuning). More power is available on higher octane fuels such as race gas or e85. Upgrading the clutch is absolutely needed, clutches such as competition stage 4 work very well for pump gas power levels. Twin plate clutches are needed for race gas power levels.
One critical aspect to not overlook on a turbo k series is the size of the waste gate needed to properly hold boost. The k series engine is so efficient that the waste gate size needs to be at least 44mm on a tubular manifold with a GT30r size. If anything less is used, massive boost creep can/will occur. On GT35r and larger turbos we suggest either (2) 44mm gates or one 60mm gate. Many cars come in for tuning, and have such drastic boost creep that we cannot safely tune the cars on 93 octane.
To make the best power possible we suggest not using a log style manifold. Just like on a naturally aspirated k series where a race header makes a substantial increase in power from reducing back pressure / increasing flow, a tubular style manifold is produces the same results. The ability to make more power is available, with much less chance of knock occuring.
Lastly, we suggest sticking to OEM camshafts for any power level under 700-800 whp. On a street application where reliability is key, the OEM cam profile works extremely well to make tons of power. We have made close to 1000 whp on OEM cams.
5. To Sleeve Or Not To Sleeve?
The OEM sleeve design is substantially thicker and more supported than a b/d/h series engine, and therefore can take much greater power levels. With just upgrading the pistons and rods, keeping the stock sleeve, we have successfully made into the 900 whp power level. While this is an extreme example, it proves how strong the OEM sleeve design is compared to b/d/h series that can have failures as low as 400 whp. Sleeving the engine will always provide the most reliable option; if you can afford to do so while building the engine by all means do so. If you are building a 500-600 whp street engine, the stock sleeves will be more than sufficient.
6. Common Failures
One of the most common issues on a K-series motor is the timing chain tensioners or the TCT. Its the biggest weak link of the k series engine, and the failure rate is exponentially increased when installing aftermarket cam shafts. While the TCT can fail with the OEM cams, they are much less likely to do so compared to aftermarket. One of the main reasons aftermarket cams cause the TCT to fail is from the ramp rate design. To get as much air into the combustion chamber to make more power, the ramp rate has to be aggressive on opening and closing of the valve. In the ramp rate design there is a engineering termed called “jerk”, which is the 4th order of movement (engineering jargon). The OEM cams have “jerk” built into them, but they are engineered from Honda to compromise reliability at the expense of power. Some aftermarket camshaft design has been engineered to reduce “jerk” and keep the stress off of the tensioner. We have found that Kelford and Brian Crower seem to have the least failure rate.
The OEM tensioner can be upgraded to an aftermarket equivalent to also reduce chance of failure with aftermarket cams. While several are available on the market, we have found that Inline Pro makes the most reliable option.
7. Other Common Failures
Throttle Position Sensor or the TPS sensor, is another known failure point on a K-series, when you do a swap or if you put stiffer aftermarket engine mounts you're going to get a lot more vibration in the chassis and also into the engine. The design of the factory TPS sensor can’t handle that vibration so the sensors fail, which causes the deceleration fuel cut to turn on while you're driving. This will make the car feel like it has a hesitation while driving. When this happens, you’ll need to replace the TPS sensor. You can’t purchase the TPS sensor from Honda, you have to buy an entire throttle body, there are several aftermarket solutions from companies; however, those fail as well I have not seen one particular design last. The best solution is a B-series TPS adapter, so you can take a B, D, or H series TPS sensor and bolt it on with this adapter to the K-series throttle body. The B, D, H- series TPS sensors are not sensitive to engine vibration as badly as a K-series. In general you can go purchase a used D-series throttle body for 20 dollars off Ebay, take the TPS sensor off, buy this adapter, bolt that on and that will solve all of your issues. K Tuned, among other companies, makes a b/d/h series TPS adapter.
Proper fuel return line routing:
If you have a swapped car, or a 8th gen or 9th gen civic that has a returnless style fuel system, a lot of people incorrectly route the fuel pressure regulator return line. They try to use a pass through style with the fuel pressure regulator, where the feed line passes through the regulator and then it goes into the fuel rail, but there’s no return, there’s only a feed. That is the way it would be stock on a returnees style system because there is no return line. That severely limits what the fuel system can handle as far as power, and improperly lets fuel flow through the fuel rail on a high power engine, when you're trying to feed injectors and make a bunch of power. The other issue i see is a lot of people do not run a vacuum line from the regulator to the intake manifold for vacuum reference. This is super critical on a forced induction application. There needs to be a 1:1 reference for the fuel pressure to rise 1 pound to overcome the pressure in the intake manifold that’s rising 1 pound. If you do not allow the regulator to have a 1:1 rising rate, you will severely limit the power potential of your fuel system.
Variable Timing Solenoid:
The Variable Cam Timing Solenoid that’s on the K-series motor is prone to have issues with higher mileage. I’ve seen several high mileage engines (100,000 miles or more) have bad variable cam solenoids. The variable cam solenoid controls your variable timing gear movement. I’ve had issues where the solenoid is bad and needs to be replaced, as well as having the pre screen located by the left side intake manifold flange get clogged up. There is a little mesh screen that can be serviced and cleaned or replaced. If that solenoid screen gets dirty it’s just like a Vtec solenoid screen, it limits the amount of oil pressure going to your solenoid, which then limits the amount of control the variable cam has.
Oil Pump with Balancer Shafts:
Another area of concern on a k-series engine, specifically for the 8th and 9th gen civic Si, is the oil pump with balancer shafts. The balancer shaft design in the oil pump can’t handle high RPM. So if you're going to rev that engine much over 8600RPM, you're going to need to replace the oil pump. The RSX type-S oil pump from an 02-04 RSX type-S is a drop in fitment and won’t have the issues of revving up to 10,000RPM. The s2000 oil pump modified by ERL is another upgrade option. The s2000 oil pump flows more oil compared to the K20a2 oil pump. Its a bit more money, but can be worth it in a road racing application.
OEM Rocker Assembly Failures:
OEM roller rockers crack and fail. Over time they get hairline cracks, and can break. The wear on the rockers gets worse with aftermarket cams, so its a good idea to inspect them as well as retainers every few thousand miles. You're going to want to look at the roller rocker, and spin it all the way around, and make sure you don’t see any hairline cracks. If they are cracking you're going to want to replace them If they break it can jam a rocker up, drop a valve or break a retainer.
When you install an aftermarket clutch in any engine, it’s going to have a higher clamping force. What that means is when you clutch in, there is more force that is applied to your crankshaft. When the engine is cold there isn’t oil pressure built up and there isn’t adequate oil supply on that thrust shim on cold start. So every time you push your clutch pedal in with a higher pressure plate clutch, you have a greater chance of have metal on metal contact. Overtime of this occurring the thrust shim will prematurely wear out. On any aftermarket clutch I always recommend taking out the factory clutch switch, so you don't have to clutch in on a cold start. You have to be mindful to keep the car in gear, or your car will jump forward when you're trying to start it. But eliminating the clutch switch will eliminate the potential for the thrust shim to fail.
Another weak link on the K-series is the transmissions. Specifically, I've seen most failures with 2nd gear. Also with doing high RPM fast shifting, the shift selectors can get bent and synchros’ wear out quickly. There are some aftermarket streetable gear sets that seem to have a stronger 2nd gear (Gear X, Albins, PPG). Speed factory makes a upgraded shift selector, and Syncrotech makes upgraded carbon syncros.
Returnless Style Fuel System:
If you have an RSX or an 8th/9th gen Civic Si, you have a returnless style fuel system in your car. If you're going forced induction the limit of the returnless style fuel system with upgraded injectors and an upgraded fuel pump in the tank is about 450 horsepower. So if you're going to make more power than that, you'll need to do a return style fuel system. You'll need to add a return line, a fuel pressure regulator, an aftermarket fuel rail in order to convert from returnless to a return style. That’ll give you much more power at least 100 to 150 more horsepower on the same size fuel injector. Also, when you do it you need to make sure you run a vacuum line from your intake manifold to your fuel pressure regulator, so it rises your fuel pressure 1 PSI per 1 PSI of boost increase. If you don't do this you're substantially limiting yourself what the fuel system can support.
Upgrading the clutch/flywheel:
If you’ve done a swap in a civic, integra, or something with a K-series motor, and you haven't upgraded the clutch and flywheel the stock clutch and flywheel can technically hold what normal bolt ons will produce for power. I have seen now multiple times over the years where someone has bought a used swap, and they haven't changed out the clutch and flywheel. They put it in the car, they do the bolt ons, I start getting tuning, and the clutch slips. Its usually because the car either has a ton of miles or it was abused in the previous car it came from, which would've been an unknown history to the person doing the swap. So if you can afford to do it, I would upgrade the clutch and flywheel. If you're going forced induction (supercharged, turbo, nitrous) you're going to want to upgrade the clutch. The factory clutch is not going to handle it. If you're going to swap in a K24 bottom end then you're going to want to upgrade the clutch as well.