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Hondata, Inc.
2840 Columbia St
Torrance, CA 90503

Tuning the K24A2 TSX engine

This article is a look at the potential of the K24A2 TSX engine (Accord in Europe / Australia). As there are no engine management solutions for the TSX engine computer this article assumes the engine has been swapped into another Honda and tuned with the K-Pro.

The Acura TSX has an excellent pedigree. 5 link Independent rear suspension, Wishbone front suspension, 0.27 drag coefficient and a double overhead cam iVTEC engine. Its 2.4l engine is a long stroke version of the highly refined 2 liter engine found in the Acura RSX-S. The K series engine is Honda's best yet; lightweight, strong and gifted with VTEC and VTC (Variable {cam} Timing Control)

Over the last 18 months the number of performance options for the Acura RSX has blossomed. There are two supercharger kits, half a dozen turbo kits, several cam profiles, individual throttle bodies, custom pistons and rods and sleeves.

Which of these parts work with the TSX and what sort of performance increases can be expected? How is the TSX's K24 engine similar to and how does it differ from the RSX's K20? Lets find out.

The Head

The two engines share an almost identical head design. Cams are interchangeable, so any Cam made for the K20 will fit the K24. Higher lift camshafts require better valve springs, retainers and spring seats.

Exhaust ports and bolt pattern are identical, but headers are not interchangeable. On the TSX the headers fit between the engine and subframe, on the RSX between the subframe and firewall and as a result are quite differently shaped.

Intake ports are identical in spacing, but the TSX manifold has an integrated water port as compared to the RSX-S separate housing. For manifold swaps, Hasport has built an adapter plate to allow any K series Honda intake manifold, ITB or supercharger made for the RSX to fit the TSX.

Hasport TSX intake adapter plate with RSX-S Hondata intake gasket overlaid

Intake Manifolds

The stock RBB manifold is uses a long narrow runner which is good for torque, whereas the RBC intake from the Accord Euro R uses shorter fatter runners optimized for high rpm breathing. The RBC intake is a direct replacement for the RBB. The RBB manifold is also used on the 160hp 2.4 Accord.

Accord Euro R intake manifold


The TSX has large primary (low lift lobes) on both the intake and exhaust. These lobes are larger than the RSX-S or ITR. This contributes to good low-end torque. The TSX exhaust camshaft also has a larger secondary lobe than the RSX-S or ITR. This makes the TSX exhaust cam a good candidate for a swap into a naturally aspirated K20A2 engine where stock Honda parts are required - such as in certain Honda race series. The secondary lobe on the intake, however, is smaller than its RSX-S cousin. This makes it a good candidate for replacement - or so we thought - but more on that later.

VTC Cam timing mechanism

The biggest gift Honda has given to tuners of the K series engine is the VTC mechanism. Located on the end of the intake camshaft the VTC mechanism, via hydraulics allows 25 [crank] degrees of continuous movement on the TSX and 50 degrees on the RSX. For all you old school tuners lurking out there still changing the jets on your carburetors, who think you have to junk the VTC mechanism and go with a good old fashioned cam timing wheel, think again. In every naturally aspirated engine K20a and K24 engine we have tuned, the intake cam needs to be rotated through 25-30 degrees between peak torque and peak power. For emissions, the ability for Honda to rotate the cam to zero at idle to dial out all overlap makes for a very clean engine with no need for EGR. EGR porting is on place on the head but is blocked off.

25 degrees of cam movement is fine for a stock TSX engine but completely inadequate for modified engine with as little as race headers and intake. A stock engine needs no more than 20 degrees of cam moment on the high cam. A well modified setup needs no less than 25 degrees on the high cam. Take a good look at the modifications we made to the VTC mechanism. If you have a TSX you are going to need these changes. Although you could probably purchase and bolt on an RSX VTC mechanism for 50 degrees travel, there is less valve to piston clearance on the TSX pistons. Our measurements suggest 45 degrees maximum cam movement is much safer. Allowing the full 50 degrees movement leads to a greater risk of valve to piston contact should you accidentally mis-shift and over-rev.

TSX VTC mechanism showing material to be removed to increase the cam advance from 25-45 degrees

Engine characteristics.

The K24 is a long stroke engine. Naturally aspirated the engine's peak torque is around 6000 rpm falling off rapidly on the way to the redline. From about 6500 rpm up the power curve is fairly flat as a result. At 7500 rpm the piston speeds are about the same as that of a K20 at 8500 rpm, while trying to ingest about 15% more air through a head with similar airflow to a Type S. This means that the naturally aspirated K24 engine is difficult to get high RPM power from. Forced induction provides an excellent fix for this problem.

The TSX and engine management

K20 engine owners for the 02-04 Hondas and Acuras have the benefit of the K-Pro - a fully tunable stock ECU. When Honda introduced the TSX it updated the ECU [Engine Control Unit]. The only component in common with its predecessor was the connector plug! To date Hondata can modify the VTEC point; rev limiter, fuel, ignition and cam angle tables for a naturally aspirated TSX. There  are no plans for a fully programmable system for the TSX.  All tuning was done with non-streetable modifications for the sole purpose of dynoing with a RSX ECU and K-Pro.

Connecting the K-Pro involved an adapter harness and an Accord throttle body to replace the drive by wire throttle body. The throttle cable already exists and just needs to be moved. A throttle cable holder for the manifold was fabricated, but probably could have been purchased for a Honda Accord. About 6 wires were run to read the throttle position and control the idle (functions that are automatically handled by the drive by wire) The downside of this conversion is that the instrument cluster, air conditioning and vehicle stability assist did not work. ABS was not affected.

Using the K-Pro in this way has allowed us rapidly test a combination of components to find what works best in what order for the TSX, but it is not suitable for everyday road use.

So, starting with a new TSX last August this is what we have tested:

- Comptech headers
- Comptech Ice Box
- Hondata Heatshield gasket
- Toda race headers
- Integra Type intake cam
- Toda N2 cams
- RBC intake manifold
- Short ram intake
- Injen cold air intake
- 45 degree VTC mechanism
- 64mm TL throttle body

For clarity, the dyno charts are presented in a different order than the order in which the parts were added. Knowing what we now know, though, this is the order we would recommend you make modifications. All of these tests were done with the stock cat back on Church Automotive's Dynapack. This dyno reads about 6-8% higher than a typical Dynojet.

First set of tests:

These three dyno runs tested the following:
- Comptech Headers
- Comptech Icebox
- Hondata TSX-Reflash

At about 1000 miles the first dyno (blue) gave us184 hp and 165 ft/lbs of torque. At about 3000 miles when we switched to synthetic oil, we added a Comptech header and Icebox and redynoed (the Pink line). Peak power grew by 20hp This is more than is usually seen with a header and intake. We suspect the additional running in time and synthetic oil contributed few HP here. The next modification was the TSX-reflash, (Red) dropping the VTEC transition from 6000 rpm to 5000 rpm, increasing the rev limit to 7600 rpm, and advancing the cam and ignition timing. Torque and power in the midrange increased substantially with a gain of 25 hp at 6000 RPM . Currently public opinion has the TSX-Reflash as the best bang for the buck modification for the TSX.

Detailed information on the reflash is available from http://www.hondata.com/reflash_tsx.html

Second set of tests:

Taking a few pages from the book on RSX-S tuning we guessed that the system we just tested suffered from too much exhaust back pressure and not enough cam advance. Too much back pressure means you need a high VTEC point, and with K24s we had tuned in the past, we knew we 4000 RPM as a VTEC point was possible. To the rescue was Toda with a set of prototype headers. The headers were supplied with a test pipe and while the header & test pipe fitted the TSX perfectly, I suspect the test pipe was designed to replace a Japanese catalytic converter, as there was no way a US Catalytic converter would fit. These are the best made and best performing headers we have tested on the TSX to date. The quality is superb.

CL9 Toda Headers with Toda test pipe

With the lower back pressure and better tuned lengths of the Toda Header, we also needed more cam advance. Advancing the intake cam allows for pressure waves from the exhaust to travel into the intake. At the right RPM range this can assist the movement of the intake charge into the cylinder.

Air travels into and out of an engine not smoothly, but in pulses. Think of blowing across the top of a beer (or wine) bottle. You will hear a note cause by the vibration of a column of air inside the bottle. An intake is the same. For a given diameter and length of tube, there is a resonance frequency. Where this matches the RPM of the engine, you will find a torque hump and lean spot. When we switched to an Injen cold air intake we found the resonance point to be around 4500-4700 rpm.

These dyno runs tested the following:

- Injen Cold Air intake
- Toda Race headers with test pipe (no cat)
- 45 degree VTC cam advance
- RBC intake manifold
- Hondata Heatshield gasket

At this point we switched the engine management to K-Pro with an adapter harness. The two reasons for doing this were speed and flexibility. Programming the TSX ECU is slow, allowing for only dyno 2 runs per hour. The second reason is that we wanted to move the cam past 20 degrees and up to 45 degrees advance.

The Hondata Heatshield gasket was not tested by itself, but temperature drops of 20-40F were noted on the surface of the intake manifold. Testing on other Hondas of similar power has netted 4-6 hp.

The red line was the best power run from the first set of tests with Comptech headers, icebox, and reflash.

The light blue line showed the switch to Toda headers, Injen intake 45 degrees VTC and K-Pro tuning. VTEC switchover point is a very low 3500 RPM and maximum cam angle is 45 degrees at 3500-5000 rpm. Substantial gains in torque - around 20 ft/lbs at 4700 rpm and solid gains all the way up to 6000 rpm really help the low end. (The apparent loss in torque under 3600 rpm is due to repositioning the Injen air intake from outside the car in early testing to its correct position. Later back-to-back testing showed no loss over the reflash) This is a great combination, well suited to the rev range of the K24A2. The additional torque is always accessible in every day driving, moving the car rapidly without out having to visit the top end of the rev range. I believe however that there is more midrange torque to be gained with the design of a race header with longer primary and secondary tubes that stretch to the length of the test pipe.

The purple line involved only one change, from the long RBB intake manifold - to the short Accord Euro R RBC intake manifold. This manifold has shorter and larger diameter runners than the RBB intake. It is well optimized for high RPM breathing. A gain of 2-3 HP from 6200 RPM to the redline though is not enough to offset the loss of torque pretty much everywhere under 6000 RPM for this engine setup.

So, time for some cams for better high RPM breathing.

Third set of tests:

Parts Added:
- Toda N2 Cams
- Toda Springs
- RSX-S valve seats and retainers

The purple line is the line from the previous dyno chart 2 with Injen Intake, Toda Headers, stock cams 45 degree VTC and K-Pro. The Green line represents the change to Toda N2 cams.

VTEC switch point was set to 4000 RPM for this setup. Gains on the top end were seen from 5400 rpm increasing to a maximum gain of 16 hp from 7000 RPM to the redline. Unfortunately there was a loss in low end torque. This is primarily due to N2's smaller primary VTEC cam lobes than the TSX. However, if your goal is maximum power, this is the way to do it.

So in all the dyno tests above, we have progressed from stock to maximum torque, then maximum power. My personal driving preference was for maximum torque, low in the rev range where it was easily accessible, so for the following tests the TSX was reequipped with the stock cams, RBB intake manifold.

Boring the Throttle body

The RSX has a 62mm throttle feeding a 2l engine. The TSX has a smaller 60mm throttle body supplying air to a larger 2.4l engine. So, lets explore using a bigger throttle body. There are two choices. The first is to bore the throttle body you have. The second is to replace it with a 64mm TL throttle body. We chose the TL throttle body -for two reasons. Firstly because it was already 4mm larger, had room for further boring if necessary and bolted straight on. Secondly, because we had one.

64mm Acura TL and 60mm TSX throttle bodies

We needed to modify the TSX intake manifold to fill the idle control air bypass - a legacy left over from its use on the Accord and no longer needed since idle control is handled by the drive by wire. On the TL the map sensor mounts on the throttle body. This was removed and an adapter added to connect an emissions line.

Stock 60mmTSX RBB intake. Ported to 64mm and welded.

Throttle body dyno:

- Injen intake
- Toda Header
- 45 degree VTC
- K-Pro


About 2hp from 6000 rpm up and pretty close to the margin for error of the dyno. A bored throttle body will probably show better gains if tested with the Toda N2 Cams and RBC intake manifold, but it is pretty low on the bang for the buck list at this point.


Many parts have been tested since TSX was purchased 10 months ago, so its time for a control test. With the current set of modifications we have, lets go back to a completely stock ECU and see how far we have come. This will show you the value (or not) of tuning: Runs were done 5 minutes apart.

Engine Spec:
- Injen Cold air intake
- Toda Header with test pipe
- 45 degree VTC
- 64mm throttle body

Only change - K-Pro to stock ECU


The K24 engine has plenty of potential with the right combination of parts, but engine management is the key to extracting that power. We are working hard to develop products to help unleash that power.

Overall conclusions

This K24A2 needs first of all a race header (long tube preferred) for cams to work. Installing cams first will result in a loss of power. For the emissions minded a high flow cat would be best mounted on the race header about 40cm behind its current position. Secondly a VTC mechanism modified for 45 degrees advance is a must.

What did not work:

On our TSX with intake and Comptech headers we replaced the intake with an Integra Type R intake camshaft. We suspected we would lose a little low end because of the smaller primary lobes, but pick up on the high cam. The results were a big VTEC torque dip and a loss in power everywhere under 7000 rpm. About 4hp was gained between 7000 rpm and redline. Why? We needed the race headers first. With them the ITR cam may have worked.

Forced induction:

TSX engine swaps into Civics are becoming popular. The engine swaps typically use an RSX-S throttle body and a K-Pro. This has given us the ability to do examine the potential of forced induction for the TSX. So, lets see what life this heart transplant brings to lesser Hondas.


Earlier this year we swapped a TSX engine into an EP3 Civic, installed an Integra Type R intake cam, and RSX exhaust cam and a Jackson Racing supercharger. In essence we went bigger on the intake cam and smaller on the exhaust cam. The reason for the bigger intake cam was to allow more compressed air into the cylinder. The smaller exhaust cam was to prevent blow through. Supercharged engines with too much exhaust cam can allow the intake charge to blow right out the exhaust during valve overlap.

Boost level was around 10 psi at 7000 rpm, and as you can see from the dyno chart there is no power drop off at redline and very little torque drop as the revs climb.

A great car to drive and very smooth. Once on the move you scarcely need to change gears.
Pictures and more info at http://www.mrrocket.com/ep3.htm


To date, there are few people who have turboed a TSX engine. We were able to find one; Hasport, masters of shoehorning big motors into small Hondas. Just recently we caught up with one of their 02 Civics fitted a turbo TSX. The tuning was not complete, but we did glean the following specifications.

- Full Race manifold
- T3/04e with 51 trim turbo
- 3” exhaust
- RSX-S exhaust cam

Pistons, rods were and the rest of the engine were left stock, as the boost was wound up to 12 psi.

Tim Kelly from Xact Dyno conducted the tuning and provided us with the following data:

Do not try this on your engine. This is far too much torque for the stock engine components to take. At this boost and power level, stronger pistons and rods are an absolute necessity. We thought we'd post it anyway as the power figures are pretty impressive.

So there you have it. More dyno tuning of the K24A2 than anyone outside of Honda, and the most comprehensive guide to TSX performance parts so far.


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