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, and on the RSX between the subframe and firewall. As a result, they 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 2.4L Accord.

Accord Euro R intake manifold

Cams

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.

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 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 in place on the head, but is blocked off.

25 degrees of cam movement is fine for a stock TSX engine, but completely inadequate for a 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 of 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. As it will be quite some time before we have the same level of programmability in the TSX ECU as we have now in the RSX, we adapted the K-Pro for use in the TSX.

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 (VSA) 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