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Testing & 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 Tests

These three dyno runs tested the following:

  • Comptech Headers
  • Comptech Icebox
  • Hondata TSX-Reflash

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At about 1000 miles, the first dyno (blue) gave us 184 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 20 HP. 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 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 fit 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 and 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

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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

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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 and RBB intake manifold.

Boring the Throttle Body

The RSX has a 62mm throttle body feeding a 2.0L 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: First, because it was already 4mm larger, we had room for further boring if necessary and it bolted straight on. Second, because we had one.


64mm 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

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Conclusion

About 2 HP 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.



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