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Project Acura TSX - Project Car

Part 3: More Power-With Stock Bottom End

Jay Chen
Dec 12, 2006
0602_sccp_01_z+project_acura_tsx+left_front_view Photo 1/10   |   Project Acura TSX - Project Car

Is it possible for our Project TSX to skin an E46 M3 on the track? We posed this question in our first installment of Project TSX back in December 2004 and we're still exploring the idea. So far, we've changed out the stock suspension, wheels, brakes and tires, all in effort to wring some M3-like handling numbers out of the Acura. Part II involved the installation of a few bolt-on parts; including intake, exhaust, headers and a Hondata K-Pro ECU. These mild modifications netted us 184 wheel-hp.

Ulitimately, our TSX could probably nudge the M3 in handling numbers, but horsepower is another story altogether. It would be tough, considering the difference between 3.2 vs. 2.4 liters is night and day. Sure, Project TSX can keep most cars honest with its streetable, naturally aspirated engine, but to beat BMW's rocket chariot, the TSX's power output needs to be upped.

We're convinced the plan is still realistic. So, Project TSX went back to Skunk2 for a barrage of modifications designed to inject some much-needed horsepower into the 2.4-liter. To help keep build costs down, we chose to keep the stock bottom-end intact. Hence, all the work done was designed to improve flow and raise volumetric efficiency at higher rpms.

An M3 will put down roughly 280 wheel-hp out of the box. All the bolt-ons in the world won't get Project TSX near that kind of output, so we had to get serious work done on the head and turn our motor into a hybrid K24A2 with K20 parts.

HeadworkSkunk2 started with a standard 30-, 45-, 60-degree three-angle valve job on the intake and exhaust valve seats. The exhaust ports were radiused below the 60-degree cut to better transition into the ports.

0602_sccp_02_z+project_acura_tsx+valves_valve_springs Photo 2/10   |   Project Acura TSX - Project Car

The majority of the head work consisted of porting the K24A2 head. Since the stock engine only spins to 7100 rpm, the head was designed to deliver more low-end response and torque, which meant smaller ports to increase flow velocity through the head. That's all fine on a stock car, but when the rev and flow range are stretched higher, the port profile has to change significantly. The valve guides were also ground down to minimize restrictions.

Skunk2 replaced the stock valves with lighter one-piece forged valves with hardened tips. Though valve size and compression were not altered, springs and retainers were replaced with slightly stiffer double-wound coils and titanium retainers to perform better at higher speeds and reduce reciprocating mass.

Bolt-OnsEven with the significant porting, Skunk2 felt its Stage 1 RSX camshafts and stock RSX cam gears best fit the flow and engine speeds that Project TSX was capable of. We switched to RSX hardware because it was designed to operate at higher engine speeds and raise the powerband. The RSX cam gear has a wider range of i-VTEC cam phasing, from 0-50 degrees BTDC, compared to the TSX cam gear, which had only 30 degrees of cam advance. The added range of i-VTEC operation lets us retain the K24's low-end torque, while making more power up top.

We threw on all the bolt-on parts we could from Honda's RSX parts bin to keep the car driveable with its new lungs. Honda spent a lot of money designing and casting manifolds that are versatile in response and flow; we'd be stupid to not take advantage of that.

Skunk2 chose to use the intake manifold from the Japanese RSX Type-R, or K20A. K20 manifolds generally have shorter runner lengths designed for increased flow at higher rpm, which fits our bill. According to Skunk2, the manifold from the K20Z found in the new Civic Si is worth 6 to 7 hp just as a bolt-on.

0602_sccp_06_z+project_acura_tsx+throttle_body Photo 6/10   |   Project Acura TSX - Project Car

Although the K20 and K24 manifolds share the same bolt pattern, using a K20 manifold requires an adaptor plate from HASport to block off the coolant port on the K24 head. The plate will leave the manifold 3/8-inch farther forward in the bay, but since everything is soft-plumbed into the manifold, the change in positioning doesn't create any interference issues. The slight change in spacing is one of the reasons Skunk2 used a custom short-ram intake for this application.

If you're on top of your Honda game, you're probably wondering what happens to the drive-by-wire e-throttle that comes with the TSX manifold. Since the RSX manifold uses a mechanical throttle, the drive-by-wire system on the TSX had to be removed.

Luckily the system isn't too complex, since the go-pedal is still physically connected to a throttle cable that runs through the firewall. On the TSX, that cable connects to an e-throttle control unit inside the engine bay that electronicaly controls the stock TSX throttle body. This makes life easy, since you can just bypass the e-throttle controller and TSX e-throttle by using a K20 mechanical throttle body and cable. Skunk2 simply replaced the cable with a RSX unit, modified the brackets on the throttle body and threw away the e-throttle actuator mounted on the passenger side firewall. Call it weight reduction. The stock 64mm RSX throttle body was also replaced with a billet 68mm unit from Skunk2 for better flow.

On the exhaust side, the Skunk2 Tri-Y header we installed in Part I was replaced with a race version, sporting revised geometry and no provision for a cat. The original Skunk2 cat-back exhaust remains. Combined, these parts add roughly 8 percent additional flow, says Skunk2.

The stock injectors and fuel pump stay, as does the Hondata K-Pro engine management, recalibrated for the added power and new 8200-rpm redline. It's in the last 2000 rpm that Project TSX makes its huge power gains; 65 wheel-hp over baseline and 54 wheel-hp over our last test. That's a 38-percent gain in output-on a stock bottom end!

0602_sccp_07_z+project_acura_tsx+gasket Photo 7/10   |   Project Acura TSX - Project Car

With power up, the tuners get to work on style. This means clean engine bays, intact interiors and most of all, no Krylon black spray paint. Skunk2 installed more supportive RSX seats in Project TSX. The seats plant in with mild modifications to the stock mounting tabs-grinding and welding was necessary. Since the new seats are black, Skunk2 also replaced all of the interior trim, from roof liner to speaker grilles, with parts from black-interiored TSXs. The results look great- the huge effort invested in aesthetics pays off.

Finally, the TSX's 18x8-inch Volk GT-7s were replaced by forged 18-inch Volk Racing CE28s, and Michelin Pilot Sport 2s now sit where BF Goodrich g-Force KD tires once did. As tested, the PS2s had less grip and underperformed in the slalom and skidpad compared to previous tests on the KDs. We also raised the ride height slightly to give the TSX some badly needed suspension travel, but the relentless body roll still isn't quelled, so we have some work to do on that front.

The majority of the work on Project TSX is done. We'll need to do some final suspension tweaks and step up to R-compound tires before we attempt to kick BMW M3 ass. Then all that's left is to see how it holds up against our rival in the real world.

Sources

Suspension
909-923-9188
www.buddyclub.us
By Jay Chen
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