The year 2002 saw the introduction of the Civic Si, a new hatchback body style with a five-speed shift lever sprouting from the dashboard and a 2.0-liter engine stuffed under the hood. With its distinctive minivan-meets-sneaker bodywork and 160-hp mill, the Si certainly stands out from its earlier Civic siblings. But the Japan-only Civic Type R spoiled us. Edgier, quicker, and a much more engaging drive, the Type R is really what the Si should have been.

Picking the Engine
Pumping out 200 hp at 7400 rpm and 142 lb-ft of torque at 6000 rpm, the engine from the RSX Type-S (K20A2) is actually quite similar to the K20A3 in the Civic Si. They share the same 2.0-liters of displacement, bore/stroke, block, head, valves, and intake manifold. However, a whole slew of internal guts and external bolt-on bits are radically different between the two.

For starters, the RSX's K20A2 boasts 11:1 compression pistons, dual valve springs, and a tri-y header with larger primaries than the Civic.

Perhaps most significantly, the K20A2 employs a more sophisticated i-VTEC system in conjunction with more aggressive cams. There's a lot of confusion of the differences between the two engines' i-VTEC systems, so here's the straight poop. On both cars, i-VTEC really consists of two features: VTC (Variable valve Timing Control) and VTEC (Valve Timing and lift Electronically Controlled). VTC, in both cases, is simply a hydraulically controlled adjustable cam sprocket that varies intake cam timing on the fly depending on engine speed and load. VTC does not affect the exhaust cam. It's the VTEC portion of these systems that differs. On the K20A2 (RSX Type-S), VTEC means there's a low-rpm set of cam lobes and a screaming, high-lift, long duration high-rpm set of cam lobes both carved into the same camshaft. At about 6000 rpm, the rocker arms stop following the wussy little low-rpm cams, and start following the big ones. This is the system that made VTEC synonymous with high-output, 8000-rpm monsters.

The Si shifter cables hook to the RSX transmission without modification. The shift mechanism, however, isn't designed to move far enough to reach the six-speed's reverse gear. Putting a notch here, as shown, allows you to reach reverse.

Unfortunately, the K20A3 (Civic Si) uses a completely different system that happens to share the VTEC name. At low engine speeds, the two intake valves operate with different cam lobes--one valve gets the "primary" lobe (33.925mm lobe height). The other valve gets a wimpier "secondary" lobe (29.638mm lobe height). When VTEC mode kicks in at 2300 rpm, both valves start following the primary lobe. That's it. No high-rpm kick, no screaming, no high output. In the meantime, the exhaust valves always get shoved open by a 34.092mm lobe with no tricks at all.

With the two engines sitting together on the floor, we picked up on some notable external differences between them as well. In addition to the different cylinder heads, the RSX has a cast aluminum oil pan (the Civic's is stamped steel) and a small oil cooler at the base of the oil filter.

The Civic Si steering rack has electric power steering assist, so the stock engine has no power steering pump.

The power steering systems are also different. The Si uses electric power steering, while the RSX's is hydraulic. Finally, the axles differ slightly. The RSX has a larger bearing to support the intermediate shaft, and uses larger splines at the hubs.

Engine Removal
Like many Hondas, removal and installation of the engine is often best done from beneath the vehicle. Unless your jackstands are 4 feet tall, use a lift.

Under the hood:
1. Disconnect and remove the battery.
2. Remove the plastic cover on top of the intake manifold, the airbox, and intake snorkel assembly.
3. Unbolt the battery lead at the fuse box. Don't forget to unbolt the cable's chassis ground located near the battery tray.
4. Disconnect the throttle linkage and remove the cables from their brackets.
5. Relieve the fuel system pressure and remove the supply hose from the metal fuel line at the engine.
6. Remove the charcoal canister hose and brake booster hose.
7. Unbolt the clutch slave cylinder and the clutch line's mounting bracket.
8. Remove the two shift cables at the transmission.
9. Disconnect the ECU (under the glove box), remove the grommet and harness hold-down tabs, and pull the engine harness through the firewall.
10. Remove the accessory drive belt, the A/C line mounting bolt at the engine, and the two A/C line clips at the subframe.
 

Where the Si engine (on the right) has an idler pulley, the RSX engine (on the left) has a conventional power steering pump. Fortunately, the Si's idler pulley simply bolts onto the RSX engine.

Beneath the car:
11. Remove the splash pan and drain the coolant, transmission fluid and engine oil. No, not into the same bucket. Remove the lower radiator hose.
12. On the suspension, disconnect the anti-roll bar end-links and lower ball joints, then remove the halfshafts.
13. Disconnect both oxygen sensors and remove the catalytic converter.
 

Under the hood again:
14. Remove the heater core hoses, then remove the radiator. This is just a precaution to avoid ventilating it with wrenches or engines.
15. If you have a hoist, attach it to the engine and raise it, then remove the nuts and bolts holding the support brackets for the transmission mount and upper engine mount. If not, you will need to keep the engine bolted to the chassis while the subframe is removed.
16. Unbolt the engine mounts on the subframe and position your tool cart--or whatever you have that can support the weight--beneath the subframe. Mark the position of the rear subframe bolts before you remove them, then remove the subframe.
17. Unbolt the A/C compressor from the engine and support it somewhere in the engine bay. This way you won't have to discharge/recharge the A/C.
18. Carefully lower the engine, checking for any interference, connected vacuum lines, coolant or fuel hoses, birds' nests, or lounging hippopotamuses.

Since the RSX uses larger splines on the hub end of the halfshafts (right), the Civic halfshafts (left) are retained for this swap.

Rather than use an engine hoist, Hasport used a homegrown engine cart. Just lower the car over the cart, unbolt the engine from the car, bolt the engine to the cart, then raise the car up and out of the way.

Chassis Prep
The only difference in the wiring harnesses is that the Si harness does not have wiring for the reverse lockout solenoid, and the ground leads at the ECU are different. We used the RSX-S harness, which is ideal for this swap since it snaps right into the Civic. Assuming you can locate a connector for the solenoid, the Civic harness could be used instead if the ground and solenoid leads are crimped and spliced in. Our RSX drivetrain included a harness, so that's what we used.

Higher output means more heat rejection. The RSX has a coolant-to-oil heat exchanger plumbed in at the base of the oil filter to help offset the increased heat load.

Like the Si harness, the RSX harness has two flying leads, one goes to the fuse box and battery while the other goes to the ECU. The RSX ECU replaces the stock Civic ECU.

The RSX's downpipe and catalytic converter are larger than the Civic's, and the RSX's cat locates further downstream than the Civic's. Plus, the flange on the RSX cat does not mate up to the stock Si exhaust. Since using the puny Civic Si exhaust on the freer-flowing K20A2 would only choke off dangerous horsepower anyway, your best bet is to have a larger cat-back exhaust made.

One of the few obstacles of this swap. The RSX catalytic converter is larger, farther downstream, and clocked differently than the stock Civic Si cat and thus will not bolt to the stock Si exhaust. Fabricating a new, larger exhaust more suitable for 200 hp makes more sense anyway, so we dumped the stock exhaust entirely.

Engine Installation
The RSX drivetrain literally bolts right into the Civic. Just reverse the removal procedure described above and sell the Si drivetrain to someone with a base Civic.

Starting It
Honda uses a very tricky anti-theft system on most of its models. Every key has a chip in the key fob. When the key is poked into the ignition, the ECU looks code on that chip and if it matches the one programmed into the ECU, the ECU allows the engine to start.
Otherwise, the engine will crank but not start.

As such, our RSX ECU wasn't particularly fond of the Civic Si key we had. And since keys and ignition switches are not sold as part of a used drivetrain, we had to find a workaround. We called a local Honda dealer and gave him the VIN printed on the ECU. Once satisfied the car had not been reported stolen, he gave us a brake code that would allow the car to be started normally for a 24-hour period. This brake code changes regularly, the idea being that you immediately drive the car to the nearest dealer, who will then perform the permanent fix.

The car won't run right until you pay a visit to a Honda dealer. Here, the tools to unlock the electronic immobilizer are available for a small fee. This is required to drive the car since the RSX ECU was originally programmed to accept only a handful of key codes. After they check the resistance value of the Civic Si ignition key, they reprogram the RSX ECU to accept the key.

At least that's how it's supposed to work. After an hour of doing the brake pedal two-step, we couldn't shake the RSX ECU's death grip on fuel and spark. Annoyed, we plugged in the Civic Si ECU and turned the key. To our pleasant surprise, the car started up, and we drove gingerly to the nearest dealer, keeping the revs below VTEC threshold. There, we plugged the RSX ECU back into the car.

With their PGM tester, the dealer reprogrammed the immobilizer code buried deep within the ECU for the specific resistance value of our Civic key. Be prepared to bring documentation showing you acquired the engine legitimately, or the dealer may not be willing to wave its magic wand for you.

In the end, swapping in the RSX Type-S drivetrain heaped on an extra 40 hp and 10 lb-ft torque, gave us 1100 extra revs to play with, and an extra cog in the gearbox. And as swaps go, this one is as straightforward as it gets.

Slowing it down
To complement the newfound forward gumption, the Si's 10.2-inch brake rotors, and single-piston stock calipers were dumped in favor of a set Fastbrakes' 12.2 x 0.81-inch thick rotors, four-piston Wilwood Superlite calipers and aluminum mounting brackets. The stock 10.25-inch rear brakes were replaced with Fastbrakes 11.4-inch rear rotors with a relocated stock caliper.

These guys can't believe this very car left their lot three days earlier and already has an engine swap completed.

The stock front brakes consist of 10.2-inch rotors and single-piston calipers weighing 22.5 lbs per side. The Fastbrakes 12.2-inch rotors and four-piston Wilwood Superlite calipers (right) are a drop-in replacement and weigh only 16.5 lbs per side.