K24 VTEC Versus G23 VTEC - Tech Knowledge

If you're reading this, chances are you've owned a swapped Honda or two in your day. If not, you probably want one. But where to start? B18A/B engines offer two cams and 1.8 liters of displacement-but also a lackluster cylinder head. B16As are cheap and offer VTEC... but are also old and relatively small. The venerable B18C is becomming increasingly more expensive and scarce, not to mention overshadowed by the K20A's i-VTEC, aggressive cams, roller rockers, and extra .2 liters of displacement. Which sound great, until you factor in its $5K price tag. And there's the boss of them all: the K24. One and a half times the size of a B16, 200 hp out of the box, and the potential to make much more power than any of the afore-mentioned options. Pull one out of a TSX, or build a K20/24 hybrid - either way, if the thought of dropping $5,000 on a K20 swap made you cringe, forget this option right now.

But what about Honda's "big block" of yesterday, the H22A? DOHC, VTEC, 2.2L of displacement, and 190+ hp all for a third of the K-series' price. Not a bad deal, apart from its fiber-reinforced metal (FRM) cylinder walls that make over-boring impossible and don't get along with aftermarket pistons. So what's an economical (read: broke), but mechanically inclined Honda owner to do? If you're Bolisbuilt's Chris Bolin, you roll all the above engines into one 2.3L, 250 hp, DOHC VTEC monster, name it the "G23 VTEC", and do it all for less than you'd spend on any of the others.

01. "I was looking for a reliable engine I could swap in my EF, make big all-motor power with, and just drive every day," Chris tells us, "A K-series would've been great, but they were too expensive. And I wanted something bgger than a GSR or B20 VTEC," he continues, "So I started thinking about swapping in a stock H22A." But then he read about a Honda-tech member's write-up of an F23/H23 "Frankenstein" project. "This guy had successfully mated a non-VTEC H23 head to an F23 block," he explains, "and my friend was selling an H22A long block with a spun rod bearing for $200, so I figured why not try it with VTEC? I bought an F23 short block for $100 and got to work."

02. Despite many similarities between Honda's F- and H-series engines, each offers advantages that the other lacks. The H22A brags a higher-flowing, DOHC VTEC cylinder head. The F23, .1 liter more displacement and iron cylinders. What's more, the F23 block features 55mm main bearing journals, while early H22As measure only 50mm, and the F23's girdle is much bigger than most Honda engines. The F23 is the only engine out of the bunch with a stroke as long as 97mm, and an 86mm bore. Because of this, conventional wisdom held that F23 pistons and rods had to be kept with the block when switching heads, but the higher combustion chamber of the H22 head brought compression down to a low 8.8:1 - great for boosted applications, but Chris wasn't after that. Since the F23's piston specs nearly mirror the K20's, and that both engines share a floating rod design, Chris found that K20 pistons would fit on stock F23 rods, inside a stock-bore F23 block. And they'd bump compression to 11.5:1 when used with the H22A head. "The valve reliefs in the K20 pistons fit the H22 intake exhaust valves perfectly," he adds, "it's like Honda took a good look at the F23 when they designed the K-series."

03. No major machine work was needed to bring everything together, but the H22 head uses eight ports to drain oil back into its block; the F23 block uses only six. All of the F's drain ports match up with the H22 head, but the remaining two Chris had to block off with DIY plugs, consisting of bolts driven into the head and then grinded flush. There was also a slight difference in external water pipe routing between the F and the H, which Chris solved with some creative use of a welder and some scavenged pipe. "But a piece of silicone radiator hose and clamps would do the trick," he notes.

04. It is often said that timing is everything. That goes double for an en engine made of two halves of different engines. Since the H22A head was used, Chris reasoned he'd adapt the F23 block components as needed. The F23 water pump was pulled apart from its gear, and pressed into an H22 unit. The H22 crank cog and F23 pulley were used, and top dead center (TDC) was found the old-fashioned way, by inserting a TDC gauge into the number Two or Four cylinders and marking on the F23 block where the crank pulley pointed at their lowest points, then lining the H22 cam gears up at their stock points. An H22 timing belt was wrapped around the mix and tensioned using OE F23 equipment. The H22 distributor was retained, the EF wiring harness was modified to work with the new engine, and the whole car was converted to OBD 1 and synched to a Crome-chipped P28 ECU. "But the stock H22A P13 ECU could also be used," he advises, "and initial timing should be about 16 degrees before TDC at a 1,100-rpm idle."

05. Finally, there was the driveline. Just how does one get a K20-infused, Prelude/Accord hybrid engine to power an EF Civic hatch, anyway? It's easier than one might think. Since the chassis originally used a cable-actuated transmission, Chris decided to start with a B16A S1 trans., coupled to the F23 block using QSD's H2B adapter kit. Consisting of a trans. adapter plate, mount adapter, flywheel spacer, and half-shaft adapter, all Chris needed to add were Hasport B-series mounts for the EF Civic all around, a stock B-series clutch, flywheel and half-shaft, a JDM Civic SiR linkage (or a Hasport one), and DA Integra axles. The stock EF throttle cable was adapted to fit the new engine.

06. With the engine assembled, bolted up to its trans and dropped into its new EF engine bay, it appeared that Chris was on the homestretch with his project. Until he discovered a new set of hurdles to clear: fitment. "If you've ever looked at a Prelude engine bay from the side," he notes, "you'll see that the H22A tilts back toward the firewall, allowing better clearance for the hood. The H2B kit doesn't give the F23 block this lean, so it sits way higher in a Civic engine bay than a B- or an H-series engine, especially in the EF bay." Chris not only had to notch his hood's skeleton for clearance, but also prop the back of it up nearly two inches. He used an Innovative Mounts alternator re-locater bracket to buy a little more room, but still had to bang out the frame rail with a sledge hammer to allow clearance for the crank and alternator pulleys. The stock H22 fuel lines and filter were all retained, but an intake and header had to be custom-made, and the stock exhaust had to be modified. "But the OE H22A intake and header could suffice with a little work," says Chris.

07. With the car up and running, Chris could've stopped where he did, with a 2.3L hybrid mill boasting K-series power and torque for a fraction of the price... but why not spend a little more to make it even faster? In researching his build, Chris learned that, for nearly the same coin as used OE K20 pistons, off-the-shelf Wiseco K20 pistons could offer even higher compression-12.8:1-and their valve reliefs could accommodate the increased lift and duration of much more aggressive cams... like the used Skunk2 Pro 3 cams and cam gears he found on eBay for $500, that he coupled with Supertech dual valve springs and titanium retainers for a few bucks more. To help the cams reach their fullest potential, Chris replaced his homemade intake with a set of 52mm TWM ITBs. A Kaizenspeed balance shaft removal kit frees up a few additional ponies by reducing rotational mass. And since the whole engine was now making more power, Chris saw it fit to strengthen its driveline, while removing a little more rotational mass, by ditching his OE B-series clutch and flywheel with Clutchmasters FX500 and ACT Prolite replacements. The result: 248.6 whp and 181.2 lb-ft of torque, as measured and tuned by the Latrobe, Pa. based HybriDynamics crew.

08. "It all worked out better than I expected," Chris confesses at the end of it all. "It's a great all-around motor; lots of power, loads of torque, and built with easy-to-find parts. It goes to show you don't need a 'K' to make a lot of 'HP'." But Chris cautions that not everyone should embark on a G23 build. "If you've got the tools and a garage, and know your way around an engine, by all means-go for it," he advises, "But if you're expecting it all to just snap together... better let a pro handle it." Words to live by. Chris has had his EF out to the strip a few times since completing its build. It's gone low 12's with a full interior and street tires, and Chris expects to be deep into the 11's after a head port, tuning, and possible over-bore. "The best part of it all," he says, "is the look of confusion on people's faces when you lift the hood. They don't know what the hell it is!"

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