I'm not a part of the Psychic Friends Network, but I can predict when Honda will give us a new Si: Every four years or so. It's pretty much clockwork. And every four years or so the aftermarket fires back with a handful of turbo kits, most of them decent, a few downright respectable.
We like the new Si. While the company's previous version left many in the Honda community scratching their heads as to why it never received the RSX Type S' more powerful K20A2 powerplant, it seems Hondaphiles have been left satisfied when it comes to Honda's most recent Si conception. There's nearly 40 extra horsepower at the flywheel here, and for that you can credit the new K20Z3 mill - an engine that's a heck of a lot closer to the popular K20A2 than the older EP3's 160-horsepower K20A3. A factory-installed limited-slip differential, an 11.0:1 compression ratio, a six-speed gearbox, cheaper than an RSX Type S - what more could you ask for? Why mess with a good thing? What, are you kidding?
GReddy's been offering bolt-on turbo kits for Honda's top-of-the-line Civic Si almost as long as there's been an Si to produce them for. They know that even a good thing can be improved upon. So when we heard they were just about to introduce their latest Civic Si turbo kit we wasted no time in meeting up with the folks at GReddy and strapping their turbocharged Si down onto the dyno.
Our initial impression when we popped the FG2's hood was one of pity for those who dare install a turbocharger system within these close quarters. Space is at a premium here and with the K series' exhaust side pointing toward the firewall, a perfect fit is a must. With a B-series in a Civic, you could overcome turbo fitment problems by swapping radiator fans, even radiators. But with the K series, it's not like you would just cut a hole in your firewall and make the turbo fit; at least we hope you wouldn't. GReddy knows all this. Their design takes this into consideration. The company's cast ductile iron, log-type manifold fits snugly against the cylinder head with room to spare between the chassis and is constructed in such a way that the T517Z turbo faces few obstructions. From there the turbine housing meets up with a cast iron adapter and steel downpipe that mates up to the Si's catalytic converter. And in case you're wondering, our tests were performed on an otherwise stock Si with the factory-issued cat in place, a feat that few competitors' kits often allow for. The intake piping, with all of its provisions, and Airinx filter also find their place comfortably under the hood, despite the space constraints.
Funny enough, we're still getting used to popping a Honda hood and seeing an airflow sensor in place instead of a MAP sensor. Honda went for so long regulating fuel curves by means of manifold pressure that many were bewildered when the company switched over. It might have been for the best. Despite the Civic's OBDII orientation and its ultra-strict, ECU-mandated emissions characteristics, GReddy's Si managed a number of dyno pulls without ever posting the dreaded check engine light. MAP sensor-based turbo kits of past have typically made it more difficult to prevent check engine lights from appearing as Honda MAP sensors are extremely boost-shy. Not the case here. This, along with fine-tuning fuel and ignition maps, is accomplished with a pre-programmed GReddy e-manage Ultimate, which piggy-backs on top of the factory ECU, and a set of the company's 370cc/min fuel injectors. The new squirters replace the primaries and are tuned for a near-stock idle and exceptional drivability. Since the e-manage Ultimate is shipped pre-tuned, the hardest part is wiring it. Actually, that's pretty easy too. The last one we hooked up took under an hour and we didn't even have a service manual. As for wiring up the new injectors - you don't have to. GReddy supplies a plug-and-play harness with the kit making for an idiot-proof install.
But you probably want to know more about that turbo. GReddy's T517Z for the Si mates up with an 8cm2 turbine housing and is capable of roughly 375 horsepower - not that the Si is ready for that just yet, but it's good to be prepared. The T517Z can best be described as a cross between the 16G and 18G turbos, and was generally reserved as an upgrade for both Nissan Silvias and Skylines. Its benefit lies in its space-saving construction in which a big 50 trim compressor wheel is housed inside a compact frame. Its trim is the result of the wheel's 68mm exducer and 48mm inducer. On the exhaust side, a 56mm inducer and 49.1mm exducer make for a fairly high-flowing 77 trim. Boost levels are regulated internally by an actuator wastegate to a pre-set and conservative 6.4psi. This all translates into roughly an 8hp increase per pound of boost in our case.
Charge efficiency is increased with the help of GReddy's Type 31V front-mount intercooler, which is based off of the tube and fin design. The Type V intercoolers are best suited for lower horsepower applications; they provide a reduced pressure loss across the core in comparison to the bar and plate Type R version but are slightly less efficient when it comes to cooling. At any rate, the reduced pressure loss translates into less backpressure, a good thing. Tube and fin designs are also generally lighter because they have less thermal mass and a lower fin density - they're also much cheaper than bar and plate designs. The Si kit's Type 31V measures in at 186mm x 600mm x 76mm - perfect for tucking itself behind the Honda's bumper. The kit also includes lightweight, mandrel-bent aluminum piping, and all of the clamps and connectors necessary for a true bolt-on installation. We've always felt that one of the signs of a true bolt-on turbo kit is whether or not you need to perform any cutting and welding. Not here.
Naturally, GReddy's Si is outfitted with the best they could throw at it, the dyno results prove as much. With the Si strapped to the rollers of XS Engineering's Dynojet, it pelted out a best of 229.3hp to the wheels - a 49.8hp improvement over a previous stock Si we've tested. But the major improvements are in the details. Look closely at the power graph and you'll no doubt see an increase of more than 66hp throughout the midrange and prior to i-VTEC engagement. We suspect moving the i-VTEC engagement point earlier will yield even better results as would some minor adjustments with camshaft timing. But what's more impressive is that the GReddy turbocharged Si holds its wide power-gain margin from just beyond 3500 rpm to just before 6000 rpm. After that, the gains are still there but are minimal in comparison to the gobs of increased midrange power, which is after all where the GReddy Si performs best. All this extra power found in this most usable RPM range is at a slight cost when it comes to high-RPM power gains though. The T517Z seems to run out of steam as it begins to approach redline with power tapering off around 7700rpm.
Torque gains are even more impressive here, and that really is what counts when it comes to driving on the street. Oh yeah, this is a street kit by the way and it wasn't designed for all-out track abuse. On the dyno, the Si produced an additional 80lb-ft of torque just before 4000rpm - that's a maximum of 198.5lb-ft and we're not even halfway through revving this thing out yet. Hmm, an 80ft-lb increase? We think we might like this T517Z. Torque values drop a bit after that, but aside from a pretty significant dip from the i-VTEC activation, the curve is fairly linear. You've got to consider numbers like these as well as power and torque curve characteristics when turbo kit shopping. Sure, top-end and peak horsepower production are fancy details to brag to your friends about, but you can't forget about both overall torque production and midrange power improvements, the stuff that really counts when stoplight-to-stoplight driving around town. And if these mid-range power gains just don't quite cut if for you, GReddy tells us that plans for making their Si turbo kit 50-state emissions legal are in the works. Combine that with the kit's quality and dyno results and you just can't go wrong here. Not impressed? You could always wait for the next Si. We'll bet there will be at least a few turbo kits for it.