What's that you see peeking out from behind the C-West front bumper cover on our EG Honda Civic project car? Could it be a front mount intercooler? Why, yes it is! A Vibrant Performance air-to-air intercooler to be precise (22x9x3.25''), but what's that needed for?
With the shackles of the Canadian Touring Car Championship rulebook removed, since our venerable EG is no longer eligible to compete in that series due to its age, it was time to make some serious power so that the car can run with the big dogs as an Unlimited class Time Attack machine. But having seen more than a few turbocharged Hondas suffer from all sorts of reliability issues associated with the high heat and high engine loads (eg. boost spikes) that come with a turbo setup, it wasn't until recently that I came across a forced induction approach that really piqued my interest.
A couple years ago at the SEMA show I spotted Oscar Jackson of Jackson Racing fame hovering over a Honda S2000 in the Honda booth. Turns out this was no ordinary S2000 but a supercharged one that Oscar and his team from Kraftwerks USA had built around an innovative new type of centrifugal supercharger from a Danish (the country, not the food) company called Rotrex. Oscar's enthusiasm for this new supercharger was infectious and although I didn't fully understand how a Rotrex supercharger differed from other centrifugal blowers, I knew if Oscar came out of retirement to build supercharger kits with Rotrex units there must be something special about them.
A year passed without looking too closely at Rotrex's technology, but when I finally started to get serious about the idea of adding forced induction to the Civic, I did some research and spent a few hours on the phone picking Oscar's brain. In fact, I wrote a story about Rotrex for Modified Mag's May 2009 issue.
In the process of writing that magazine story, I learned a fair bit about Rotrex's core-technology — its patented traction drive system. Visually, Rotrex superchargers look a lot like conventional centrifugal superchargers, both of which use a compressor side similar to that of a turbocharger and are belt driven so that boost pressure increases with engine speed (since the pulley on the supercharger is spun by the main accessory belt that is powered by the crankshaft pulley). However, at the heart of a Rotrex supercharger there are three planets or rollers that are fixed in place 120-degrees from each other. They are enclosed within an annulus or drum that is turned by the input shaft via the serpentine drive belt. According to Oscar, "If you consider that the annulus/drum, planets, and compressor shaft are all just smooth steel parts spinning on themselves without gears, it makes sense that at some point when there is a high load from the compressor making boost that these parts are going to slip on each other [causing inconsistent torque delivery]. But the "ramp effect" keeps this from happening. One of the planets is actually allowed to move slightly from its fixed bearing position. As the annulus/drum rotates, it exerts load onto the planets such that one planet is allowed to rotate slightly loose from its normal position. This "loose" planet then exerts a downward load onto the compressor shaft and the compressor shaft then loads up against the other two planets, preventing slip and keeping the torque consistent from low load to high load conditions."
The relative size of the annulus/drum and planetary rollers inside it is how a Rotrex supercharger creates its very high overdrive and compressor shaft speed. In Oscar's words, "When the annulus/drum rotates, its larger surface area moves across the smaller planets, accelerating the speed of the planets in the process. These planets in turn have a greater surface area than the output shaft that turns the compressor wheel. It is these two multiplication factors that give the Rotrex its high overdrive ratio." This makes overdrive factors as high as 12.7:1 possible, compared to most centrifugal superchargers that run at overdrives of 2 or 3:1. What this means is that if a supercharged engine makes 10psi at maximum RPM, the Rotrex-powered engine will have over four times the airflow up to the point where both superchargers make the same 10 lbs of boost. So it's the high overdrive system that allows the Rotrex to use smaller more efficient compressor housings, very much like a turbo would use, making it easier to install in tight engine bays like our K24 EG Civic's.
But the advantages of Rotrex's supercharger design don't stop there. Because these are sealed units that have their own separate oiling system, there's no need to tap the engine's oil pan. This means, unlike a turbocharger, the Rotrex blower doesn't tax the engine's existing oiling systems, helping keep under-hood and engine oil temperature under control. And since superchargers don't use the energy supplied by exhaust gases to power the compressor the way a turbo does, there isn't all that excess heat to worry about either. According to Oscar, "The problem with turbo-related heat buildup and the fact that the turbo spools so rapidly at mid rpm levels without being controlled by the crankshaft is that ECU tuners are forced to throw a ton of fuel into the combustion chamber and pull timing at the point of full spool to protect against detonation. With a Rotrex supercharger you can actually do the exact opposite, leaning out the a/f ratio and adding timing because the system runs so cool. As a result, you end up with improved fuel efficiency and more consistent and reliable power production."
With higher compressor speeds than a conventional supercharger, comparable efficiency to that of a turbocharger but without all the engine-killing heat production or risk of boost spikes, all in a very compact and low NVH (noise, vibration, and harshness) package, I couldn't identify a downside to installing a Rotrex supercharger on the EG. I placed my order with Kraftwerks for one of their new K-series Race kits, opting for the bigger C38-61 supercharger since I wanted the most power possible at high RPM. After consulting with Oscar Jr. and Tony at Kraftwerks about pulley sizes and my target horsepower level and RPM range, we opted to stick with the 152mm K24A2 crank pulley along with a 100mm pulley on the supercharger. This should give us about 10-11 psi of boost at 7600 RPM, right where we'll set the fuel cutoff so that we don't over-rev the stock K24 block or the supercharger.
As you can see from the photo, the Kraftwerks K-series Race kit comes with the bracket required to mount the Rotrex to the block in line with the crank pulley (using stock threaded bolt hole locations where the a/c bracket normally mounts, so you cannot run this kit with air conditioning), as well as the Rotrex oil reservoir with mounting brackets (top right of the picture), a high quality Setrab oil cooler (top left of picture) with lines to run to/from the reservoir and the supercharger, the special Rotrex oil (which is very thin, low viscosity stuff), and a bypass valve (which we're venting to atmosphere and is therefore functioning as a blow-off valve rather than a recirculating bypass valve). What the kit doesn't include are a programmable ECU, bigger fuel injectors, a bigger fuel pump, an intercooler setup or a serpentine belt since it's designed to be a custom installation, so we had to figure those parts of the puzzle out for ourselves.
Since the EG already had 550cc RC Engineering fuel injectors and a HondataKPro ECU, those two areas were already covered. The 195 LPH Walbro fuel pump in the car might have been a bit on the small side for the expected 400 or so ponies at the front wheels, so I ordered up a Walbro 255 LPH pump from my friend Chris at Stage Four Motorsports. The only major piece of the puzzle remaining was the front mount intercooler setup. For that I busted out the Vibrant Performance catalog and ordered the afore mentioned air-to-air intercooler along with a bunch of 2.5'' diameter tubing in a variety of lengths and mandrel bent shapes, plus some silicone couplers, hose clamps and a velocity stack for the intake.
Bolting up the Rotrex using the high quality Kraftwerks bracket was a piece of cake, but from there things get a little more complicated since space is tight on the front end of an EG chassis and we needed to fit the front mount intercooler and Rotrex oil cooler while retaining the full width rad and engine oil cooler. Handling this brain-teaser of an install, including fabricating all the necessary brackets, intercooler charge pipes, and rad relocation was SG Motorsport, owned and operated by Sasha Anis, a highly respected race car driver and race car fabricator located in Brampton, Ontario. Sasha and his right-hand man Chris "Keezee" Budgell did all the heavy lifting on the install while I stood around cracking wise and taking pictures and video (ok, I helped make a bracket or two as well).
Once we finished installing the Rotrex and its oiling system and oil cooler (in the passenger side brake duct area), we could see the first major hurdle to overcome would be how to retain the full width radiator while leaving enough room for the intercooler tubing from the Rotrex to the front mount intercooler. We could have swapped in a half width rad, but having seen Loi from Sportscar Motion struggle with cooling when using a half width rad on his Kraftwerks supercharged K24 EG Civic race car, I was determined to keep a full width rad under the hood.
Having measured how far towards the driver's side we'd need to move the full-width Fluidyne radiator in order to give just enough room for the intercooler tubing, we notched the upper rad support and trimmed the back of the headlight housing (without damaging the headlight's ability to function). Then all we needed to do was fabricate some new upper and lower rad mounts and have Sasha weld the lower ones in place. Done and done!
With the radiator securely relocated, it was now time to mount the front mount intercooler so that Sasha could start to work his magic with all those mandrel bent tubes from Vibrant. Positioning the intercooler carefully for proper fitment with the front bumper cover, Sasha and Keezee fabbed up an upper bracket and two lower brackets that were welded to the intercooler such that it could be bolted to the chassis. Once that was taken care of, intercooler chargepipe fabrication could begin.
Because of the position the Rotrex supercharger must be mounted in to align with the crankshaft pulley, there's really only one way the chargepipe from the Rotrex to the intercooler can be routed. There's no space to go down and around the rad support structure like you'd normally see on a front mount setup since that's where the Rotrex lives, so instead we had to go through the rad opening (which necessitated the rad relocation process). On the upside, this does keep the length and volume of this side of the intercooler tubing short, which is a good thing for spool up.
On the driver's side the chargepipe could go around and up into the engine bay in a more traditional fashion, with the only tricky part being the step up from 2.5'' diameter tubing to 3'' diameter tubing as it approached the throttle body. For this we picked up a 3'' to 2.5'' reducer that Sasha welded in between the different diameter sections of the chargepipe, as you can see here.
Lots of small but important details had to be dealt with along the way, including trying to figure out how to mount the aluminum Intake Air Temp sensor bung to a stainless steel chargepipe. Since you can't weld aluminum to stainless, Sasha had the aluminum bung threaded and then welded a stainless nut with matching thread pitch to the chargepipe. This way the IAT bung can be threaded nicely into the nut, correctly positioning the sensor in the process. Sasha also welded a 1'' diameter tube to the chargepipe so that we could mount the bypass (blow-off) valve to it.
Using Vibrant silicone couplers and clamps to secure the chargepipes to the intercooler, supercharger and throttle body, the completed front mount setup looked totally at home on the front end of our little green EG! All that was required was a tiny bit of trimming of the C-West front bumper to clear the lower corners of the intercooler. After that the only thing left to do was fabricate the intake using a Vibrant velocity stack, K&N filter, and a fairly straight shot of tubing (supported via a bracket to an available threaded bolt hole on the block) and this sucker was ready to fire up!
Dan from U2Ndyno.com was kind enough to drop off his portable Dynapack hub dyno setup at SG so that Sasha could work his magic retuning the HondataKPro ECU. But first we siphoned all the 94-octane pump gas out of the tank and filled it with 110-octane Pro Race Fuels Mark II race gas for a little extra detonation protection. After that we bolted our trusty old EG up to the Dynapack and hit the ignition switch!
In his usual methodical fashion, Sasha inspected the base tune and slowly began to make adjusts to the air/fuel mixture as he added RPM and engine load. After about a half hour of tweaking the fuel maps he finally let it rip all the way to the 7600 RPM redline. As I mentioned earlier, Oscar Jr. and Tony from Kraftwerks had told us to expect about 400whp with the setup we'd be using, but to be honest I had set my expectations a littler lower than that, convincing myself I'd be happy with anything over 360whp. Well, on that first pull to redline the dyno graph showed 398 horsepower at the front wheels, a number that had Sasha and I high-fiving like a couple of hyped up high school football players.
According to Sasha the fuel and ignition mapping Kenneth "Turtle" Lau from Project Motoring had done when the K24 was normally aspirated turned out to be surprisingly close to what the Rotrex needed. That's because, as Oscar Sr. from Kraftwerks had told me, the cool-running Rotrex supercharger builds boost in such a linear fashion that it behaves very much like a normally aspirated engine in terms of the required fuel and ignition timing maps. Obviously Sasha had to throw some more fuel into the equation given the higher horsepower and torque output, but changes to the cam timing and ignition timing in the upper RPM range did not produce any meaningful gains. Instead, Sasha focused his attention on the area around the VTEC crossover point, where the first dyno graph showed a dip that he didn't like. By lowering VTEC engagement a few hundred RPM and adjusting ignition timing in that area the dip was eliminated and area-under-the-curve in the midrange improved.
Satisifed that the tune was safely optimized, we let the engine cool down and then did one last pull for glory. The final dyno graph speaks for itself, with a tasty 412 WHP and 283 WTQ being pumped out of an engine that made 240 WHP and 185 WTQ prior to the supercharger installation. That's a 72% increase in horsepower and should definitely allow our 2,050 lbs Civic to blow past Porsches and Corvettes up the back straight at Mosport International Raceway.
It is, however, worth mentioning that due to the linear progression of boost with a belt-driven centrifugal supercharger like the Rotrex there isn’t the same mid-range area-under-the-curve for horsepower or torque when comparing our graph to a turbocharged K24. For example, below is a graph for a K24 EG with a Full-Race GT35R turbo kit that I pulled off of K20a.org (thanks Steve Duncan, whoever you are!). As you can see, the torque curve flattens out at just over 300 WTQ starting at 5,000 RPM. On the Kraftwerks graph for our EG, torque climbs steadily all the way to redline (does not flatten out like the turbo does) but is "only" making about 230 WTQ at 5,000 RPM. So if you’re after big mid-range power delivery then a turbo setup will give you that, but be prepared to deal with the heat issue we’ve already mentioned as well as increased fuel consumption and higher engine loads when reaching full boost at lower engine speeds.
For a FWD Time Attack platform like our EG, I believe the linear power provided by the Kraftwerks kit will be the fast ticket, since it should make the car more drivable coming out of the corners. Instead of lighting up the front tires with the big mid-range torque surge of a turbocharged engine, the more progressive power delivery of the belt-driven Rotrex should mean we can get on the gas more aggressively without having to fight a ton of wheel spin. Of course we won’t know if this holds true until we do some track testing.