A supercharger conversion has given Jason Marsden’s Jeep Wrangler a new lease on life.
Not even overly generous motoring journalists would have described the 3.8 litre V6 engine of the Jeep JK Wrangler as adequate. The American minivan motor was no doubt chosen as a known and reliable runner. Slightly more fuel efficient than the revered 4.0 litre straight six found in earlier Wranglers, the motor soon displayed a lack of highway power as JK owners started bolting on bigger steel wheels, bars, winches and all the rest of the tens of thousands of upgrade parts available for the platform. The latest Pentastar 3.6 engine released in 2011 combined more power with better fuel economy, but for owners of the previous model who had invested heavily in upgrades the prospect of starting from scratch again may be daunting from both a cost and time/ effort perspective. Small and sometimes debatable power gains were to be had from tuners using headers, exhaust and throttle body spacers. However, for 3.8 owners the only option to gain real additional power was a V8 engine swap or forced induction.
A V8 engine swap was my first choice for my 2009 four-door JK Wrangler. Unfortunately the bolt on Hemi kits (complete with ECU to maintain CAN bus and dash functionality) were only available for left hand drive Jeeps. Working some numbers it also looked like such an exercise could potentially be very expensive. Other V8 options such as LS (Chev) engines were also considered but the complexity of a non-standard install and loss of dash functionality soon relegated them to the too hard basket. This just left forced induction. The primary process of using forced induction to get more power out of an engine is to cram more air and fuel into it. The more fuel and air in a cylinder then the more work it can do. Specialist 4WD mechanic, Rick Crosbie, of Summit 4WD in Christchurch had done some preliminary work on the V8 option and when that was abandoned he suggested a RIPP Supercharger kit. RIPP Superchargers is a Staten Island, New York-based designer and manufacturer of forced induction products for all Fiat Chrysler (Jeep, Dodge, Chrysler etc) vehicles. And as I discovered, there are several supercharger kits available for the JK along with turbo options also.
Not only that but superchargers are available in both centrifugal/dynamic and positive displacement types. The main difference between these two types is that the positive displacement type delivers constant pressure but is less efficient at high revs whereas a dynamic centrifugal blower delivers more boost as the revs climb and is more efficient at higher boost. And of course the main advantage of a crankshaftdriven supercharger over an exhaust gas-driven turbocharger is a lack of lag. Typically turbochargers suffer from lag and really only come into their own at high revs. The RIPP kit we settled on utilises a Vortech brand centrifugal compressor, driven off the serpentine belt which then passes the compressed air through an intercooler to bring the gas temperature down (increasing density) before entering the manifold. I jumped on the RIPP website and was immediately pleased to see “we fit RHD”. After surfing around various websites and forums I was satisfied that RIPP appeared to be one of the most popular and proactive manufacturers of superchargers for Jeeps. There are always going to be some negative comments for any product online but every negative comment on forums seemed to be immediately followed by a response from RIPP.
Satisfied that RIPP was the right company to go with I pushed the go button and the order was placed. The kit comes complete with all the necessary parts along with very detailed and comprehensive instructions. Parts not only include all the necessary supercharger and intercooler plumbing and brackets but new spark plugs, injectors, MAP sensor and Diablo tuner for installing the new engine map. An added advantage of the kit is that if need be it can be bypassed by just reinstalling the factory serpentine belt, effectively taking the supercharger out of the loop and the vehicle will still run? The instructions suggest the install will only take a day but with an aftermarket trans cooler (another JK must-have) already in front of the radiator the question was do we stack the intercooler on top or look to relocate the trans cooler. The final decision (due in large part to lack of obvious options) was to stack them. There was just enough space between the seven slot grille and radiator to allow this to happen.
Proof of the pudding
Never one to trust manufacturer’s claimed power gains we took the opportunity to conduct a dyno run before work commenced as a base line. With its wide wheel track the Jeep only just cleared the edges of the dyno roller pit and I had visions of it drifting sideways, hitting the edge and either jumping off the dyno or stripping the sidewall treads off my new Coopers. Fortunately the Jeep stayed straight and true for the run and two days later we were back at the dyno tuner’s repeating the exercise. The stock run produced peak power of 93.1kW and 797Nm of torque. With the supercharger installed peak power rose to 139.0kW and torque jumped to 1158Nm. That was an increase of 49
percent power and 45 percent torque! Behind the wheel the first thing you notice on start-up is the sound. Superchargers have a distinct whine/whistle. This disappears as revs climb but is certainly noticeable at idle, crawl and will gain the attention of those petrolheads who know their engine sounds. There is also a blow-off valve to release pressure when coming off heavy boost, noticeable on occasion but nowhere like the boy racer trumpets fitted to most Subaru WRXs.
Sense of urgency
The engine almost has an urgent feel to it now. In the past an increase in engine noise did not necessarily translate to a corresponding increase in forward movement, now the more noise means more acceleration and as the revs climb so does the boost. Up to about 3000rpm the intake is running at negative pressure as the engine sucks air in and the initial supercharger boost is just negating this until it hits positive pressure. The supercharger is rated to max boost of 11psi but in reality normal driving will deliver enough performance well below this and within the normal rev range. One additional project was the necessity to connect my Safari snorkel back up. The supercharger sits in some of the space taken by the factory airbox and if you are happy to run just an open pod filter then all good. Most of us of course rely on snorkels so it was off to see Corey Taylor at Da Vinci Steelworks to have a custom airbox made up to fit the very tight remaining space. Corey did a great job working around the various projections in the area to end up with a watertight aluminium box that even used the factory engine bay airbox mounts.
At 2.35 tonnes the Jeep is never going to be a race car but on the open road the extra power makes inclines and passing a breeze. Off-road the extra torque allows obstacles to be climbed at slower speed rather than having to rely on momentum and bouncing up and over. Fuel economy for constant speed driving seems to be about 2-3 litres/100km better but short trips with lots of starting and stopping or heavy acceleration will see you use correspondingly more fuel. One downside is slight surging when cruise control is engaged. If you are a long distance cruise control user then this may be annoying. In summary if you are looking for serious power gains from your 3.8 and are not prepared to take on the cost and challenges of a V8 swap then a supercharger is probably your best bet. You can expect to invest $12-13K in a RIPP supercharger and installation (there are cheaper kits out there) but this will still be significantly less than a V8 swap unless you are doing the work yourself. Big thanks to Rick Crosbie at Summit 4WD and Corey Taylor, owner of Da Vinci Steelworks.
The effort was worth it (see before and after lines).
Intercooler tucked in behind grille.
Only just fits on the dyno!
RIPPS kit parts laid out on workshop bench at Summit 4WD.
Engine bay shot before the supercharger was fitted.
Engine bay after install but no snorkel connection.
And the engine bay afterwards.
And complete with custom airbox for snorkel connection.