The 2.0-litre turbocharged 4G63 engine which powers the Evo IV to IX models of the Mitsubishi Lancer is something of a tuning legend. Responsive, strong and capable of being tuned to very high power outputs, it can be enlarged to 2.4-litres and deliver 1000bhp output, which means that few would dispute that 4G63 motor has stacks of performance potential.
But, as with all engine tuning, extracting that extra performance means eliminating the weak links in chain, which in the case of the Evo’s 4G63 engine are remarkably few. How else can roughly the same engine have been used in different power outputs ranging from 260bhp on the basic Evo 8 to 400bhp on the FQ-400? Even so, beyond a certain level of power output even the 4G63 engine’s components start to present performance limitations.
And one of these is the design of the standard Mitsubishi Evo intake plenum, as Torque Development’s Technical Director Sam Borgman explains, “The stock Evo intake has three main design shortcomings – a low volume plenum chamber which is borderline under size even on the standard car, as well as relatively long intake runners, plus some inherent flow problems.”
What’s wrong with the factory 4G63 intake set up?
Let’s deal with the plenum size issue first. When a tuner increases the power output of any engine – 4G63 included – the amount of air mass required by each cylinder during the induction stroke increases. If required air mass isn’t freely available in the main plenum then the inducting cylinder ‘steals’ as much air mass as it can from where ever it can be found, which tends to be neighbouring cylinder’s intake runner. Unfortunately this causes increased air velocities and turbulence inside the intake plenum, resulting in a far less efficient overall induction process.
Secondly, the long intake runners. Here’s where we get a little more technical, because the length of a plenum’s intake runners (allied to the duration of the inlet camshaft) dictates what’s known as the ‘harmonic length’ of the intake manifold, another term for it’s frequency characteristics. Long runners mean a low frequency intake manifold, which will promote maximum torque at low engine speeds, where as short runners produce a high frequency design better at high engine speeds. “In this case, the stock 4G63 intake manifold is designed to produce peak torque before 3500rpm meaning that past 4500rpm when the engine could really do with some support from the intake runner design, none is forth coming” Borgman explains. “This is especially counter productive when you’re building a higher revving engine with a turbocharger which is only really coming into play after 3800rpm for example.”
The third and probably least obvious drawback of the factory 4G63 inlet plenum is, as Sam Borgman describes it, “an inbuilt end to end flow bias, which means the air charge density varies across the cylinders.” The culprit here is the basic nature of the design of the stock Evo intake, which draws air straight through the throttle body into the small volume plenum, where it’s extracted in turn as each cylinder requires it. “This causes an imbalance of pressure from one end of the plenum to the other, and due to flow characteristics it’s the two cylinders nearest the throttle body which run at a lower air density than the two near than the cambelt end of the motor, this might not necessarily seem logical to the casual observer.” On a standard 4G63 engine the low cost, basic nature of the stock plenum design isn’t really a drawback, but when ultimate performance is the required this in-built bias becomes a major stumbling block.
Clearly then, if a very high output 4G63 engine is the goal, replacing the stock intake manifold sounds like a good idea, which probably explains why a quick Google search reveals a number of aftermarket performance Evo plenums are already available. “The problem with those is that they’re designed for 8 second drag race cars with a 1000bhp, so they have large runners, drain pipe style plenums and still use a design with an end to end bias,” Sam comments. Which means that no one had yet designed a really well thought through 4G63 intake plenum system that overcame all these issues and was suitable for the fast road / track day market. Until now, which is where Jenvey steps in.
The Jenvey Evo inlet plenum.
Even to the untrained eye, the Jenvey Evo plenum looks very, very different to the factory 4G63 intake. Sand cast from aluminium, the most obvious change is that designed in three main pieces – a plenum cover, the main plenum body and the intake manifold, which all bolt together.
Cleverly, the throttle body bolts onto the plenum cover, which feeds inlet air through a diffuser into the main plenum body. “This means it’s fed an evenly pressured curtain of air from the top of the intake evenly down its entire length of the plenum, with no end to end bias. There’s a much more even gas flow distribution – but it’s tricky to produce, because it’s hard to cast and it’s not cheap,” Borgman says.
This means that the air is being introduced in a very linear fashion without advantaging any one of the cylinders over the other, which gives a nicely balanced inlet feed and holds the potential to greatly increase performance.
As does the design of the Jenvey intake manifold, which bolts onto the bottom of the large volume plenum. “The intake runner length is approximately half the length of stock 4G63 item, which is better suited to high engine speeds, plus the runner’s ports are nicely profiled, they change from a round cross section at the bellmouth end to matching the profile and size of the inlet ports on the 4G63 head.” This design benefits gas flow and efficiency, as does the design of the ends of the intake runners where they enter into the body of the plenum chamber on the Jenvey unit. “On the stock Evo plenum the ends of the runners are sharp,” says Sam Borgman, “whereas the Jenvey plenum uses individual, radiussed bellmouths to channel the air into each cylinder, which makes it very, very efficient.”
It also offers flexibility when it comes to fuelling requirements. Throttle body wise it can accommodate single units of 70mm or larger, or alternatively, individual throttle bodies for each cylinder. The inlet manifold offers a choice of two fuel injector mounting positions, either very close to the cylinder head spraying directly onto the inlet valves (which provides more stable low speed running and emissions control,) or 75mm further back up the intake runners, which improves fuelling characteristics at higher engine speeds. Or, there’s the possibility of mounting eight injectors in one go, four smaller items for low speed and four larger ones for top end power and the ultimate in all round efficiency.
It sounds great in theory, but what’s the Jenvey Evo plenum like in practice? These neat touches mean that it’s obviously a clever design, but unlike the one piece cast stock Mitsubishi Evo inlet plenum, the bolt together Jenvey unit requires careful hand assembly and surface preparation, plus it lacks take offs for the brake servo and other sensors.
The main components are held together using 6mm cap head bolts and the key surfaces feature machined grooves which run ‘O’ ring rubber seals to ensure that the package remains air tight. Meanwhile, as Sam Borgman says “Thread lock and Pipe sealant are a must on the bolts to ensure that they stay air tight and torqued,” as the consequences of ingesting a loose fitting would be costly to say the least.
That’s particularly true on Torque Development’s chosen candidate Evo IX FQ-320, which runs a superbly specified MIVEC 4G63 engine and is the ideal test bed to see how well the Jenvey performed. Indeed, with a Cosworth 2.2-litre stroker steel crank, Cosworth rods and pistons and a Cosworth gasflowed head, it’s a great specification, particularly as it also boasts an FQ-400 turbocharger, HKS F-Con V Pro engine management and HKS 1000cc injectors and high flow fuel rail. In this specification, at 1.85 bar of boost it produced a very healthy 403bhp at 6500rpm at the hubs on TDi’s Rototest chassis dynomometer, allied to 370lb.ft of torque at 4790rpm. Post Jenvey install, we’re hoping to beat that, without having to run more boost, with the goal of a 7250rpm being the usual gearchange speed, with an 8000rpm rev limit. Currently, with the stock inlet, the power ‘plateaus’ from 6500-7500rpm.
Given these requirements, TDi opted for a 62mm single Jenvey throttle body, with Jenvey’s own throttle linkage. “It has a nice geometry, so it gives it an excellent ratio of opening acceleration compared to the pedal input, so giving a nice linear response. We also binned the stock Mitsubishi throttle position sensor (TPS) and used a hall effect pick up with its own microprocessor and trigger wheel instead,” Borgman explains. The advantage of doing this is that the TPS operation isn’t reliant on physical contact, so the output is consistent, free of ‘noise,’ very durable and repeatable. At £100.00 plays £30.00 for the standard item it’s not cheap, but if you want the ultimate in throttle position measurement, this is it.
Fuel wise, the Jenvey plenum is supplied with its own fuel rail, but TDi opted to carry over this Evo’s existing HKS large volume fuel rail, which required special aluminium adaptor spacers to be machined by TDi, while the 1000CC HKS injectors were reused and mounted in the ‘high’ position on the Jenvey intake manifold.
Further machining was required on the plenum body to enable the fitting of the brake servo vacuum feed, fuel pressure regulator take off and boost feeds, as well as a MAP sensor location. One item that isn’t catered for is the stock 4G63 air idle valve, which bolts onto a machined boss on the original plenum, so idle control has to be achieved by different means with the Jenvey intake – more on that later.
And so with the hard machining complete, the fully assembled Jenvey Evo plenum bolts straight onto the 4G63 cylinder head. “The locations are very good and we haven’t even needed to alter the original intercooler pipework,” says Sam Borgman, “other than a few minor tweaks.”
Fully fitted the next task was to attend to the mapping requirements of the new plenum and high on the list was idle control, which given the lack of air idle valve, will present a big issue on Evo’s which don’t run highly capable engine management systems. Fortunately this Evo IX was already running an HKS V Pro ECU, which offers users the facility to control idle via ignition timing – advancing the ignition timing increases the idle speed, while retarding it reduces it, all in a fraction of a second. A combination of the throttle stop and ignition timing work very effectively to control idle, so now the Evo ticksover at 1100rpm when cold and 950rpm when warm, but that said, Sam Borgman would like to see an idle control valve facility on the Jenvey plenum. “It’s a good way to control idle and also you can exploit the air idle valve to deploy a mild anti-lag strategy, but that’s not possible in this case.”
With the idle characteristics perfected, initial dyno running and mapping began, but this highlighted a new problem with the Evo, caused by the efficiency of the Jenvey inlet. “Very quickly we picked up that exhaust back pressure in front of the catalyst had increased from 0.08 bar to 0.6 bar, which was restricting power,” Borgman says. In effect, now the Jenvey inlet had ‘derestricted’ the intake side of the Evo IX’s 4G63 motor, the shortcomings on the exhaust side of the car where now making their presence felt. The solution was to remove the sports catalyst and fit a 3 inch cat bypass pipe as an interim measure, while a larger volume twin catalytic converter design is envisaged as a longer term MOT friendly solution.
That done, then the mapping started going places and with boost pressure set at the same 1.85 bar for power runs as before, the Evo IX cranked out a mighty 460bhp at the hubs on TDi’s dyno, allied to 399lb.ft of torque. That’s a healthy 57bhp gain at the hubs, achieved at 7500rpm, with the engine still producing over 450bhp at 8000rpm. Moreover, there are significant power gains from 4250rpm right to the rev limit, which is a seriously impressive result, as the Jenvey Evo plenum has enabled this highly tuned Evo to be both devastingly powerful and driveable.
TDi’s Sam Borgman for one, is impressed. “It’s a fantastic product and if you’re this side of 600bhp it’s the only piece of kit for the job. This particular combination works together beautifully as a fast road / trackday car as it pulls from nothing in sixth gear.”
But what does it cost? Approximately £900.00 plus VAT for the Jenvey plenum, a full day’s fitting and half a day’s mapping. Plus, you’ll need an ECU with idle control capability, so it’s not going to be on everyone’s shopping list. But as Torque Development’s has demonstrated, if you want the ultimate in driveable high power 4G63 performance, then make no mistake, the new Jenvey Evo inlet manifold really delivers.
