Power tech: superchargers versus cams

Posted in Tech
From stock to wild, we follow one car’s transformation

When it comes time to step up the performance of your late-model V8 engine, there are a lot of options — from exhaust systems and cams, through to stroker kits and nitrous. With all of these options, it can be hard to choose the path that will give you the results you want. The owner of this late-model VE Commodore wasn’t sure what to do with his car, but he knew he needed more power. 

Being a bit of a perfectionist, though, he did know what he wanted out of his car. Lots of power and throttle response, without sacrificing drivability or fuel economy. Sounds too good to be true right? Well, he tried a few different options before settling on his current spec list. It isn’t too often that you get to see such a wide range of upgrades compared on the same car, so we’re going to have a look at the journey and see what was settled on and why.

The baseline

This 2007 VE SS sedan rolled off the production line with a decent 270kW and 530Nm of torque. More importantly, it was also fitted with GM’s popular L98 all-alloy six-litre V8 engine. With the L98 coming from the LS engine family, the options for upgrades are literally endless. The hard part is choosing which direction to take.

Getting your feet wet

One of the biggest disappointments with these cars is the lack of any real exhaust note to indicate you’re driving a V8. About the only time you get a gentle reminder of the powerplant is when it comes time to fill up at the gas station, so a starting point was to address this.
A set of stainless tubular headers, coupled to a full 2.5-inch cat-back system was enough to let out that distinctive V8 rumble, while freeing up a few kilowatts at the same time. At this level of modification, the exhaust really doesn’t do too much for performance, though. But, as the mods stack up, a decent free-flowing exhaust is an essential item, so this mod gave the right sound while setting things up for the rest of the plan.

The next modification dealt with the restrictive factory airbox, thanks to a new over-the-radiator cold air intake fitment. These intakes are one of the best bang-for-your-buck mods on a late-model Holden or HSV, and can free up 20kW-plus. To make the most of the new hardware, the factory ECU was re-flashed to address the tuning. This optimized the fuel and ignition tables to suit the improved airflow through the engine.

The result at this stage was an increase in power and torque to 324.6kW and 623.6Nm. The car now made the right sounds, and as a pleasant addition, fuel economy was now improved by around 8–10 per cent. The improved economy comes as a result of removing restrictions from both the intake and exhaust. Basically the engine doesn’t need to work as hard now to make power.

Upping the ante

This level of modification was enough to whet the owner’s appetite, and it wasn’t long before he was back and asking for more power. His last modifications were near the limit of what could be achieved with simple bolt-on parts, so the next step required a little more commitment. Having discussed the options and having given him a drive of our own 422kW-cammed VE Commodore, he ticked the box for a cam upgrade.

Now, before going further it pays to explain just what you are getting if you decide to swap cams in an engine. The camshaft controls the opening and closing of the valves, and can have a massive influence over the torque and power production. Changing the cam specs can affect where the engine makes power, and how much. The important part, though, is that to gain high-rpm power, you will usually lose some low-rpm torque. Increased fuel consumption and some loss of drivability at a low-rpm cruise are also side effects.

In this case, more power was wanted, but not at the expense of totally destroying fuel economy, so the cam we went with was a middle-of-the-road cam from Kelford’s catalogue. It offered a good increase in mid-to-high-rpm torque and power without totally destroying the low-rpm torque. To match the cam, we also fitted stronger valve springs and a stronger double-row timing chain to keep everything under control.

Tuning the new cam requires the factory airflow meter to be removed, and the factory ECU to be re-flashed to run in speed-density mode, relying on the input of the manifold pressure sensor. This eliminates tuning issues that can be seen at idle with large cams, and gives superior drivability.

On the dyno the car responded exactly as planned, offering up a huge increase in both power and torque with the final numbers coming in at 393.8kW and 683.3Nm. The selection of a mild cam had given a good all-round result without significantly affecting the drivability. 
Fuel consumption had taken a hit, but it was still liveable, given the huge hike in power. With the new valve springs and double-row timing chain we could also extend the rev limit out to 6500rpm to make better use of the power band.

These mods once again kept the owner happy for a while, but before long, the itch was back and he was looking at his options once again.

Forcing the issue

At this point, increasing power via natural aspiration was going to be expensive. Without affecting drivability, the options really were limited to a stroker kit to increase engine capacity. However, while this was a great option, it wasn’t going to be enough to meet the owner's aims. Forced induction was the only other angle that made sense.

Superchargers and V8 engines tend to go hand in hand. They have a long history together and are a match made in heaven. Despite this, a lot of the older supercharger kits left us unimpressed, as they used old technology that was terribly inefficient. The other issue was that packaging a decent intercooler into the valley along with the supercharger was difficult. The result was a lot of hot air and only a modest increase in power.

Fortunately, some of the modern supercharger offerings have addressed these issues and produce some impressive results. For this car, we went with Harrop’s newest HTV2300 Black Series kit. This kit uses a high-flow Eaton positive displacement supercharger to give instant response and high efficiency. To keep the intake air cooled, a water-to-air intercooler is included in the manifold. This is an essential element for power and reliability, particularly given the high compression ratio of the stock engine.

Fitting the supercharger isn’t difficult, however, it does take a little time and requires some care. While we were at it, the factory fuel pump and injectors were both replaced with larger items to cope with the expected power from the supercharger.

The last part of the puzzle before the car was ready for the dyno was swapping back to the factory cam. This might sound like a step backwards, but while the mild cam was great for a naturally aspirated engine, it just wasn’t going to work for a supercharger. The extra overlap would have the boosted air blow straight out the exhaust valves, destroying both power and fuel economy. 

Back on the dyno, and the supercharger instantly showed who was boss. With around 8psi of positive pressure right from idle, the engine response was incredible and the throttle response was instantaneous. Boost rose to a peak of 12psi by 6500rpm, offering up a massive 471kW and 902Nm of torque. Tuned properly, this combination has proven to be perfectly reliable on a stock LS V8 engine, although going any further would require some internal upgrades.

Weighing up your options

There’s no right or wrong answer when you’re deciding which path to take with your own modifications. Everyone has a goal in mind and everybody has a budget too. These three upgrade packages span the range of both power and cost, but give you some idea of what you can expect from each option.

The basic bolt-on package is great value for money, and it isn’t going to break the bank. There’s an improvement in power and torque right throughout the rev range, plus fuel economy is improved. This is how these cars should have left the factory — there really are no downsides! A cammed V8 is always something a little special. There is no mistaking that aggressive lumpy idle, and the power and throttle response has a crispness that tends to get lost when you move to forced induction. For some, staying naturally aspirated and making huge power is a preference. The downside with a serious cam is poor low-rpm drivability and an increase in fuel consumption.

On the other hand, drivability and fuel economy are really where the supercharger wins. On the road at normal highway speeds, the supercharged engine will produce very similar fuel economy to factory. The car also drives just like factory, with none of the bucking or pushing associated with a big cam. Crack the throttle though and you instantly know where your money went, as both rear tyres try in vein to transmit 471kW to the blacktop.

A lot of your choice will come down to how deep your pockets are, although hopefully this car's journey and the accompanying dyno sheets will help others make up their mind without going to the trouble of trying all three upgrades for themselves.