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Blowing Harder

Watching the step-by-step upgrade of a blown Holden V6.

by Julian Edgar

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This article was first published in 2002.
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With the price of the earliest supercharged V6 Holdens dropping rapidly, there's never been a better time to get behind the wheel of a factory blown car. And with the availability of a bolt-on supercharger upgrade kit from Yella Terra, even more performance is cost-effectively available. We decided to watch the step-by-step fitment of the kit, and then further refine the package with a real-time engine management dyno tune. The workshop was ChipTorque, in Queensland.

The Kit

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The kit costs AUD$1395, and can be fitted in about 2.5 - 3 hours. The most important part is a new snout for the supercharger, complete with a smaller diameter pulley. While in theory the original pulley can be removed and swapped for a new one, this is a messy and time-consuming process - the pulley is an interference fit and so needs the use of an oven, special puller, and so on. It's much easier to replace the whole front section of the supercharger, complete with the different-sized pulley.

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Also in the kit you'll find a tube of 'Three Bond' gasket sealant (silicone sealant modified to be safe with oxygen sensors) and 150ml of synthetic gear oil.

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The final component is a factory replacement supercharger gasket. Oh yes, and wrapped with the new snout is a larger diameter idler pulley - the original belt is retained.

Removing the Supercharger

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The very first step was to run the car up on the dyno, confirming that the engine was healthy and making the right starting-point power. Already fitted with extractors and a sports exhaust (ChipTorque recommend this prior to the fitting of the supercharger upgrade kit), the car in fact proved to be very strong, with a peak power of 130kW recorded at the wheels. Usually, the early supercharged V6 Holdens make about 116kW. (And 116kW makes sense - with the Dyno Dynamics 30 per cent losses, 116kW at the wheels equates to 165kW at the flywheel - exactly what the engine is rated at.) Anyway, this car was sure in fine health - perhaps the extractors and exhaust were making a really major difference.

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Always careful and exacting, mechanic John Nash started the process by making drawings of the paths that the serpentine drive belts on the front of the engine take. There's one belt to drive the accessories, and another to drive the supercharger. Those belts can go back on in all sorts of ways... best to make the drawings!

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The supercharger drive belt was then removed. This is straightforward as the tensioner pulley spring adjustment can be rotated (by means of a spanner), de-tensioning the belt and allowing it to be slipped off.

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A larger idler pulley is required if the original belt is to be used (which makes sense - it's cheaper than sourcing another belt and it means that new drivebelts can be bought from any Holden dealer.) The old idler was removed and replaced with the new upsized one - a simple bolt-on proposition.

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The fuel plumbing - which winds back and forth over the supercharger - was then detached and lifted aside as one piece, complete with injectors. (Note that the engine cover had already been removed to allow a tacho pick-up to be attached when the car was on the dyno.)

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The wiring plug connections to the throttle body were unplugged, and the several vacuum/pressure feed hoses pulled off their nipples. These hoses should be inspected carefully - with the high underbonnet temps, they have sometimes started to perish.

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The airflow meter, its duct and the throttle body brackets were then detached. Note that the throttle itself stays solidly bolted into place - just the cables and their brackets are removed.

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The bolts holding the supercharger in place were then undone, and - as simply as that - the supercharger could then be lifted from the engine.

On the Bench

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The Eaton blower should be inspected carefully for any signs of damage - you wouldn't expect any if the engine was running perfectly, but it's an opportunity that shouldn't be missed.

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A plug was then unscrewed and the oil drained into a container. This oil lubricates only the front timing gears - it's contained within the snout that will be swapped over, so must be drained first.

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The bolts that hold the snout of the supercharger in place were then 'cracked'. This is a two-person job - the bolts are quite tight. When working on the supercharger, the working area should be clean - you don't want any grit ending up in amongst the lobes...

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Bolts all undone, the snout could then be pulled straight off the front of the blower.

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With the front of the supercharger off, the straight-cut timing gears were revealed. Again it's wise to make a check of these for any signs of damage - eg chipped teeth or metal fragments in the oil residue.

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The gasket surface of the supercharger was then scraped to remove any traces of previous material...

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...and then the new sealant applied. This seal holds the timing gear lubricating oil inside - it doesn't have to withstand boost pressure.

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The new front assembly was then placed on the supercharger.

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John chose to coat the bolts with a 'removable' Loctite, ie the bolts will still be able to be undone with a spanner but won't shake loose of their own accord.

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With the bolts all tight, the new oil could be added. In this case a little oil had leaked from the kit's bottle and so John topped it up so that the full 150ml could be used.

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The gasket surface on the intake manifold was then scraped clean....

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...before the new gasket was positioned in place.

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The blower could then be replaced on the engine, with the process a reversal of the 'blower removal' steps.

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The final step was to plug in the new chip, provided with the kit.

Back on the Dyno

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No 'running in' time is needed, so the car could go straight onto the dyno to see what the improvement was. The result was a bit disappointing - the peak gain at the wheels was only 7kW - or 5 per cent. Boost had risen to 10 psi (factory spec is 7 psi but the guys at ChipTorque say that it's more realistically about 4-5 psi), but the power wasn't responding in kind. Or was it? In fact the 137kW now being seen at the wheels is what is normally seen after fitting the kit - but with a much lower starting point being the norm. Hmmmm.

However, a close inspection of the dyno graph shows that on-road performance of the car would be noticeably stronger - even with this relatively small peak gain. This is because the power improvement was over a very wide range of revs - up to about 5300 rpm, the power increase was constantly 7-10kW. However, at the top end the power improvement dived - by the redline it was just 2kW.

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While the kit is supplied with a ChipTorque-developed chip, better results always come from specific real-time tuning to optimise the fuel and ignition maps for the individual car. So it was decided that a custom tune would be undertaken on this car - a cost-effective extra AUD$125. But after an hour of work, it looked like the peak power was about the limit - Lachlan Riddel did temporarily improve this to 142kW, but only with accompanying knock retard figures that he deemed unacceptable. (Software was being used that allowed the accurate analysis of the amount of knock retard that the engine management ECU was providing. The higher this number, potentially the more susceptible this engine is on the road to suffering knock-induced damage. The knock sensors are a safety device... rather than a tuning device!)

So, even with the chip re-tune, peak power rose only one more kilowatt to 138kW. (Assuming the Dyno Dymanics '30 per cent rule', that would imply a flywheel power of around 195kW.)

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However, at the top end of the rev range, Lachlan was able to make the power improvement hang on much longer - keeping the gain over standard at 9-10kW right through the power band. Given that it is the average power lift across the engine's working range that will determine how improved the performance is (ie not just the difference in peak power), while the improvement in peak power is modest, the overall performance gain will still be quite marked.

This graph shows the as-driven-in power curve (green), the power after the supercharger upgrade kit and chip were fitted (blue), and after the custom re-tune (red). Note also the tractive effort curves - especially the gain provided by the blower mod (bottom end) and the custom re-tune (top end).


The Yella Terra supercharger kit looks beautifully made and is a straightforward swap (Chiptorque's fitting cost - AUD$220 - reflects this). The amount of performance gain that you get appears to depend a lot on the starting point - if it's already a strong car, then the gain may well be much less than if the car in standard form is putting out a more typical 116kW at the wheels.

But even with this car, given the way the improved grunt is right through the rev range, it's still a worthwhile upgrade. We'd be always plumping for the customised chip, though - too many hit-and-miss possible outcomes, otherwise...

The Supercharged V6

Introduced in September, 1996 for the VS Series II Caprice, Statesman and Calais, the supercharged 3.8 litre V6 then was (and remains) one of the cheapest blown cars available in Australia. At the time of writing, an early supercharged Calais will cost from around $15,000, with a Statesman about $1000 more.

The engine developed 165kW at 5200 rpm and a strong 370Nm of torque at 3200 rpm. In addition to the placing of the blower in the 'V' of the engine, a number of significant mechanical upgrades were also made.

  • The Blower

The blower was a Roots-type Eaton M90 unit. Unlike a conventional Roots blower, the Eaton unit used rotors which had a 60-degree helical twist. Three intermeshing epoxy-coated rotors were used with specially designed inlet and exhaust port geometry to give low pressure variations and a quiet operation.

The M90 designation refers to the 90 cubic inches (just under 1.5 litres) which is displaced each revolution. At the front of the supercharger the drive system comprises gears, bearings for the rotors, and the oiling system. The blower was driven from the crankshaft by its own belt at a ratio of 1.8:1, meaning that at maximum engine revs the blower was turning at 10,500 rpm. The blower was therefore passing nearly 550cfm at maximum speed.

Boost was 0.5 Bar (7 psi) and was controlled by an air bypass system, with the vacuum-operated bypass valve situated at the rear of the blower. When boost was not required, the air from the blower was returned to its inlet. The valve operated on air pressure signals from the inlet tract and supercharger outlet, with electronic over-ride from the Power Control Module also used.

  • The Engine

The comp ratio was reduced from 9.4 to 8.5:1 by enlarging the dish in the crown of the pistons. The piston crown and top ring area was hard anodised to increase strength and temperature resistance, with the second and third ring lands deepened to provide extra support for the compression rings. The piston pin diameter was also increased and the camshaft timing altered.

  • Engine Management

The injectors were moved from the intake manifold to the heads to allow more room for the blower. Upgraded ignition coils and high tension leads were used with platinum tipped plugs. An adaptive knock control system was implemented, using the two knock sensors standard on the VS V6. As a result normal ULP could be used in emergencies, with PULP the preferred fuel.

The fuel pump was upgraded from 1.5 litres/minute to 2.4 litres/minute, with delivery pressure rising from 350 kPa (51 psi) to 410 kpa (59 psi). Interestingly, a fuel pump speed controller was used so that fuel supply tracked demand, reducing the circulation of fuel and so keeping the fuel cooler.

  • Auto Trans

Upgrades to the standard 4160E tranny included a larger torque converter (258 versus 245mm) and recalibrated management software. A larger tranny cooler and associated plumbing was also used.

  • Exhaust and Intake

A twin exhaust was used with dual cat converters, while the intake was increased in size with a large damping volume built into the cowl to quieten the operation of the blower gear drive.

  • Performance and Economy

On Holden's figures the supercharged V6 Calais got to 100 km/h in 7.8 seconds, compared with 9.1 for the standard V6 and 7.7 for the V8. On the urban cycle the blown Calais used 13 litres/100 km, with 7.6 litres/100 km achieved on the highway cycle.

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