Many performance mods add weight to a car, so reducing their real world effectiveness by at least a little. A big exhaust, a supercharger or turbo – all make the car heavier than it was standard. (Of course there are a couple of mods that make the car a tiny bit lighter – eg porting a cylinder head or lightening a flywheel – and there are other modifications that make no difference at all to car weight – eg increasing turbo boost.) But in general, even changes like bigger wheels add mass.

Recently I had the opportunity of comparing the weight gains made to a naturally aspirated car that was firstly supercharged, and then the supercharger removed and the engine instead turbocharged. How much weight was gained by each approach? The car was my first series Toyota Prius.

The blower installation involved the fitment of:

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Drove a car the other day that’s a good example of a fundamentally excellent design ruined by some strange decisions. The car? A Mark II BA Falcon XR8 – that’s the one with the 6-speed trans.

So what is wrong with it? Well firstly – and probably most critically – the gearing is simply way too tall. The very sweet 260kW 5.4 litre DOHC-per-bank engine has peak torque (a massive 500 Nm!) up at 4250 rpm. That’s not a problem in itself, because the engine is also superbly mapped, being tractable and progressive at any rpm. However, with an engine like this, you can’t run ultra-tall gearing and expect a strong performer. Not unless you drive around always two or three gears lower than ideal.

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When Japanese import engines and gearboxes first started flooding into wreckers, I can remember writing cautionary tales spelling-out the fact that while the engines were incredibly cheap, by the time you got one installed in a car and had provided engine management, engine mounts, radiator modifications and sometimes a new tailshaft, the price may well had gone up three or even four times. These days, with many engines available with uncut looms and the factory ECU, you could probably reasonably budget on a doubling the in-car price.

And a similar price multiplication also occurs for individual engine parts.

Over the last few months I have fitted firstly a Japanese-import supercharger, and then latterly a Japanese-import turbo. Both were installed on a car that is normally naturally aspirated. And rather like the old days of buying cheap engines, I’ve found that the main cost of both the supercharger and turbo conversions hasn’t been the initial cost of the blower or turbo, but instead all that is required to accompany it.

The little supercharger cost me $250 from a wrecker, while the turbo was even cheaper. (All dollars are Australian.) Hell, that’s good value! In both cases, the devices were in excellent condition and compared with buying new, represented savings of hundreds and hundreds of dollars. In fact, you could get very excited walking out of the wrecker with one of these in hand….

But you really need to budget at least another $1000 to get either a supercharger or turbo into a car and working. And that’s doing as much work as possible in your own garage at home…

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The matching of a turbo to a particular application is something about which the ignorant knowledgably proclaim – and about which the experts are very cautious and tentative indeed.  In short, matching the compressor to the required airflow is difficult (what with the variations in air density caused by temperature changes and boost, and with the variation in engine air consumption caused by throttle position, variable valve timing and different engine speeds), and sizing a turbine to suit both the compressor and available exhaust gas flows is something that can send you around in over-decreasing circles of frustrated indecision.

So when confronting a unique turbo situation, one of the best ways is to take the lead from OE manufacturers. In short, they’ve done the hundreds of hours on the engine dyno and road (chassis dynos are rarely used in new car R&D labs, except for emissions testing) that result in a turbo that has minimal lag, flows enough air, has low exhaust backpressure, and is durable in the application. If you’re dealing with modified road car engines developing sane power levels, the role models are the single and twin turbo production engines of the world. Sure, you can run a different turbo arrangement (for example, one huge turbo instead of two smaller ones), but usually that will involve a drawback that a car manufacturer wasn’t prepared to embrace. (Terrible lag from the single turbo versus the twin – especially sequential – turbos, for example.)

All these thoughts have been running through my mind. You see, today Michael Knowling and I were prowling the wreckers of Adelaide looking for a turbo to suit my Toyota Prius. Adelaide is the cheapest city in Australia that I’ve found for bits, and furthermore, the available range is second to none. And the Prius? As regular readers will know, the small supercharger that I had fitted to the hybrid petrol/electric car worked superbly in every respect – except for noise. If you wanted a small police siren hard at work under the bonnet, it was good. But if you wanted a quiet, effortless power – well, it wasn’t. So despite the massive amount of work that fitting the supercharger had involved, it was time to move to the other forced aspiration option. A turbo.

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Every now and again we get to drive cars where for a variety of reasons, it’s not worth writing a full test. Over the last few months three such cars have been sampled.

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I made the decision at 4 am. Or perhaps a little after, in fact. Lying awake in bed I realised – with the startling clarity than only predawn ratiocination can bring – the project on which I had been spending every free hour for more than four weeks was a disaster. Well, not a disaster, but it didn’t meet the criteria that I had (retrospectively!) laid out for it.

So rather than going on, it was better to stop.

It was ironic. Every single aspect that I had expected to cause problems was working superbly. The belt tensioner, the blower mount (which had also become the new right-hand engine mount), the intercooling and the engine management. Even the hybrid control system had coped with the increased engine output like it was, well, made for it. There was no detonation and the standard injectors had enough capacity to flow the required extra fuel.

In short, the positive displacement supercharger that I’d fitted to my ’99 Toyota Prius – making it the world’s first supercharged, intercooled, petrol/electric car – worked brilliantly.

Except for one aspect.

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I bought a metalworking lathe the other day. It’s something that I’ve wanted for years, but now the purchase has occurred, I am filled with trepidation. Why? Because I know nothing about metal turning.

I first decided that I really needed a lathe when a few years ago I was building a small wind generator. The design was based around a stepper motor salvaged – I think – from a printer. The impeller comprised the blades taken from a plastic fan. But when I came to match the two up, the shaft of the stepper motor was much smaller than the hole in the mounting hub of the fan blades. Easy solution? Well, there would have been if I’d had a lathe: just turn-up a bush with the right internal and external diameters. But without the lathe, I was forced to scrounge for tubing that had just the right wall thickness. In the end, all I could find was the plastic barrel from an ink pen – hardly a good choice for long-term strength.

Then, when I was building my electric bike (series starts at Building an Electric Bike, Part 1 ), I needed a lathe like no other tool. I was making an assembly that would couple the electric motor’s shaft to a roller that would bear on the tyre, so transmitting the torque. I kind-of had the shaft, but the roller part had to be a larger diameter. I stuffed around drilling-out old sockets and the like until I had something that could be force-fitted over the shaft. Of course, the thing turned out eccentric, and so ran with a wobble that in fairly short order destroyed the bearings. I ended up paying money to small machine shop that turned-up a beautiful, knurled roller/shaft assembly. The skills to machine that (and to silver-solder on a splined section of the original shaft) were beyond any beginner, but still, if I’d had a lathe, I would have been ahead from the beginning of the project.

And then there was the fitting of a supercharger to my Toyota Prius. For that project a lathe would have been more than handy at least a number of times. Firstly, part of the bracket had to stand proud of the surface to which it was being bolted. Needed was a bush of exactly the right length and internal diameter – length, so the plate sat flat; and ID, so the bolt passing through it was subjected only to shearing forces and not bending. (The bush would be welded to the plate.) But without a lathe, I was reduced to grinding-down an oversize and over-length bush that I found. Secondly, while I was lucky and the original supercharger pulley turned out to give the desired boost, during most of the development it was odds-on that a new 3-rib supercharger pulley would be needed – another use of the lathe.

The lathe which I didn’t have.

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In many parts of the world, the requirement to pass annual or random emissions tests is taken for granted. But here in Australia , while there has been talk about roadside sniffers and the like, unless you are a company selling a bolt-on upgrade package or you otherwise wish to stick very closely to the letter of the law, you can ignore emissions performance.

And so nearly everyone with a modified car does just that.

For example, none of my modified cars has ever been formally emissions tested – a full test cycle costs thousands of dollars and is simply not a requirement of a normal individual enthusiast. (There are some exceptions to this – say a major engine transplant, or other mods requiring engineer approval for registration.)

That’s not to say that I consider emissions performance irrelevant – not at all. At AutoSpeed we’re one of the few publications that’s actually had a good look at emissions testing procedures (see our Dirty Stuff series starting at Dirty Stuff – Part 1 and Emissions Testing ). And personally I think those people who punch a hole through their cat converters are environmental vandals. But at the same time, I’ve never felt the need to check that my own cars meet emissions.

So when yesterday I found myself subjected to a Queensland Government Transport Onroad Vehicle Emissions Random Testing inspection, I was a bit taken aback. Especially given the car I was driving…

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A while ago we covered the costs and benefits of buying a half-cut versus just a bare engine, loom and ECU (see Buying a Half-Cut). In short, the positives of a half-cut are huge – sure, you pay more, but you get the gearbox, front suspension, gearbox, dashboard, ECUs and so on. But as I said in that article, man-handling a half-cut around is a much bigger ask than doing the same for just an engine. In a front-wheel drive, a half-cut may well weigh 60 per cent of the mass of the entire car – so even with what today is a fairly small car, three-quarters of a tonne.

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