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Some of this week's Letters to AutoSpeed!

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Re New Car Tests

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I was reading Response this week and noted John Masson's feelings regarding the latest Subaru WRX STi (Response). It got me thinking about something I've been wondering for quite a while...

Going through the list of new car tests on AutoSpeed, it would seem that the frequency of new car tests where the car is provided by the manufacturer is diminishing. Please do not take this as criticism. The way I see it, because you guys write honest opinions - without sugar-coating anything – I would surmise that you guys are not that popular with the new car manufacturers any more.

This, as I'm sure many readers would agree, is highly distressing. If it's true, it is pretty unprofessional behaviour on the part of the manufacturers - not to mention that, by their own reluctance to loan AutoSpeed any cars, could be regarded as tacit admittance that their cars may be bad. Regardless, I'm glad to see that you guys haven't gone down the path of kowtowing to the manufacturers in order to get road tests. It's just sad to see manufacturers behave this way. I'm sure others would agree - I think it doesn't do them any favours.

Example - the Renault Megane 225. Many criticisms were made about this car's handling and other issues in the media. Shortly thereafter, the updated model released late in '05 had these issues addressed. If motoring journalists didn't provide valid criticisms of motor engineering, how are manufacturers supposed to receive feedback? The average customer test drive? Not much expertise there and the drive is far too short. Sales figures? Never a true indicator of automotive design. No, it's the humble motoring journalist with their honest opinions that can - and must - make the difference. So come on car manufacturers. Don't be chicken. Let AutoSpeed drive your cars.

Michael Adamantidis

Making Stuff

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Interesting reading your articles on making stuff - Making Things, Part 1 and Making Things, Part 2. I imagine a lot of readers are the 'DIY' or 'making' type of people - like you. If you haven't already, check out for a whole heap of DIY projects ranging from low-tech to high-tech and everything in between. It is now my second favourite website...

Ross Goddard

Re Dual Pipe Induction #1

Just read Dual Pipe Induction - Part One and Dual Pipe Induction - Part Two and I'm interested to find out where you obtained the calculation for the potential 200kW output requiring a cross sectional intake area of approximately 46cm2? How did this figure come about?

On another note, are you going to be road testing the RenaultSport Clio series (172/182/Cup) at all? Seeing the positive opinions from the UK car mags/shows, I just wanted to compare this with an unbiased Aussie perspective.

Andrew Hew

The 46cm2 figure is the same cross sectional area as a 3 inch pipe. Based on previous manometer testing, we’ve seen that a 3 inch feed pipe into a vehicle’s airbox causes almost zero restriction at outputs up to about 200kW. And, yes, we’ll try for a hot Renault to test!

Re Dual Pipe Induction #2

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I have a question about the following passage from your article Dual Pipe Induction - Part Two).

“With the Magnehelic gauge again hooked up to the intake we saw pre-airbox restriction slashed from 17 inches of water to just 4 inches of water. This represents a 52 percent drop in the overall intake restriction – we’re now down to 12 inches of water from 25 inches of water!”

Now, I currently run a pod filter on my S13 with SR20DET and am thinking of returning to a factory style airbox with a decent 'drop in' filter and a better feed pipe. The question I have is about the 4 inches of water figure - this is figure is PRE filter, yes? So I would lose some flow by going to an airbox over the 'direct to atmosphere' pod filter element (since I'm assuming zero pre-filter restriction due to there being nothing there). However, at my power level (170rwkW target) this might not be noticeable due to the engine not needing to suck a great volume of air. I'm also ignoring heat soak issue as my other option is to box the pod up - as I have planned to all along.

Jarich van Horck

Yes, the 4 inches of water measurement was taken upstream of the air filter. With an airbox, you will generally have more restriction than an exposed pod air filter – but, in your scenario, we doubt whether the difference in performance would be measurable. Oh, and be aware than enclosing a pod filter (to prevent ingestion of hot under-bonnet air) is effectively the same as having an airbox...

Re Dual Pipe Induction #3

I would like to congratulate you on your articles on the "Dual Pipe Induction" - (Dual Pipe Induction - Part One and Dual Pipe Induction - Part Two). The articles show that the mod I have done to my Holden Monaro will have produced similar benefits. Adding a second pipe from the cold air intake to the air box has seemed to provide a much more responsive engine and a slight but noticeable improvement in usable power.

David Carmody

Valve Search

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I’ve been reading an old article - (Shooting the Overboost) - about using a needle valve to control turbo boost. I am trying to get hold of one of these valves, but either no one has heard of them, or a minimum number have to be custom made by hydraulics companies. There are lots of bleed valves/ball bearing boost valves about but these aren't the same. Can you please advise where you got the one you used?

Christian Jull

An adjustable brass needle valve should be available from most pneumatics supply stores. You can also use a Festo 6509 GRA -¼-B flow control valve, as seen in Brilliant Boost and Bumped Up Boost

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