Some of this week's Letters to the Editor!

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I was wondering if you were going to continue with the technical articles on aerodynamics, in particular under-car aerodynamics. I have been searching in vane for information on diffuser design principles on the web, there doesn't seem to be much written about it, on the internet at least. I have seen pictures of the underside of the Lotus Elise and R34 GTR, but no technical details (like size and shape of the diffuser, ground clearance etc) were to be found.

The reason I am interested is because of a project of my own, a Datsun 1600. I realise that they are certainly not the most aerodynamic car in the world, but I am still considering some minor aerodynamic aids to make things a little better than stock. After seeing a certain yellow 1600 at a track day at Oran Park, I decided a rear wing was not the way to go for my car. The yellow 1600 has a narrowed Group A V8 wing suspended on aluminium posts at least a foot off the bootlid; I was hoping for a more sedate look to my car than this.

Obviously to catch some smooth airflow at the rear of a 1600 is not an easy task. Looking under my 1600 I realised that the floor is pretty flat, the spare wheel well pretty flat, rear suspension not too untidy. I thought maybe some flat carbon fibre sheets positioned to smooth the airflow in this area, and direct the airflow into a larger area under the boot could act as a diffuser, but as I said before I haven't been able to find any tech info to help me in the design. Obviously a lot of other things need to be considered like how much air is coming in under the front of the car, perhaps here I need an air dam, flat tray section etc etc. Or perhaps I am wasting my time and should start with something more aerodynamic to begin with.

I thought you might be able to point me in the right direction for information.

Your article on the ion propulsion system used on NASA's Deep Space One was very good; I had read a few things about it on the official website but you managed to find a lot of very good information (and it was a great story).

Phillip Spencer

The book 'Racecar Aerodynamics - Designing for Speed' by Joseph Katz is a good place to gain relevant material on diffusers. However, to be honest we'd just start experimenting, using thin sheets of plywood that are easy to bend into curves.

If Only...

The RX 2.5 Turbo ["RX With Extra"] looks promising, if only he had have gone to AVO in Melbourne, they do a complete bolt in kit for the RX2.5 that is AWESOME in comparison to the back yard effort shown here.

Karl Jensen

Six-Speed Swap

In the table of gearbox conversions at the end of the gearbox swap story ["Gearbox Swapping"], I noticed that the kit for the Nissan RB sixes to Toyota Supra 5-speed is mentioned twice. Should one of these have been a Supra 6-speed, or was it a misprint (ie, should I give up the idea of converting my R31 Series 3 Skyline to 6-speed)?

Why I ask this is because I always tend to keep going for a sixth gear, and (of course) it's never there. If I had a sixth gear I could get better economy on the highway, and still keep a diff ratio that makes it fairly quick at the lights. As it is, I've changed this to be the Holden VL 6's ratio of 3.45:1 (in a not-so-successful attempt to get rid of the diff noise) instead of the Nissan manual 6's ratio of 3.70:1, or the Nissan auto 6's ratio of 3.89:1, so I don't want to change the diff again to give me even better economy, because then it will be too sluggish at the lights.

Danny Barrett

That particular entry is a misprint, but we've heard of a 6-speed (other than the late factory GT-R gearbox) being put behind an early RB-series engine, so it is possible...

Holden V8 Fuel Economy

Just read your comments on the fuel economy of the HSVs you've tested recently and am writing to tell you what I've experienced with my Gen III over the last 6 months and 36,000km. My car is an ex New South Wales police highway patrol VX SS which has the 255kW engine (I believe this is only a dual cat exhaust with a matching chip). Bought it with about 54,000 on the clock and it was obviously very well used as a country patrol car around Singleton as little telltales like fractured front disks (only ever seen fracturing like this on Kenworth drums and the GIO Group A Godzilla ) and both the gearbox and diff needing to be replaced under warranty.

That's all beside the point. I have driven this car as a courier vehicle (recently changed careers) in and around Sydney over the last 6 months and can honestly say it isn't much worse on fuel than previous cars (a VR V6 and Lancer GSR on 18 psi). I regularly get 13 to 14 litres per 100 km in stop-start Sydney (with an auto g/box and the AC on all the time) and as low as 8 per 100km on cruise control down the F5 to Goulburn. It does tend to drain the tank a bit faster than the VR but I put this down purely to the VX having virtually double the power and me using all of it on a regular basis (amazing how hard you'll push when it's your job... plus there's a lot of red lights in Sydney.. all in good fun).

The VR (which I used for work for 3 years and 180,000 km without ever leaving Sydney) wasn't too bad economy wise but when the $1 per litre fuel scare hit I put an ex factory LPG system in it to perhaps save some money. It wasn't really worth the effort, seemed fine while LPG was 30% the price of petrol but as it rose to 40% or more it was just the same cost as running unleaded as performance was way down on gas, (hyper sensitive to plug gap, only stayed in tune for about 2 weeks, then started guzzling the fuel and backfiring - was a joke most of the time). Litres per 100 went way up when it was out of tune and LPG is so agricultural I'd never bother with it again. Even the factory system doesn't really have a lean cruise cycle as there just isn't enough control for the computer to lean it out that much.

I also used the '93 Lancer GSR for work for 3 years and over 200,000 km and wasn't blown away with its economy as it required PULP all the time (I haven't even tried PULP in the Gen III yet, perhaps if I find something that blows me away one day I might be spurred on a bit) and to be honest used about the same litres per 100 km as the Gen III while being driven in the same manner (i.e. an average day was about 350km within Sydney in an 8/10 hour period with at least half the day involving sprinting while the other half you'd drive on the torque curve to get more mileage out of your tank of fuel.... as a sub contract courier, the fuel bill was mine and we're talking about 50 litres per day with either car). The only mods to the GSR (it was leased and insurance was already ridiculous without wild mods) were adjustable boost set at 18 psi, a water spray on the intercooler, 4-inch cold air duct, boost gauge, EGT gauge, a relay to turn off the AC clutch at high vacuum to help it spool up faster and save a little fuel, and an extended gear lever to make the gate of the H pattern less than half that of standard as with a close ratio box, 5:1 diffs and a peaky motor, gear changes were virtually constant and the cable selectors were pretty hard on 2nd and 3rd gears.

Most people I know are surprised to hear me say how converted I am now that I have the VX. I never wanted to sell the GSR but as it hit 380,000km I finally realized it was probably past double its designed use-by-date (Japanese cars get expensive to own at about 150,000km) and it had to go. But the Gen III wins hands-down in every area bar traction. The NSW cops, (in their wisdom???) delete traction control from their 255 kW SS's; beats me but it'd be nice to have in the rain at times when you're in a hurry.

One last comment. It was a Lancer that sold me on the Gen III. A friend brought around one of those press loan cars Evo 6.5s about 2 weeks after I'd taken an ex-porker for a test drive from a dealers yard. I didn't have much to measure the Gen III against at the time as I'd been stuck in a VR V6 for 3 years and the fastest car anyone I knew had was a 195kW VS ute. I was sure the Gen III was way faster than the VS and had often given my GSR a run for its money and in fact my first impression was the VX was over-kill as a road car, you just didn't dare touch the throttle to stay at the speed limit. But then I took the Evo 6.5 for a 30 minute blast and even though the clutch fried itself on my 1st 5000 dump and I never had a chance to test out the rear diff, driving a Lancer instantly came back to me and I almost immediately thought "bet a Gen III would be almost as quick in a straight line as this", but only cost less than half the price, actually be affordable to insure and you'd have a chance of parking it somewhere and not having someone trying to rip it off.

Great mag BTW.

Paul Evans

More on HSV Fuel Economy

I don't suppose you would like to be as passionate and expressive about the copious amounts fuel consumed by any large (full size) 4WD on the market, would you? For a small country we produce high quality cars to supply a niche market, I worked in an HSV dealership for about two years in your home town, I've seen the smiles, the pride and the sheer satisfaction that people have owning these "petrol guzzlers" that you slay. Keep up the concept, but don't lose sight of the goal.


The goal isn't to use as much petrol as possible...

Washing Cars

Congrats for a great mag. I think it is the basic honesty and lack of bullshit that is appealing. I really like the human interest story recently (you washing cars) ["The Plastic Penis"] - more of this on an occasional basis would be great. My suggestion - the cash-flow of running on online publication, where does the income come from, what proportions, what outgoings...just general roundup of these topics and the gotchas you have come across. No I'm not setting up an online anything although I am a software engineer that knows very little of the business side of online technology. Just my 2 cents worth, hope you aren't washing too many cars these days.

Mick Williams

Thanks for your positives. We'll consider doing a more detailed story on the running of AutoSpeed some time in the future.

CD-ROM of Articles?

I placed my first [shop] order with you earlier this year. I found your staff to be very helpful and my order was processed promptly and accurately. Since I am in the USA, I expected a significant delay in receiving my parts. I was pleasantly surprised to have such a rapid turnaround time and my order was fulfilled with no mistakes (seems like a rarity these days).

Upon processing my order, your company granted me a 6 month free subscription to the online magazine. I have been viewing it every other week and I have found AutoSpeed to be a great information resource and a genuinely interesting site. My problem is that there are too many intriguing articles! I catch myself reading one and then linking into another one and so on and so forth. Before I know it, I've spent an hour and a half indulging myself.

I can honestly say that I find AutoSpeed more interesting than the other magazines to which I have subscribed and I feel that an annual subscription on the order of $25US is very reasonable. At then end of my gracious trial period I know I want to continue on with the magazine.

As you are formulating the changes at AutoSpeed - I think it would be nice to be able to obtain a CD-ROM with a compilation of all the articles (annually) available through AutoSpeed. I would like to start a collection.

Thanks for the service!

Mark Bergee

Changing Emissions Legislation?

As you are probably aware, there are quite a few people building kit cars around Australia, most notably the Lotus 7 clone.

Given that we are all using imported engines (mine an SR-20 DET ), which the authorities seem to frown on, would it be possible to do an article on the new ADRs relating to emissions which come into force on January 1, 2003, and also to comment on the state of play on which engines comply with this new reg. I hope to have my own car completed and on the road before the new ADRs come into force, however there are at least 20 people that I know of that won't meet the deadline.

Love the mag, keep up the good work.

Dave King

We're always a little reluctant to do a complex story that will interest less than half of our readers (about 50 per cent live outside of Australia), but if it can be done in the context of a general articles on emissions, yes we'll look at doing it.

Intercepting the Oxy Sensor Signal?

I have read a couple of your articles on fuel interceptors, with the same conclusion that you cannot change closed loop mixtures, fair enough! But what about using a potentiometer in line with the lambda sensor output to alter the closed loop mixtures? i.e. increase the voltage available to the ECU to lean out the closed loop mixture and vice versa for a richer mixture. If you have already covered this in an article, please point me to it, if you haven't, how about an article on it?!

Ben Hoyle

At least one programmable interceptor is shortly to come to the market that will have sufficient resolution and sensitivity to work on oxygen sensor signals. That would be our preferred approach - we'll keep an eye on its progress.

Test the Pursuit Ute!

Just wondering if you are going to do a new car review on Ford's Pursuit 250 XR8 ute?? Or any performance utilities for that matter?


Tim Shute

We do reviews on every single new car that we can get our hands on. If the review isn't in AutoSpeed, it's because the manufacturer either wouldn't make the car available or we couldn't hire it.

FWD Turbo Traction

I've been reading AutoSpeed for quite a while now and finally have decided to write in with a query of my own. I have to say it is a top online magazine (e-zine?) where I have found to be a lot of useful information. The move to weekly issues has satisfied my cravings for the magazine even more. Back to business... I've recently obtained the Corolla Sportivo Turbo and after a few breathing (and boost!) mods, I have found an inherent weakness in the car... GRIP! Being FWD doesn't help this either. Wet weather handling is fun but nerve wracking to say the least. I've been trying to come up with a modification plan that would allow for better grip during a standing start and all around better grip in the wet as well, but I'm unsure where to start. Would a few suspension mods do the trick or should I start with changing the tyre and/or wheel combination? Ultimately I would like to change both but I want to know which modification path would be the best and cheapest (of course) solution.

Thanks for your time and keep up the good work guys!

Andrew Hew

Move to weekly issues? When haven't we been weekly? To get better traction, firstly select the stickiest rubber you can find. A simple approach is to find tyres with the lowest treadwear number - they're the softest. You could then stiffen the rear springs to reduce rearwards weight transfer - but be aware that this will also alter the cornering behaviour of the car. Finally, an aftermarket LSD may be available for your car.

CAI Design

Thanks for a great magazine! I've read just about all your articles on CAIs and have decided to fit a cone filter. I was wondering where the best place to put the filter would be on a 97 N/A 2.2L Celica? I'm aware of the many factors (eg. getting cold air to it, shielding it from the heat of the engine bay etc...) involved and it seems that ideally it could be behind the headlight.

However, I think that the air supply to the original airbox comes from outside the engine bay (through the guard) and siting the air filter where the box used to be would be the easiest answer. (Next step being to make this piping larger.) But then you have problems with heat. Also, what is the best (and cheapest) way to make a heat shield? If the shield is made reasonably air tight, can the filter be starved of air if CAI isn't large enough? Is it likely that changing the amount of piping between the air filter and the air flow sensor (or between the air flow sensor and the throttle body) would affect intake tuning and therefore cause power loss? I suppose the best way to find out would be to test different pipe lengths but this will probably end up being expensive or too subjective. And would the best way to make this piping be using mandrel bent exhaust or will PVC withstand the temperatures?

I've made a meal of this, but thanks very much for your help.

Paul Di Giovine

Paul, every single one of your questions has been covered in depth in articles that we've done on the subjects. Read the articles!

Turbo + Supercharger?

Firstly, want to say that you have an excellent website. I find every article you guys do extremely interesting! My problem is this: a friend tells me that an engine that is both supercharged and turbocharged is better than having either or. It sounds like it makes sense, but for some reason it sounds like a load of crap. Can you clear this up for me?

Adam Gan

Turbos work best in the mid- and upper power areas of an engine, while a supercharger can be designed to produce boost from idle rpm. However, to an extent a turbo is getting 'something for nothing', in that it is making use of the heat and flow characteristics of the exhaust gas which usually go to waste. A supercharger is always a direct power drain on the engine. So, one approach is to use a supercharger at low engine loads, then switch it off as the turbo spools up to speed. This can give the best of both worlds, and has been used on at least a couple of production cars. However, it is expensive.

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