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I have got to take you to task with the latest tech tips. A larger waste gate does not reduce back pressure! The turbine and the WG are in parallel, the DeltaP across one is the same as the other - mixing losses aside. I have had this argument out with many people, many of whom would not see the truth in it. In the end, I contacted Rob Cadle, engineer at Garrett USA and the man behind the 'Disco Potato', and got his word on it. He wrote a lengthy piece for me confirming what I had written.

The upshot is; a larger WG will simply have to close more in order to maintain the power requirement of the turbine.

Additionally, if you were hinting at small turbine AND large compressors, and you may not have been, but this is just a disaster. Large compressors will have much slower operating speeds than small turbines. The little turbine must operate at high RPM or else its efficiency takes a major dive. By using this combination (example, 2540 turbo), you force a small turbine to operate at low RPM (in order to not to over boost the large compressor) and run it in really low efficiency parts of it flow map. This forces up back pressure, makes it very laggy and is just, generally, a dog.

Pete de Vries

We agree that the larger wastegate will not reduce backpressure during normal turbo operations, and have revised the article appropriately. But on your other point, what is a ‘large’ compressor and a ‘small turbine’? Much depends on how you categorise these. Many OE equipment turbo cars run relatively small turbines and relatively large compressors.

Expensive Model Car

Compliments for your interesting site and the articles. You probably could be interested in our story. It's a bit "off-topic", but it's a good story anyway: THE BLUE CAR. Autominiature on a scale 1:6 and unique in the world. Took us more than 15 years to develop the car. Each car is handcrafted using parts of pressed steel, formed by the aid of a set of moulds on a 650 tons press, or casted aluminium (seats, bumpers, steering wheel etc.). We sold the car to Bahrein, the US, Liechtenstein... . Come for a visit at our homepage Mabye it's worth a story for "autospeed" - mabye not. We would be glad to get a feedback anyway.

Michael Herter

Acetone in Diesel

Hi Wanted to say what an excellent online mag i love your tech articals & approach to modding cars just wish i had my old Saab 900 on the road to apply your ideas to. at the moment im driving an 3.5 ton LDV pilot van with a 1.9  pug diesel which  has the same engine as your pug has, there is a forum at where i came across the idea of adding acetone to the diesel to improve the combustion of process. if memory serves it reduces the surface tension of the diesel molecules. i've been using add it to my tank at approx 1ml per litre before i fill up  for the last 2 years at a total cost of £18, a 5l tin from a local body shop supplie store its used for cleaning fiberglass moulds. It works well no dark smoke on start up & improved pulling power most noticeably on the motorway. i changed my flue filter soon after starting to use it as it helps keep every thing clean. i seem to rember some diesel "octaine" boosters are based on acetone. woundered if would be of any use if u don't want to join the forum ill be more than happy to mail u some more info over from the site. keep up the good work

Dan Wilmshurst
United Kingdom

Recycled New Car Tests

Hey guys, i'm dealing with the recycled articles quite well, even though i've read almost all of them before its nice to revisit occasionally... today, for the first time however i was a bit miffed... a 9 year old story on an MX5? your short tech features on stuff less related to cars like bike lighting and tool care are more interesting and valuable i think. If people are desperate to read about MX5's then they'll find whatever they need to


Our view is this: a recycled new car review gives the unique perspective of how the car was judged at the time, rather than with the benefit of hindsight. Was it a breakthrough car – or an also-ran? It’s for this reason that we love going over old new car tests in magazines – we almost always gain something from them. Given that the value of such cars is vastly lower now than when they were new, such a story also has a broader potential readership. However, the reader ratings of recycled new car tests have proved to be poor (although ironically the MX5 repeat has rated fine!), so clearly plenty of people agree with you rather than with us. As part of our future repeated component, we’ll be running less new car tests.

Luxeon LEDs 1

I notice you are doing a series of articles on luxeon powered lights. These make me more keen to go out and create my own lighting project.

In these articles you generally state that the LEDs should be driven by proper LED power sources, and not be driven with just a resister as thats inefficient.

You also wrote this article about creating your own luxeon LED power source: Luxeon Lights Is there anyway you could power a 3w LED using a similar set or is it a strictly 1w LED thing?  I want to build a circuit for fun and just experiment, but don't want it to get to pricey by buying a power source and multiple LEDs.  I'm was just thinking of starting with a single 3w LED and going from there.

Your help would be appreciated.

New Zealand

For experimenting just use a resistor. In our own experiments we use a variable voltage / variable current power supply with current and voltmeter displays. This makes supplying the right current very simple.

Luxeon LEDs 2

I have been following your article on high-powered LED lighting with some interest, I remember Silicon Chip doing a similar article a while ago too - LED technology has progressed in leaps and bounds of late - there are LEDs with higher lumenous efficiencies out than compact fluroescents - 90 lumens per watt! This is in a 10W LED - pretty mindblowing stuff.

But I digress - there are some fairly serious LEDs out there that would also suit this project - the Lamina Atlas is available in an 8.6W 250 Lumen (!) led, with a lambertian pattern - combine that with a decent lens pair (for example, a headlamp projector lens + narrow angle fraen optic for the LED) and you would have a pretty serious piece of hardware.

If you can take a funky beam pattern (or a more diffuse light) there are Endor Stars, 3 X 200Lumen, and for the rich and truly insane (all relative) there is a 1885 Lumen Lamina Titan Turbo light engine. The lens requirements would be a tad difficult with multiple emitters though!

Keep up the good work - as a follow-on, maybe some information on LED automotive headlamps would be good as well. There are a few production vehicles with this in use.

Heath Young

Illegal Taillights?

One comment about your second article "Building a High Performance LED Lighting System, Part 2"...  Having super bright tail lamps could be illegal particularly if there is a possibilitiy that drivers approaching from behind the vehicle can be blinded by the beam. Using a lens to intensify or direct the tail lamp beam worsens the situation.

Mal Land

The local police have never been fussed.

Carby AFRs

I have read with interest your 'In - car - air / fuel ratio' measurement buyers guide, part 1. As it only provides info for fuel injected applications, it doesn't address my needs for my 76 Triumph Spitfire, which runs on 2 SU carbs. Do you have any AFR info to meet my requirements?

Helmuth Vorkoetter

If the car uses unleaded fuels a normal oxy sensor and simple meter can be used to give an indication of the mixtures, irrespective of whether car use fuel injection or a carburettor.

DIY Night Vision

I know you guys have an interest in electronics as well as cars – ever thought about putting together a custom night vision or infra red camera for driving at night? Would commercially available IR surveillance cameras be suitable?

I do a lot of highway driving and while I have never (touch wood) hit a kangaroo or run over a blown tyre carcass I'd hate to face that situation. Something like this would help a lot. The big automakers seem to be dabbling in this kind of technology so perhaps it is more difficult than I can comprehend. Either way I'd like to hear what you think.


While it’s technically quite possible, we don’t think that there would be enough reader interest in such a project.

Speed Alarm

I am looking for a cheap unit that will give an alarm when a set speed is exceeded. My ideal unit would have four or five speed inputs. An alarm would sound when any of these speed settings is exceeded.

Peter Vaile
New Zealand

The Frequency Switch, Part 1 could be used to indicate when a single speed has been exceeded.

(Literally) Flat Torque Curve

Your article about Turbocharging for economy was great in itself, but what I found even more interesting were the graphs of power and torque for the VW group engines.

All the turbo engines featured torque curves that had clearly artificial limits, the torque would rise in the expected curve and then suddenly plateau into a dead flat line that would be maintained until the "natural curve" fell below this limit. Obviously some german engineer decided what the peak torque should be, and drew it in with a horizontal ruler.

The 1.8 litre turbo it also had an artificial power limit.
This has obvious implications when it comes to increasing the performance of these engines, you can restore the natural curve, "modify it back to normal" and get what I estimate as 350 Nm on the 2 litre, or 300 Nm and 150 kW on the 1.8.

Patrick McAuliffe

This shape of torque curve is typical of all modern factory turbo engines – it simply means that the turbo is sized to develop boost early and then the boost is limited to a fixed value.

Volvo HPV

I have been readeing the storys about Julian Edgars building a HPV trike. I have decided to build one by my own. This is a way to combine my interest of bikes and my profession as test engineer at Volvo Cars at front wheel suspension.

Is it possible to get any drawings or sketches of the final air150? I'm going to model it in SolidWorks.

ThankYou for many interesting articles. I have shared this web site with my collegues.

Lars-Erik Neikter

No drawings were made of the trike (just lots of sketches!). The series on the Air 130 (starts at Another Human Powered Vehicle Part 1 - Finding the Lightest Springs ) is of fundamentally the same design and is shown step by step in much greater detail. If any would-be constructor needs any approximate measurements or angles, we’re happy to supply them.


Great article on scopes (Using Oscilloscopes on Cars, Part 1). Just one quibble: you mistyped our URL as at the end. Could you please correct it to

Jeff Bronks
Technical Author
Pico Technology
United Kingdom


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