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LPG Fuel Consumption

In your recent article "LPG vapour injection' the engineer suggested that there would be up to a 20% INCREASE in feul use over petrol using LPG. However the article goes on to indicate that over a standard test procedure there was actually a reduction of 6% feul used.

How can this be so?

Are there some situations where the LPG ECU allows the car to run lean? or are there situations (like low loads for example) where LPG is more efficient that petrol?

It certainly would be good if the reducation in feul use was true – it would be like having your cake and eating it too..... And i hope that it wasnt a calculation error, or inconsistant testing or otherwise different testing situation, but it would certainly be great to have any sort of definitive answer you can suggerst as to weather feul use will increase of decrease using LPG.

Craig Dunn


John Parnell indicated to us that there is usually a 20 per cent increase in LPG fuel consumption. However, the emissions test he provided us showed that on that particular car, in that particular test, this was not the case.

Ferrari Engine

Nothing wrong with recycling old stories - especially stories on old Ferraris - but recycling the errors? I am pretty sure the Testarossa and 512TR were FLAT 12s not V12s!

Robert Mitchell


As described in the story, the car has a 180-degree V12. Many people incorrectly call this a flat 12.

LPG Turbo Skyline

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hello i read your article on vapor injection. you mentioned Parnell doing a turbo gas conversion.i installed a prins kit on my 98 R34 GTT skyline about 6 months ago and its the best mod i have ever done.

The car is a R34 GTT 5 speed with a stock turbo @ 14psi or 244rwhp. Power FC piggy backed by a Prins gas ecu running 6 x 75cc injectors

 I think probly the greatist thing about this car is that the stock computer has been ditched and replaced with a apexi Power FC. The skyline was then tuned agressivly for 98 octane fuel. this made the car run much better on LPG but still allow the dual fuel set up. In reality there could be more power made if it was tuned solely for LPG but i enjoy knowing that i probly own 1 of maybe only 3 knowen LPG skylines in aus that can drive 700 klm's with out seeing a service station.

there are many Pro's and Cons to a setup like this.

PRO's being a massive increase in driving dont normaly have to worry about what brand or octane the gas is, exactly the same power and mainly the price per litre.

Con's being  very few people will install a kit like this, some times hard to diagnose EXACTLY were problems lie, also it can take a while to tune and set the car up proply and no spare tire.

There are a few things i would love to tell people or companys who are thinking of installing any gas kits. what they must do is wire in 2 relays for there petrol pump. 1 to initaly kill power to the fuel pump when ever the gas lock off has power or gas flow and  the 2nd to over ride and apply power to the fuel pump when the petrol injectors have power. you have to wire it this way for when the car changes over fuel types as the gas computer turns the petrol injectors off 1 at a time.

If something like this isn't done the fuel pump never turns off and constantly is supplying pressure to the fuel rail and heating it up, i know for a fact that when i have a full tank of petrol and run on gas that alot of petrol is lost.

and lastly LPG is a waist of time IF you are planning for over 300KW @ the wheels. LEGAL tanks simply can not supply enough gas flow. you can get around this by running duel tanks but simply cost vs effect just doesn't add up.

I hope my experience with my car can help some people out. i would deffinitly do it to my next car.




Hi, I'm a very happy reader of your website from Singapore, keep up the good work! Anyways, I would like to suggest an article about LSDs (especially torsen ones)? I'm very intrigued by them, and how about a before and after test thrown in as well?

Todd On


Keeping Memory

I read your articles on batteries. Very good. My question is this. when you remove and replace a battery how do you maintain the electronic(computer) so you don't lose the computer. Would appreciate an anwer. thank you

Dennis Scanlon

United States

The most common way is to use a diode and a small battery (eg a 9V one) and plug it into the cigarette lighter, such that the battery powers the radio and ECU memories but cannot be charged when the car battery is reconnected.

Battery Developments

Thought this may be of interest to autospeed

Robert Seymour


Step by Step for Insight Mod

I very much enjoyed Julian's article, my wife and I both drive Insights. Would it be possible to get a little more detail on his circuit and its installation in the car? I'd be happy to report back on any mileage changes we see; good or bad.

1) part numbers for the capacitor and pot, or a suggested fixed resistor

2) loom wiring color to attach to

John Heller

United States

There is enough information in the article for anyone with even a tiny electronics knowledge, and with the ECU pin-outs, to install the modification. If you can't understand the installation, and can't source the parts, it's probably not a do-it-yourself mod for you.

Intercooler Maths

In your recent artical "Intercooler Maths" I don't get the part of the formula that is suppose to equal 1.236, what is the (2.1) to the 0.286 is it the power of or what. Theoretical outlet temp = 293 x (2.1)0.286 = 293 x 1.236 appriacte your help, great magazine love it.

Anthony Parle


The number is raised to the 0.286 power.

DIY Hydrogen

Have there been any articles on hydrogen generators, "Joe Cells", "Browns Gas" or HHO gas used in cars? I've read loads on the net, and there's a Range Rover here in Toowoomba with "Powered by Hydrogen" stickers on it and a phone number, but I've never been quick enough to get the number.

From the web pages, it seems relatively easy to home-make a hydrogen generator and run a vehicle on it, or in some cases, use the hydrogen produced to supplement the existing fuel, be it petrol, diesel or LPG. As there's no problem with storage of the produced hydrogen (only works when the engine's on), this is a huge advantage.

Can you investigate and produce an up-to date article for us?

Paul Engelhardt


We haven’t covered this topic but we’ll put it on the list of possible stories.


A couple of small glitches with your recent story on the Corvette ZR1's LS9 engine:

You blokes should know that with roots-type supercharger, "incoming air is" NOT "squeezed between the rotors and pushed under pressure into the engine". Incoming air is carried in the cavities between the outsides of the rotors and the inside of the casing "and pushed under pressure into the engine".

Also, if the charge cooler drops the inlet charge temperature by 140 deg F, that's equivalent to a temp drop of 77.8 deg C, not 60 deg C. To convert a temp DIFFERENCE between deg F and deg C you just multiply by 5/9, WITHOUT first subtracting 32 from the deg F value. You only first subtract 32 when converting an actual measued temperature of an object from deg F to Deg C, not temperature differences.

Hope you will accept this as constructive criticism.

Ian Petersen


Re the description of the supercharger, we’ll let the description penned by GM ride. However, the slip-up on the temp conversion was our fault – it’s now been corrected.

Throttle-less Engines

RE: Brake Specific Fuel Consumption, you comment that diesels are more efficient than petrol engines due to reduced pumping losses at part throttle since the diesel engines lack a throttle. Am I right to think BMW also eliminated a throttle butterfly from their valvetronic engines, such as the four cylinder units used in the 3-series? I assume these use valve timing and/or fuel injected to control engine speed?

Ben Garside

United Kingdom

They use variable valve timing and valve lift – see

Wankel History

Pertaining to 'The History of Mazda's Rotary Engine', "By this time, no less than 49 years had already passed since young Felix Wankel dreamed of the rotary engine..."

Do you mean 39 years?

Gary Ng


Well spotted - fixed

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