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straight gas or petrol?

brenz

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fuel prices are killing us these days and i have read around about how lpg can be just as good with power if its straight gas and tuned for it. Has anyone done this and believe it is power or does anyone have proof of lpg being more powerful then petrol.

Also i was thinking if i done a straight gas conversion on my vr and put on a supercharger would this give out a fair amount of power equivilant to a supercharged vr on petrol?

Whats your opinions or expiriences have to say ?

Cheers Brendon
 

bennzy

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it really doesnt matter if you have straight gas or duel fuel no matter what you are saving money anyway.

but having straight gas on a highpowered car using turbo, ive heard is a really good thing, can be better than petrol but then ive heard that there is a little problem with the gas in high powered vehicles something about when the gas is combusting is something like that, not a hundred percent sure since i found out the little bit of info a fair while ago and now have forgotten.

my old car was on duel fuel, it didnt really loose any power at all, but then again i had one of the best systems on the market at the time. but of course i dont have the car anymore since i upgraded, but **** it was using alot of gas, problem i think is it needs a decent tune since i put a sports exhaust system with pacemaker comps extractors on
 

Streetvision

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They also say to run fuel in it from time to time to stop the fuel lines and **** messing up
 

Soybean

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does lpg have a lower octane level then petrol?
 

Shounak

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Higher.. LPG is abot 105 RON. ULP is 91RON..

Straight gas can be better, much better.. You will need tougher heads and valves to deal with it though..
 

94 Stato V8

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I have 3 vehicles on LPG and wouldn't have it any other way, my 4th car is a supercharged 350 chevy in a T Bucket so that one I dont care about fuel prices as it wont get driven that often anyway. But any daily driver car that does 15-20,000km's per year has to be better off using LPG. You have to do your sums and see if its feasable for you though. Factor in about $1800-$2500 for a basic LPG conversion, then think about how long you intend to keep the car. How long is it going to take to re-coup that outlay? Well how long is it going to take you to spend about $6500 in Petrol in your car now?
The other downside is the reduced boot space if you take your car on trips or whatever. Even if you do decide to go the Dual Fuel route, it still pays to run it on petrol each week for a little while to keep the injectors clean etc.

Now if you go LPG ONLY with a supercharger, you'll be blowing a whole wad of cash, but you will have a cheap to run (Well....ROFL) fairly quick car. You can get twin mixers and convertors and all sorts of performance stuff if you really start looking around for it. $$$$$$$
 

Patrio7

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i like the feel of my car on a full tank of bp [ runs smooth on bp regular, better than caltex which i normally get ]

but 105ron on lpg?, wouldnt be too bad.
 

Cheap6

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Unfortunately there is little or no octane increase with LPG as it is currently sold and used in Aust. The minimum octane rating is guaranteed to be 92 MON only. Sometimes it may be more, depending on what is in the mix, but you have to tune to the lowest octane that may end up in the tank. If it were possible to introduce it as a liquid spray, the effective octane may be higher but I don't think that there are too many of such systems around and certainly not cheaply. In the past, and perhaps still in the USA where a lot of the (performance) literature is sourced from, LPG was mostly propane, which does have a higher octane than petrol, hence the misconception.

The change was brought about because it allows the inclusion of other (cheaper) components from the refinery stream - mostly butanes, and because most users of LPG don't modify the engine to take advantage of any extra octane and so it would be wasted.

There is a minor maximum power loss associated with LPG because it is almost always introduced as a vapour, displacing some of the air in the manifold. This is not noticeable in normal driving in my experience - how often do you use anything approaching full throttle during normal driving? If you need or want performance switch to petrol.

In assessing the economic benefit of an LPG conversion be aware that the price at the pump is per litre, not per unit of energy. Petrol has a greater energy content per litre than LPG. Exactly how much depends on what is actually in the LPG (and the petrol). Depending on which LPG system is used, there is likely no fuel cut on decel. or lean cruise either. And you get to carry about an extra 40kg of gas equipment.

I get 13.8l/100km on petrol and 18.2l/100km on LPG, mostly urban driving. I have seen as low as 16.4 and as high as 19l/100km on LPG, same driving conditions. Hence, multiplying the price of gas by 1.3 will give the approximate cost relative to petrol.

The price of LPG will also increase as fuel excise is applied (starting 2008, +2.5cpl/year going to 12.5cpl (all X 1.3 X 1.1 GST :) ) in 2012) and, more people may switch to using it (it will still be cheaper than petrol), increasing demand.

The actual cost of running dual fuel will depend on what mix of running distance/time is spent on each fuel. Currently, about $12/100km for me, using mostly premium petrol fuels.

I'll make the distinction here that by dual fuel I am referring to two separate fuel systems for each each fuel rather than integrated fuel systems (my term) where both fuels are used concurrently or consequeutively under some circumstances eg. cold start, WOT.

While there is some scope for optimising an engine to run on straight LPG - ignition timing maps, cam profiles and timing more biased to inlet flow, and reducing inlet manifold heating - for an economy application they are not cost effective, (changing the ign. timing maps may be, depending on how they are obtained) so I see little benefit to running straight LPG for economy. Take the extra range available and the virtual impossibility of running out of fuel with dual fuel. (I occasionally run my LPG (but never petrol) tank dry). Running dual fuel systems also reduces the number of possible causes of engine stoppage - only a crank angle sensor or possibly ignition module failure will stop the engine.

In a performance application, it may be cheaper (acknowledging the savings in fuel costs) to use a straight LPG system for fuel and avoid the expense of remapping or replacing the ECM/PCM, upgrading injectors and fuel pump. You are still stuck with regards to ignition timing, although it will be cheaper to change just that than to map/remap fuel as well. If the engine is to be rebuilt anyway, then it may make sense to optimise it for LPG too but the gains won't be dramatic, about on par with a similar petrol engine.

Another way is to run two completely separate fuel system allowing the total volume of available fuel supply to be doubled (or more) at zero extra cost other than mapping. Instead of upgrading to a high volume fuel pump and injectors, the extra fuel can be provided by switching in the petrol at high loads. ZOOM magazine issue 101, pp72-75 has an article on one way this has been done. Other variations have been tried before, including by me.

It would be interesting to try a liquid to air intercooler on a boosted engine, using the intercooler coolant to vapourise the LPG (straight gas). Might be tricky to avoid freezing the convertor at low loads (boost) and so require some integration with the engine cooling system though. I believe that this has also been done before.
 

Clacker

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While there has been some excellent discussion, I thought the firing order of the V6 on ignition is what stops dedicated LPG.

Probably wrong though.

Clacks
 
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