Ford - Check.
V8 - Check.
LPG - Check.
Grunt - Ummm, well you know... kinda.

I want MORE! !

The mod road for petrol V8's is well known and even better driven; Exhaust, Snorkle, AFM, Throttle body, Intake Manifold, Cam etc...

The question I'm asking is what's the best way about going harder using LPG? I'm pretty sure there's not much point doing the bigger AFM/Throttle body, as the LPG mixer will then negate any gains... Does this follow for other standard mods? I've already got HM headers, high flow cats and a oversize snorkle, but what's next?

Your first step would be to make sure you have a good mixer. Lots of the standard ones choke the stock engine already. Other than that, look at the same mods for petrol. Intake and heads are the main point of restriction, then I would look at cam, TB etc.

Yeah, figured. I had an Impco in my XF auto and that used to pull 87 kW on gas or petrol at the wheels with nothing more than a baby cam and decent pipes. Doesn't sound that impresive, but it was a 20 year old car that had done 350,000 k's and was essentially stock. The guys who dynoed it actually said it was making more rwKw than most Gas Research set ups (for the XF).

It's the next step that I want to take with the V8 that I'm not sure about... Will I see the same benefits on dual fuel for head/manifold changes or is it worth biting the bullet and going for a quality straight gas setup...

OK.
You need a dyno.
First you need to make sure the gas can keep up with the engine. You also need to see how much od a restriction the mixer is (vacc guages will help)
Getting air in and out will give power so standard mods ie exractors and exhaust, also CAI. Abviously cam and heads will help heaps.

Change the cam to a gas specific as the overlap and duration differences will give benefit and go aftermarket ECU mapped for the gas.

I have done some testing on my dyno in regards to lpg mixer resiriction.
I have found that with similar mods to what you have, an 8rwkw drop is recorded when the car is run on petrol with the mixer inline. I increased the centre diamater of the mixer on the lathe by 5mm and that improved it by 3rwkw.

The dyno also helps to set the AF to insure max lpg under open throttle.

Dont buy safeway lpg.

why not buy safeway lpg?
is it different to other lpg?
i've ran safeway lpg and hav'nt noticed any
problems. but then i haven't really looked.

Done the dyno at APS. Runs about 106 rwkW on petrol, 102 on gas. Not enough for either I say. It's not a great LPG system (fitted before I bought the car) as it features a stupid worm screw attachment to the throttle body so I was surprised at the minor difference b/w petrol and gas on the dyno.

I've spoken to Mick Webb a couple of times about performance mods and as much as he dislikes LPG he agrees about the heads but also says he can make 250kW with the stock cam...

All petrol companies use a different mix of butane and propane for their LPG. The ratio determines which LPG is the best. I used to work in the industry and found that most people prefered BP or Shell LPG over other brands such as Vitalgas. (Most Safeway's use Vitalgas)

Easiest way to see which is best for you is to fill up with one brand, see how far you get and repeat, trying to keep the conditions similar. ie. which brand gives the best consuption figures...

BBQ gas is straight propane because of the no carbon dioxide spin off. In remote country areas it is known that sometimes intead of sending two deliveries the auto tank is filled with propane as well. Most run better on straight propane .

I was lead to believe that butane was put in to reduce the octane level down to around 90, as straight propane is well over 100 and not suitable for the majority of cars on our roads.

Safeway use Caltex fuels including LPG. Vitalgas is Caltex's LPG

Butane is put into propane as the Australian government is the oil company’s b**ch. The butane is a by-product in normal fuel processing and the easiest and most profitable way to dispose of it is mixing it with LPG and selling it to those who get what they are given.

Butane is RON 92 and propane is RON 100 so depending on the split is where you get your octane at the pump approx 60%propane 40 butane.

There was talk about regulating a minimum octane for autogas in Australia but haven’t herd anything since (guessing oil companies prob killed it ) . a nice steady RON would help tuning though.

Cheep companies prob use more butane. Wish they had to advertise the RON of the LPG at the pump might put some quality pressure on the servo’s.

Any hooo, Sorry to hijack my own topic back, but I was originally after the most effective way to get more power out of my LPG V8. Is is worth going straight gas? Or is is more sensible to just keep modding it as if it was a normal petrol car?

best way to overcome the disadvantgages of lpg IMO is to speed up & condense the intake charge by forcing the induction. lpg is far less prone to detonation so higher boost can be run than on the same motor with petrol. none of the induction you have would need much attention, just let the boost do the work, but make sure the lpg system can suply enough gas to maintain a safe air:fuel ratio under boost (12:1 or there abouts i think). mod engine as for any turbo/supercharged conversion (mostly to strengthen, or just keep boost levels modest, improve exhaust etc...)

the next best alternative if N/A must be used is to raise compression to approx 10.5:1 and stop using petrol. use more base advance timing and less total advance. do all the other things that would improve a petrol motor (ie. performance matched cam, induction, exhaust, heads/porting etc...)

with either path use straight propane as it has a road octane number of well over 110 ron, more like 118-120 ron. the higher the ron, the slower the burn, the less prone the fuel is to pre-ignition, the higher the boost or compression can be, releasing more potential power. i asked a fellow i know who works for elgas where to buy a 100% automotive propane and he told me that unigas, which elgas is tied with, uses only propane, no butane. it is one of the major selling points of unigas.

There are no laws on what consititutes LPG and no legal requirements to even specify propane & butane %ages let alone a RON. Result is that you don't really know what fuel you get and can never be sure that you are runing with optimum settings for any given tank of lpg.

You can spend big dollars on engine and lpg system improvements only to be let down by the variable fuel you use. All lpg users might find that the best performance improvement may be to write to their pollies and ACCC demanding RON & %age labling and the removal of the excise the government added to an environmentally cleaner (that petrol) fuel...

After all, a 100RON LPG will perform much better than 80RON LPG if your car is tunerd to used it (which it can't be at the moment)

Cheers.