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Hi I have a FJ73 cruiser with a 3F 4 litre petrol motor witch was rebuilt about 5 years ago but has only got about 60,000 on it I am hoping to run at tuff truck next year so I wanting to get rid of the problems that carbie have on hills so im thing of putting it on gas. As im getting only just over 300 km's to the tank about 70 litres with my 35's it's rather thirsty also I don't have the money for an engine swap so this the alterative. So im interested in anyone running gas on a carbie motor is the gas reliable and worth the cost and I have heard that when there dual fuel they can not be tuned well for both its one or the other or in the middle. So should I just get a dedicated gas system so its tuned right to get the most out the motor. Im not worried about gas alibility as its not a touring truck.
Regards,
Nathan
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300km from 70 l is not to bad, esp with 35s. expect more with LPG.
Duel fuel is a compromise but in low range you would not tell, around 10-15% power loss for good systems. if you dont need the range go straight gas and retune to suit.
LPG is simple and reliable, more than petrol and carbies anyway
krusty182 wrote:Yeah, I reckon since you're not worried about availability of gas, a straight gas setup with the right tune is your best bet.
Spot on.
A Gas reseach setup or a couple of IMPCO 425 mixers running off a custom manifold with twin B2 converters is the way to go. You could run one 425 mixer but your top end may suffer.
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The Impco CA-425 is rated to 287HP. That's more than a 3F carby engine is going to put out. I personally use OHG X-450 mixers, which are rated to 350HP, but they are out of production and a problem if not set up right.
If you want to get the same power as petrol or more, here are a few things that I'd suggest:
* Raise the compression by shaving the head &/or changing pistons. Generally, cast iron heads shouldn't go past 10.5:1, alloy heads 11.5:1.
* Fit an EFI inlet manifold if available, with the mixer adapted to the input of the throttlebody. Failing that, you need a carby manifold with larger runners than original. A 4 barrel Holley pattern manifold is the 2nd best option if using an Impco 452, as the base of the mixer bolts directly to a squarebore holley throttlebody.
* If there is any heat from coolant or exhaust going into the inlet manifold, eliminate it. Fit a heat shield between the exhaust and inlet if necessary.
* If you don't have extractors, fit them.
* LPG does not need or respond well to heat in the intake air. A snorkel or other method of getting cold air from outside the engine bay will make a lot of difference.
krusty182 wrote:Yeah, I reckon since you're not worried about availability of gas, a straight gas setup with the right tune is your best bet.
Spot on.
A Gas reseach setup or a couple of IMPCO 425 mixers running off a custom manifold with twin B2 converters is the way to go. You could run one 425 mixer but your top end may suffer.
i run a impco 425 on a 5.7L....no probs with top end
so I wanting to get rid of the problems that carbie have on hills so im thing of putting it on gas. As im getting only just over 300 km's to the tank about 70 litres with my 35's it's rather thirsty also I don't have the money for an engine swap so this the alterative. So im interested in anyone running gas on a carbie motor is the gas reliable and worth the cost and I have heard that when there dual fuel they can not be tuned well for both its one or the other or in the middle. So should I just get a dedicated gas system so its tuned right to get the most out the motor. Im not worried about gas alibility as its not a touring truck.
