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Small under bonnet fire after backfire EF V8 on LPG 

 

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 Post subject: Small under bonnet fire after backfire EF V8 on LPG
Posted: Sun Nov 15, 2009 4:28 pm 
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As stated in tipic question. Car done a big backfire yesterday (30 degree day) blew off the gas inlet tube from mixer ring, blew off intake resonator and blew up airbox. I smelt smoke, and opened the hood and noticed a small fire catching on the sound proofing stuff under the bonnet, also the lpg inlet tube that blew off had a little flame coming from it. Can normal backfires do this?? Start small fires I mean? Luckily there was no major damage- it blew the sprint gas ring off the throttle body too I might add.

 

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 Post subject: Re: Small under bonnet fire after backfire EF V8 on LPG
Posted: Sun Nov 15, 2009 11:00 pm 
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Certainly can.
Old/defective ignition components can contribute to backfires. Make sure your leads, plugs, cap and rotor are in good nick. Pretty important in an LPG system that the ignition side is in good order.
Good idea to put a pressure relief in the induction system - I have a piece of tyre inner tubing acting like a flap - vacuum seals it whilst running, flap opens during a backfire to relieve pressure up the line.
NCII_Lane did something like this in his V8 induction - it's in his build thread IIRC.

 

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 Post subject: Re: Small under bonnet fire after backfire EF V8 on LPG
Posted: Mon Nov 16, 2009 8:06 am 
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Thanks snap0964, I am heading off to a mates tonight to add a little piece of rubber flap to an airbox I got from the wrecker, to hopefully alleviate this problem. Trying to locate a sprintgas mot004 ring as well.
Must admit i s**t myself when i seen the fire- never happened before. But I guess a combination of a super hot ambient day, plus the naturally warm under bonnet temp in the windsor would have helped contribute to this. Also as it blew off at the throttle body, as I guess if all was still attached there would have been no chance for such a small flame to "live" through the pipe and out the airbox.

 

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 Post subject: Re: Small under bonnet fire after backfire EF V8 on LPG
Posted: Mon Nov 16, 2009 11:12 am 
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Try not to open the bonnet all the way when you see smoke under there, as the rush of oxygen can cause the fire to spread rapidly. Could have been real dangerous if the underbonnet area had filled with dense gas vapour, and the sudden rush of oxygen mixed with a spark could have caused an explosion.

 

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 Post subject: Re: Small under bonnet fire after backfire EF V8 on LPG
Posted: Mon Nov 16, 2009 12:15 pm 
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That's actually a good point ^^^^.
I've got a fire extinguisher in each of my cars also.
You might want to put your relief further toward the TB - have a look at NCIILANE's build thread as I've said.

 

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 Post subject: Re: Small under bonnet fire after backfire EF V8 on LPG
Posted: Mon Nov 16, 2009 4:20 pm 
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snap0964 wrote:
I've got a fire extinguisher in each of my cars also.


Cheap insurance really! :)

 

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 Post subject: Re: Small under bonnet fire after backfire EF V8 on LPG
Posted: Sun Aug 01, 2010 5:34 pm 
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snap0964 wrote:
That's actually a good point ^^^^.
I've got a fire extinguisher in each of my cars also.
You might want to put your relief further toward the TB - have a look at NCIILANE's build thread as I've said.




wait till ya have a 4b petrol carb backfire ......................
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 Post subject: Re: Small under bonnet fire after backfire EF V8 on LPG
Posted: Sun Aug 01, 2010 5:43 pm 
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someone once gave me a suggestion to drill a little hole in the air box and cover it a bit of tape so that if it backfired the tape would just come of rather than the whole box splitting. also i think occy straps around the box is another half decent way to manage backfires. i think you can also buy some kind of special screws with springs for the air box to manage backfires.
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 Post subject: Re: Small under bonnet fire after backfire EF V8 on LPG
Posted: Sun Aug 01, 2010 7:31 pm 
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BlueBlooded wrote:
someone once gave me a suggestion to drill a little hole in the air box and cover it a bit of tape so that if it backfired the tape would just come of rather than the whole box splitting. also i think occy straps around the box is another half decent way to manage backfires. i think you can also buy some kind of special screws with springs for the air box to manage backfires.

my old intake had about a dozen 4mm holes drilled in it, covered by a stubbie holder. [see pic]
Image
i didnt do this, previous owner did, so i can only assume it was to stop the airbox being blown apart.
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 Post subject: Re: Small under bonnet fire after backfire EF V8 on LPG
Posted: Mon Aug 02, 2010 12:17 am 
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A proper mixer setup will be fit with a backfire relief / pop off valve so when a backfire occurs, the valve opens & stops things blowing to bits. Very few mixer setups are equipped with these.

Image

Something like above. Can be found on Ebay, this one is about $35 plus shipping from the UK.

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ToranaGuy

 

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 Post subject: Re: Small under bonnet fire after backfire EF V8 on LPG
Posted: Mon Aug 02, 2010 12:31 am 
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Buy a bath plug. Cut a hole in the airbox to match. Get a little chain. Attach one end to the plug and the other to something solid in the engine bay. Easy home-made backfire protection... :)

 

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 Post subject: Re: Small under bonnet fire after backfire EF V8 on LPG
Posted: Mon Aug 02, 2010 12:47 am 
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Yeah, there's plenty of methods for relief's - my favourite is a piece of inner tube rivetted over a hole as a flap - normal vacuum seals it when running.
Make sure you have a reasonable seal.

 

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 Post subject: Re: Small under bonnet fire after backfire EF V8 on LPG
Posted: Mon Aug 02, 2010 1:29 am 
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snap0964 wrote:
Yeah, there's plenty of methods for relief's - my favourite is a piece of inner tube rivetted over a hole as a flap - normal vacuum seals it when running.
Make sure you have a reasonable seal.


I have seen that done before, works ok. If your on very tight money, it wouldn't be a bad idea, if you have a couple of $$ to spend, a proper valve is the way to go....

Speaking of that, i should get one for my Xr8 soon! Before i get it on the road at least.

Cheers

ToranaGuy

 

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