Blown up air box d2 v8 on lpg - no suprise

[alanbettison]

Engine now seems to have settled down

would like to find cheap alternative air box, home made or otherwise to replace the silastic/duct tape box I am using now

thanks

[bee utey]

Try an early EFI (86-89) Range Rover cylinder style air cleaner, at least you have a functioning can after a backfire.

[Lotz-A-Landies]

Allan

Not answering the aircleaner box question, however where is your crankcase (PCV) rebreather port into the intake system?

By rights it should be moved prior to the LPG mixer but is often not moved because it requires other modification.

The reason is that if any crankcase flame manages to occur and bypasses the flame trap, you are putting an ignition source in a fuel rich mixture which explodes in the plenum. The result as you have found is destruction of the weakest point - the plastic airbox.

[alanbettison]

thanks for the reply

the breather is before the lpg squirter

I think the unit has leaned out too much before as I have a had a few air leaks

[bee utey]

Allan

Not answering the aircleaner box question, however where is your crankcase (PCV) rebreather port into the intake system?

By rights it should be moved prior to the LPG mixer but is often not moved because it requires other modification.

The reason is that if any crankcase flame manages to occur and bypasses the flame trap, you are putting an ignition source in a fuel rich mixture which explodes in the plenum. The result as you have found is destruction of the weakest point - the plastic airbox.

Not withstanding that you are correct for the breather, your reasoning does not strike me as correct. The D2 doesn't have a flame trap, the breather must be upstream so that the PCV (positive crankcase ventilation) valve on the other rocker cover doesn't cause combustible gas/air mixture to be drawn into the engine. I have seen a Ford engine that combusted inside due to faulty breather and it wasn't a pretty sight. Imagine a bomb set off in a tin can.
Backfiring is 90% electrical: ignition voltages rise with lean mixtures, engine load and ignition timing (higher cylinder pressure), plug gap, lead type, loose/broken leads etc. This leads to cross firing, especially with coil packs. Anything that reduces firing voltages will reduce backfiring. That is why you need to deal with all of these issues to get a successful run out of your lpg conversion.
The other common causes of backfires are a heavily carbon fouled head, and head gaskets leaking between cylinders.

[wakamole]

thanks for the replies all

I put in the direct injection and she runs like a dream!

Thanks for all your help

[GEK064]

Bee Utey, I've gone for a 1988 RRC round box with a K&N filter. The filter was not cheap as i went for a clean-able one. What happens to the filter inside a steel box if a LPG induced blow happens?

[bee utey]

Bee Utey, I've gone for a 1988 RRC round box with a K&N filter. The filter was not cheap as i went for a clean-able one. What happens to the filter inside a steel box if a LPG induced blow happens?

A big enough explosion may burn holes in the element, or blow enough filtering medium out to make it no better than a sieve. Personally there's no way I'd use an oily K&N upstream of a hotwire MAF, just keep a spare paper element ($20-25) and inspect the security of the system after every backfire. The main reason to run the tin can air cleaner is that at least you have an intact housing after the bang, this doesn't remove your responsibility for checking the element. Sometimes the filter retaining plate bends a bit, you then have to do up the nut.