The V8 Owners Forum -

I've got a 1986 Rangie on LPG and it's got a backfire protection release valve thing, plenum side of the airflow meter.

I guess the name is pretty self explanatory as to what they do, but are they strictly needed? Will the system function properly without it?

I'm asking as I've got an airflow meter off a 4.2 Jag to replace the standard one, and while the mixer looks like it will fit, the backfire valve won't. Would it be ok to fit it now, before I've got the backfire valve (got one on order, it's about a week away...)?

Cheers, Martin

The system will work ok without the backfire unit, BUT - if it backfires you will most likely destroy your AFM!
You say the mixer fits the jag AFM, surely the internal diameter of the mixer is the most restrictive part of the inlet system, so why go to the hassle of fitting the jag AFM? You won't get any more power from the engine as the gas mixer is the restriction on airflow and hence bhp.
Just my thoughts.....

Agree with Badger about the merits of the Jag AFM. I have a EFi with std flapper, and it's the mixer that limits power.
Just leave the air pipe clips loose, then in the event of a backfire it will blow the pipe off rather than destroy the AFM.

Chris.

Cheers for the replys, I'm going to try and use the AFM from the jag as it was given to me (rather than trying to gain performance), and I'll try it without using the backfire valve until it arrives.

As an aside, if I were to use a larger mixer, say one designed for a 4.2 Jag, would that be likely to increase power at all?

Cheers, Martin

Only if it offers enough of a restriction to the airflow to allow the correct venturi effect for correct operation of the gas vapouriser. I found when changing from a 3.5 to a 3.9 engine some years back (and modifying the flapper efi system to suit!) that I gained a few bhp back by boring the mixer out by 2mm, but taking it to 3mm extra killed the vacuum response to the vapouriser at idle so I had to get a replacement and bore it to 2mm again!

I'm going to be putting on a 3.9 EFI intake manifold onto my engine soon. Thing is the EFI manifold obviously holds a lot more volume then the standard carby manifold.... Where can I get one of these valves? Last thing I want is to have something broken in the unlikely event of a backfire.

www.wtv-uk.co.uk lists them online. They do 70mm ones and 80mm ones. I'm sure plenty of other places do them to, but they actually list them.

Cheers, Martin

And cheers for the reply Badger, top information, thanks!

Tinley Tech also sell them.

Chris.

That's the one I use on the old blown Rangie

I haven't got a backfire valve on my disco. I noticed there are two versions listed on the WTV site. An airbox saver device & an Airflow meter saver. Question is, what is the best way to go & where do they fit in to the induction system ??
Sorry to sound a bit thick, but i've worked on lpg systems before ( 20 years ago )but nothing that used these valves.

Martin, which AFM is on the car at the mo?? And did you get the back fire valve??

Cheers,
Stu

Hi mate, it's the Rangie 3.5 AFM on the car with no anti-backfire release valve on it (leaving the pipe from AFM to Plenum loose works well enough!). It did have the anti-backfire thing on, but it didn't do a great deal!