Air Flow Meter Swap

[anonymous-user]

Might have been asked before so apologies in advance...

If I can get hold of a Jag XJ AFM can you just swap it with the existing one that’s on a 350 flapper? I am led to believe the fuel injectors can take the increased airflow.

Can anyone let me know what needs to be done?

Cheers

Doug

[petros]

Somebody is selling some for £30 each in the classifieds

[grahamw48]

Wedg1e !!!! ...

[wedg1e]

ALmost a straight swap apart from the mountings being different, the hose size being different and the spring tension will need adjusting. Oh, and the air filter fittings are different.

But apart from that, yes it's a straight swap!

[tallbloke]

I believe the plenum hose from a 3.9 Range Rover will go straight on. Are those bosch ones for sale hotwire rather than flapper type? I though the bigger flapper ones were Lucas 4AM.

>> Edited by tallbloke on Saturday 8th October 09:00

[wedg1e]

tallbloke said:

I believe the plenum hose from a 3.9 Range Rover will go straight on. Are those bosch ones for sale hotwire rather than flapper type? I though the bigger flapper ones were Lucas 4AM. >> Edited by tallbloke on Saturday 8th October 09:00

Funnily enough, I thought the smaller-bore AFM was an 4AM and the larger Jag one a 2AM, but I've seen both sizes with 2AM labels on them...

[GreenV8S]

The 20AM is a black plastic unit that is often used as an upgrade from the 4AM, is this anything to do with the 2AM you mention? I got the impression from comments Mark Adams made a few months ago that the 3AM is a precursor to the 4AM, so it would make sense for there to be a 2AM too. I've never seen one though.

[Wedged1]

Is there any obvious benefit to swapping?

[wedg1e]

Wedged1 said:

Is there any obvious benefit to swapping?

Almost certainly not, if that's all you do.

Even the twin-plenum 3.5L still used the standard AFM, as did the 390SE (though it was supposed to be recalibrated along with the ECU), so it's probably only worth doing as part of a package of mods to increase airflow.

Ported heads and manifold would be a start (a la 390SE), maybe a larger throttle body (and note that even the 4.2 Range Rover still used the same throttle bore as the 3.5 SD1).

Then of course a high-lift cam to get that air in and out of the engine... and perhaps some big valves... then you'll need fatter injectors... where do you stop?

From my experience, you can drop the larger AFM into a 390SE but it needs recalibrating just to get the car to idle. The throttle response changes completely.
Haven't tried one yet on a 3.5L but I do have a guinea pig in mind...

[anonymous-user]

Some great info! thanks chaps. Who is selling them in the classifieds? can you point me in the right direction...

Cheers

Doug

>> Edited by anonymous-user on Saturday 8th October 19:38

[stainless_steve]

Sidewinder said:

Some great info! thanks chaps. Who is selling them in the classifieds? can you point me in the right direction... Cheers Doug >> Edited by Sidewinder on Saturday 8th October 19:38

try this
www.pistonheads.com/sales/49449.htm

[anonymous-user]

I thought I needed a like for like i.e. Lucas "L" but the lager one?

[350zwelgje]

Hijacking a bit. What about replacing a flapper with a hot-wire? Any sense in that? Or is remapping of an old-flapper system with the non-mapable ECU also a possibility if you want to keep the engine capacity the same?

Thanks.

Rob (350i '87)

[wedg1e]

350zwelgje said:

Hijacking a bit. What about replacing a flapper with a hot-wire? Any sense in that? Or is remapping of an old-flapper system with the non-mapable ECU also a possibility if you want to keep the engine capacity the same? Thanks. Rob (350i '87)

I've heard it said that the flap system can be modified to give more absolute power than the hotwire but at the expense of some refinement and driveability, whilst the hotwire gives a smoother delivery and thus aids progress
Hotwire is also better for economy.
As usual there is probably some truth and some myth; perhaps Mark Adams will drop in and elaborate?

The flap system can't be remapped as such but it can be optimised to your particular engine and/or required delivery (all or nothing, for example). This is what I'm attempting to do with my car; in effect the only recent change I've made is to the injectors and now it runs like cr@p mostly, with occasional bursts of when it all comes together...

[leorest]

wedg1e said:

...with occasional bursts of ...

Sounds like fun

[anonymous-user]

Ive got a 2AM flapper is that the 80mm or 70mm? (haven’t had time to take it out yet). I was looking through "The wedge epistles" and wedge1 refers to this probably being a jag one...

[blaineuk]

350zwelgje said:

Hijacking a bit. What about replacing a flapper with a hot-wire? Any sense in that? Or is remapping of an old-flapper system with the non-mapable ECU also a possibility if you want to keep the engine capacity the same? Thanks. Rob (350i '87)

i was told that the hot wire gives better economy and smoother running, but you have to change the hole efi system, although not a big job

blaine

[wedg1e]

Sidewinder said:

Ive got a 2AM flapper is that the 80mm or 70mm? (haven’t had time to take it out yet). I was looking through "The wedge epistles" and wedge1 refers to this probably being a jag one...

If you can't compare the two side by side, the quick way to tell is by the position of the mounting threads.
On the smaller bore unit they're on the side; on the Jag AFM they're on the top.

I looked in my stores, and sure enough I have both sized units marked as 2AM.

[350zwelgje]

blaineuk said:

350zwelgje said: Hijacking a bit. What about replacing a flapper with a hot-wire? Any sense in that? Or is remapping of an old-flapper system with the non-mapable ECU also a possibility if you want to keep the engine capacity the same? Thanks. Rob (350i '87) i was told that the hot wire gives better economy and smoother running, but you have to change the hole efi system, although not a big job blaine

Looking for a full backup system anyway. But understand that with hotwire I need to change injectors then also for the type that doesn't need the power-resistors.

Rob