Griff 500 AFM gauze

[geoffvalenti]

I'm in need of a gauze/mesh for the hotwire AFM on my Griffith 500.

I've done the usual google searches but they haven't been fruitful.

Any ideas where I may be able to pick one up

TIA

[jesfirth]

I heave 2 dead AFM's in my garage rubbish bin at present - you are welcome to the gauze bit.... BUT my experience of the AFM's is that once they cause problems just bin them and buy a new one. £140 on ebay for a genuine bosch

[geoffvalenti]

jesfirth said:

I heave 2 dead AFM's in my garage rubbish bin at present - you are welcome to the gauze bit.... BUT my experience of the AFM's is that once they cause problems just bin them and buy a new one. £140 on ebay for a genuine bosch

Thats very kind
PM'd

[jesfirth]

hi Geoff - didn't get the PM - email me on [e-mail]

[blitzracing]

You dont really need the gauze on the TVR- its there to smooth the airflow on the Ranger Rover due to turbulence in the short intake distance from the air filter. The TVR has a lovely long pipe from the filter so the airflow is nice and laminar already so the gauze is just a restriction. Just because Im weird like this is two shots of the AFM output- one with gauze and one without so you can see what it does - note these are open ended tests- not with the TVR intake pipe connected.

with grid:




Without:

[jesfirth]

that's interesting so getting rid of the gauze in theory on a TVR will increase airflow, but would that actually produce more power or I assume make no difference if the airflow volume is already adequate?

[Rob_the_Sparky]

I was told to think about a petrol engine as an air pump, the more air you get in the more power you get as you then add the right amount of fuel to get the required fuel air mix. I.e. more air = more fuel = more power. However, you are not improving flow overall unless you address the greatest restriction as this will be the limiting factor.

I suspect reality is way more complex...

[blitzracing]

What the gauze is doing is breaking the turbulent airflow into multiple tiny jets of air that have no swirl in them, so the hot wire element gives a stable output. In the process you will get a pressure difference between one side and the other that will equate to lost power (as you say its a pump and the gauze is a restriction) but what that is in HP terms at W.O.T I don't know. I think the effect of not having the gauze is an unstable idle as the turbulence makes the AFM output jitter and the fuel load points jump around in the map a bit but Id say far less pronounced at higher airflow though, and as I say the TVR has the lovely long intake pipe anyway. Ideally you would put a bell mouth directly onto the AFM to get smooth airflow and maximum gas velocity but you simply dont have room to do this with a filter. As a matter of interest JE engineering used to recommend the ITG foam filters direct onto the back of the AFM as they have a huge bell mouth type profile on the back of the filter element, but they are pretty bulky in the process.

[geoffvalenti]

Thanks for all the replies, and especially to jesfirth, who kindly sent me a replacement gauze.

I think I'm going to do some real world driving tests, with and without, and see if I can actually notice any difference.

The car seems to be running smoother, with noticeably less shunting since I replaced the damaged gauze, but I also replaced the air filter at the same time, so it's not an accurate test.


I've got Rovergauge.
Would it show up anything if I ran with or without the gauze.

I know that it continually shows different parts of the fuel map that are being used, but will freely admit that I don't understand what I'm looking at, when viewing that part of it.

Maybe a Rovergauge tutorial would be handy, but I suspect that's a topic for another day.

[blitzracing]

The only definitive test you could do is look at the load points in the map you have during idle- this will jump around a bit- but basically let says it moves around 3 load points at idle (working on the basis the idle is never that smooth)- then see if it moves around any more without the gauze in there- if it does you know its jitter from the AFM voltage output causing it. Probably quite difficult to quantify though.