The V8 Owners Forum -

Hi all
looking to upgrade my air flow meter from a 3am is there a straight drop in that increases the cross sectional area
shaun

Is that a hotwire or flapper type?

Chris.

Its the same as the 5AM, just made by Hitachi IIRC.

No drop in upgrade, folks use later Bosch (20AM?) versions, but you have to change some wiring. Whether remap / chip is required may be arguable.

Shaun

The 3AM and 5AM are completely interchangeable. These are extremely reliable air flow meters. Unfortunatly they have an ID of only 55mm. This might be a problem on a highly tuned engine at full throttle.

You can machine the inlet and outlet of this AFM. Here is a picture of how I machine the inlet to flow air much better, and also to fit a standard 3" hose or filter:


The center section of th AFM creates a restriction which causes a small portion of the air to flow over the "hotwire". The most that this center section can be bored out is 5mm. Does not sound like much, but if you do the math it is ~20% more cross sectional area. Unfortunately boring out the inside by 5mm also messes up the air flow thru the hotwire. Especially at idle. It would require a lot of experimenting to get the idle correct with the inside bored out to 60mm.

Randall

Actually...that photo is after I have machined the outlet.

But my machined inlet does look similar. Razor thin wall with a 3' OD and no screen.

Shaun,

The standard A/F meter is ok for a standardish 3.5 but gets restrictive for larger capacity engines.

What capacity engine are you running and what spec re heads and cam?

You can swap in an A/F meter from a jaguar hotwire system that will give more flow and can be further improved if the internal radius on the inlet side is radiused.

If of interest i can look up the part no.

kevin.

Nobody tried Torqueflow AFM ?