3AM / 5AM / other airflow meters

[Barkychoc]

I actually have a V8S with the 4.0 pre serp engine, but I guessed I might get more V8 info here.
Whats the deal with airflow meters?
I have a 3AM airflow meter, which I guess has been fitted from new.
Is the 5AM a straight swap, whats the difference, is there any difference? Will it work?
Are there alternatives at reasonable cost which will allow more air in?
At this point in time I don't want to be fiddling with the ECU, I just thought if there is any easy (budget) upgrade path to allow it to breath a little easier I'd consider it.

Any info appreciated.

Chris

[GreenV8S]

I've never compared a 3AM against a 5AM so I can't say for sure, but comments from others seem to imply that they're interchangeable. I wouldn't expect any performance gain though. The problem with changing individual components like this is that the power is restricted by the rest of the induction system and you can only get very small gains from changing any one point. Something that is well worth doing IMO is to make sure that the air filter is big enough, and clean, and drawing in cold air rather than hot, and make sure the intake pipe from the filter to the throttle is big enough and has a smooth inner surface and is insulated from exhaust heat.

[P100]

Tend to agree with the above.
I have found that the 3AM is fitted to engines that are not fitted with cats, the 5AM is fitted to cars with cats.
I do not think that there is any performance advantage in using either, as dimensionally they are the same.
However, I do know that if you have a cat car and fit the 3AM AFM it will store a fault code in your engine ECU, so I guess there must be an internal circuit difference between the two.

I have heard some tuners are having some success with overboring the inside diameter of the AFM, this allows more air into the plenum, but I would think that you need to do some serious plenum work to make it count!

Cheers Roy

[OscarT]

A plenum throttle body bored out to 72mm diameter, an AFM bored out by 6mm, shortened trumpets and a slight ECU remap can give good mid-range improvements IMO.

[GreenV8S]

OscarT said:

A plenum throttle body bored out to 72mm diameter, an AFM bored out by 6mm, shortened trumpets and a slight ECU remap can give good mid-range improvements IMO.

So can an uprated cam, and bored out trumpet base / inlet manifold / gas flowed heads.

The thing is though, that all of these changes complement each other - if you only do some of them then then you won't see the full benefit from the ones you have done because you will still have a bottleneck. To do the whole lot isn't cheap though.

[dwgriffith]

The 3am and 5am are direct fit equivalent where the 3am was the original. The 3am were made for Lucas by Hitachi and the 5am were made by Lucas (presume under license?) Replacements can be found on jaguar saloons and Saab 900 turbo. The cheap one's on eBay are NOT genuine Lucas items so beware.

[OscarT]

I was trying to make the point that by improving induction through relatively simple and cheap measures appreciable gains can be had without resorting to expensive major engine surgery.

OscarT

[Barkychoc]

Thanks folks - my view at the moment is that I'll leave it as it is - it runs well, and always starts first time with a steady tickover.
Just thought if I could get something for nothing I'd do it.
Thanks for the responses.

Chris