Ok due to a modification I needed a smaller (as in thinner) oil filter than a z9.
A z9 oil filter is 94mm in diameter (or seam size) & I need one that is around 82mm in diameter.
Not worried about length, and it can be the same length as a z9.
I did some checking and found a few that are similar in dimensions to what I need but some are Agricultural & plant machinery specific filters which means that some wouldn't have pressure relief valves or drain back etc.
So,, just to be certain, I sent off an email to Ryco Australia explaining my situation and asked them if there was an oil filter that I could use to replace the z9 on a BA 4.0 6cy motor.

Ryco told me to use a z418 which is a teeny tiny filter compared to a z9:
Ryco part -----Height -------Seal Diameter -----Seam Diameter -----Thread
Z9 -------------142mm------------70mm ---------------94mm ----------- 3/4-16-UNF-2Bmm
Z418 -----------89mm ------------71.2mm -------------77.5mm ----------3/4-16-UNF-2Bmm.

Now I know that it will spin on & fit ok... But.. I don't think I want to bolt on an oil filter that was designed to fit a 4cyl EcoBoost falcon. Do you think that maybe ryco has made a mistake, or just made a wild guess,, or do you think they know what they are talking about.

I dont think it will be a problem, some of the au xr8s run a z89a witch isn't narrow like you need but are much smaller in length, so only difference would be the capacity and it may suffer in flow if you don't change it for a long time and it clogs up..

I dunno,,, but anyway, I'll give it a go for a while & see if there are any problems, I don't hold a lot of faith that it will be a success though because it wouldn't even be half the size of a z9. I expect that the oil pressure may increase & as you said there would be more likelihood of it clogging up quicker.
But if they are the only downsides to using this filter it shouldn't be a drama.
Just hope that the top end won't starve for oil.
EDIT: OK ,,I have now had a long discussion with Ryco AUS again (phone this time) about the z418 oil filter & asked for the complete rundown on the specs & it turns out that it is the exact same filter as a z9 just with a different can size. Flow & drain back are all exactly the same. Only noticeable difference will be that the motor will now have a little higher oil pressure due to the smaller (more restrictive) can size. So in every other way the z418 is just a smaller version of the z9.
Ryco said that many people including racing enthusiasts etc have done the change over for one reason or another without issues, so I feel more confident to use it now.

The 4.5Litre Toyota 1FZ-FE uses the Z148, I have successfully ran Z9's in those although dropped pressure slightly. You should get the reverse effect with a slight rise in pressure, which isn't necessarily a good thing for the OHC Ford 6 so worth consideration.

And just for clarity for the post subject, the BA and BF had different filters. Unfortunately it's been too long since I sold my BF to remember if the Z9 was interchangeable so can't comment.

Z89A is the smaller oil filter for the BA with an Oil cooler.

Z516 is the oil filter for the BF.

all falcons up to ba i6 has the 3/4 unf fitting in the block for the filter, where bf onwards went to a metric m22 fitting in the block..

Z9 (BA and earlier) is 3/4-16-UNF-2B and the Z89A is also 3/4-16-UNF-2B

The Z516 (BF onwards) is M22-x1.5-6H

OP,

What is your restriction in height?

The Z9 is 139mm in height, does the new one need to be shorter. I understand that you require it to be approx 82mm in Dia or slightly smaller.

Have you considered a remote oil filter?

I have & I am eventually going to run an oil cooler so I will fit a sandwich plate.
This should resolve all clearance problems..
About the length,, no it doesn't need to be shorter, actually it could be longer than the z9 & it would be OK.
When I modded the cast alloy plenum chamber so I could run an inter-cooler I accidentally read the wrong markings & welded the supercharger plenum outlet tube 10mm to far to one side.
It has no noticeable affect on performance but it now sits directly over the oil filter instead of being off to one side.
This makes it a very tight fit & virtually impossible to get any intercooler piping connected in there without a smaller filter.
I could only just make the intercooler piping fit with a 45 degree silicone hose, but it still sits hard on the z9 filter & it also collapses under vacuum anyway.
So I had to fabricate an aluminum version which isn't quite as easy to get into position & that is why I need to run a smaller diameter filter at the moment.
With a z418 filter fitted I can fit my home made 3" to 2 1/2" aluminum bend & still have about 5mm clearance to spare underneath.
It all seems to be working fine now without any noticeable problems & my tuner says the oil pressure is only up a smidge,,, even at WOT, & it's not enough to worry about so I'm sure it will be OK for the time being..