It's not a big difference, out two filter system uses smaller diameter Almost as if on purpose. You can install single larger diameter intake and will have the same flow

 

If indeed the stock filters flow 300 cfm each I wouldn't call it undersized, maybe they get undersized for the tuned 5.0 ltr engines (same filter as far as I am aware). The flow could be right when I read the K&N replacement flow 385 cfm, so if the stock filters are part of the small restriction you measured (0.6 psi), then these K&N would already give the max for minimum effort imho. Larger sized filters (full filter surface area) will help in extending the service interval as they are able to catch more dirt whilst still perform well, though not sure if that where design criteria's.

600 CFM for the stock 4.2 setup is already pretty good, and explains a large part of the 20 hp increase compared to the x100 models who had much lower flow filters, which I can only estimated based on filter size like maybe 420 CFM.

When looking at the box you are making, I notice the different connection very short before the MAF compared to the stock box, which potentially can cause different flow over the MAF and thus different readings (higher or lower), so you can't rely anymore on the MAF reading to check if you have more flow.

 

Most of the 20 hp gains are more then likely coming from dual intake setup which lowers the restrictions the older cars have like your STR.

So larger filter/air piping will definitely help for the older setups. For the STR/XJR changing the main aluminium intake pipe to the ones from a Range Rover will help as well, they flow more, here is one as example:
https://www.ebay.co.uk/itm/RANGE-ROV...oAAOSwb91dNZ~c

 

Which connection you referring to? From maf to box there is a 90 degree elbow from 3.5 reduces to 3 on stock connection wasn't there.
The graph of my filters follows the stock graph just with higher top end flow

 

If the 5.0 was naturally aspirated it would be sucking in 580 cubic feet of air every minute at 6,500 RPM. (5 liters X 6,500 divided by 28). The supercharged engine is clearly sucking in more air that the NA engine.

Where did you see the CFM rating for the filters? The 300 CFM would be about right for the NA engine since there are two filters, but it wouldn't be enough for the supercharged engine.

 

The stock air filters on the 4.2L XKR are too small, but somehow the exact same pair of air filters on a 5.0L XKR can deliver >600hp worth of air.... righty-o then...

 

I checked with the Wix the manufacturer and supplier to Jaguar dealers. Their rating is 330cfm per filter.
I used this online calculator and I get a minimum required cfm of 722 for our cars if volumetric efficiency is around 150. For the 5.0 the cfm requirement is even greater .
https://www.widman.biz/English/Calculators/CFM.html

 

Thanks avos....it looks to be physically larger internally.....is that correct.....with the inlet and outlet the same as my str

 

I'm sure that you can pump air of a 1000hp motor through them but at what cost is the question..

 

Of course its bigger ;-), the intake part is la bit larger, though the outlet that goes on the TB is te same size. The curving towards the TB is better which allows for a better flow into the TB.

 

That's what the vacuum measurements will show. You mentioned 0.6 psi, which is already low, could be for the most part of the filters, but that is wat you should check 1st imo to know what you need to work on. If for example it is indeed for most of the part the filters, then a simple K&N swap would take care of it already.
If you would get it down to maybe 0.3 psi, then my best guess would be somewhere around 6/7 hp, potentially hard to measure on a dyno, but always welcome of course.

 

The point was to maintain OEM filtering efficiency and not go down to lower kn filtering level and offer more air flow. I still think that .6 psi is a restriction per side so 1.2 is the total.

 

What measurement do you get from the pressure sensor in the intake?

 

So confusing info back, scratching my head here. I'm getting higher maf readings of around 10% max but It appears that by measuring vacuum on one side intake , where part load breather connects. With new intake I'm hitting higher not lower vacuum of 18.7 inch of water vs before Around 16.5-17 inch of water. If theoretically I'm making 20hp more due to higher flow, would that offset the vacuum restriction since we are now getting 5% more power?

 

Ok, so the 0.6 psi, and with the new intake 0.68 psi was from the MAP sensor I was referring to?

Could be granularity, measurements with the IDS are best taken with just 2 sensors max, so RPM and MAP, and ideally in 3rd of 4th gear.
and/or, the outside pressure (barometric pressure) could play a part as well, is .08 psi is already very low

The values of the MAF are for me not comparable anymore as you changed the flow.
.
You need to understand 1st where the (small) restriction is coming from the original intake (the 0.6 psi right? So is it the tubing, the MAF, the filters or all combined? If the measurement is from the MAP you also have the TB as extra restriction.
.

 

Avos I do measurement of restriction by inserting a manometer which reads vacuum , inserted into part load breather hole on driver's side intake. So only one side is measured and only before the part load breather hole. So it's a combined restriction up to that point of the intake tube. How it translates to the over all vacuum I'm not sure , I just figured take measurement from the single tube and multiple by two since there are 2 intake tubes. But now I'm confused as why I'm getting slighly higher restriction reading with the new intake... If we take the new maf reading percentage difference compared to stock and we take the percentage difference of intake restriction that number is around the same and proportional,, hmmm..

 

Vacuum does not add, it averages. Two tubes each .6 would equal .6 for both. NOT 1.2.

 

You might be right , I might be right.
In our ECU maps there is a map which is regarding intake restriction and there is a number which is 1.45 psi in there for restriction. So going by that number my calculations would be closer to that... Although I would like to know the exact scientific method to figure this out.

 

Am sure one day you will realize how it works.

What is holding you back from making a MAP measurement as suggested?

By having measurements at different places you will be able to also determine where restrictions are, and at least the MAP one closed to the SC and matters most when it lso comes to ECU behavior as you indicate.

You could already draw the conclusion that the 500 cfm filters don't change the vacuum significantly compared to the stock ones, an easy way to know for sure the impact on restriction is to do a run without filters, than all will be clear and you know where to work on for improvements.

 

Avos you lost you with the map measurement.. you meant just to measure two values for faster refresh Map and RPM? But what would measurment from map tell me ? it won't show a restriction since it's inside the crankcase no?
Yes I agree on trying a run without filter , maybe just adding a nylon stocking so at least protect from the sand?