That was quite a bit in shock when I was replacing my XXR air filters and I had air filters laying around from a 2000 e55 they only made about 350 horsepower. Was shocked to see the difference in size, our XKR air filters are tiny in comparison they are definitely undersized for our cars or Mercedes filters are way oversized for 350 hp, and yes the Mercedes set up uses dual filters just like on our cars.

 

I wonder what avos uses on his 700HP car? You could ask him...

 

He isn't around it seems , I sent him pm no answer. I really doubt he would use these tiny stock filters, can't believe I'm still using them and making the power that I am

 

I have no real knowledge of the physics or flow rates that go into calculating airfilter requirements, but 2 thoughts that occur to me to explain the difference in size

1. The XKR is forced induction vs the naturally aspirated Mercades.

2. The pipework from the air box to the engine could be of larger diameter on the XKR and/or have better flow characteristics than that on the Mercades as understanding of air flow has developed over the years negating the requirement for such large panel filters.

 

A 5.0 engine, running at 110% Volumetric Efficiency (because 'blower') will use approximately 632 cubic feet of air per minute at 7000 RPM. Since two air filters, each filter would have to flow 316 CFM of air with low restriction.
Since most of us use CFM and that correlates to Square Inches, let's do it this way...........
Filter Area must be greater than CUBIC INCHES X MAX RPM divided by 20,840 (which is an Air Filter Ratings Comparison Figure I used for building race cars).
SO:
Square Inches = 305 X 7000 / 20840 = 102.5 Square Inches.
Since TWO, each filter needs 51 Square Inches. Factor in extra dirt and filter inefficiencies, say 55 Square Inches PER FILTER.
What size are the XKR filters? I don't have any handy, and it's been awhile since I changed mine. I seem to remember something like 8" x 12", which would be about 72 Square Inches, disregarding any mounting flanges or whatever.
Seems OK to me.

EDIT:
I just found the filter size, it is 9.75 x 6.3, so 61.4 square inches. Still enough.
Also remember........ Horse Power is just BETTER use of the air that goes into an engine. Airflow only increases with Volumetric Efficiency (and RPM), so that would only affect the flow rate by maybe 10% with a better supercharger or over-driving the stock one with a smaller pulley. Not by much though. Peak VE would remain the same.

 

Cee Jay nice work! Although I think there is some corrections that must be done. Let's convert grams per second mass air flow readings for my car which go up to 400 grams per second into CFM, if I'm doing this correctly it's 400x4x20 divide that by 29.92 = 1069 CFM requirement,. Now this is on a 4.2 supercharged not reving anywhere near 7000
So if we use your formula 1069/2=534.5 x6250 /20840 we get 160.29 ci / 2 = 80.14 is the air filter size that we need

 

Well, fine then. I will go hide my face.

 

The filters on the XKR models are smaller than typical considering the displacement of the 5.0 supercharged engine. To me they are sized o.k. for a normally aspirated engine. I am sure the size or lack of size is down to packaging.
I change mine every year just for this reason.

 

Jaguar are just better engineers than Mercedes...

 

Did I do it right? Since I have peak air flow readings in grams per second that would be a requirement of 1069 CFM correct? Which seems more than I expected honestly

 

Did you remember to divide by two because Four-Stroke?

 

I could only find one formula to convert g/s into CFM , when I used it it came up to 1069 CFM https://sciencing.com/how-8394741-convert-gsec-cfm.html

Either way when I tested vacuum restriction at wot I came up with .6 psi on one side with clean air filter and .7 with dirty when I multiply this by two since two intake tubes I get 1.2-1.4 psi vacuum restriction , seems significant no?

 

So I just found out some interesting information from wix since they're the ones who make OEM air filters for our cars and are pretty much identical Wix 49500 has a CFM rating of 330.

What's really confusing that 49033 Wix is an identical size but is listed for 5.0 cars only. they don't have a rating for the CFM but by the looks of it 49033 has a bunch of metallic mesh which is absent on 49500 which would probably mean the later would flow better

 

Whichever and however, 1069 CFM is about what a 7.4 liter needs at 8200 RPM @ 100% VE. My P/S Mustang has a 557 CID/9.2 liter and it's running a 1295 Dominator (1500-style). I don't RUN it at 8000 RPM, my shift point is 7400 though. No huffer or anything, and the V.E. on it is about 94%.
Since I have NO IDEA about grams per second, I'll let you do any research on that.
For your Vacuum Restriction, the .6 on one side and .7 on the other would be 0.65 when combined, not a sum.

 

I think both of you forgot to carry the 1.

 

Sorry but how you got .65 of restriction? when .6 is per intake side so times 2
, there are two on 08xkr

 

I used the clean for one side and the dirty for the other. What, you change BOTH filters? My right filter is original from the factory, I only change the left one. Easier that way.
Regardless, if one vacuum tube holds .6 in/hg and another vacuum tube holds .6 in/hg, combined they would still have .6 in/hg.
I averaged the .6 and the .7 in your example.

 

Of course I have the same new filters on both sides, if one is at .6 you would add 2 for total intake restriction which will give you 1.2 psi. Think of it this way if one filter is completely closed off you would now have double the restriction because now all air is only going through one filter instead of two which split the restriction under normal operating condition

 

Looking at it YOUR way; if you had 25 intake tubes, all at .6 drop, that'd total 15 PSI and therefore ZERO FLOW WHATSOEVER. Doesn't work like that.

 

Not exactly sure how flow Dynamics work but if you have 25 tubes for example with same restriction you would have to have hell of a flow to cause it , but if it's the same total cfm flow, each tube would be at minimal restriction since flow per each tube would be 25 or 24 times less now and restriction even less not sure by what factor.
Either way I can't see how in this case if we have two tubes .6 psi restriction each it would not calculate up to 1.2 psi total restriction for both tubes, this is the total restriction that is going up against the air pump which is our engine, so I stand behind my calculation but if I'm wrong would like to know where.