The Stovebolt Site Forums The Shop Area The HiPo Shop Subtle but important details on things like air cleaner assemblies

This is one of those stories that started very innocently, but soon bloomed into another full blown lesson on attention to detail.

I need an air cleaner assembly for my SLURP project (described in my SLURP postings on this board). My project vehicle being a 1955 Chevy Advance-Design series pickup, I have a lot of underhood area and height compared to more modern vehicles. So, I have bought a GM LQ9 6.0 liter LS series engine, very similar but larger to the one used in my earlier SSR project vehicle. That engine comes with a very mild cam that I am replacing, and also with fuel injection that I am discarding in favor of an Edelbrock dual quad carbureted intake system, and MSD “black box ignition” that works with the engine’s factory sensors and coil packs. I mention these details only because you will soon see how they play into the scenario here.

Air cleaner assemblies that will work with dual 4-barrel carburetors that are mounted 6.5” center to center, aren’t exactly found on every street corner. So, I was pleased to see that Edelbrock itself offers an air cleaner assembly, a really nice one, in its “Elite” series, that is even available with the same Endurashine finish I got for the intake and the two carbs. The assembly is 13.5” long by 7” wide, and 3.5” high. Very nice.

I thought. At first.

Then, I noted that the height of the air cleaner element itself is only 2.5” versus the 3.5” of the assembly height. I did a rough calculation based on the dimensions and photos of the assembly, and realized that the filter element had at MOST 87 square inches of surface area. Now, that surface area is pleated, so the actual “surface area” is larger, BUT I checked at the K&N air filter website, and sure enough, K&N says that their filters will work with very low restriction on the air flow, provided that you provide one square inch of surface area (actual dimensions, not pleated area) per every 6 CFM of air. So, this maximum of 87 square inches of area would handle 522 CFM of air flow.

This is a bit of a problem. We do not yet know how much power my modified LQ9 will make, because we don’t yet know if we can fit headers into the installation space (potential steering box and cross member issues), and we don’t have good reliable data on how well that dual carb intake will actually flow (I plan conservatively). However, the “best case” scenario for the projected engine power curve shows incoming air flow of close to 700 CFM. The worst case scenario still shows close to 650 CFM. Oops.

This means that the air cleaner assembly would be a bit of a restriction on power output, and that the air filter itself would also need to be changed rather frequently to minimize the restriction.

So, I went searching on The Web and in my speed catalogs.

Speedway offers a “Cobra style dual quad air cleaner” that is physically much more impressive in size. We’re talking 21.5” long by 10.5” wide, by 4” tall. Repeating my rough surface area calculations, I came up with a potential for up to 165 square inches of surface area – enough to support 990 CFM, or to enable far less frequent air filter changes.

To put this in perspective, the air filter on the SSR I just sold had a surface area of 128 square inches, and that was designed by GM to handle the 400 crank hp = roughly 600 CFM air flow of a stock Corvette LS2-equipped SSR, with an allowance for less than frequent replacement of the air filter.

The only potential problem I saw was that while the Speedway ad said that the air cleaner assembly baseplate was “adjustable” for different carb-center to carb-center spacing, it did not specify the RANGE of adjustability (some have very little range). I need 6.5” center to center. So, I called and asked. It turns out that this setup apparently comes with multiple pieces that enable a very broad range of adjustment, and I was assured that 6.5” c-to-c was no problem. I ordered one.

Obvious question: Why did Edelbrock undersize the air cleaner assembly THEY offer? The answer is that they wanted one standardized air cleaner assembly for all their dual quad intake setups (actually one design available in 2 or 3 different levels of finish and construction), and they had a serious constraint: many (most) of their dual quad intakes are used on Smallblock Chevy engines, not LS engines. The smallblock engines have that distributor right up high on the rear of the engine assembly. If Edelbrock made the air cleaner assembly any larger, it would have tried to occupy the same space as the distributor! So, they did the best they could, but it creates an automatic, but not obvious, restriction that would limit engine air flow and therefore engine power a bit. They could have stretched the air cleaner FORWARD, but then the air flow to the two carbs would no longer be symmetrical.

If you read the Edelbrock advertising text on the dual quad intake and air cleaner, it actually SAYS that the air cleaner will not interfere with the distributor. This sort of subtly warns a prospective buyer that the air cleaner assembly is limited in size, but it IS pretty subtle.

The LS series engines do not have a distributor. The coils are instead fired by an electronic system whose timing is controlled by sensors on both the crankshaft and camshaft, that precisely define the current status of the engine’s rotating assembly. So, on an LS series engine, the “distributor constraint” does not exist, and the air cleaner assembly can and SHOULD be larger.

You see what I mean about attention to subtle details?

Here are photos of the two air cleaner assemblies. The Speedway one is the one with no obvious retainer nuts visible anywhere.

http://i252.photobucket.com/albums/hh16/JimGnitecki/aircleaner-Edelbrock4235.jpg

http://i252.photobucket.com/albums/hh16/JimGnitecki/Aircleaner-Speedway.jpg

Jim G

Your air flow problem can be solved by stacking two elements. This will double the filter area, thus doubling the capacity. Off road racers have done this for years. With all of the under hood room on an AD this should not be a problem.

Just need to get a longer set of hold-down bolts that secure the air cleaner lid to the carbs?

Jim G

An off the shelf air cleaner on an otherwise nearly all custom truck sounds lame as you will see others with the same thing. I probably made mine in less time than your analysis.

http://s176.photobucket.com/albums/w186/curt160/engine/?action=view&current=aircleaner.jpg

That is VERY nice. Looks really sharp. But . ..

unless those filters are a lot bigger than I think (estimate from the photo 7" diameter and 2" high?), they have about the same filter area as the Edelbrock kit I discussed above! Do the math!

Jim G

Oh gosh, you must think I am MUCH more skilled than I actually am!

I assume these are program instructions for a CNC machine?

WAY beyond me!

But, maybe someone smarter than me can use them!

Jim G

Wow. I don't know what all that is supposed to be, but the Edelbrock looks to me like you might be able to go with a taller element from K&N. The K&N's are flexible, so all you need really is the circumference to be the same, and stick the taller filter in, and you're good. Unfortunately, you can't be sure of the exact circumference until you buy one. But then I'm sure you can return it if you just can't get it to work.

By the way, Edelbrock as you say undoubtedly had to make the filter fit with their rather tall intake manifolds under a "typical" car's hood. There usually isn't enough room under a musclecar's hood without some kind of a hood scoop for most combinations of aftermarket (better) intakes with many filter combinations. I know that's true with my '68 Firebird and '68 Corvette. On those, to get a good-enough round filter to fit, I had to use a drop base. I was concerned enough about not enough CFM being allowed past a drop base that I got Extreme-Flow top filter lids also.

Anyway, there's another question I had. You said you were running dual 5-barrel carbs??? I have NEVER heard of a 5 barrel carb. Why wouldn't you just run dual 4 barrel carbs? Or was that a typo?

That must have been a typo. 4-barrel of course. 500 cfm each.

I just edited the posting to repair it!

Jim G

Well, here's another consumer alert:

The Cobra style dual quad air cleaner assembly arrivd today and is disappointing enough that it is going back tomorrow.

There were four serious issues with it, despite its high price which I THOUGHT would ensure some level of quality:

1. The plating finish on the top cover was awful - you could see unplated metal in a number of areas

2. It really requires a lot of custom fabrication to actually assemble into a working assembly. More like a "kit" than an "assembly"

3. That advertised 4 inch height, which I had thought might translate into a 3 or 3.5 inch air filter element height between the top and bottom plates turned out to be "extremely rounded up" - it was nowehere close to 4 inches. The bigger problem was the height of the air filter element itself; that was barely 1 4/8 inches GROSS, and after subtracting out the "glued" area top and bottom that could not concerivably pass any air, was a NET of only 1 1/8 inch!! That's not a misprint. One and one-eighth inch net air inlet height.

Since the total circumfrence of the oval air filter was 52 inches, that gives a working area of only about 58 square inches!! That would only suppport 58 x 6 = 350 CFM of air flow into the engine!

4. The air filter used was a paper type, not a K&N type, so actually its flow abilities were even lower.

It is hard for me to believe that back in Cobra days, this type of dual air cleaner assembly was apaprently actually used to feed the Cobra engines. If so, they must really have "sucked" to make the power they did.

I ordered the Edelbrock assembly today, along with a second air filter element for it, and will pick up some 1/4-20 running thread tomorrow that will enable me to, as suggested by others, STACK TWO of the filters (one of the advantages of having a vehicle like "Red" with fairly enormous hood clearance)!

Jim G