Carburetor and air cleaner: How we found the fantastic fit

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Update by Tim Suddard to the Ford Mustang Fastback project car
Feb 9, 2023 | Ford, Ford Mustang, Holley, Summit Racing, Cobra Automotive

When we purchased our used race engine from Cobra Automotive, it did not include one crucial piece–the carburetor.

We talked to our friends at Holley and they recommended their Ultra XP racing carburetor. With the size of our engine and power output, they told us that their 650cfm, 0-80812HBX model would work well for what we are doing.

Summit Racing Equipment sells the carburetor for about $1000. It weighs roughly 38% less than a regular Holley carburetor. The carburetor also has 20% greater fuel capacity, fully tunable metering blocks, hand-adjustable idle screws and a host of other racer-friendly features.

While we have not started or tried tuning the engine yet, we have used these Ultra XP racing carbs on other projects and have found them to be far superior to trying to rebuild an old street-oriented carburetor.

For an air cleaner, we started with a 14-inch-diameter Moroso air cleaner, with a 3-inch-tall filter. This air cleaner has a recessed base to allow hood clearance. Our engine has a GM-style distributor (larger than the original Ford one), and the air cleaner would not clear the distributor. A spacer plate solved that problem, but we still had a hood clearance problem.

Part of our clearance problem resulted from the intake manifold that came on our engine is taller than some of the Edelbrock manifolds available, so we would need to figure out a solution.

Combing through the Summit website we found a K&N filter assembly that was only 2-5/16 inches tall. The K&N X-Stream Airflow assembly listed for around $200. We had real good luck with this air cleaner on our Sunbeam Tiger project years ago, and it had provided 47 horsepower over the tiny stock Tiger filter. The top is actually an additional filter and these filters breath very well.

We ended up combining the recessed Moroso base with the K&N filter and filter top for what should be a perfect, yet a bit expensive filter solution.

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Asphalt_Gundam HalfDork
2/13/23 10:44 a.m.

What does the base look like? The base has a big affect on airflow into the carb and can drastically hurt power.

I did some testing years ago and a K&N form fitted base for a Holley (the expensive one ironically) was down 13HP over no air cleaner at all.......Then I tested a large radius, drop base that was uniform curve from carb flange to the filter. It make 3HP MORE than no air cleaner when used with the same filter and flow through top. IIRC a regular old hard radius base like you get from the parts store was down 10/11HP from no air cleaner.

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