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To someone just getting started in the high performance automotive scene, all those custom hoses and connectors and odd nomenclature may seem almost like a foreign language. It can be a bit of a struggle to figure out what all those terms and abbreviations mean. This story will help make the world of high performance hoses and their connections much more understandable.
Let’s start with some basic information. All of the hoses and connectors in this story are referred to as AN components. The acronym originally stood for Aeronautical Navy which was the term used in the aviation industry for the specific type of fuel, oil, and coolant hoses used in high performance aircraft. Today, Army Navy is another genuinely accepted version of AN. The high performance automotive AN hose business began as an offshoot of the aviation industry.
It didn’t take long before specialty high performance automotive hoses and connectors began to make a big impression in the street car market. Today, this AN lineup has evolved into somewhat of a bewildering array of multiple hoses, materials, designations, and requirements for use. We will lay down a solid foundation of information that should make choosing the hoses and connectors for your next project a little bit easier. The focus of this story will be mainly on plumbing fuel and specifically pump gasoline.
These four hoses offer a useful size comparison. The smallest is a -4 hose used for vacuum or steam lines. The next is a -6 hose (3/8-inch) with the next a step up to -8 (1/2-inch). The largest of this quartet is a -10 (5/8-inch). All hose sizes are rated based on inside diameter (i.d.).
The sizing references may seem odd but the reality is the entire numerical approach is based on 1/16-inch inside diameter hose. As an example, -6 refers to an inside diameter of 6/16- or 3/8-inch. Similarly, a -4 is ¼-inch and -8 equates to ½-inch. This also applies to hose ends that match a specific hose size.
In the early days, all AN hose was reinforced rubber hose wrapped with a very stiff braided stainless-steel outer covering that protected the hose from abrasion. Today, rubber alone is not enough to keep up with gasoline additives and the many, readily available alternative fuels. All Earl’s “rubber” hose now uses a synthetic rubber formula. The more sophisticated Earl’s hose uses a PTFE inner liner. This acronym stands for poly-tetra-flouro-ethylene. This is the material used in more rugged Earl’s hose that offers some amazing and interesting benefits that we’ll detail in a moment.
Let’s start our look into hoses with Earl’s affordable Vapor Guard. Normal automotive rubber fuel line, such that you might find at your local auto parts store, is surprisingly permeable and not very chemical resistant against today’s harsh fuel additives (especially the ethanol content found in most pump gas), which means it allows fuel vapors to easily escape through the wall of the hose and doesn’t hold up well to long-term use. Once fuel lines are degraded, hose particles can contaminate and obstruct fuel injectors and carburetor passages stopping your car in its tracks.
Aptly named since it employs four separate layers to protect against vapor leakage, Vapor Guard’s primary innermost Primary Barrier Layer offers high resistance to heat and aggressive fuels. The middle Earl's Vapor Guard Barrier is a Thermoplastic layer that provides superior fuel isolation and virtually eliminates vapors from escaping through the hose. The Exterior Cover Barrier provides extreme tolerance to heat and ozone providing a three-way shield against hose deterioration.
Vapor Guard hose can only be used with matching Vapor Guard hose ends. Here, we’re connecting to a Holley street fuel pump. Note that the Vapor Guard hose ends employ a smooth radius barb to prevent damaging the inner liner on the hose. Final sealing is accomplished with a hose clamp.
Vapor Guard hose is offered in only two sizes: 5/16- and 3/8-inch along with a choice of either a 50 psi burst pressure carburetor rating or an EFI-rated hose with a 225 psi rating. The Vapor Guard hose is designed to only be used with Earl’s specific Vapor Guard hose ends. The reason for this is the hose end’s single smooth retention bead that prevents damage to the Vapor Guard’s inner liner. Vapor Guard hose ends are also affordably priced and should be secured with the specified outer hose clamps.
In addition to the conventional Vapor Guard line, it is also available in a submersible variety. Earl’s Vapor Guard submersible fuel hose is ideal for use inside fuel tanks to attach the in-tank fuel pump or pickup. Most other fuel hoses are designed to handle fuel only on the inside of the hose & can cause damage to the hose when submersed in fuel. It is compatible with race gas, pump gas, alcohol & ethanol blend gasoline, biodiesel, and diesel fuel.
Super Stock hose is a budget-oriented hose that can only be used with specific Earl’s Super Stock hose ends. These push-on hose ends use sharp barbs (unlike Vapor Guard) to ensure a leak-free seal.
Another rubber fuel line option is Earl’s Super Stock hose that has been formulated to be more tolerant of pump gas additives. A common misconception is that ethanol is the main perpetrator causing damage to older fuel line but there is mounting evidence that the family of benzene additives called aromatics (toluene, xylene, and others) contribute to serious hose degradation. These additives can be found in concentrations of 25 percent or more in pump gasoline and have been found to be far more damaging to even synthetic rubber lines compared to ethanol.
Super Stock hose (and all of the remaining Earl’s rubber hose lines for that matter) is not designed to totally withstand the damaging effects of these additives for a long period of time. However, the Super Stock hose is an inexpensive upgrade from normal rubber fuel hose. We have included a small chart that lists fuel compatibility relative to each style of Earl’s hose in this story. Super Stock hose comes in a variety of sizes from -4 through -12 sizes.
Super Stock hose is intended to only be used with matching Earl’s Super Stock hose ends. These hose ends feature twin barbs that retain the hose along with the use of its red outer socket. The beauty of this arrangement is that installation is extremely easy as the hose ends easily push into place and no special tools are required.
Auto-Flex hose is the next step in the tiered family of Earl’s hoses and is is a competitively-priced stainless steel braided hose. Auto-Flex comes in a multitude of sizes from -4 all the way up to -18 and even in odd sizes like -5 (5/16-inch) that is commonly used for automatic transmission cooler lines. Auto-Flex is a high-quality, stainless-steel braided, competitively priced hose. Earl's Auto-Flex stainless hose is manufactured in the USA and is intended as a budget friendly, reliable option for sportsman racers and streetcar builders. Auto-Flex features a partial coverage textile inner braid that is imbedded in the liner during manufacture, and the hose is finished with a full coverage stainless steel braid which is bonded to the reinforced liner. The liner is known as H.T.E ( not to be confused with PTFE ) and is one of the highest quality of synthetic neoprene liners on the market. Continuous use temperature rating for Auto-Flex is - 40 to + 350 degrees F. and Auto-Flex hose is intended for use with Swivel-Seal, Auto-Fit and Auto-Crimp hose ends only.
The next step up is Earl’s Pro-Lite 350 hose that offers a nylon-braided exterior instead of stainless steel. The inner hose starts with Earl’s synthetic blended rubber and is strengthened with impregnated nylon sheathing. The hose is available in seven sizes ranging from -4 to -20. Living up to its name, Pro-Lite is half the weight of traditional stainless braided hose which is always a concern for competition vehicles. Perhaps worthy of greater praise is the ease with which this hose can be cut and the hose ends installed. Maximum working pressure is 350 psi.
The issue of rubber fuel lines deteriorating due to a variety of issues related to pump gas or race fuels has brought about some interesting solutions. Earl’s accepted this challenge with the UltraPro fuel line that uses a highly flexible, PTFE liner that is impervious to all fuels, oil, and coolants and can be counted upon to not deteriorate over long-term use. Its double-helix construction makes UltraPro both incredibly flexible and light weight.
It’s worthwhile to point out an important UltraPro feature that is often overlooked. When fuel passes through a white PTFE-lined hose, this movement will cause a buildup of static electricity. Since white PTFE is not conductive, this static electricity builds up on the surface of the liner. When sufficient voltage is created, the energy discharges to any nearby ground. This spark will cause eventual damage to the PTFE hose and must be avoided. UltraPro solves this issue by using a carbon-infused PTFE liner that is black in color which automatically conducts this charge to ground, preventing any static electrical buildup and discharge.
As you might expect, this UltraPro PTFE hose requires specific UltraPro hose ends. The main difference is the inclusion of an olive used to seal the inner liner to the nipple and hose assembly. While both the UltraPro hose and hose ends are more expensive than rubber-lined versions, UltraPro’s extended life expectancy more than compensates for the added expense. While the UltraPro hose ends appear complicated, installing the hose ends is not difficult, and can be accomplished with hand tools.
The next hose up is Speed-Flex, which features a lightweight stainless-steel outer braid over an extruded PTFE liner. It is an extremely versatile hose that is compatible with a multitude of fluids such as brake fluid (-3 and -4), power steering fluid (-4 and -6), and oil and fuel (-4, -6, -8, and -10). One note is that only -6, -8, and -10 Speed-Flex hose is carbon lined to prevent static electricity build-up with fuel. Because Speed Seal uses an "olive" between the socket and hose end to seal the hose, it is easy to assemble and completely field serviceable. Speed-Flex in -3 and -4 sizes is most commonly used for brake line and is available with a PVC outer layer to prevent the braided steel from "sawing." Maximum pressure is dictated by the size of the hose. Speed-Flex hose ends are available in steel, stainless steel, and aluminum. The aforementioned benefits, plus Speed-Flex's backwards and forwards compatibility with nearly all fluids makes it one of Earl's most versatile hose lines.
Speed-Flex Hose Size Max Working PSI
2 AN 2000 PSI
3 AN 2000 PSI
4 AN 2000 PSI
6 AN 1500 PSI
8 AN 1000 PSI
10 AN 500 PSI
The Auto-Fit hose end (left) uses a pair of barbs to seal the nipple to the hose. The Swivel-Seal hose end (right) uses a cutter that pushes into the rubber hose creating a leak-proof seal that has been proven through decades of use.
The two rubber-lined Auto Flex and Pro-Lite 350 hoses require the same grouping of hose ends that include the Swivel Seal, Auto Crimp, and Auto-Fit hose ends. We’ve omitted details on Auto Crimp hose ends in this discussion mainly because the hose ends require a professional crimping machine to install the hose ends. These are best suited for race shops but we will have an article about them shortly.
The Auto-Fit hose ends look similar on the outside compared to Swivel-Seal versions and are among the most affordable. The Auto-Fit nipple uses a pair of barbs to seal to the hose instead of using the Swivel Seal’s cutter-style nipple connection. Installing either the Auto-Fit or Swivel-Seal hose ends use similar procedures. The socket is placed over the hose and then the nipple is inserted into the hose, then the socket tightened over the nipple to complete the installation.
Swivel Seal hose ends are the most popular, compatible with four of the rubber-lined hoses. These hose ends use what is called a nipple and cutter style of retention that has been the aerospace standard for high-pressure sealing since the early 1950s. This design employs a sharp, outer ring that slices into the rubber liner, creating a leak-proof seal once the nipple is fully threaded into the socket.
This tight view of a black-anodized black-8 hose end readily reveals the cutter (arrow) portion of the hose end. The round inner tube slides inside the hose while the outer portion cuts into the thick rubber hose to create a leak-free seal.
This Swivel-Seal gets its name from a stainless steel swivel pin retaining a pair of O-ring seals. This pin allows the hose end to rotate. The limitation of the Auto-Fit nipple is that it is fixed in its permanent position once installed on the hose. Auto-Fit requires the installer to aim a 90-degree hose end (for example) in its correct clocked position to minimize inducing twist into the hose. Conversely, a Swivel Seal hose end is free to rotate 360 degrees, making installations much simpler. If you are a rookie hose builder, the Swivel-Seal hose ends are worth it to make building hoses much easier.
Auto-Fit hose ends (top) are among the most affordable AN hose ends for braided steel or nylon outer braid hose but they are limited to a fixed position. The Swivel-Seal (bottom) offers a major advantage. The Swivel-Seal uses a stainless steel pin (arrow) that allows the hose end to spin 360-degrees. This makes building hoses much easier as the final clocking position of a 90-degree hose end can be easily adjusted.
For high–pressure power steering applications, Earl’s also offers a steel and fabric reinforced, high-pressure Power Steering hose and hose ends. The hose has a heavy wall thickness and carries a maximum working pressure rating of 2,250psi and maximum pressure rating of 5,000.
While the majority of the attention in this story has been placed on hose for fuel, oil, and coolant lines, Earl’s also offers an extreme high pressure hose intended for custom Power Steering hose. This is a thick-walled, heavy-duty hose in your choice of blue or black with a 2,250 psi pressure rating, far in excess of the pressure-relief valve settings on all power steering systems. This hose is complemented with specific steel or stainless steel hose hose endsavailable in straight, 45º, 90º, and 120º configurations. These are simple tapered nipple style hose ends that are easy to assemble.
Finally, we’ll quickly mention the two other Earl’s hoses that complete the lineup, Ultra-Flex 650 and 660. These hoses require dedicated crimping tools and our designed for extreme duty and with professional race teams in mind.
Ultra-Flex 650 is a braided Kevlar hose that is 60% lighter than Earl's standard stainless braid-protected synthetic rubber hose. These race-oriented hoses require their own specific hose ends that must be crimped in place using Earl’s Ultra-Flex hydraulic crimping machine. Ultra-Flex 650 combines a woven Ultra-light Kevlar braid with smooth-bore PTFE tubing for increased flow and a convoluted outside for incredible flexibility. It also has significantly higher flow and pressure ratings than conventional convoluted PTFE hose. It's maximum operating pressure is 1180 PSI and maximum temperature is 500ºF. Being made of PTFE resin, it has a large range of applications that are capable of handling fuel, oil, water, methanol and air.
Ultra-Flex 660 uses the same inner PTFE inner tubing as Ultra Flex 650 hose, but with a high tensile grade 304 stainless steel outer braid. Ultra-Flex stainless is 40% lighter and has an average of 14% larger ID than Earl's premium stainless braided rubber hose. It still offers all of the same flow rate and flexibility advantages of the Kevlar® hose but with additional protection. It also offers a very high vacuum rating of 29Hg. Ultra-Flex 660 accepts all of the same hose ends and crimp collars made for the Kevlar® Ultra-Flex line. This means that the same crimper and dies used for the Kevlar® hose can be used with the stainless, so your Earl's universal crimper and dies are all you need for all of your high end line assemblies. (All trademarks are property of their respective owners.)
As you can see, there are multiple layers to the Earl’s fluid transfer process, offering the enthusiast a wide range of options when it comes to plumbing a custom, high-performance fuel or cooling system. Leaks of any kind are the enemy of a quality build and the best way to avoid the dreaded drip path is to use quality parts with a pro-like installation.
