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Naturally Aspirated vs. Forced Induction Part 1: Naturally Aspirated Fox Body Motors

Written By: Connor MC

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Fox Bodies were formidable opponents in their day. Unfortunately, with today's modern muscle cars this is no longer the case. You can still even the score by upgrading your Fox Body with the right power mods.

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We will examine all avenues for making serious power with the 5.0L Fox Body Mustang and hopefully after reading you’ll have a good idea of which is right for your Mustang’s future.

American Muscle

Naturally Aspirated Fox Body Builds

Which power adder is best, you ask? Well, the short answer isn’t really an answer at all. Rather, each setup has their own distinct advantages, disadvantages and requirements. With that being said, however, we can go through the specifics of each setup to better aid you in your decision.

Naturally Aspirated Engines

Worked 5.0L Fox Body Motor

A naturally aspirated engine, as the name implies, breathes on its own without any external help (external help being a power adder). Moving on from that great insight…

An engine, at the most basic level is essentially one large air pump. The more air you can get into it, the more fuel you can dump in. Then, provide the two with a spark and BOOM, work will be accomplished. At what rate said work will be accomplished (aka how much power is the motor producing) is reliant on how big we can make that boom. Right, enough physics. Let’s dig into the topic at hand.

Getting a Fox Body to Make More Rear Wheel Power 

Fox Body Mustang Top End Kit

In terms of making power, the key is not only to get as much air flowing into the engine as possible, but to use it efficiently. With a stock 5.0L Fox Body engine, the best way to do this is to do what is referred as an HCI swap (heads, cam, intake). The stock cylinder heads and intake manifold are major restriction points. Slapping on some aftermarket cylinder heads with matching intake from any of the big names such as Trickflow, Edelbrock or Ford Racing can have some momentous gains. The stock HO cam is actually a good piece and will work fine, but an aftermarket bump stick will maximize the fresh top end. A proper aftermarket street grind cam can see gains of up to 30HP over the stock cam in conjunction with a better flowing top end. Overall, a street driven naturally aspirated 302’s top out at ~380 HP (at crank). Furthermore, properly done, a naturally aspirated engine will be able to get up and go at virtually any point in the RPM range.

Naturally Aspirated Fox Body Motors - The Facts

  • A Naturally aspirated engine(n/a) breathes on its own without being forced air from a power adder, like a turbocharger or supercharger
  • A key to making more power with any engine is to get as much air into the motor as efficiently as possible
  • When adding horsepower or increasing the engine's airflow, your n/a engine will also need a larger supply of fuel
  • A naturally aspirated motor is hard to beat in terms of all-around reliability

Looking for more than that? No problem! Ever hear the age old adage ‘no replacement for displacement’? Well, with a naturally aspirated motor, this is irrefutably true. If you need power beyond the 380HP available from a 302 cu motor, stroke it! Longer cylinders (which is what is created by stroking a motor, you are changing the stroke length) can pull and fit in more air, allowing for more fuel and consequently, more horsepower.

Fox Body Engine Internals & Hardware 

Rolling out of the factory with a cast crank, forged pistons (hypereutic were used in 1993) and rods, the stock 5.0 internals are ready to handle whatever you can throw at it. In fact, the block will let go before the internals do, which usually occurs at power levels around 500 HP. The only need to dig into the bottom end is if stroking to a larger displacement, or you wish to change the compression with a set of aftermarket pistons.

Fox Body Fuel Delivery & Ignition

Fox Body Fuel Injectors

Of course with more power comes a need to supply more fuel. Luckily enough, with a naturally aspirated motor, the fuel system needn’t be complicated. Up the stock 88 liter per hour pump and 19 lb/hr injectors and that’s pretty much all you’ll need – dead simple. Best yet, most natural aspirated engines can run on regular gas, saving you cash at the pump.

Same goes for the ignition – make sure the plugs, coil, cap, rotor and wires are in good shape and you should be set. Maybe throw in a digital module to aid spark generation at higher RPM, but it isn’t necessary. If you want to squeeze out every last pony possible, you can opt for a custom chip and corresponding tune, but the stock EEC-IV does a fine job too. Make sure the timing and fuel pressure is good and that’s it, no need to drop some more Benjamins on a custom tune.

Effects on Your Mustang's Reliability 

In terms of reliability, a naturally aspirated motor is hard to beat. Relatively low stress is placed on the internals and if all parts are correctly installed, expect a long life. Maintenance remains the same – regular fluid changes and the odd ignition and fuel system tune-up will see a naturally aspirated engine last many a mile.

Bottom Line 

All in all, a naturally aspirated small-block Ford V8 is a great choice for pretty much any application, be it track or street duty. Overall build and maintenance costs will be lower as compared to a forced induction car and you won’t need to dig into the bottom end. At the end of the day, the naturally aspirated motor is always going to be the iconic motor for any muscle car. It is a passed the test of time and boy, they do sound perrrrrty.

Checkout part 2 of the guide by clicking here

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