Hey guys! Ever found yourself scratching your head trying to figure out the firing order for a modified 351 engine? You're definitely not alone. Getting the firing order right is absolutely crucial for your engine to run smoothly, efficiently, and without any of those nasty vibrations or misfires. In this article, we're diving deep into the world of 351 modified firing orders. We’ll cover everything from understanding what a firing order is to how it affects your engine's performance and provide you with some handy diagrams to get the job done right. So, buckle up and let’s get started!

Understanding Firing Orders

Let's start with the basics: What exactly is a firing order? In simple terms, the firing order is the sequence in which the cylinders in your engine ignite. This sequence is carefully designed by the engine manufacturer to ensure balanced operation and minimize stress on the engine components. When you modify your 351 engine – maybe you've swapped the camshaft, changed the intake, or done some head work – the original firing order might not be the most optimal anymore. That's where a modified firing order comes into play.

Why Modify the Firing Order?

So, why would you even consider changing the firing order? Well, there are a few compelling reasons. First off, a modified firing order can improve engine balance. By strategically sequencing the cylinder firings, you can reduce vibrations and stress on the crankshaft, leading to a smoother running engine and potentially extending its lifespan. Secondly, a modified firing order can enhance exhaust scavenging. This means that exhaust gases are more efficiently removed from the cylinders, allowing for better intake of fresh air and fuel. The result? Improved combustion and increased horsepower and torque. Lastly, certain modified firing orders can reduce the load on the front cylinders, especially in engines where the front cylinders tend to run hotter due to cooling limitations. This can help maintain consistent cylinder temperatures and prevent issues like detonation or pre-ignition.

Understanding the role and benefits of a modified firing order is the first step in optimizing your engine's performance and longevity. Whether you're aiming for smoother operation, better exhaust scavenging, or reduced stress on engine components, knowing the correct firing order is crucial.

Stock 351 Firing Orders

Before we jump into modified firing orders, it's essential to know the stock firing orders for the 351 engine family. The 351 family includes the 351 Windsor (351W), the 351 Cleveland (351C), and the 351 Modified (351M). Each of these engines has its own unique characteristics and, importantly, its own firing order. Knowing the stock firing order is the baseline from which any modifications are made, and it helps in understanding why certain modified firing orders are beneficial.

351 Windsor (351W) Firing Order

The 351 Windsor is probably the most well-known of the 351 engines, and it has a firing order of 1-3-7-2-6-5-4-8. This means that cylinder number 1 fires first, followed by cylinder number 3, then 7, and so on. The 351W is a popular choice for performance builds, and many aftermarket parts are available to enhance its capabilities. When modifying a 351W, some builders stick with the stock firing order, while others opt for a modified one to achieve specific performance goals. The key to remember is that changes to the camshaft or other engine components can significantly influence the optimal firing order for your particular setup.

351 Cleveland (351C) Firing Order

The 351 Cleveland is another beast altogether. Known for its high-flowing cylinder heads and robust design, the 351C also uses a firing order of 1-3-7-2-6-5-4-8, identical to the 351W. Despite having the same firing order, the 351C's unique head design and valve angles make it a powerhouse in the right configuration. Modifying a 351C often involves optimizing the airflow through those famous heads, and the firing order can be adjusted to complement these modifications, further enhancing its performance. Many enthusiasts swear by the 351C for its potential to produce serious horsepower, especially in vintage racing applications.

351 Modified (351M) Firing Order

Lastly, we have the 351 Modified, often referred to as the 351M. This engine shares many characteristics with the 400 cubic inch Ford engine, and it also uses the 1-3-7-2-6-5-4-8 firing order. The 351M was designed to be a versatile engine, and while it may not have the same high-performance reputation as the 351W or 351C, it can still be built into a strong and reliable engine with the right modifications. When working with a 351M, it’s important to consider its intended use and the overall build plan to determine if a modified firing order will provide any benefits. Swapping to a different camshaft is a common modification that can influence the need for a changed firing order.

Understanding these stock firing orders is crucial before considering any modifications. Whether you're building a high-revving 351C, a torquey 351W, or a reliable 351M, knowing the baseline will help you make informed decisions about your engine build and how a modified firing order can benefit your specific application. Each engine has its own unique strengths and weaknesses, and the firing order is just one piece of the puzzle in unlocking its full potential.

Common Modified Firing Orders for 351 Engines

Okay, now that we’ve covered the stock firing orders, let’s get into the fun part: modified firing orders! When you start tinkering with the internals of your 351 engine, especially the camshaft, the stock firing order might not be the most optimal choice anymore. Swapping to a modified firing order can bring a host of benefits, such as improved engine balance, enhanced exhaust scavenging, and reduced stress on certain cylinders. But with so many options out there, which modified firing order should you choose? Let's take a look at some of the most common ones.

1-5-4-2-6-3-7-8 Firing Order

One of the most popular modified firing orders for the 351W and 351C engines is 1-5-4-2-6-3-7-8. This firing order is often chosen because it can significantly improve engine balance. By changing the firing sequence, you can distribute the power pulses more evenly across the crankshaft, reducing vibrations and stress. This is particularly beneficial for high-performance engines that operate at higher RPMs. Many aftermarket camshaft manufacturers offer cams specifically designed for this firing order, making it a relatively straightforward swap. Keep in mind that you'll need to ensure your distributor and wiring are correctly set up to match the new firing order.

1-5-4-8-6-3-7-2 Firing Order

Another common choice is the 1-5-4-8-6-3-7-2 firing order. This setup is known for its ability to improve exhaust scavenging, which can lead to better cylinder filling and increased horsepower. By strategically sequencing the exhaust events, you can create a more efficient flow of gases out of the cylinders, allowing for a better intake of fresh air and fuel. This firing order is especially useful in engines with performance headers and exhaust systems. As with any firing order change, it’s crucial to double-check the distributor phasing and spark plug wire routing to avoid any misfires or timing issues.

Benefits and Considerations

When choosing a modified firing order, it’s important to consider the specific goals of your engine build. Are you aiming for smoother operation, increased horsepower, or better fuel efficiency? Each firing order has its own set of advantages and disadvantages, and the best choice will depend on your unique needs. Also, remember that changing the firing order is not a standalone modification. It often requires other supporting mods, such as a new camshaft, updated distributor, and proper tuning, to realize its full potential. Always consult with an experienced engine builder or tuner to ensure that your chosen firing order is compatible with your overall engine setup.

Switching to a modified firing order can be a game-changer for your 351 engine. It can unlock hidden horsepower, improve engine balance, and enhance overall performance. However, it’s crucial to do your homework and choose the right firing order for your specific application. With the right planning and execution, you can take your 351 engine to the next level.

Diagrams and Resources

Alright, let's get visual! Understanding the firing order in theory is one thing, but having a clear diagram to follow when you're under the hood is a game-changer. Whether you're verifying your current setup or making the switch to a modified firing order, these diagrams will be your best friends. We'll cover how to read these diagrams and point you to some awesome resources to ensure you're firing on all cylinders – literally!

Reading Firing Order Diagrams

Firing order diagrams are pretty straightforward once you get the hang of them. Typically, they show a top-down view of the engine, indicating the cylinder numbers and the corresponding order in which they should fire. The diagram will also show the direction of distributor rotation, which is essential for correctly positioning your spark plug wires. For a 351 engine, you'll see eight cylinders arranged in two banks of four. The cylinders are numbered sequentially, usually starting with the front cylinder on the driver's side as number one, and then continuing down that bank. The next cylinder on the passenger side is typically number five, and so on. The firing order is then indicated by a series of numbers, showing the sequence in which each cylinder should fire. When installing your spark plug wires, you'll need to match the firing order to the correct terminals on the distributor cap. This means following the diagram closely to ensure that each wire is connected to the right cylinder.

Visual Resources

To help you out, here are some visual resources that you can use as a reference:

• Online Diagrams: A quick Google search for “351 firing order diagram” will yield a ton of images. Look for diagrams that clearly label the cylinder numbers, firing order, and distributor rotation. Websites and forums dedicated to Ford engines often have detailed diagrams specific to the 351W, 351C, and 351M.
• Engine Manuals: Your engine's repair manual is an invaluable resource. It should contain diagrams specific to your engine model and may also include information on modified firing orders if applicable. If you don't have a physical manual, many are available online in PDF format.
• YouTube Tutorials: Sometimes, watching someone else do it can make all the difference. Search for videos on “351 firing order” to find tutorials that walk you through the process step-by-step.

Having these visual aids at your fingertips will make the process of verifying or changing your firing order much smoother. Remember to double-check everything before you start your engine to prevent any costly mistakes!

Step-by-Step Guide to Changing a Firing Order

Ready to get your hands dirty? Changing the firing order might seem daunting, but with a clear plan and a methodical approach, it’s totally manageable. This step-by-step guide will walk you through the process, ensuring you don't miss any crucial steps. Safety first, guys – make sure to disconnect the battery before you start working!

Step 1: Identify Your Current Firing Order

Before you change anything, you need to know what your current firing order is. If your engine is running, observe the spark plug wire arrangement on your distributor cap. Note which cylinder each wire is connected to. If you're unsure, consult your engine's manual or use one of the diagrams we discussed earlier. This baseline will help you avoid confusion later on.

Step 2: Plan Your New Firing Order

Decide which modified firing order you want to switch to. Make sure it’s compatible with your camshaft and other engine modifications. Have a clear diagram of the new firing order handy. It's a good idea to print it out or save it on your phone for easy reference while you’re working.

Step 3: Disconnect the Battery

Safety first! Disconnect the negative terminal of your battery to prevent any electrical accidents while you’re working on the ignition system. This is a simple but crucial step that can save you from a nasty shock.

Step 4: Remove the Distributor Cap

Carefully remove the distributor cap. Inspect it for any signs of wear or damage, such as cracks or corrosion. If it’s in bad shape, now is a good time to replace it. Keep the cap and wires organized. You can label each wire with tape to indicate which cylinder it belongs to.

Step 5: Re-Route the Spark Plug Wires

Using your new firing order diagram as a guide, re-route the spark plug wires on the distributor cap. Ensure that each wire is securely connected to the correct terminal. Double-check your work against the diagram to avoid any mistakes.

Step 6: Verify the Distributor Phasing

After re-routing the wires, verify that the distributor phasing is correct. This ensures that the rotor is pointing to the correct terminal on the distributor cap when each cylinder is ready to fire. If necessary, adjust the distributor position to align the rotor with the correct terminal.

Step 7: Reinstall the Distributor Cap

Once you’re confident that everything is correctly aligned, reinstall the distributor cap. Make sure it’s securely fastened to prevent any issues with vibration or moisture.

Step 8: Reconnect the Battery

Reconnect the negative terminal of your battery. Now you're ready to fire up the engine and see if your changes have made a difference!

Step 9: Start the Engine and Check for Misfires

Start the engine and listen carefully for any signs of misfires or unusual noises. If the engine runs smoothly, congratulations! You’ve successfully changed the firing order. If you notice any problems, double-check your work and consult with a professional mechanic or engine tuner.

Changing the firing order can be a rewarding experience, but it’s crucial to take your time and follow each step carefully. With the right tools and a bit of patience, you can optimize your engine's performance and enjoy the benefits of a modified firing order.

Troubleshooting Common Issues

Even with the best planning, sometimes things don't go as smoothly as we'd like. If you've changed your firing order and your engine is acting up, don't panic! Here are some common issues you might encounter and how to troubleshoot them.

Misfires

Symptom: The engine runs rough, and you can feel it shaking or stumbling. This is often accompanied by a loss of power.

Possible Causes:

• Incorrect Wiring: The most common cause of misfires after changing the firing order is incorrect spark plug wire routing. Double-check your wiring against the firing order diagram.
• Faulty Spark Plugs: If your spark plugs are old or damaged, they may not be able to ignite the fuel mixture properly. Replace them with new ones.
• Distributor Issues: A worn or damaged distributor cap or rotor can cause misfires. Inspect these components and replace them if necessary.

Troubleshooting Steps:

1. Verify Wiring: Double-check each spark plug wire to ensure it’s connected to the correct cylinder.
2. Inspect Spark Plugs: Remove the spark plugs and inspect them for signs of wear or damage. Replace them if needed.
3. Check Distributor: Inspect the distributor cap and rotor for cracks, corrosion, or other damage. Replace them if necessary.

Poor Performance

Symptom: The engine starts and runs, but it lacks power or feels sluggish.

Possible Causes:

• Incorrect Timing: The engine timing may need to be adjusted to match the new firing order. Use a timing light to check and adjust the timing.
• Vacuum Leaks: Vacuum leaks can disrupt the air-fuel mixture and cause poor performance. Check all vacuum lines and connections for leaks.

Troubleshooting Steps:

1. Check Timing: Use a timing light to verify that the engine timing is correct. Adjust it as needed.
2. Inspect Vacuum Lines: Check all vacuum lines and connections for cracks, leaks, or loose fittings. Replace any damaged lines.

Engine Won't Start

Symptom: The engine cranks but refuses to start.

Possible Causes:

• Incorrect Firing Order: If the firing order is completely wrong, the engine may not be able to start at all. Double-check the wiring against the diagram.
• Distributor Position: The distributor may not be properly aligned, preventing the engine from firing. Adjust the distributor position until the engine starts.

Troubleshooting Steps:

1. Verify Firing Order: Double-check each spark plug wire to ensure it’s connected to the correct cylinder.
2. Adjust Distributor: Loosen the distributor hold-down bolt and rotate the distributor slightly while someone cranks the engine. Once the engine starts, tighten the bolt and adjust the timing.

Troubleshooting these common issues can help you get your engine running smoothly after changing the firing order. If you’re still having problems, don’t hesitate to seek help from a qualified mechanic or engine tuner. They can diagnose and fix any underlying issues to ensure your engine performs its best.

Conclusion

So, there you have it, guys! A comprehensive guide to understanding and modifying the firing order of your 351 engine. Whether you're aiming for smoother operation, increased horsepower, or better fuel efficiency, changing the firing order can be a powerful tool in your engine-building arsenal. Remember, it’s all about understanding your engine's specific needs and choosing the right modifications to meet those goals. By following the steps outlined in this article, you'll be well-equipped to tackle this task with confidence.

From understanding what a firing order is and why it matters, to identifying the stock firing orders for the 351W, 351C, and 351M engines, we've covered a lot of ground. We also explored some common modified firing orders and provided diagrams and resources to guide you through the process. And, of course, we didn't forget to address some common issues you might encounter and how to troubleshoot them.

Modifying the firing order is not just about changing a few wires; it's about optimizing your engine's performance and unlocking its full potential. So, take your time, do your research, and don't be afraid to experiment. With the right knowledge and a bit of elbow grease, you can take your 351 engine to the next level.