How to buy the right engine parts for your build

Introduction

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Building an engine can be a daunting task, especially for those who do not do it daily. Managing a budget while selecting the right components should be enjoyable, not anxiety-inducing.

Choosing parts without a plan can be costly. One ill-chosen part can lead to total engine failure, introducing a weak link that could have been avoided with proper knowledge. Winging it might result in a mismatch of components capable of high power but failing due to minor parts like wrist pins.

This guide aims to clarify the differences between parts, suggest the right questions to ask, and provide the knowledge needed to answer them. By the end, you should feel informed and confident in your choices.

If you have any questions during this guide, feel free to reach out for a second opinion. We are here to help.

GOALS DRIVE THE PROJECT TO SUCCESS (OR FAILURE)

Building a car is less stressful when you have a clear plan. Just like constructing a house, planning is crucial to avoid extra costs, delays, and poor results.

Having a defined goal simplifies parts selection since many options will naturally filter out when aligned with your objectives.

1. What type of fuels do you plan on using? This decision will affect compression ratios, boost levels, and the overall power you can make.

2. How much power do you want to make? This helps in deciding wrist pin thickness, rod beam style, and compression ratio based on the required horsepower.

3. How will you be using the car? Knowing your usage (daily driving, racing, etc.) helps in choosing components like rod bolts, stroke length, and bearing clearance.

Spend some time establishing a realistic goal based on these questions. For example, you might want a car for daily driving but with the capability to make 175hp per cylinder for weekend track days on E85.

The Strength vs Weight vs Price Compromise

Engine parts face a common dilemma: balancing between strength, weight, and price. Every part has a lifespan, influenced by the materials used and how they are treated over time. High-performance engines often have shorter lifespans than factory engines.

Stronger parts often require more material, making them heavier. Using advanced materials can reduce weight without compromising strength, but these materials add to the cost.

Pistons > Bore Size

Choosing the right pistons involves knowing the correct bore size. The "bore" is the cylinder where the piston moves. Pistons must fit perfectly inside the bore—neither too tight nor too loose.

Over time, cylinder bores change size and shape due to wear, which can lead to compression leaks and reduced engine performance. Bored blocks are often needed to restore cylinder shape and surface finish.

After machining, the block will require oversized pistons to match the new bore size. This ensures optimal piston-to-wall clearance, vital for engine performance.

Piston > Bore Size > Summary Notes

1. Bore size is the diameter of the piston or cylinder.
2. Cylinder size, shape, and surface finish change over time.
3. Piston-to-wall clearance is the gap between the piston and cylinder wall, critical for performance.
4. A too tight or too loose clearance can cause engine failures.
5. To control clearance, bore the cylinder for a larger piston.
6. Excessive boring can weaken the block.
7. Always bore the minimum needed.

Pistons > Static Compression Ratio

Compression ratio affects engine power and susceptibility to detonation. A higher compression ratio generally means more power but requires careful tuning and high-quality fuels.

• Factory forced induction engines should stay close to the original ratio.
• For naturally aspirated engines planning for forced induction, lower the compression ratio.
• Increase the compression ratio to boost power in naturally aspirated engines without forced induction.

Pistons > Material

Pistons are typically made from either 2618 or 4032 aluminum alloys. 2618 is softer and better for high abuse, while 4032 expands less with heat, making it better for tight sealing and daily drivers.

Piston > Material > Summary Notes

1. 4032 is harder but more prone to cracking; ideal for tight sealing and longevity.
2. 2618 is softer, handles high abuse better, but requires more clearance due to thermal expansion.

Pistons > Forging/Skirt Style

Piston forging styles vary between maximizing strength and minimizing weight. Full-round designs have more material and are stronger, while other designs remove material for reduced weight.

Piston > Forging/Skirt Style > Summary Notes

1. Lightweight pistons are too weak for high power builds.
2. High power applications require heavier, stronger pistons.

Pistons > Rod Length + Stroke + Compression Height = Deck Height

The deck height equation ensures pistons, rods, and crankshaft fit properly. Changing stroke requires adjustments in rod length or compression height.

Piston > Rod Length, Stroke, & Compression Ratio > Summary Notes

1. To alter engine displacement, you need a stroker crank.
2. Altering stroke affects rod length and compression height.

Pistons > Wrist Pins

Wrist pins connect pistons to rods. Thicker, stronger pins handle higher power, while thinner pins are lighter but less robust.

Piston > Wrist Pins > Summary Notes

1. Wrist pins connect pistons to rods.
2. Standard pins balance strength and weight but may not suit high power builds.
3. Lighter or stronger pins can be purchased separately.

Connecting Rods > Beam Profile vs Weight

Beam profile alone does not dictate rod choice. Weight and material strength are crucial. Heavier rods handle more power but make the engine work harder.

Connecting Rods > Material

Rods can be made from steel or aluminum. Aluminum rods are lighter and absorb more shock, but steel rods are longer-lasting and generally stronger.

1. Steel rods are durable, strong, and cost-effective.
2. Aluminum rods are lightweight and absorb shock but may need frequent replacement.

Connecting Rods > Rod Bolts

Rod bolts hold rods to the crankshaft and must withstand high RPM forces. Upgraded bolts for high RPM engines are expensive but worthwhile.

Connecting Rods > Rod Bolts > Summary Notes

1. Rod bolts secure rods to the crankshaft.
2. A failure can destroy the engine.
3. High RPM engines require stronger bolts.

Connecting Rods > Rod Length

Changing rod length affects engine performance. Lower rod-to-stroke ratios are better for low-end torque, while higher ratios are better for high RPM durability.

Consult your transmission capabilities to decide your rod length. High RPM transmissions benefit from higher rod-to-stroke ratios.

Crankshafts > Stroke

Stroke determines engine size. Increasing stroke makes engines more powerful but can accelerate wear at high RPMs. Decreasing stroke can reduce wear and improve high RPM durability.

Crankshafts > Stroke > Summary Notes

1. Longer strokes increase power but also wear.
2. Shorter strokes extend life at high RPMs.

Crankshafts > Weight & Material

Crankshaft strength vs. weight trade-off also applies. Types include cast, forged, and billet. Billet offers the strongest but most expensive option.

Crankshafts > Weight & Material > Summary Notes

1. Factory cast cranks are generally unsuitable for high performance.
2. Lightweight cranks suit naturally aspirated engines, not those with forced induction.

Bearings > Material (Race vs Non Race)

Race bearings are softer and absorb more shock but wear faster. Non-race bearings are harder and last longer but handle less shock.

Bearings > Size

Bearing size is crucial for oil clearance, affecting longevity and performance. Crankshaft machining requires appropriately sized bearings to maintain ideal clearance.

Studs & Fasteners > Lifespan & Reusability

Important engine fasteners like head and main studs should be premium grade for high performance. Factory fasteners designed for OEM power levels may not suffice.

Gaskets > Bore Size

Gaskets should match or be slightly larger than the bore size to prevent overhang and potential detonation.

Gaskets > Thickness

The thickness of head gaskets can adjust compression ratio and compensate for machined surfaces. Overly thick or thin gaskets can lead to issues.

Gaskets > Material & Layers

Aftermarket performance gaskets are typically multi-layer steel, offering better durability than stock composite gaskets. OEM multi-layer steel gaskets can often suffice.

Sleeves > Material

Aftermarket sleeves replace weaker factory cylinders, allowing larger bores and compatibility with high-performance pistons.

Sleeves > Wet vs Dry

Open deck engines may utilize "wet sleeves" that integrate with factory cooling, while "dry sleeves" don't.

Sleeves > Flanged vs No Flange

Flanged sleeves offer added support and are recommended for high horsepower builds. Non-flanged sleeves are for stock rebuilds.

Summary

Choosing the right engine parts can be complex but is essential for success. Take your time to make informed decisions. Professionals are available to assist with planning and advice.

Resources

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