Modern restomod builds bring together the soul of a vintage ride with the precision of modern engineering. Classic cars upgraded with electronic fuel injection (EFI), modern engine management systems, and high-performance components represent the best of both worlds: timeless styling combined with contemporary reliability and power. But one critical component often overlooked in the excitement of planning headers, choosing a transmission, or selecting wheel fitment is fuel selection. Choose the wrong fuel, and all the EFI hardware, tuning expertise, and careful engine work can't fully deliver on the build's potential. Choose it right, and you gain consistency, performance, and reliability that transforms how your restomod drives and feels.
The challenge with fuel selection for these builds is that restomods occupy a unique space. They're not stock classic cars that were designed around leaded fuel from the 1960s and 70s. They're also not modern performance cars with extensive factory development and recommended fuel specifications. They're custom creations that blend vintage platforms with modern technology, and that means fuel selection requires understanding both worlds. You need fuel that can handle modern EFI systems' precision requirements while also accommodating the reality that many of these cars sit idle for periods between use, requiring excellent storage stability.
In this comprehensive guide, we'll walk through why fuel matters specifically in EFI conversions, how to understand your particular fuel demands based on your build specifications, and which fuel types make the most sense for restomod and EFI-equipped builds. Whether you're daily-driving a modernized classic, prepping for weekend track runs, or building a show car that fires up for cruise nights, this guide will help you make an informed fuel choice that supports your investment and enhances your driving experience.
When you upgrade a classic car from carburetion to EFI, you're committing to a higher level of precision in how the engine operates. You're installing injectors that deliver fuel in precise quantities calibrated by the ECU. You're adding closed-loop oxygen sensors that provide real-time feedback about combustion. You're implementing variable ignition timing that adjusts based on load, RPM, and knock detection. In many cases, you're also increasing compression ratios beyond factory specifications or adding modern turbocharger or supercharger systems that the original engine designers never imagined.
All of these upgrades mean your fuel becomes a tuning partner, not just "whatever's available at the pump." Accurate fuel delivery depends on consistent stoichiometric behavior, reliable injector calibration, and stable fuel chemistry. EFI systems make thousands of calculations per second about how much fuel to inject based on air mass, engine temperature, throttle position, and sensor feedback. When fuel chemistry varies significantly (as pump gas often does between regions, seasons, and brands), the ECU's carefully calibrated fuel maps become less accurate.
Higher performance expectations come with increased demands. Modern EFI conversions often enable more power, higher RPM operation, increased boost pressure, and tighter tolerances than the original engine. A stock 1970 small block might have been happy on whatever regular leaded fuel was available at any gas station. That same engine with 11:1 compression, aggressive camshaft timing, and modern EFI needs consistent high-octane fuel to avoid detonation and extract the power the modifications enable.
Long-term reliability becomes a fuel consideration because restomods often sit idle for periods, then fire up and are expected to perform flawlessly. A modern daily driver burns through its fuel tank regularly, never giving fuel time to degrade. A weekend restomod might have fuel sitting in the tank, lines, and rail for weeks or months between drives. Your fuel choice affects throttle response, detonation margin, engine longevity, and storage behavior when the car sits between use.
Electronic fuel injection transformed automotive performance when manufacturers adopted it universally in the 1980s and 90s. For restomod builders, EFI retrofits bring precise fuel delivery through electronically controlled injectors, real-time feedback through oxygen sensors and lambda monitoring, highly tunable fuel maps adjustable for specific conditions, and dramatically improved cold start behavior and overall driveability. Modern EFI systems also offer excellent compatibility with high-performance fuels including oxygenated blends, high-octane race fuels, and ethanol-based fuels that carburetors might struggle with.
The flip side of EFI's precision is increased sensitivity to fuel variations. Pump gas suffers from significant variability through regional and seasonal blend changes, fluctuating ethanol levels, variable oxygenate content, and volatility shifts. For a stock vehicle with conservative factory tuning and wide safety margins, these variations don't matter much. For a highly tuned restomod operating near its performance limits, these variations can cause real problems. Tune stability depends absolutely on predictable fuel chemistry. When fuel varies, tunes must be conservative enough to remain safe with the worst-case fuel you might encounter, leaving performance on the table.
Modern pump fuels typically contain ethanol blends ranging from E10 (10% ethanol by volume) to E15 (15% ethanol) depending on location and seasonal regulations. In restomod and classic car environments, ethanol presents several challenges. Ethanol is hygroscopic, meaning it naturally absorbs water from atmospheric moisture, creating increased risk of phase separation when fuel sits in the tank. Phase separation occurs when absorbed water causes the ethanol to separate from the gasoline, creating distinct layers. The ethanol-water mixture settles to the bottom and is corrosive, while the remaining gasoline loses octane rating and has altered combustion characteristics.
Older fuel system components often aren't compatible with ethanol's chemical properties. Rubber fuel lines formulated decades ago can deteriorate when exposed to ethanol, becoming soft, swollen, or cracked. Even some early fuel injection components may not have been designed with ethanol compatibility in mind. The U.S. Department of Energy's Alternative Fuels Data Center provides comprehensive information on ethanol's properties and material compatibility issues that classic car owners should understand. Variable ethanol percentage from tank to tank means variable effective octane rating and energy content, making consistent tuning challenging.
If your build features classic hardware that's been restored to original specification, is intended for occasional use where storage matters, or runs compression ratios or boost levels demanding predictable octane ratings, ethanol-free or very low-ethanol fuel becomes highly advisable. For performance car owners interested in understanding how environmental factors affect fuel performance, comprehensive resources are available covering everything from altitude to humidity effects.
Understanding the broad categories of fuel available helps narrow your selection. Unleaded ethanol-free performance fuels are ideal for storage concerns, older fuel systems, and builds where you want maximum shelf life and minimal variability. Products like Sunoco 260 GT offer 100-octane performance in a street-legal, unleaded formulation with excellent storage stability (often a year or more when properly stored) and complete compatibility with fuel system components.
Street-legal oxygenated performance fuels include controlled oxygenate content specifically designed for performance applications rather than just meeting emissions regulations. Sunoco 260 GT Plus offers approximately 104 octane with high oxygen content, supporting aggressive tuning in performance EFI applications. The oxygenation improves combustion efficiency but requires appropriate tuning adjustments.
Race-only high-octane fuels deliver maximum detonation resistance for extreme builds but typically aren't street-legal. Products like Sunoco Standard at 110 octane or Sunoco Maximal at 114 octane serve dedicated race applications. Match your build goals, fuel compatibility requirements, and usage patterns to choose the right category rather than assuming "race fuel always equals better."
Octane rating measures a fuel's resistance to knock or pre-ignition of the air-fuel mixture. In restomod builds, several factors typically increase octane requirements beyond what the original engine needed. Higher compression ratios from modern pistons or milled heads create higher cylinder pressures. Forced induction conversions using turbochargers or superchargers effectively raise compression through boost pressure, dramatically increasing octane requirements. Research from the Society of Automotive Engineers has extensively documented the relationship between compression ratio, cylinder pressure, and octane requirements in modified engines. Modern EFI systems allow more aggressively advanced ignition timing than was safe with older distributor-based systems, but only if sufficient fuel octane provides the necessary knock resistance.
Different build specifications require different octane levels for safe operation. A mild street EFI conversion with 10:1 or lower compression and naturally aspirated operation typically runs safely on fuels like Sunoco 260 GT offering approximately 100 octane. Performance EFI builds with 10:1 to 13:1 compression or mild boost pressure (8-12 psi) benefit from Sunoco 260 GT Plus with approximately 104 octane. Track-day or high-boost builds exceeding 13:1 compression or running 15+ psi boost need serious octane support, often 110 or higher.
Having high-octane fuel doesn't automatically deliver more power. The tune must be adjusted to take advantage of the fuel's characteristics. With higher octane you can safely advance ignition timing, raise boost pressure in forced induction applications, or in some cases lean the air-fuel ratio slightly. But all of these adjustments require retuning. For more detailed information on octane selection principles, our guide on Understanding Octane: How to Pick the Right Rating provides comprehensive coverage.
Most restomod owners drive their builds anywhere from 500 to 3,000 miles annually rather than the 12,000 to 15,000 miles a daily driver accumulates. This means fuel sits in the tank, fuel lines, fuel rail, and injectors for extended periods. A tank filled in May might not be empty until August or September, creating challenges that daily driven cars simply don't face.
Fuel degradation occurs through several mechanisms that accelerate with time and temperature. Volatility changes as lighter hydrocarbon fractions evaporate, causing starting issues or rough running. Oxidation and gum formation create varnish deposits that clog injectors and coat sensors. Phase separation in ethanol-containing fuels occurs when absorbed water causes the ethanol to separate from the gasoline base, effectively ruining the fuel and potentially causing corrosion or complete failure to start.
Fuels engineered for storage stability maintain tight specifications on vapor pressure and volatility, include stabilizers and additives that resist gum formation and oxidation, and use reduced ethanol content or completely ethanol-free formulations that eliminate phase separation concerns. Quality manufacturers provide specific storage recommendations, often stating that properly stored fuel in sealed containers maintains its specifications for a year or more.
Proper storage practices maximize fuel life. Store the vehicle with a full tank to minimize air space where oxidation can occur. Use sealed metal containers for any fuel stored outside the vehicle. Keep stored fuel and the vehicle in cool, stable environments away from direct sunlight and temperature extremes. When possible, rotate fuel stock by using older fuel first rather than letting the same tank sit for many months.
Even excellent fuel can't overcome poor tuning. Fuel provides the raw potential, but your tune unleashes it. Wideband oxygen sensors and comprehensive data logging should be active for both initial tuning and ongoing monitoring. The tune itself must support your fuel's specific characteristics including octane rating, oxygen content, required air-fuel ratios, and optimal ignition timing. Injectors, fuel pump, pressure regulator, and fuel lines must be properly sized for your chosen fuel and power goals.
Different fuels require different tuning approaches. Highly oxygenated fuels require increased fuel flow compared to non-oxygenated fuels because the oxygen in the fuel itself must be accounted for when calculating stoichiometric air-fuel ratios. Sunoco 260 GT Plus is highly oxygenated and requires richer air-fuel ratio settings than the same engine would need on non-oxygenated fuel. This doesn't mean the engine is running rich; it means you're delivering more fuel to account for the oxygen already present in the fuel itself.
Professional tuners choose fuel based on build goals, compression ratio, boost levels, and usage patterns first. They baseline tune on that specific fuel, establishing ignition timing maps, fuel delivery tables, and boost control strategies optimized for that fuel's characteristics. Comprehensive data logging including exhaust gas temperatures, knock sensor activity, and wideband oxygen sensor readings verifies tune safety and performance. If you change fuel type, plan for retuning. The calibration developed for one fuel won't be optimal for another with significantly different characteristics.
Putting modern fuel through vintage fuel systems requires attention to component compatibility. Older rubber fuel hoses, gaskets, and components may not be ethanol-compatible, with rubber formulations from the 1960s through 1980s often deteriorating when exposed to ethanol. EFI conversions typically add higher-pressure fuel pumps (45-60 psi or higher versus 5-7 psi for carburetors), return fuel lines, and fuel rails that must all be compatible with your chosen fuel.
Replace older rubber fuel lines with modern ethanol-resistant or PTFE-lined braided hoses rated for EFI pressures. Install filters specifically rated for modern fuels and EFI applications, with appropriate micron ratings (typically 10-micron or finer before the pump, and 6-micron or finer after). Technical guidelines from Holley Performance and other EFI system manufacturers provide detailed specifications for proper fuel system design in retrofit applications. Check injectors for compatibility with your chosen fuel, especially if switching to high-oxygen content or ethanol blends. Ensure tank ventilation and sealing meet requirements for pressurized fuel systems. Consider fuel tank cleaning or replacement if the original tank has decades of accumulated deposits, rust, or contamination.
Sunoco 260 GT offers street-legal, oxygenated unleaded fuel with approximately 100 octane rating, ideal for older muscle cars, classic imports, and EFI conversions that need reliable performance with added protection. The fuel provides excellent storage stability, consistent combustion characteristics, and adequate octane for mild performance builds while remaining street-legal and compatible with catalytic converters.
Sunoco 260 GT Plus steps up to approximately 104 octane with high oxygen content, suited for performance EFI builds with moderate upgrades demanding extra knock resistance. This fuel supports higher compression ratios (11:1 to 13:1), mild to moderate boost levels, and aggressive ignition timing. The increased oxygen content requires tuning adjustments but delivers improved throttle response and combustion efficiency when properly calibrated.
For dedicated track cars or extreme builds, Sunoco Standard at 110 octane and Sunoco Maximal at 114 octane provide detonation resistance for very high compression (13:1+) or significant boost pressure (15+ psi). Use Sunoco's fuel comparison resources to review detailed specifications for each fuel. Choose the octane level that matches your build specifications, then consider moving up one tier for additional tuning margin and safety buffer.
Tuning shops working with restomod EFI conversions consistently report several benefits when customers use quality performance fuels. More stable ignition timing advance is possible with fewer knock events under boost or high load, allowing tuners to run aggressive timing maps with confidence. Cleaner startups after storage periods are common, with reduced injector fouling and more reliable cold starts even after the car sits for weeks. Consistent performance from session to session occurs because fuel chemistry doesn't vary, making dyno results repeatable and track times predictable.
Professional tuners working with turbo restomods report trusting their timing tables not to shift between fuel batches when customers run consistent race fuel. This reliability means less time chasing mysterious tune issues and more time optimizing performance. Builders of high-compression naturally aspirated restomods note that premium fuels allow them to run the compression ratios their builds were designed for without constant knock concerns or overly conservative timing. Insights from motorsport engineering communities consistently emphasize that fuel consistency ranks among the most critical factors for achieving repeatable performance in modified engines.
Quality performance fuel costs more per gallon than pump premium, typically ranging from $8 to $15 per gallon compared to $3.50 to $5 for 93 octane pump gas. However, the relevant calculation is value per mile driven, performance margin gained, and reliability assured.
Your build definitely benefits from performance fuel when the engine has been significantly upgraded with higher compression ratios, EFI conversion replacing carburetion, or forced induction adding boost. These modifications create octane requirements that pump gas simply can't safely support. Cars used for track days, high-RPM operation, or serious performance driving benefit from the consistency and knock resistance performance fuels provide. Builds where you want fewer tune changes, fewer fuel-related diagnostic mysteries, and better long-term engine longevity find value in fuel consistency and quality.
Stock compression naturally aspirated engines running as daily drivers with no significant modifications don't benefit meaningfully from race fuel. Cars driven lightly where you rarely push the engine to performance limits similarly don't fully utilize what performance fuel offers. Budgets requiring priorities elsewhere in the build might be better served spending money on cooling, handling, or safety equipment rather than premium fuel if the engine runs acceptably on pump gas.
For many restomod builders, mid-tier performance fuels like Sunoco 260 GT hit the sweet spot. These fuels provide significantly better characteristics than pump gas, retain street legality and usability, tolerate storage well, and support moderate performance upgrades without requiring full race-fuel territory pricing. The cost premium over pump gas is noticeable but manageable for vehicles driven a few thousand miles annually.
Learning from others' mistakes helps you avoid common pitfalls. Not all race fuels are equal or appropriate for every application. Octane rating, oxygenation level, street legality, and intended usage all vary significantly between products. A 118-octane leaded race fuel designed for top-fuel dragsters won't be appropriate or legal for your street-driven restomod. Match fuel to actual requirements rather than just buying the most extreme option available.
Some high-performance fuels are explicitly race-only and cannot legally be used on public roads. Using non-compliant fuel on street-driven vehicles creates legal liability, can damage emissions equipment like catalytic converters, and provides no benefit if your build doesn't require that level of performance. Premium fuel still requires proper storage practices if the car sits for extended periods. Leaving fuel exposed to temperature extremes or in improper storage containers accelerates degradation.
Higher octane or oxygenated fuel without appropriate tuning changes can hide problems or prevent you from realizing performance gains. The ECU doesn't automatically know you've switched fuels. Tuning must be updated to leverage the fuel's characteristics. Finally, variability between fuel types or between fresh and degraded fuel defeats the benefit of using consistent, high-quality fuel. When possible, use fuel completely before switching to a new batch rather than continuously topping off and mixing different ages of fuel.
Fuel selection represents a foundational decision in your restomod or EFI conversion build that influences everything from daily driveability to maximum performance capability. When you properly match your engine's demands, tuning strategy, storage and usage profile, and budget with the right fuel choice, you set yourself up for smooth performance, long-term reliability, and genuine enjoyment of your build.
The restomod community has learned through decades of experience that details matter. The same attention you apply to selecting pistons, choosing camshaft specifications, or dialing in suspension geometry should extend to fuel selection. Whether you're bringing a fresh EFI swap online or polishing a classic for cruise nights and track days, align your build with fuel that fits your actual usage patterns and requirements. Quality fuel manufacturers offer calibrated ranges of products spanning from street-friendly options through aggressive race blends, giving you choices backed by real specifications and testing data.
Take time to honestly evaluate your goals and usage patterns. Is this a daily driver, an occasional weekend cruiser, or a dedicated track car? Does your build have mild upgrades working within pump gas octane limits, or have you built an engine that genuinely demands race fuel for safe operation? Understanding these factors leads to informed decisions that deliver value rather than simply spending money on products you don't actually need or can't fully utilize.
The investment in your restomod reflects passion for classic cars combined with appreciation for modern technology's benefits. Proper fuel selection protects that investment while enabling the performance you built the car to deliver. When every component works together as intended, including the fuel feeding your precisely tuned EFI system, the result is a restomod that drives as impressively as it looks and provides the reliable performance that keeps you enjoying it for years to come.
Ready to make the right fuel choice for your EFI conversion or restomod? Explore Sunoco's Fuel Finder to locate dealers near you carrying the specific fuels recommended for your application, or contact Sunoco's technical team for personalized guidance on matching fuel to your particular build specifications. Their expertise spans decades of supporting everything from grassroots weekend projects to professional-level restomods. Choose wisely, tune carefully, and drive confidently knowing you've addressed every detail in your build.