E85 ethanol fuel has become the secret weapon of the performance tuning world. It's cheaper than race gas, widely available at pumps across America, and delivers power gains that can rival expensive octane boosters—all while running cooler and cleaner than pump gas. But E85 isn't without its challenges and requirements.
After converting hundreds of vehicles to E85 and flex fuel here at Raw Exotics, I've learned what works, what fails, and what you absolutely need to know before making the switch. This guide will cover everything from the science of ethanol to the real-world costs and power gains you can expect.
What is E85?
E85 is a blend of approximately 85% ethanol and 15% gasoline, though the actual percentage varies by season and region. In winter months, E85 can contain as little as 51% ethanol (sometimes called E70) to improve cold-start performance. In summer, it's typically 83-85% ethanol.
Ethanol is alcohol-based fuel derived from corn and other plant materials. While it has a lower energy density than gasoline (meaning you need to burn more of it to make the same power), ethanol has several properties that make it exceptional for performance applications:
- Effective Octane Rating of 100-105: E85 resists detonation far better than 93 octane pump gas, allowing for more aggressive timing and boost.
- Cooler Combustion Temperatures: Ethanol's evaporative cooling effect lowers intake air temps by 30-50°F compared to gasoline.
- Cleaner Burn: Ethanol combustion produces fewer carbon deposits and runs cleaner than gasoline.
- Oxygenated Fuel: Built-in oxygen content helps with more complete combustion, though this requires significantly more fuel flow.
Power Gains: What to Expect
The million-dollar question: how much power does E85 add? The answer depends heavily on your existing setup and how conservative your pump gas tune is.
Naturally Aspirated Builds
On naturally aspirated engines, E85 allows for more aggressive timing advance due to its knock resistance. Expect modest gains:
- Stock or mild builds: 5-15 hp gains. Your engine is usually not knock-limited on pump gas, so E85 doesn't offer huge advantages beyond slightly more timing.
- High compression builds (11:1+): 15-30 hp gains. These engines are often knock-limited on 93 octane, and E85 allows you to run the timing your compression ratio demands.
- Aggressive cam/heads builds: 20-40 hp gains. More timing, leaner AFR in certain zones, and better cylinder filling from cooler intake temps all contribute.
Forced Induction (Turbo/Supercharger)
This is where E85 truly shines. Boosted applications see dramatic gains:
- Mild boost (6-8 psi): 30-60 hp gains over 93 octane. You can typically add 2-3 psi more boost safely.
- Moderate boost (10-15 psi): 60-100+ hp gains. The cooling effect and knock resistance allow significantly more timing and boost.
- High boost (18+ psi): 100-200+ hp gains. At high boost levels, pump gas simply can't handle the cylinder pressures safely. E85 allows you to push into territory that requires race gas on pump fuel builds.
For example, a Hellcat Challenger making 650 whp on 93 octane can easily push 750-800 whp on E85 with just a tune and no other changes. A built turbo LS making 700 hp on pump gas might jump to 900+ hp on E85.
Fuel System Requirements
E85 requires approximately 30% more fuel volume than gasoline to make the same power. This means your fuel system must flow 30% more fuel. Additionally, ethanol is corrosive to certain materials, so compatibility is critical.
Fuel Injectors
The single most important upgrade for E85 is larger fuel injectors. Here's a simple calculation:
Take your current injector size and multiply by 0.77 to determine your effective size on E85. For example:
- Stock 42 lb/hr injectors × 0.77 = 32.3 lb/hr effective on E85
- 60 lb/hr injectors × 0.77 = 46.2 lb/hr effective on E85
- 80 lb/hr injectors × 0.77 = 61.6 lb/hr effective on E85
If your engine is pushing the limits of your injectors on pump gas, you'll max them out immediately on E85. Most naturally aspirated engines can get away with stock injectors if they're not heavily modified, but forced induction absolutely requires upgraded injectors.
Our recommendations by platform:
- LS3 NA builds: Stock injectors work for mild builds. 60-80 lb/hr for cammed builds.
- LS boosted builds: 80-120 lb/hr depending on power level. We like Injector Dynamics or Bosch EV14 injectors.
- HEMI NA builds: Stock injectors often adequate. 52-72 lb/hr for bigger builds.
- HEMI boosted builds: 72-100+ lb/hr. ID1050X or ID1300 are popular.
- Coyote builds: Stock Mustang GT injectors are surprisingly stout. 47-60 lb/hr for most E85 builds, 80+ for big boost.
Fuel Pump
Your fuel pump must flow 30% more volume to support E85. Many stock fuel pumps can handle the increased demand on naturally aspirated engines, but forced induction almost always requires an upgraded pump.
Fuel pump options:
- Drop-in high-flow pumps: Walbro 450, AEM 340, DeatschWerks DW300. These are direct replacements for stock pumps and support 500-700 hp on E85. Cost: $150-300.
- Dual pump setups: Add a second pump for 800-1000+ hp builds. More expensive and complex. Cost: $500-1000.
- External pumps: For serious race builds. Aeromotive, Weldon, or Fore fuel systems. Cost: $1000-2500+.
Fuel Lines and Fittings
Most modern vehicles (2000+) already use ethanol-compatible fuel lines and fittings. However, older vehicles or those with aftermarket fuel systems may have rubber lines or fittings that ethanol will degrade over time.
Ethanol-safe materials include:
- PTFE (Teflon) lined hoses
- Stainless steel braided lines
- Viton O-rings and seals
- Aluminum fittings with proper coatings
Avoid:
- Standard rubber fuel hose (will swell and crack)
- Buna-N O-rings (will dissolve)
- Bare aluminum (can corrode)
Flex Fuel vs Dedicated E85
You have two options when converting to E85: dedicated E85 tune or flex fuel capability.
Dedicated E85 Tune
A dedicated E85 tune means your car is tuned specifically for E85 fuel and nothing else. If you put regular pump gas in the tank, the car will run rich, make less power, and potentially foul plugs or cause issues.
Pros:
- Simpler and less expensive (no flex fuel sensor needed)
- Tune can be optimized specifically for E85 with no compromises
- Slight power advantage since the tune isn't splitting the difference
Cons:
- Can't use pump gas if E85 isn't available
- Must ensure you're always filling with E85
- If you accidentally put in pump gas, you need to drain the tank
Flex Fuel System
A flex fuel setup uses an ethanol content sensor that reads the fuel composition in real-time. The ECU then adjusts fueling and timing on the fly to accommodate anywhere from pure gasoline (E0) to full E85.
Pros:
- Can run any mixture of gasoline and E85
- Fill up with whatever is available—pump gas or E85
- No need to drain the tank if you get the wrong fuel
- Can blend fuels for cost savings (E30-E50 is very popular)
Cons:
- Requires flex fuel sensor installation ($200-400 installed)
- Slightly higher tuning cost ($200-400 more)
- Tune is a compromise between E85 and pump gas—slightly less power than dedicated E85
We typically recommend flex fuel for street cars. The convenience of being able to run any fuel mixture is worth the minor power sacrifice and extra cost. For dedicated race cars, a straight E85 tune makes sense.
Tuning for E85
E85 requires significant tuning changes compared to pump gas. Here's what your tuner will adjust:
Fuel Tables
The ECU needs to deliver 30% more fuel across the entire fuel map. This affects base fuel tables, injector pulse width, and VE (volumetric efficiency) tables. Your tuner will rescale these tables to ensure proper air-fuel ratios on E85.
Ignition Timing
E85's high octane rating allows for significantly more timing advance. Naturally aspirated engines typically gain 2-5° of timing. Forced induction engines can gain 4-8° or more depending on boost level. More timing equals more power, so this is where much of the E85 power gain comes from.
Air-Fuel Ratio
E85 burns differently than gasoline, so target AFR changes. On gasoline, we typically target 12.5-13.0:1 AFR for peak power. On E85, the target shifts to around 11.5-12.0:1 measured with a wideband O2 sensor calibrated for gasoline (the actual stoichiometric ratio for E85 is 9.765:1, but most tuners use gasoline-equivalent AFR for simplicity).
Cold Start and Warm-Up
Ethanol is harder to vaporize than gasoline, especially in cold weather. Your tuner needs to enrich the cold start fueling significantly (sometimes 50-100% more fuel) to ensure reliable starts in cold climates. In Houston, this is less of an issue, but in northern states, cold starts on E85 can be problematic below 30°F.
The Downsides of E85
E85 isn't perfect. Here are the challenges you need to be aware of:
Reduced Fuel Economy
Because E85 has lower energy density, you'll burn 20-30% more fuel to travel the same distance. If you get 20 mpg on pump gas, expect 14-16 mpg on E85. For daily drivers, this adds up quickly.
E85 Availability
While E85 is common in the Midwest (corn country), it's less available on the coasts. In Houston, we have decent E85 availability, but you need to plan your fuel stops. Apps like Gas Buddy can help locate E85 stations.
Ethanol Content Variability
As mentioned earlier, E85 isn't always 85% ethanol. Seasonal blends and regional variations mean the ethanol content can range from 51% to 85%. If your tune is optimized for E85 and you fill up with E70, you might experience slight power loss or need a tune revision. Flex fuel systems handle this automatically.
Cold Weather Performance
E85 is difficult to start in freezing temperatures. If you live in a cold climate, you may need to keep a gallon of pump gas on hand to add to the tank in winter, or switch to a pump gas tune during cold months.
Corrosion Concerns
Ethanol absorbs water and can be corrosive to fuel system components if left sitting for extended periods. For vehicles driven regularly, this isn't an issue. For garage queens or race cars that sit for months, it's wise to drain E85 and run pump gas through the system before storage.
Real-World Cost Analysis
Let's break down the actual costs of converting to E85.
Typical E85 Conversion (Naturally Aspirated)
- Flex fuel sensor and installation: $350
- Upgraded fuel injectors (if needed): $600
- Upgraded fuel pump (if needed): $250
- E85 tune: $800-1000
- Total: $2000-2200
Typical E85 Conversion (Forced Induction)
- Flex fuel sensor and installation: $350
- Upgraded fuel injectors: $800-1200
- Upgraded fuel pump: $300-500
- E85 tune: $1000-1400
- Total: $2450-3450
Fuel Cost Comparison (Houston Prices)
- 93 Octane Pump Gas: $3.20/gallon
- E85: $2.40/gallon
- Race Gas (110 octane): $9-12/gallon
E85 is significantly cheaper than pump gas per gallon, but you burn 30% more of it. Here's the math for a 500-mile tank:
- 93 octane at 20 mpg: 25 gallons × $3.20 = $80
- E85 at 15 mpg: 33 gallons × $2.40 = $79.20
So fuel costs are roughly the same per mile. The real savings come from comparing E85 to race gas. If you were running 110 octane race gas to make the same power, you'd spend $225-300 per tank instead of $79.
Best Platforms for E85
Some engines respond better to E85 than others. Here are the platforms we see the biggest gains on:
Forced Induction Engines (Best ROI)
- Hellcat/Redeye (supercharged HEMI): 100-150 hp gains with just a tune
- Ecoboost F-150/Mustang: 80-120 hp gains, responds incredibly well
- Turbocharged LS/LT: 100-200+ hp gains depending on boost level
- Whipple/VMP Coyote: 100-150 hp gains over 93 octane
- BMW N54/N55/B58: 60-100 hp gains, allows more boost safely
High Compression NA Engines (Good ROI)
- LS7 (11:1 compression): 30-50 hp gains with aggressive timing
- Coyote 5.0 (12:1 compression): 25-40 hp gains
- Heavily built HEMI (11.5:1+): 40-60 hp gains
Should You Switch to E85?
E85 makes sense if:
- You have a forced induction setup and want maximum safe power
- You have a high-compression naturally aspirated build that's knock-limited on pump gas
- You want to make race-gas power without paying race-gas prices
- E85 is readily available in your area
- You drive your car regularly (not a garage queen)
E85 might not be worth it if:
- Your engine is stock or mildly modified and not knock-limited
- E85 isn't easily available near you
- You're concerned about reduced fuel economy
- You live in a very cold climate and need reliable winter starting
- The car sits for long periods between drives
"E85 is the best bang-for-buck modification for forced induction cars. The power gains are massive, the fuel is cheaper than race gas, and it runs cooler and cleaner. If you're serious about making power safely, E85 should be high on your list."
Ready to Go E85?
If you're in Houston and want to convert your car to E85 or flex fuel, we can help. We'll assess your fuel system, recommend the right upgrades, handle the installation, and dial in a custom E85 tune that maximizes power while maintaining reliability.
Call us at (713) 299-1168 or stop by Raw Exotics. We'll discuss your goals and build a flex fuel package that delivers the power you want.