Forbidden Fuel Experiment: E85 In a Mostly Stock Square

Ovals_and_Bowties · May 7, 2026

Alright the title gives y'all the gist of it so I'll hop right into the what and how.
The test subject is an 85 C10 Silverado, 350 small block, with dual tanks. The passenger side tank is filled with straight E85 from a local gas station. Regular 87 E10 in the driver's side tank. Normal rubber fuel lines, a Precision brand mechanical pump from O'Reillys. The non-stock part is a Edelbrock 1406 carb feed through a Wix fuel filter with a ball shut off valve half-closed as a "regulator". The carb is being operated in "2 barrel" mode, i.e. secondary throttle linkage is disconnected.

I'll be adding 1/2 ounce to 1 ounce of tranny fluid per gallon of E85 to the fuel in an attempt to keep it from drying anything rubber in the system out and hopefully prevent corrosion.

In so far, I had to jet the carb as rich as I could with the calibration kit I had on hand. That is 0.101" main jets and 0.070" X 0.037" metering rods. I'm about 2 turns out on the idle mix screws. It's running maybe slightly rougher than normal at idle? Could just be placebo.

Normally I get about 9 MPG on E10, I haven't drove further than from the gas station to home on E85. So MPG is currently unknown. By my math I should be getting about 6 MPG on E85. Just based off the change cross sectional surface area of the jet and rod.

I'll report back sporadically to document how she fares running on corn juice.

TotalyHucked · May 8, 2026

I'm curious, why? Just as an experiment? At least you're in corn country where it's usually as cheap as or cheaper than regular. It's rare around NE Ga and way more expensive so it doesn't make any sense for us to run

Sad Sack · May 8, 2026

Ovals_and_Bowties said:
Alright the title gives y'all the gist of it so I'll hop right into the what and how.
The test subject is an 85 C10 Silverado, 350 small block, with dual tanks. The passenger side tank is filled with straight E85 from a local gas station. Regular 87 E10 in the driver's side tank. Normal rubber fuel lines, a Precision brand mechanical pump from O'Reillys. The non-stock part is a Edelbrock 1406 carb feed through a Wix fuel filter with a ball shut off valve half-closed as a "regulator". The carb is being operated in "2 barrel" mode, i.e. secondary throttle linkage is disconnected.

I'll be adding 1/2 ounce to 1 ounce of tranny fluid per gallon of E85 to the fuel in an attempt to keep it from drying anything rubber in the system out and hopefully prevent corrosion.

In so far, I had to jet the carb as rich as I could with the calibration kit I had on hand. That is 0.101" main jets and 0.070" X 0.037" metering rods. I'm about 2 turns out on the idle mix screws. It's running maybe slightly rougher than normal at idle? Could just be placebo.

Normally I get about 9 MPG on E10, I haven't drove further than from the gas station to home on E85. So MPG is currently unknown. By my math I should be getting about 6 MPG on E85. Just based off the change cross sectional surface area of the jet and rod.

I'll report back sporadically to document how she fares running on corn juice.

Holy cow, my '85 C1500 with a 305 and an Edelbrock gets about 16 mpg but I run only premium.

Ovals_and_Bowties · May 8, 2026

TotalyHucked said:
I'm curious, why? Just as an experiment? At least you're in corn country where it's usually as cheap as or cheaper than regular. It's rare around NE Ga and way more expensive so it doesn't make any sense for us to run

A bit part experiment and a bit part hedging my bets. I suspect gas is still gonna jump up a lot in price.

E85 is about $2.40 a gallon down here. So it's a LOT cheaper.

Ovals_and_Bowties · May 8, 2026

Sad Sack said:
Holy cow, my '85 C1500 with a 305 and an Edelbrock gets about 16 mpg but I run only premium.

Yeah I've never figured out why she gets such crappy mileage. Even with no secondaries, tuned for lean cruise, and with a 2.73 rear I don't think I've ever seen better than 12MPG out of it. That was all highway 55-75MPH to get double digit MPG.

I normally run regular 87. I don't see it getting any better with premium without re-curving the dizzy.

Ovals_and_Bowties · May 8, 2026

Experiment update: Despite driving home from the gas station on E85 without too much issue. She really REALLY didn't wanna move this morning.
Near as I can tell she goes piss lean trying to run off the transfer slots just off idle.
I tried one wire restricting the bypass idle air bleed, made it a little bit better but not enough. I plugged the BIAB off temporarily, that made idle and tip in fine but it quickly runs out of steam on accel.

I can't tell if it's slobbering rich on light accel (which it should be) or sucking the bowls dry. Really acts like its the bowls though?

I'll have to play around with the carb more. No buildup or corrosion inside the carb yet.

Sad Sack · May 8, 2026

Ovals_and_Bowties said:
Yeah I've never figured out why she gets such crappy mileage. Even with no secondaries, tuned for lean cruise, and with a 2.73 rear I don't think I've ever seen better than 12MPG out of it. That was all highway 55-75MPH to get double digit MPG.

I normally run regular 87. I don't see it getting any better with premium without re-curving the dizzy.

I argue with my friends on my use of premium fuel I guess I’m just quirky but things have been good for me on trying to avoid fuel system issues but I will run a non ethanol if necessary.

Ovals_and_Bowties · May 8, 2026

Sad Sack said:
I argue with my friends on my use of premium fuel I guess I’m just quirky but things have been good for me on trying to avoid fuel system issues but I will run a non ethanol if necessary.

Yeah I got an neighbor that's hardcore premium fuel and a bottle of Lucas every oil change type of guy.

I'm not sold on that kinda stuff but y'all can do whatever gives ya peace of mind.

I don't have a high strung motor, just an old stock/mild 350 in an old work truck. So I don't see any need for fancy go-go juice.

Ricko1966 · May 8, 2026

Sad Sack said:
I argue with my friends on my use of premium fuel I guess I’m just quirky but things have been good for me on trying to avoid fuel system issues but I will run a non ethanol if necessary.

You very possibly do get better mileage,performance,and less knock with premium in your truck. The 80s 305s are little ping monsters,they raised compression on them in 1981 for LE9 engines and went knock sensor ignition. The more you can keep it out off the knock sensor with octane,the more power and milage you'll get. More octane then you need doesn't make more power or mpg. But less than you need hurts you. It's very likely that your truck does like more octane.

Ricko1966 · May 9, 2026

I

Ovals_and_Bowties said:
Alright the title gives y'all the gist of it so I'll hop right into the what and how.
The test subject is an 85 C10 Silverado, 350 small block, with dual tanks. The passenger side tank is filled with straight E85 from a local gas station. Regular 87 E10 in the driver's side tank. Normal rubber fuel lines, a Precision brand mechanical pump from O'Reillys. The non-stock part is a Edelbrock 1406 carb feed through a Wix fuel filter with a ball shut off valve half-closed as a "regulator". The carb is being operated in "2 barrel" mode, i.e. secondary throttle linkage is disconnected.

I'll be adding 1/2 ounce to 1 ounce of tranny fluid per gallon of E85 to the fuel in an attempt to keep it from drying anything rubber in the system out and hopefully prevent corrosion.

In so far, I had to jet the carb as rich as I could with the calibration kit I had on hand. That is 0.101" main jets and 0.070" X 0.037" metering rods. I'm about 2 turns out on the idle mix screws. It's running maybe slightly rougher than normal at idle? Could just be placebo.

Normally I get about 9 MPG on E10, I haven't drove further than from the gas station to home on E85. So MPG is currently unknown. By my math I should be getting about 6 MPG on E85. Just based off the change cross sectional surface area of the jet and rod.

I'll report back sporadically to document how she fares running on corn juice.

If you want to do this long term to try to save money on fuel. I'd suggest smaller combustion chamber,better burn heads. Like Vortec or TBI heads,or even some 305 heads,and thin head gaskets. I'm assuming you are running 76cc smog heads.Smaller combustion chamber heads will bring up compression You might even consider Rhodes lifters all this to help bring up the dynamic compression.With the extra compression you'll make more power on less fuel,it'll get you closer to regular fuel mpg,plus more power. If you can find a usable 750 Holley to rebuild you can get E85 metering blocks compatible floats,and larger needle and seats. Your ball valve choking off fuel doesn't sound like a good Idea. Neither does the wix filter unless it's stainless. The reasons,ethanol breaks down paper,and as to the ball valve,you need a bunch more fuel now than you did before,and you've restricted your inlet. I'd be afraid of starving it for fuel.

Rustisbest · May 9, 2026

Ovals_and_Bowties said:
A bit part experiment and a bit part hedging my bets. I suspect gas is still gonna jump up a lot in price.

E85 is about $2.40 a gallon down here. So it's a LOT cheaper.

At that price a 50/50 mix with 85 /87 octane might be worth it and you wouldnt have to take such a big swing at it carb wise.

Ovals_and_Bowties · May 11, 2026

Ricko1966 said:
I
If you want to do this long term to try to save money on fuel. I'd suggest smaller combustion chamber,better burn heads. Like Vortec or TBI heads,or even some 305 heads,and thin head gaskets. I'm assuming you are running 76cc smog heads.Smaller combustion chamber heads will bring up compression You might even consider Rhodes lifters all this to help bring up the dynamic compression.With the extra compression you'll make more power on less fuel,it'll get you closer to regular fuel mpg,plus more power. If you can find a usable 750 Holley to rebuild you can get E85 metering blocks compatible floats,and larger needle and seats. Your ball valve choking off fuel doesn't sound like a good Idea. Neither does the wix filter unless it's stainless. The reasons,ethanol breaks down paper,and as to the ball valve,you need a bunch more fuel now than you did before,and you've restricted your inlet. I'd be afraid of starving it for fuel.

I had been planning to do this for the short to medium term. I don't know much about Rhodes lifters, I'll have to look into that. Using vortex heads hadn't even occurred to me. Probably easier to find than 305 heads. I had been keeping an eye on FB marketplace for a cheap 305 to have an as a spare engine but haven't seen a single one pop up.

It is in fact a stainless filter Wix filter, I probably should've provided the part number for it or a better description in my starting post.

I found out about the fuel flow issue the hard way. After I finally got the bypass idle air bleeds dialed in for ethanol, I had opened the ball valve all the way it became very apparent very quickly that I needed more flow to do anything more than idle around.

In fact it would seem my mechanical pump isn't capable of flowing enough fuel. When I start to accelerate she jumps then promptly falls on her face, sputters for a bit then dies. The drive's side fuel bowl keeps running empty in particular.

Kinda surprising to me because I had to have that valve closed most of the way to keep pressure reasonable for the carb. I thought I'd need it about halfway opened for ethanol, oh boy was I wrong.

Ovals_and_Bowties · May 11, 2026

Rustisbest said:
At that price a 50/50 mix with 85 /87 octane might be worth it and you wouldnt have to take such a big swing at it carb wise.

Nobody sell 85 octane down here. The same station that sell the E85 sells a range of ethanol blends. If I recall correctly: E15, E20, E30, and E85. At 87, 89, and 93 octane respectively. For the E85 I don't remember the octane rating. Probably close to 100.

Found out I can't flow enough fuel with the mechanical pump to run on E85 unless I plan on going 10 MPH everywhere. At that point I'm better off taking my electric scooter and switching to my Chevrolegs when I inevitably run out of battery.

I think your onto something with the blend idea. I'll probably try their E20 or E30 blend. That should be more compatible and a least a bit cheaper than E10.

Forbidden Fuel Experiment: E85 In a Mostly Stock Square

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