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Thread: E85 boost levels

  1. #1
    Half Boost
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    E85 boost levels

    I have been considering a move to E85. My car is street driven with a fresh bottom end already broke in with cast iron Bo port stage 3 porting and 2.1 cam. Rods header and 3" from the turbo back to a single 2 1/2" over the axle tail pipe. Turned intake and large NPR charge cooler. Running 18 lbs of boost with ball bearing turbo. All pimp controlled. My goal was more than I got from these mods. My question is how much more boost could I run safely with E85 vs 93 premium?

  2. #2
    Some Boost Laredo's Avatar
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    Quote Originally Posted by brsvo View Post
    ...how much more boost could I run safely with E85 vs 93 premium?
    Safely...?? That depends.
    The octane rating of E85 is normally around 105, but when combined with its cooling properties, the actual knock resistance of E85 is much higher than the octane rating would suggest.
    E85 has a very high ‘latent heat of evaporation’ which means that when E85 is injected into the engine, it goes through a phase change from liquid to gas and during this process it absorbs a lot of heat from the intake charge. A colder intake charge is denser and improves power, but also has the effect of making the engine less prone to detonation. Nice, yes? Considering this, if you're currently running 18 lbs on 93 premium, you should have no issues running at least 2-3 lbs more without concern of detonation.

    However...detonation is not your only concern in regards to "safely" running more boost.
    - You didn't mention the size of your turbo. More boost pressure and volume may require larger turbo to go beyond 18 PSI. Unfortunately, the turbo is not getting the benefit of the E85 cooling properties 'cuz it's pumping just air. Too small of a turbo at 20+ is going to super-heat your charge air.
    - Head gasket, more boost will add risk to the longevity of your head gasket.
    - Larger injectors - you'll need injectors 30% larger to prevent maxxing out your duty-cycle.

    I would recommend, add boost but within the limits of your turbo, larger injectors, then...take it to dyno tuner to get your mixture & timing set right on the E85
    Bad choices make great stories....!

  3. #3
    Half Boost
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    Well stated. My turbo is already sized for 22 psi without a problem. The head gasket is my concern and 2/3 lbs of boost doesn't seem like enough to justify the cost of larger injectors. My setup spikes from 18 to 21 briefly before settling at 18. I would love to run 22 but a spike to 25 could cause a lot of work.

  4. #4
    Some Boost Laredo's Avatar
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    Quote Originally Posted by brsvo View Post
    ...2/3 lbs of boost doesn't seem like enough to justify the cost of larger injectors...
    It's not just the added boost that will necessitate larger injectors. Even without adding PSI, E85 will require 30% more volume of fuel.


    Quote Originally Posted by brsvo View Post
    ...The head gasket is my concern...a spike to 25 could cause a lot of work.
    Completely agree!
    Bad choices make great stories....!

  5. #5
    Half Boost
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    The whole point of going to E85 is to turn up the boost. I understand the need for more alcohol than gas. Just ask anyone who has a flex fuel vehicle about mileage. Been there done that!

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