Page 2 of 2 FirstFirst 12
Results 21 to 25 of 25
  1. Member
    Join Date
    Feb 2018
    Posts
    3,153
    #21
    Quote Originally Posted by lpugh View Post
    87 octane burns faster and much cleaner than 91 octane,

    I wont go fully into my credentials on this subject, I have many years of experience dealing with alcohol blends and was the first person on the west coast to get a computer controlled carbureted motor to properly function on M-85 (85% methanol-15% gas) or any mix percentage of from 100% gas to 85% alcohol way back in 1985. I learned a lot about it and how to deal with it.
    Let's take a look at a motor that has is designed to run, and produce maximum HP, on gasoline rated at 87 octane. Its ignition timing is X degrees BTDC at 6000 RPM so as to produce peak HP at 6000 RPM.

    If slower burning gasoline rated at 91 octane is used, would that result in less HP being produced at 6000 RPM? My thinking is that it might given that the location of peak pressure is now occurring later than it would when faster burning 87 octane is used. Less peak pressure at a later point in the power stroke.

    Your thoughts?

  2. Member lpugh's Avatar
    Join Date
    May 2009
    Location
    Sacramento Ca
    Posts
    5,168
    #22
    In most cases torque is falling off at max rpm, combustion pressures are beginning to fall off as well, due to the fact it has passed the point of it highest volumetric efficiency, horsepower may be at max because of the rpm (Torque times RPM divided by 5,252).
    Easy answer is a minor if any HP loss at max rpm, however a different story at 4500 rpm and WOT as torque made will be a little lower due to some energy going out the exhaust do to a slower burn. You brought up very complicated subject and there are a lot variables that would come into play.

    Here is an example of effects of octane: I used to crew chief for my son for a late model circle track car. Track rules forced us to use a specific race fuel that was 110 octane. We also had a rule of 9-1 compression and a 500 cfm carburetor. With those rules in place a 91 octane pump gas would have been a better choice. That fuel burned so slow we had to replace the headers every year do to the extreme heat in the exhaust system, they would run red hot all the way back to the collectors, To combat this we ran 42 degrees of total advance and a leaner fuel mix to obtain a faster burn. When running other races with a 100 octane fuel, the headers only glowed for about 18 in or so. This was really apparent in night races
    I can assure you that peak horsepower was similar but acceleration off the corners was not as good...…….Something to ponder over for sure
    Three octane is not a lot of difference and you will never feel the difference except in maybe real cold weather, but it does make a considerable difference in reducing carbon deposits
    Last edited by lpugh; 12-06-2018 at 01:20 AM.
    Thank You Leon Pugh

  3. Member reelman's Avatar
    Join Date
    Jun 2004
    Location
    Palatka, FL 32177
    Posts
    8,185
    #23
    I add a can of Sea Foam 3x a year....it tends to clean out the carbon...

    2018 Z19/200 Optimax 2 stroker 24x3 Fury Ultrex 112
    Lowrance HDS 12/9 Lives with 3 in 1 ducers

  4. Member
    Join Date
    Dec 2008
    Location
    claremore
    Posts
    1,685
    #24
    Real gas and a quality synthetic oil is best! Seafoam and ring free cant hurt either.

  5. Member
    Join Date
    Apr 2008
    Location
    Bolivar, MO
    Posts
    196
    #25
    The guys at Hydrotech say nothing but 91 ethanol free, yamalube and ring free for my 06 HPDI with a phase 2 kit. They have 30yrs of experience with Yamaha. Just going by what they have told me to do.

Page 2 of 2 FirstFirst 12