Octane Boost
Road Captain
Joined: Sep 2019
Posts: 689
Likes: 339
From: Dayton OH
My stage 3 is 11-1 don’t know the cpp but sounds feels pulled perfect in Florida heat on 90 octane no ethol. Did on the dyno also.
If you deck it for 12-1 and go with an over 230 cpp custom cam you might actually need more octane. Plastic bottle stuff in auto parts stores is crap. If it says raises octane up to 7 points it means you might do as well as going from 87 to 87.7 octane.
Cheap effective home brew is Xylene from a paint store. It’s 117 octane but has no lubricant so you must add a little Marvels Mystery oil. You can only effectively mix up to 30 percent for up to about 98 octane when starting with 90 octane gas. Back in the late 80s I ran it in my Grand National when I wanted to wick up the boost.
If you deck it for 12-1 and go with an over 230 cpp custom cam you might actually need more octane. Plastic bottle stuff in auto parts stores is crap. If it says raises octane up to 7 points it means you might do as well as going from 87 to 87.7 octane.
Cheap effective home brew is Xylene from a paint store. It’s 117 octane but has no lubricant so you must add a little Marvels Mystery oil. You can only effectively mix up to 30 percent for up to about 98 octane when starting with 90 octane gas. Back in the late 80s I ran it in my Grand National when I wanted to wick up the boost.
Last edited by VernDiesel; May 19, 2020 at 02:51 PM.
Ultimate HDF Member
Joined: Oct 2016
Posts: 5,063
Likes: 2,582
From: On my bike!
Not with my M8 but on my way home from Sturgis in 1996 there was a 76 gas station that had 103 octane on the pump. I filled it up and she ran like a beast. The inside of my thunderheader was white as a ghost... Must of cleaned her out good. Here in Commiefornia we have 91 octane that's as good as it gets, I wouldn't hesitate to throw in some Klotz 106 or 108 racing fuel maybe 30% fuel to 70% gas just to clean things up but wouldn't make a habit out of it.
Grand HDF Member
Joined: Oct 2009
Posts: 3,919
Likes: 3,721
From: Hill Country, TX
I had a older BMW M3 that used to give me a hard time passing the damn smog test, so when test time came around every two years, I would put about 3/4 of a tank of 100 octane in her, plus a gallon of denatured alcohol. That car would run like a raped ape with that rocket fuel in the tank, and always pass the smog test after running her hard for about an hour. Probably not advisable to do this very often, but once every two years did the trick for me!
Seasoned HDF Member
Joined: Jul 2013
Posts: 11,185
Likes: 7,961
From: In my head
Yea, I was running a 96" EVO Stroker with S&S B heads at the time.
HD EFI Guru
Joined: Jan 2008
Posts: 4,480
Likes: 4,762
Octane booster does work but some of the advertising is way over what it will do. You can plan on getting about 2 points over the base fuel and that's it. Also adding more than the recommended amount doesn't do any good and in many cases will cause the increase amount to decrease. I have a friend that is a gasoline engineer and has been for 30 years, I got to go to the lab he works at and he really knows his $hit. He showed me the test results of what octane boosters really do and it was very interesting to say the least. Then he said watch this and added a double dose to a batch and them ran the measurements again. The first go around was just under a 2 point octane increase on the double dose the total increase over the base fuel was 0.02 point! So he recommend only using as much as they say on the product and that your better off being just a little short than using more as your just wasting product and hurting the possible amount gained.
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Seasoned HDF Member
Joined: Sep 2009
Posts: 17,145
Likes: 6,168
From: SE Michigan
The manual calls for 91. East of the Mississippi we can get 89 or 93. I use 93. When I travel west of the Mississippi (say on Sturgis trips), of course you can only get 91. I used to obsess about carrying octane boost for those trips, but I stopped worrying about it last year. If the manual calls for 91, and thats what I can get, then it makes zero sense to jerk around with octane booster. If your engine pings, you've got problems that boosting octane will either not solve, or cause other problems.
Seasoned HDF Member
Joined: Jan 2008
Posts: 13,653
Likes: 11,423
From: State of Confusion
Octane booster does work but some of the advertising is way over what it will do. You can plan on getting about 2 points over the base fuel and that's it. Also adding more than the recommended amount doesn't do any good and in many cases will cause the increase amount to decrease. I have a friend that is a gasoline engineer and has been for 30 years, I got to go to the lab he works at and he really knows his $hit. He showed me the test results of what octane boosters really do and it was very interesting to say the least. Then he said watch this and added a double dose to a batch and them ran the measurements again. The first go around was just under a 2 point octane increase on the double dose the total increase over the base fuel was 0.02 point! So he recommend only using as much as they say on the product and that your better off being just a little short than using more as your just wasting product and hurting the possible amount gained.
JK, interesting and learn something new all the time here
