RMC List - Octane boost question

[Michael Brittan]

Hi Eric:

Maybe I'm confusing terminology (forgive my ignorance).  What I experienced
with 87 octane gas with my Spyder was run-on (dieseling) after I turn off
the ignition.  This did not happen after I added the octane booster.

Best,
Michael

On Mon, Apr 27, 2026 at 10:59 AM <gearhead066 at gmail.com> wrote:

> Michael,
>
>
>
> I’m curious about the rpm and load where your Spyder detonates. I had a
> couple of 180 turbo Corsas in my youth, and recall that even with the 98
> octane leaded ‘Hi-Test’ of the era, there was always a little buzz of
> detonation on throttle tip-in. I initially addressed it by opening the
> passage to increase the accelerator pump shot.
>
>
>
> Turbos are an awesome secret weapon. Linae’s Mazda CX-5 has a turbo 2.6
> four, and the thing runs a quarter-mile as quick as my 1971 455 Pontiac
> Trans Am!
>
>
>
> Eric
>
>
>
>
>
>
>
> *From:* Michael Brittan <mibrittan at gmail.com>
> *Sent:* Monday, April 27, 2026 9:17 AM
> *To:* gearhead066 at gmail.com
> *Cc:* Rick Beets via RMC-List <rmc-list at corvair.org>
> *Subject:* Re: RMC List - Octane boost question
>
>
>
> Hi Eric,
>
> Now you're talking!  A 140 with 10.4:1 compression and a turbo.  In the
> interests of Corvair science though, you'll have to run the experiment on
> two cars - one with fuel with ethanol and one without.
>
> FYI, a can of VP Racing Octane Booster (purchased at Walmart) added to a
> full tank of ethanol-free 87 gas took care of the detonation on my Spyder.
> This can was the cheaper of the VP options so I'm not sure if it contained
> alcohols.  The can blurb did not provide the ingredients.
>
> Best,
>
> Michael
>
> Michael
>
>
>
> On Sun, Apr 26, 2026, 10:22 PM <gearhead066 at gmail.com> wrote:
>
> Michael, for what it’s worth, I’ve ignored all warnings and online threads
> talking about detonation and engine wear and simply used standard Tier 1 91
> octane pump premium with ethanol at Denver’s altitude for years. I dislike
> the hassle (and occasional clothing disaster) of diddling with octane
> boosters and fuel additives. Even in engines with cylinder heads milled to
> raise compression to a true 10.4:1 range, detonation and wear have not been
> issues. I can’t comment on a turbo engine at this point, but I’m thinking
> of tossing a turbo onto a set of 10.4:1 compression 140 big-valve heads to
> see how long it takes to melt the piston tops. If I do that and ethanol
> helps with piston top life, I’ll let you know!
>
>
>
> Eric S.
>
>
>
>
>
> *From:* RMC-List <rmc-list-bounces at corvair.org> *On Behalf Of *Michael
> Brittan via RMC-List
> *Sent:* Friday, April 24, 2026 1:47 PM
> *To:* rmc-list at corvair.org
> *Subject:* RMC List - Octane boost question
>
>
>
> Hello All,
>
>
>
> I like to use only non-ethanol gas in my cars (Spyder and 2x164/110
> Monzas).  87 non-ethanol is available in my area of SE Denver at a
> reasonable price.  Preferred 91 octane non-ethanol is available at the
> Mobil station in Lakewood, but at a huge price premium and a 30-mile
> round-trip (+- 2 gals of gas consumption right there) from my home.
>
>
>
> I can eliminate the pre-ignition with expensive octane booster containing
> MMT.  Cheaper brands contain alcohols, so defeat the purpose of using
> no-ethanol gas and don't raise the octane as much per ounce of dosage.
>
>
>
> I'd welcome members' views on using such octane boosters and whether they
> may have preferred brands.  Could any harmful side-effects be experienced
> with our trusty Corvair engines using these boosters?  What do members feel
> about using standard pump 91 octane containing ethanol?
>
>
>
> Best,
>
> Michael
>
>
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