RMC List - Octane boost question

[gearhead066 at gmail.com]

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 <mailto: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 < <mailto:rmc-list-bounces at corvair.org> rmc-list-bounces at corvair.org> On Behalf Of Michael Brittan via RMC-List
Sent: Friday, April 24, 2026 1:47 PM
To:  <mailto:rmc-list at corvair.org> 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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