99 octane leaded fuel

[ricksta56]

My owners manual recommends running 99 octane fuel, best I can get here in MA is Sunoco 93 unleaded any recommendations on additives etc. I'm looking for a good fuel recipe.

[simplyconnected]

That is absolutely correct. Your engine was designed and built for fuel that no longer exists, LEADED Premium. The oil had zinc and phosphorous that attacks catalytic converters, so that is gone as well.

I quit 'compensating' years ago and overhauled my engine to modern standards. Meaning, I now use common dinosaur oil sold everywhere and I run pump fuel available across the nation. Diehard classic owners dial back their ignition timing, using unburned fuel to help quench the combustion chamber. The result is; lower hp, terrible gas mileage and performance that is abysmal. The engine will run however, with the potential of receding valves (that ain't pretty).

Modern engines run on pump gas including high powered Mustangs and Camaros. (So, the energy IS in modern fuel.) They also run on 'over the counter' oil. But how, and why do they last three times longer than our classic engines between overhauls? What secrets do modern engines possess?

• Modern engines use roller cams instead of flat tappets, that operate well on modern oils.
• They use stainless valves and hardened valve seats, that don't require lead in the fuel. No more potential for receding valves.
• They use hypereutectic alloy pistons with moly rings that last far longer than OEM (cast iron) rings.
• They use aluminum, both for the intake and heads, which saves weight up front and improves over-steer. Aluminum transfers heat 4X faster than cast iron which allows us to return to 10.5:1 compression ratio without ping and knock.
• Aluminum also allows us to raise the coolant pressure/temperature for a more complete combustion without run-on or preignition.
• Modern timing chains are double roller sets that last 3X longer than OEM, also available for FE engines at a decent price.
  Seals, gasketry, bearings and silicone sealants are all far better today.
• That puny 3/4" diameter sway bar is a joke and should be replaced with an 1-1/8" bar.

All the internal improvements cannot be detected from the outside, making the 'new' FE look stock but with renewed (OEM) power.

You can see why modern engines cost more than classic engine overhauls. But do they really? If you don't get 250,000 miles out of a modern engine, there's something wrong whereas we only got 80-100,000 out of our classic builds. That's three times longer in overall cost savings and constant fuel savings along the way. - Dave

[ricksta56]

What I meant by recipe is something like 5 gallons of Sunoco 93 plus 4 oz of O'Reilly octane boost plus 5 drops of marvelous mystery
Or 5 gallons of 93 plus one quart moonshine?

[simplyconnected]

Aircraft fuel is sold (for off-road use only) at airports but it's illegal to pump it in your car. Aviation gasoline is also called avgas, which is typically used only in older piston engines of sports aircraft and small private aircraft requiring high octane leaded fuel. Globally, only 100 LL avgas is still available, a standard low-lead (LL) gasoline. The cost is about US$7.25/gal. and it comes in 5-gal and 55-gal drums.

At this price, it ends up being cheaper than buying all the additives and it is uniform and perfect for our classics. Let's face it, five gallons won't get you far so the 55-gal drum makes sense to fill your tank ~2.5 times. Instead of going this route, I believe it's still more cost effective and convenient to build the engine to modern petroleum standards. - Dave

[ricksta56]

OK, that idea is worth looking into as we do have 2 local small airports. Brings back memories too as a friend had put fuel from the airport into his Triumph Bonneville to wake it up.
Thanks for this info Dave.

[simplyconnected]

I don't know what compression ratio his bike had but if it was low, higher octane won't help, like putting premium gas in your lawn mower. We do know that your 352 has 10.2:1 compression ratio and it absolutely does need high octane (as described in the owner's manual). High octane slows the burn so the engine doesn't ping and knock.

Was 99 octane available in England, for the air-cooled Triumph motorcycle? That's a serious consideration because I don't think so. - Dave