Re: [St] Using Regular Gas In A Sprint ST

[Jonathan West <triumphnutter@xxxxxxxxx>]

Here's a quick lesson on Ping or Detonation

Factors that affect Detonation: 1) Heat, 2) Ignition Advance,  3) Fuel Load (lugging, that is, large throttle opening along with low rpm),  4) Compression Ratio, (carbon buildup will increase the comp ratio), 5) OCTANE!  Increasing any of 1-4 will require an increase in #5 or you will get detonation. 

The highest performance from any engine will come from the lowest octane fuel possible without detonating.  Lower octane fuels have a higher amount of stored energy .  The octane is used to slow combustion so that it does not fire prematurely and reduce flame travel.  It is false thinking that high octane fuels are for adding performance.  High octane fuels are required for high performance engines that use high compression ratios and lots of advance.  They are simply at a higher state of tune and require the high octane to survive, not to add performance.  In other words, it doesn't add horsepower, it maintains it at a given state of tune.

After smoking two automotive engines from detonation, I became an expert on the matter.  The noise from knock and ping is your piston skirts slapping the crap out of the cylinders.  Yes they do actually rock on their wrist pins a minuscule amount.  They will let you know that they've had enough when you break a skirt (cast pistons) and send it somewhere it never saw before.  Or you may just squash the piston (alloy) into a shape that no longer fits the bore.  I've heard of cracked heads and broken valves from detonation, but have never seen those first hand.  

It's fun stuff that I really wish I didn't know a thing about.   

Triumph designed the engines to a solid medium performance spec that is safe to us the midgrade of 89.  My ST pings on rare occasions with 89... putting 87 in it would prolly be doable if I was runnning at a very relaxed pace at constant small throttle opening in an emergency, like droning down the highway.  I sure wouldn't make a habit of it.  Just remember, if it is detonating, that is the sound of your pistons begging you to stop it!  If it doesn't detonate, you're fine with whatever octane you're running.  

Hope this helps,
Cheers,
Jonathan West


Date: Thu, 13 Mar 2008 05:13:27 -0700 (PDT)
From: Steve Boudreaux <steveboudreaux@xxxxxxxxx>

I know what usually happens when lower-octane gas is used, but one near-full tank fill recently, I tried mid-grade fuel.  No detonation that I could hear, power was still fine.  I also know that a vehicle's miles per GALLON drops a bit when using a lower octane fuel, but it's miles per DOLLAR is actually better with the lower octane/less expensive fuel.  
  
  I wonder: if one were doing a mostly Interstate highway trip, not carrying a pillion or excess luggage/gear, and planning on going about the traffic pace (say, 70 to 80 mph), would a Sprint do fine on regular fuel for that trip?  Anyone have any experience with this?


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