$5/gal is cheap for 105 IMO. 116 at the track near me is something like $12-16/gal IIRC. I know you're paying for the convenience of having it right there at the track, but I sure wouldn't mind paying $5/gal for 105 at the track!

Anything FI should be running premium. Heck, anything that requires premium should be running it. Too many people try and get away with running lower grade to save a buck or two. A 10 gallon tank fillup every week with premium running $0.30 more per gallon is $3 more per week, $156 more per year. Is $156 (in this situation) worth contributing to engine failure leading to engine replacement? This is mostly directed toward vehicles that require premium but I just never understood the logic behind using a lower grade because it's cheaper.

 

Im not sure on 2nd gen,but with me having a 1st gen there is a bypass wire under the passenger side dash,i can unplug it,adjust timing,then plug it back in. then the computer will run that timing,unless knock happens,then the computer retards it until it stops.

 

WOW! You guys have the cheapest fuel in the nation. We're paying $3.40 for 87! And I thought that was a bargain ...

I run hi test in the Silverado, only because I have a program that requires it. Still pings on heavy throttle. It;s about $3.80 for hi test up here ...

 

The Low-Down on High Octane Gasoline

» High Octane Gas Myth

High Octane

 

In the owners manual for my '94 it recommends 91 octane if I remember correctly, but can compensate for lower octane

 

All octane does is slow the burn down to prevent pre-ignition/detonation. So 89 burns a bit slower than 87 .. and 92 93 94 burn even slower. Race gas is the slowest. Actually aviation fuel is, but we're not running that on a daily basis.

By using high octane fuel when it's not required, you actually LOSE power. I've seen it many times on the dyno in the motorcycle world. Kids putting 110 octane race gas in their crotch rockets thinking they're gonna gain mega hp. Dyno showed a 5 hp loss at the rear wheel when compared to the recommended 92/93 octane. Sometimes more than that. If it's built - I.E. has very high compression - then you can benefit from it.

 

Ah... knowledge!

But there should be some further definition for those who care.

Spark knock, Detonation, preignition, and burn rate are often related to octane but are distinct issues.

Detonation is caused by the temperature of the air/fuel mixture reaching the point where the fuel ignites by itself. That is purely a function of ambient air temp/stoich ratio eg 14:1/ and cylinder compression ratio. Detonation breaks piston rings and can burn the top right off a piston, let along the plug electrodes. Mainly caused by 'too lean' and/or too low octane for compression ratio.
It's how diesels run

Pre ignition however only happens in a 'warmed up' cylinder where the mixture is ignited by a 'hot spot', eg glowing deposits or a glowing plug tip, before the spark is sent.
It's how model airplane engines work
- Detonation can cause preignition
- and BTW, that is what caused 'dieseling' in old carb engines. It wasnt really dieseling it was hot spot ignition

Both can be reduced by enriching the mixture or raising the fuel igntion point.

Now we come to spark knock. The flame front - never mind what ignited it- burns so fast the maximum pressure is reached before the piston goes over top dead center. eg the timing is too far advanced for the compression ratio and burn rate {octane}. The burn is most efficient when the piston is already starting on the downward stroke when the peak pressure is reached.

* Too long -or timed too late- a burn will result in actual flame front going out the exhaust valve and heating headers cherry red at idle -common in the olden days when most of us had limited timing tech skills and some were stupid enough to run 12.5:1 pistons in street SBC's
- reason being you need 105 octane at least for that ratio and even with the superpremium pump gas you got anywhere from 97 to 100 octane, max.
SO... you had to retard timing too much to start the freepin engine, and couldnt change the curve nearly enough in the stock dist. Could have been helped by modding the point plate for more travel and hooking up a 'retard to start' cable or solenoid to get to a couple deg ATDC, but we were dum. Set base timing to 12 deg BTDC @ 850 rpm. Should have been at least 20 but the engine balked at spark which I recall was about 2 deg BTDC in crank.

*Now THIS * is why it's not smart to even think of running 105 octane in the stock 9.3:1

First, it's not efficient in either cost of operation or fuel mileage. Second it can do real damage and there's only so much you can tune for.
This is why production turbo cars used reduced compression ratios {dished pistons} along with requiring premium gas for full boost.

 

This topic has been discussed before. As already pointed out, too high of an octane can actually waste fuel & potentially damage your vehicle.

To anyone considering running higher octane than the manufacturer states, how your engine reacts to each type of fuel (octane level as well as different brands of fuel) should be observed over time. 3-4 tanks of each fuel type/source should be used and compared with the others on a $/mile basis.

This is something that I do with all of my vehicles when first purchased. My '00 Bravada ran best on 89 until I decarboned the engine & did a complete tune up, then the $/mile was higher with 87. My '04 Rainier ran best on 87 with a stock PCM, but after a PCMforLess tune, the best $/mile was with 93 (premium) due to the tune. I just completed the testing on my '04 Tahoe and it currently has the best $/mile with 89 octane.