87 vs. 89 vs. 91 Octain fuel. My findings....

That you know of....

you can have detonation that isnt audible to the human ear.

I always run 91..even before I was boosted. E85 is next

 

yeah semantics but you're right. It's the audible ones that kill.

 

Interesting Chris. I have to admit that despite my bias based on octane ratings (as posted); if I had the experience you relate, I'd use higher octane fuel, . . . or inquire about whether there is some other reason my truck did not operate well on 87.

 

And the next time they say that fuel does not make a difference; just keep this in the back of your head. NASCAR and NHRA don't use street fuel to make their horsepower, neither do War Birds. The Drag Racers use Nitro Methanol, and NASCAR uses 120 Octain Nitro Alcohol Blended Gasoline, (Racing Fuel). As for the War Birds, well they use an Avaiation Gasoline called AvGas 100LL, (100 Octain Low Lead). Pretty good for a 5000 Horsepower Dragster, don't you think?
Take care
vbibi

 

I don't think anyone is suggesting 'that fuel does not make a difference. The two hydrocarbons of most significance for gasoline are heptane, which has seven carbon atoms, and octane, which has eight. The octane rating is significant because octane can withstand much higher compression than heptane, and it's the high compression that increases power.

 

I believe the 3.4 in mine is 9.6 to 1 which is in the high compression ballpark too

 

You cannot fairly compare compression ratios for older, carburetted engines without engine management systems ] with newer ones. For example, from http://www.faqs.org/faqs/autos/gasoline-faq/part3/

"For a typical carburetted engine,
without engine management [27,38]:-

Compression Octane Number Brake Thermal Efficiency
Ratio Requirement ( Full Throttle )
5:1 72 -
6:1 81 25 %
7:1 87 28 %
8:1 92 30 %
9:1 96 32 %
10:1 100 33 %
11:1 104 34 %
12:1 108 35 %

Modern engines have improved significantly on this...."

The current 4 cyl. Toyota has a compression ratio of 9.6:1, yet only requires 87, not 98 as the chart above would indicate. The entire article ref'd above is illuminating, but I'll paste just one more selection:

"If you use a fuel with an
octane rating higher than what the engine can use, you are just wasting
money by paying for octane that you can not utilise. The additive packages
are matched to the engines using the fuel, for example intake valve deposit
control additive concentrations may be increased in the premium octane grade.
If your vehicle does not have a knock sensor, then using a fuel with an
octane rating significantly below the octane requirement of the engine means
that the little men with hammers will gleefully pummel your engine to pieces.

You should initially be guided by the vehicle manufacturer's recommendations,
however you can experiment, as the variations in vehicle tolerances can
mean that Octane Number Requirement for a given vehicle model can range
over 6 Octane Numbers. Caution should be used, and remember to compensate
if the conditions change, such as carrying more people or driving in
different ambient conditions. You can often reduce the octane of the fuel
you use in winter because the temperature decrease and possible humidity
changes may significantly reduce the octane requirement of the engine.

Use the octane that provides cost-effective driveability and performance,
using anything more is waste of money, and anything less could result in
an unscheduled, expensive visit to your mechanic."

 

Bottom line is you can run 87 if you want-the ECU will retard the timing according to the detonation it detects, then yeah there won't be any knock but you'll give up some power and FUEL EFFICIENCY. I'll take 91-thank you