Using 91 octane to boost MPG?

[Willie Williford]

I run 87 in the LRR with no problems. I can also run higher octane, with very little "seat of the pants" performance. (Even when boosting to 6 psi.)
It's all developed in the ECU programing.
HTH
Willie

[Cobb]

Wow, sounds like I need to take it for a test drive. My supercharged tacoma with the trd kit and flash loved preminum from shell v power with a bottle of 104 octane booster on top. It hauled and went right to 4th gear, locked the toraue converter and kept it there. Anything less and it would hop back to 3rd gear under the slightest load. On regular it would stumble and acted like I was out of fuel when the torque converter locked up.

[3-Wheeler]

Originally Posted by AbCaRed00

Top Tier brand 87 aki for me. No diff with higher octane 92 aki. This one is well worn topic.

Red,

Good point!

Theaveng, engines are specially designed to use a small range of octane in combustion chambers.

The main reason is achieving a desired flame-front burn speed across the squish area between the piston and cylinder head.

Going from the recommended octane level to a higher grade slows the flame front speed and reduces engine efficiency.

If one uses too high of an octane level in the engine, the fuel burns so slowly that it still may be burning as the exhaust valve opens and the gases move out of the cylinder. Not an optimum situation. You're still burning fuel that is not moving the car forward.

The other end of the spectrum is burning the fuel in the chamber too quickly. Pinging and detonation. Piston destruction in action.

The optimum octane to put in the car is what the factory engineers recommended.

Jim.

[olrowdy01]

Originally Posted by theaveng

While researching the Chevy Volt I saw that it's 10.5:1 engine requires 91 octane. The GM engineers explain that the higher compression provides 5-10% better fuel economy. The insight has a 10.8:1 engine. Perhaps it too could see 5-10% better economy like the Volt engine?

But I'd almost bet the Chevy guys didn't say that the 91 octane itself is what gave the increase in mileage.

I've tried using 91 octane fuel but can't say I've seen any difference in MPG. It does seem to have better mountain-climbing ability though.

Probably because the knock sensor allows more advance with the higher octane fuel when the engine is under high loads. But when going for higher mileage (as the Chevy guys were talking about) the engine shouldn't be under high load conditions where the higher octane would help.

This might help:

InsightCentral.net - Knowledge Base

You want higher octane? Add 10 cc/gallon of Toluene to the fuel when you fill up. It used to confuse the heck out of gas station guys when I pulled out a graduated beaker to measure it out.

[jime]

I also tried a tank of 91 octane, but it didn't seem to make any difference with my hypermiling results. If one drove higher speeds and made stronger power demands on the ICE, it might help. It is damn difficult to test small changes on a Gen1. I could detect absolutely no difference when I added Moon caps, but they are pretty, well pretty to me anyway

[kaypee171]

You can't compare the Chevy engine to the Honda engine. It is operating under VERY different conditions than the Insight's is. I doubt it is ever under light load. Even when directly connected to the drive wheels on the highway, it is an 80 horsepower engine pushing a 3700 pound vehicle down the road. When used as a generator, I imagine it makes more sense to run it hard then shut it off than it does to run it under light throttle.

[talonmike]

I red somewhere in the owner manual that the I1 should use 91 octane.

I will try to find this tonight.

[theaveng]

Originally Posted by 3-Wheeler

Going from the recommended octane level to a higher grade slows the flame front speed and reduces engine efficiency.... it still may be burning as the exhaust valve opens

That sounds wrong. The charge of fuel is so small the combustion time is near instant & any difference between 87 and 91 "time to burn" is probably not measurable.

Originally Posted by somebody_else

But I'd almost bet the Chevy guys didn't say that the 91 octane itself is what gave the increase in mileage.

QUOTE FROM GM'S WEBSITE: "According to Volt vehicle line director Tony Posawatz, there are two main reasons. 'The Volt is all about efficiency. Premium fuel offers the opportunity to have a little bit more spark.' Ninety one octane fuel also offers the opportunity to be a little more efficient, he added. 'So technically its a five to ten percent fuel economy improvement.' http://gm-volt.com/2010/07/30/why-th...emium-gasoline

But when going for higher mileage (as the Chevy guys were talking about) the engine shouldn't be under high load conditions where the higher octane would help.

It's weighed down by a 75 horsepower generator that is being used to supply electricity to the battery & motor. I would consider that a high load. Like driving your insight while pressing on the brake.

[Cobb]

I seriously doubt that its a "GM" engine in the first place. Most of their engines are large, heavy and inefficient.

Really you need to dial in the engine and or octane to the load. Putting high octane in an engine that doesn't use the knock sensor in the first place is a waste. Now if its retarding the timing, then yeah, higher octane will help. Back in the day we use to retard timing on those who needed mid grade or premium fuel could make due with the dog crap stuff with no ill effects than less performance.

I haven't filled up the i2 with premium yet, but i have used an octane booster and find bp gives better over all performance. Now my sidekick, you can really haul ass with a tank of premium in him. Of course his timing is maxed out and he also has another 5 degrees on top of that with the cam gear.


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[talonmike]

For those using octane booster, read this.


[sx] Octane Boosters <long_but worth the read>

It does not boost that much