Octane requirement?

[someotherguy]

I lived at 7500 ft up in Evergreen CO for a couple years. A stock 93 454 will be absolutely so slow. Run the cheapest, there is hardly any oxygen at that altitude anyways. The DA at Bandimere routinely hit 10,000 ft in the summer and that was 2000 ft lower. Try driving to the top of MT Evans at 14,000 feet and my C5 Zo6 couldn't get out of its own way...

If that's the case (I'm not used to high altitude driving - at all) - I wonder if the 85 would be a smarter bet? It's at least 2 octane points more volatile than 87.

Richard

 

[Supercharged111]

If that's the case (I'm not used to high altitude driving - at all) - I wonder if the 85 would be a smarter bet? It's at least 2 octane points more volatile than 87.

Richard

That's where I can't get a good answer. In closed loop, I'd say no. But in open loop, I still say no. Dependent upon the margin of the tune of course. I can't speak for TBI stuff, but I know for a fact the Vortec stuff leaves a ton on the table everywhere. All you're doing there is eating into your margin IMO, I still don't think the altitude buys you margin on an EFI vehicle.

 

[PlayingWithTBI]

I can't speak for TBI stuff, but I know for a fact the Vortec stuff leaves a ton on the table everywhere

TBI did too, especially with lower compression than Vortec but, I thought higher octane helped to reduce KCs in higher elevations? Of course you can always reduce SA and make it a dog too

 

[thegawd]

here let me google that for you... haha heres a screenshot.... it would seem supercharged is absolutely right. 85 octane works well in carbureted engines but not so well with modern EFI.

You must be registered for see images attach

 

[Schurkey]

I used to drive through Casper/Rawlins WY and got fuel there and other places at high altitude on I-80.

My '92 and '93 Lumina 3.4L DOHC engines tolerated 85 octane just fine at altitude.

I wouldn't be the least bit concerned about 85 octane at ~7K altitude. But a person could connect a scan tool and look at the knock sensor activity. No, or mild knock sensor activity, no problem.

 

[GoToGuy]

When Rome Fails.

Correction " When Rome Fall's so goes the Empire. "
Cessna 152, why?

 

[GoToGuy]

Using an 85 in computer controlled engine, would conflict with operating parameters of powertrain. Regular octane fuel 87. Manifold pressure, temp, timing, all factors and conditions based on first element of equation 87 octane.

 

[LC2NLS6]

TBI engines have minimal timing anyways. It'll be fine. Octane is just a rating of resistance to detonation. Raise your hand if you lived at 7500 ft, as in my place was at 7500 ft and I'd drive to the resorts to snowboard every chance I could. It'll run rich most likely to start with anyways.

 

[LC2NLS6]

30 year old TBI is hardly modern fuel injection, more like spray and pray electronic carb.

 

[1992prime]

So you’re voting for 85?