Octane requirement?

[1992prime]

Hello,

Live at 7,500’ and wondering what fuel
I should use in my 93 7.4L suburban.

85, 87, and 91 are available.

Previous owner used 91.

 

[someotherguy]

Wow! 85 available in your area... that's weird. 87 is lowest I've ever seen (TX) - most likely your engine is designed to run on 87, but confirm via your owner's manual. If you don't have one you can likely find one scanned on the interwebs.

These are "regular fuel" vehicles. They run best on the fuel they are designed for. That means not only is the engine built as relatively low compression, the spark advance and fuel tables in the tune are meant for the lower grade fuel, too. Running higher grade fuel is simply a waste of money.

The 85 might be a stretch, though. Your engine can experience spark knock that you may not notice, but your knock sensor does, and will pull timing, costing you power.

Richard

 

[Supercharged111]

85 is normal at higher elevations. . . and it's stupid. EFI knows you're at altitude. Factory specs 87, so if timing is set to stock then 87 is what it calls for.

 

[F4U-1A]

What-s that in Metric? I remember piloting a Ces 152. Engine would fail at 10,000 feet. Only in Canada, I says.

 

[Supercharged111]

What-s that in Metric?

Who cares?

 

[F4U-1A]

Who cares?

When Rome Fails.

 

[1992prime]

thanks, will use 87

 

[Supercharged111]

thanks, will use 87

Where exactly are you in this fine state?

 

[1992prime]

west of denver

 

[LC2NLS6]

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...