Premium in an 8?

[Cheapsnake]

The owner'w manual for the TR8 calls for 93 octane fuel, but at a CR of 8.15:1, I can't imagine why the high octane is needed, especially with aluminum heads. With premium gas getting close to $4 per gallon, I really have to question whether the extra octane is really necessary. I've run mid-grade with timing advanced to the max with no apparent preignition but it's the things that aren't apparent that make me question the lower octane.

Any thoughts on this?

Tom

 

[tdskip]

Hi Tom - I'd get several opinions on this but I'd think you should be able run a mid-grade fuel if you adjust your timing.

 

[swift6]

I haven't looked at that section of my TR8 owners manual, but in my TR6 owners manual it call for higher octane as well. My thoughts are that when Triumph people wrote these manuals, they were referring to British Octane ratings.

US octane ratings are derived from averaging two different rating methods. Research Octane Number (RON) and Motor Octane Number (MON). This is why you see (R+M)/2 on gas pumps in the US. The British use only the Research Octane Number. The RON is determined in a test engine running at 600rpm while the MON is determined in an engine running at 900rpm. The RON is usually 5-10 points higher than the MON number.

As long as you are not getting any pinging/detonation you are fine. Higher octane gas won't increase power, nor will it clean deposits any better etc... Add altitude into the mix like I deal with and you can get away with even lower octane numbers. Doesn't seem to lower our gas prices though as our prices are above the nations average.

 

[StagByTriumph]

The owner'w manual for the TR8 calls for 93 octane fuel, but at a CR of 8.15:1, I can't imagine why the high octane is needed, especially with aluminum heads.

Any thoughts on this?

Tom

I run 85 octane in my tuned Rover 3.5 with 3.9 EFI, higher compression Chevy pistons, and about 12 degrees of advance at about 5500 feet altitude. No problemo, performance is fine.

 

[philman]

i use regular in my range rover classic with the 4.2 liter v8, doesn't seem to present a problem even under load at high altitudes.

 

[Mickey Richaud]

Tom -

Before mine cratered due to wrist pins taking a walk, I was using mid-grade (89?) with no problems. Compression readings were 150-160 across the board (135 is "normal").

Run what you got - just be sure it's timed so's you don't get pinging.

Mickey

 

[Cheapsnake]

Thanks guys. I feel better (and slightly less impoverished) now about the use of lower octane. Shawn, your explanation of the octane ratings was right on and makes perfect sense.

Mickey, how bout an update on your engine?

Tom

 

[Mickey Richaud]

Thanks guys. I feel better (and slightly less impoverished) now about the use of lower octane. Shawn, your explanation of the octane ratings was right on and makes perfect sense.

Mickey, how bout an update on your engine?

Tom

Sigh... If I had one, I'd give it!

I'm almost afraid to report it, but last Thursday they told me it would be ready this week. Got my cell phone at the ready!

I don't know how much more "cleaning" my shop can take while I wait!