----- Original Message -----
From: "Arakelian, Peter" <arakelianp@mossmotors.com>
To: <triumphs@autox.team.net>
Sent: Wednesday, May 12, 2004 3:37 PM
Subject: octane/timing/performance
> I have a stock 1971 TR6. I currently run premium gas, which is what is
recommended. With all the vacuums, etc attached I time it at 8 BTDC. No
ping, runs great.
> My understanding is that lower octane gas burns faster and a little
hotter, but at 20 cents/gallon cheaper it is tempting to switch to the lower
octane and retard the timing until it doesn't ping.
> Any thoughts? What are the down sides? Has anyone done this? Am I
missing something?
Peter-
I agree with Uncle Jack here. I have run my TR6 on regular fuel without
spark knocking and have not suffered in the power loss. Unless you are
running a high compression ratio like a 10:1 or higher, you should be able
to do the same.
Remember that there are no more BTU's in premium gas than there are for
mid-grade or regular gas. The higher the octane, the more it resists
detonation in the cylinder. Factors causing early detonation or knocking
include-
1.) Octane number of fuel
2.) High compression ratios
3.) Turbocharging
4.) Ignition advanced too far (advanced)
5.) Operating temperatures
6.) Carbon deposits
7.) High intake temperatures
8.) Fuel mixture too lean
Our Triumphs suffer from #7 due to the design of the straight six. #8
certainly is part of the equation too. Depending on your geographical
location, #5 comes into play as well. Living in Maine, ambient air temp
never gets too high and the engine runs cooler than in your sunny
California. The cooling system plays a big role in the performance of any
car and if it not up to snuff, it can effect a lot of other components and
systems, thus contributing to performance (or lack there of). Optimally
tuned you should be able to run regular gas with good results. YMSNV. (Your
mileage should not vary)
Let us know what you learn..
Tim Hutchisen
71 TR6- 87 octane
80 TR7 Spider- 87 octane
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