high octane?

[Gel]

Hi,
I'm sure this has been discussed to death but all I require is a "yes" or "no"
Should I use high octane fuel??

 

[Bugeye58]

Gel, if your compression ratio is below 9:1, no. If above, yes.
Jeff

 

[Gel]

Okay, I was afraid of that.
I'm a beginner! I know nothing about compression ratios. All I can confirm is that it's a Jan. '73 car

 

[Rob_Edwards]

You should run the lowest octane that runs properly in YOUR car. For some people that may be low octane, for some it might be the highest. This late in the game, every car is different -- different amounts of wear, different states of tune, etc.

Many people believe that because high-power engines run high octane, high octane therefore makes high power. It's a myth. Octane (or more properly "octane equivalency rating" or "octane rating" is simply the resistance of the fuel to being ignited -- higher octane fuel is harder to burn. It actually contains fewer BTUs by volume than lower octane fuel, but the difference is probably negligible. In theory though you'll get slightly less power and fuel economy with a higher octane fuel than you need (other things equal).

So try some midgrade -- if that works without pinking and running on, use it. You could even try some low octane if you wish. If it works, use that. Using higher octane than you need does nothing but wastes your money....

HTH!

 

[Steve_S]

Unfortunately it isn't a yes or no question. My recommendation is to run the lowest octane the car runs properly on. My cars require 92 octane to run their best. Other people have good luck with 89 or even 87. Try 89 next time you fill up. If it pings, loses fuel economy or doesn't run as well then go back to high octane. If it runs as well or better, try 87 and see what happens.

 

[Gel]

Running on? Sometimes, but not always when I switch off my car doesn't die straight away? Could this be related?

 

[Bugeye58]

Gel, in standard knick, the '73 runs a compression ratio of 8.8:1. Steve's suggestion is excellent. Try a bit of experimentation, and find which grade of fuel works for you. For instance, my stock '72 runs just fine on the 87 octane here in the States. My '65, which is built to a much higher stage of tuning, requires a minimum of our 94 octane, but prefers even higher.
Jeff

 

[tony barnhill]

Let me tell you what my experience has taught me: 93-octane is what my MG's like! My '79 that I've owned since brand new & that has only had the carb rebuilt once has never had anything else done to it - & its only had 93-octane.....so, figure 100,000+ miles with no major repairs since '79.

I'm going to pull the head this Fall just because - & I'll bet the valvetrain looks like new.

 

[Tom_Fisher]

I use high octane gasoline because it's always been my understanding that the MGB has a high compression ratio. I DO understand Rob's comments about high octane being a waste of money on engines that don't need it.

 

[Guinn]

My 78 runs fine on 87 and no better on 93 which I tried because one of us suggested it. Waste of money to use 93 unless you have a problem with 87. I have never found a problem with any of my cars that was helped by going to higher octane than the book recommended.

Guinn

 

[Hap Waldrop]

Only reason I use 93 in my GT is that 93 has a longer shelf life, in case the car sits for awhile, I use 93 in the generator and ATV as well. Race gas can literally sit in a fuel cell or fuel jugs for a few years without going bad, so based on that, all I can tell you is if you might let the car sit awhile or it takes you a while to run through a tank of gas, the higher the octane the longer the shelf life. I had 87 gunk the carb up on the ATV in less than three months.

 

[jlaird]

That's intresting Hap, never heard that before. Something to keep in mind as winter approches for our northern folks.

 

[Bugeye58]

It's just for that reason that when I put mine to bed for the winter it has a full tank of either 93 in it, or a mixture of 87 and leftover 110 leaded.
Jeff

 

[Steve_S]

I've never heard that, Hap. Very interesting!

 

[Gearhead]

When I put my car away for the winter I always add a healthy dose of Sta-Bil fuel stabiliser use it all my mowers and have never had a problem with fuel related gumming problems try it yull like it /ubbthreads/images/graemlins/driving.gif

 

[Steve_S]

Don't need to. I don't put my cars away for the winter. /ubbthreads/images/graemlins/laugh.gif

 

[Bugeye58]

Crikey, Steve, up here I put <u>myself</u> away for the winter!
Jeff /ubbthreads/images/graemlins/grin.gif

 

[53caddy]

Well i put a 104 octane in my caddy but thats what it likes.

 

[Steve_S]

104 octane around here is something like $6.50 per gallon!

 

[53caddy]

yea its expensive. why do you think i havent drove it in almost 2 years.