Fuel grade

[Chumley]

I've had some informative discussions at work about octane. I had been burning 92 in my big block 402 per the owners manual recommendation. Then I dropped down to mid grade ( 89 ) which still burns fine without ANY pinging or knocking whatsoever. I'm thinking of trying 87 octane now, mainly for economy reasons. Any problems with this I might not be aware of? Engine is all stock inside with low compression.( 8.5 ) Thanks

[Lippyp]

Wow, the lowest grade fuel we can get in the UK is 95 octane, going up to 98 for super, and no leaded except for a very small number of stations acros the country, Lead Replacement Petrol only with an unknown, untested additive.

[longhorn man]

There should be no reason what so ever that you can't run 87 on a stock 8 to 1 engine.
You gotta remember too, the fuels were not the same as they are today when these trucks were built.
If you run a higher octain than you need to, you are literally throwing away your $$, and actually poluing more.

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'69 G.M.C. (http://geocities.com/andys_69_gmc/) 350/350 and a heluva cam. Still trying to clean up the left over damage from the Dope-Smokin-Old-Man.
The 1970 One ton Longhorn (one of only 1404 built) with only a TH350...soon to be CADDY powered and a TH350.
Check outThe Longhorn Website (http://www.longhorntrucks.freeservers.com/) Andy, in Columbus Ohio...Home of JEGS
And now...another site. The caddy swap page (http://geocities.com/caddyoneton/) is under construction!

[L&Lblue72]

The lower the grade the more gas per gallon.
Higher octans just have moer cemichels in them to get octan levels.

[DennyB]

8.5:1 compression should run on 87 octane.

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Toms River NJ (Transplanted Hoosier)
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56 working Street Rod(under construction 71-2 coil chassis)

[Chumley]

Thanks guys, that was my feeling too. Just wanted to verify. I'll try 87 on my next tank.

[longhorn man]

Just to be on the safe side, only fill it 1/2 way. That way IF you get the marbles on glass sound, you can top off with some higher octain and all will be good.

------------------
'69 G.M.C. (http://geocities.com/andys_69_gmc/) 350/350 and a heluva cam. Still trying to clean up the left over damage from the Dope-Smokin-Old-Man.
The 1970 One ton Longhorn (one of only 1404 built) with only a TH350...soon to be CADDY powered and a TH350.
Check outThe Longhorn Website (http://www.longhorntrucks.freeservers.com/) Andy, in Columbus Ohio...Home of JEGS
And now...another site. The caddy swap page (http://geocities.com/caddyoneton/) is under construction!

[vt05091]

Hi folks,

I have a 1972 350/V8 C10, all original with 45,896 actual miles. The mechanic I talked to about fuel said to use 91 Octane and run some system cleaner through it every 10 tank fills or so.

My truck runs like a top. I have a tiny bit of blue smoke on startup - nothing to write home about. However, if I punch it on the freeway while going about 50-60 mph or so, when it drops a gear and the rpms go up I get a significant cloud of black smoke out the back. Blue = oil, white = water and black = fuel - is that correct?

Since I moved the truck to CA, I have used 91 Octane from Arco. I have not run any system cleaner through it recently, but that doesn't seem to matter when I do.

Is there anything here that I should be concerned about or do differently? It appears that I may be wasting some hard earned cash on Premium gas too?

I think I will try the half tank of 87 suggestion and see what happens.

I am interested in your opinions and experience.

Thanks,
VT05091

[longhorn man]

Try the low grade fuel.
Octain levels, in reality, measures the resistance to ignite. Some vehicles will actually run WORSE on higher grade fuels. My wife's 92 4.3 Vortec powered S-10 Blazer will run like total doggie doo if you try to feed it 93 octain.
Your smoke colors are normally right. One thing also though, black will pour out if you are very very lean too...like when the engine is getting a couple drops of fuel when your trying to rev the crap out of it, but that is not a common problem.
Sounds like your smoke on start up is worn valve seals.
The smoke when you nail it on the free way is a slightly rich carb.
As far as the cleaner, you don't need to run it so often. Some of them do absolutly nothing, while others are very good. However, many are highly corrosive, and speed up rust and deteriate rubber fuel lines.

------------------
'69 G.M.C. (http://geocities.com/andys_69_gmc/) 350/350 and a heluva cam. Still trying to clean up the left over damage from the Dope-Smokin-Old-Man.
The 1970 One ton Longhorn (one of only 1404 built) with only a TH350...soon to be CADDY powered and a TH350.
Check outThe Longhorn Website (http://www.longhorntrucks.freeservers.com/) Andy, in Columbus Ohio...Home of JEGS
And now...another site. The caddy swap page (http://geocities.com/caddyoneton/) is under construction!