Is 91 octane gas a must?

mj.23bulls · Posted: Sun Jul 17, 2011 5:42 pm Post subject: Is 91 octane gas a must?

Just got my first bus up and running. Went to put gas in and it says to use 91 octane gas. Is that necessary? Did fill it up with 91 but it's pricey. Thanks.

Randy in Maine · Posted: Sun Jul 17, 2011 5:44 pm Post subject:

The old 91 octane is the new 87 octane.

mj.23bulls · Posted: Sun Jul 17, 2011 5:46 pm Post subject:

Great, bus driving will be much cheaper!!!

Desertbusman · Posted: Sun Jul 17, 2011 5:47 pm Post subject:

Does it say 91 octane or 91 RON?
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mj.23bulls · Posted: Sun Jul 17, 2011 5:49 pm Post subject:

91 RON. I just assume it was referring to the octane.

Randy in Maine · Posted: Sun Jul 17, 2011 7:16 pm Post subject:

It does.

Been here?

http://type2.com/bartnik/octane.htm

SGKent · Posted: Sun Jul 17, 2011 8:14 pm Post subject:

We find that our best mileage comes with the mid-grade gas. It also gives a little more knock protection. If you don't know the compression ratio on your engine, there is always a chance the last owner put in a higher compression piston.
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guanella74 · Posted: Sun Jul 17, 2011 9:41 pm Post subject:

I was told that my engine was rebuilt with a low compression ratio - would that mean I would benefit more from using...which grade of gasoline?
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Wildthings · Samba Member Joined: March 13, 2005 Posts: 52718

guanella74 · Posted: Sun Jul 17, 2011 9:47 pm Post subject:

In general, do low compression engines like low or high octane better? Thanks Wildthings
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1974 Westy CampMobile - the OG!
1979 Transporter
1979 Transporter
1977 Transporter
1974 Transporter
1973 Transporter
1971 Westy

Desertbusman · Posted: Sun Jul 17, 2011 10:21 pm Post subject:

With your very high damaging engine temperatures you might try different grades of gas to see if it makes a difference. Compression ratio, octane and timing are all closely related factors. Experiment with both the gas and the timing to see what it does with temps. Cautiously watch out for pre-ignition. Another thing, Gene Berg recommended switching spark plugs from 8's to 7's for a hot running bus.

I always use mid octane 89 in both my engines.
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guanella74 · Posted: Mon Jul 18, 2011 6:23 am Post subject:

I'll probably start using mid and see how that goes.

For my education, if I have a racing engine, for example (not talking buses now), it's going to be a HIGH compression engine and want high octane gas then, right? More compression = more power but higher temps because of tighter clearances, is that correct?
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- Travis

1974 Westy CampMobile - the OG!
1979 Transporter
1979 Transporter
1977 Transporter
1974 Transporter
1973 Transporter
1971 Westy

Randy in Maine · Posted: Mon Jul 18, 2011 6:34 am Post subject:

VAVWFAN · Posted: Mon Jul 18, 2011 9:44 am Post subject:

What is engine knock; and why does higher octane gas "sometimes" solve it?

THE BASICS:
Knock or pinging is simply a term for pre-ignition. Preignition can also be classified as "dieseling" because (if you know the difference between gas & diesel engine theory), that's exactly what is happening! The compression in you engine is high enough, thus hot enough, that it's firing the fuel/air mixture from the induction system (carb or FI), before the plug does!

Often you'll hear a rattle (pinging) or a clugging sound because the cylinder that just had it's intake valve open (taking in fuel/air mixture) is coming up on TDC of the compression stroke, and fireing prematurely. As this is happening., another cylinder's "stroke" (in it's Otto cycle) is being interrupted, thus the connecting rods are fighting one another.... The pinging you hear is actually the rods dueling it out!

As many herein explained, this occurs more in high compression engine, and is not desireable, in fact,,,,,it's destructive!

Higher octane often solves this problem because (and I'm using this term "very" loosly), it has a higher flash point, which allows the crankshaft to turn to it's desired degree BTDC where it should be firing at (or in other words, where the points open, sending spark to the plug!)

If you undertand this, you can understand the relationship of valve and ignition timing, as well as the interrelationship of ignition (distributer) advance, whether it's vacuum or centrifugal!!
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telford dorr · Posted: Mon Jul 18, 2011 10:39 am Post subject:

As an aside: my understanding is that there is no such thing as "mid-grade" gas - it's just a mix of 'regular' and 'premium', and the mixing is done at the pump. So you're dependent on the integrity of the pump to get that 91 octane rating. Not trusting gas stations any farther than I can throw them, I'd be inclined to make my own mix. Add some 'premium' gas first, then top off with 'regular'. Also, you can mix in any ratio you want, with a little math. More of a hassle, but at least you're in control of the result.

Just a thought...
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CarlIseminger · Posted: Mon Jul 18, 2011 11:03 am Post subject:

I find with my beetle, that during the winter, I have to use Premium gas as that is the only gas in my city that doesn't have ethonol in it. And only a couple of stations have the ethonol free premium gas. I find my car runs better in the winter with this gas. Summer, I can run the 87 without a problem.

SGKent · Posted: Mon Jul 18, 2011 11:18 am Post subject:

Desertbusman · Posted: Mon Jul 18, 2011 1:35 pm Post subject:

SGKent · Posted: Mon Jul 18, 2011 3:29 pm Post subject:

Go here and read Top Tier Gasoline standards. The list of companies who are members are also listed on the site.

http://www.toptiergas.com/deposit_control.html
_________________
Rolling Eyes

Canned Water - the new California approved parts cleaner (except in a drought in which case rub it with sand). Rolling Eyes

George Carlin:
"Most people don't know what they're doing, and a lot of them are really good at it."

Skills@EuroCarsPlus:
"never time to do it right but always time to do it twice" Rolling Eyes

Mal evolent · Posted: Mon Jul 18, 2011 5:36 pm Post subject:

my personal rule of thumb: compression ratio X 10 = necessary octane rating
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