fuel octane?

[mcknight77]

I have a 73 SB with 1600 DP. Should I be running 93 octane or 87?

Jim

[Namocsid]

For a stock engine, 87 octane is fine
_________________
ITMC - Backyard chapter

Hold the pickles, it's 100% pure beef Namocsid!

[79SuperVert]

Unless your engine pings (knocks) you should use the lowest octane. Not only is it cheapest, it has the fewest additives. The difference between regular and premium is that premium has more additives (and therefore less gas) per gallon than regular. And all gas by law has to be detergent-type gas.

[dart-bug]

[Namocsid]

a higher octane rating means more resistant to detonation (as opposed to combustion, which is good)

now how they do that, i have no idea.
_________________
ITMC - Backyard chapter

Hold the pickles, it's 100% pure beef Namocsid!

[Jimbug57]

The additives in gasoline that increase octane are there to retard combustion. Higher octane fuel allows you to advance your timing and increase your compression ratio to develope more power, without having pre-detonation, AKA ping and knock.

[dart-bug]

[Glenn]

Stock... 87 is fine.
_________________
Glenn
74 Beetle Specs | 74 Beetle Restoration | 2180cc Engine
"You may not get what you pay for, but you always pay for what you get"

Member #1009

#BlueSquare

עַם יִשְׂרָאֵל חַי

[Namocsid]

[quote="dart-bug" How bad is it to use 92 octane on an engine made for regular? I just dont get as good gas mileage right? Because precombustion.....[/quote]


Your mileage should be the same.... Unless you get more mileage out of a lighter wallet. Other than that, it's not bad to run 92... nor is it good.


You can run it if you like paying more at the pump, otherwise just go with 87.
_________________
ITMC - Backyard chapter

Hold the pickles, it's 100% pure beef Namocsid!

[Jimbug57]

there is actually more explosive power in lower octane gas. I run high octane in my bug so I can run the the timing advanced. My Subaru has a computer to adjust my timing so I run low octane.

[Ozmodius]

This was written by Bob Donalds .. you can find the entire article
<a href="http://www.bostonengine.com/articles/todaysfuels.html">HERE</a>

The idea that gas is the same today as it was in the ‘60s and ‘70s except for the lack of lead is an easy notion to follow. It’s also not something that is given much thought, but I'm here to tell you that there is a world of difference between the two! Let’s start with the price. Back in the good old leaded fuel days I can remember pumping fuel at 28 cents a gallon. Today it’s as much as $1.49 (or more) for high test. The next thing that comes to mind is the alcohol that’s blended in today’s fuel. At the end of ‘94 many of us in the U.S. have had to switch to "reformulated" fuel containing oxygenated additives to reduce ground level ozone. The most common of these is ethanol which is alcohol and MTBE which is an ether. This makes the fuel more expensive to produce and also produces 15-17% less pollution than non-reformulated gas. Unfortunately this alcohol or ether makes the fuel more likely to boil in the injectors and fuel pump of my air-cooled VW engine. Older engines can suffer valve and ring damage that can occur under full load conditions when pre-ignition and overheating is most likely to happen.

Finally, there is the formula for determining octane which is displayed on the pump. It has changed to the (R+M)/2 method from the old MON (Motor Octane Number) method. While in Europe the RON method is the standard. The "R" in the (R+M)/2 equation stands for Research Octane Number (RON). The "M" in the equation stands for MON. RON serves as the essential index of acceleration knock. The Motor Octane Number (MON) provides an indication of the tendency to knock at speed under loads. The MON figures are lower than the RON numbers. For instance, 93(R+M)/2 method octane "high-test " is not even sufficient for the upright VW engine with a posted minimum RON octane number of 91. I see the results of this inadequate octane in the number of early failures I’ve torn down and seen evidence of over-heating and pre-ignition. What do these changes in gasoline mean to the guy or gal pulling up to the pump?, not too much unless you’re driving a classic machine from the sixties or earlier under full load conditions (on the highway, or with a trailer in tow), or you have an modified air-cooled engine with its normally hotter head temps. These were designed to run on yesterday’s higher octane leaded fuel. Obviously there are some vehicles out there, albeit a declining number, that are at risk. The manufacturers of our "reformulated" gas were well aware that it would not meet the needs of some vehicles at the time, but it compromised so little of their market and the environmental needs were more paramount, that they had to proceed with new fuels. This began in the 70’s with unleaded fuel and has continued right up through today with continually evolving fuel formulations. Avoiding the "reformulated" fuel was an option at first, but is no longer one. In addition, most older engines had carburetors, not fuel management systems which do a much better job of fuel delivery. Today’s cars also have knock sensors that retard the timing when they detect pre-ignition. Pre-ignition is a very destructive force that increases peak combustion chamber pressure and temps. The pinging noise of pre-ignition is not always heard but must be prevented to ensure maximum overall performance and ensure long engine life. The VW air-cooled engines that I build for ice machines and for street have a lowered compression ratio to help keep the head temps where they belong. This change by itself has made the aircooled engines last two to three times longer in the ice re-surfacer machines that we are frequently supplying engines for. The other things to prevent the air-cooled engine from thermal overload include making sure the tin work is in place, including thermostat and linkage. Also, the fan should draw in fresh air that has not been through the engine’s cooling system, or that has passed by or through the exhaust system. In other words, the coolest air possible. Scoops and duct work can help a great deal in getting the coolest air to the fan. Timing is also a large factor in engine temps. As little as 10 degrees off in timing can melt pistons and decrease performance. Also frequent oil changes can keep the internal friction to a minimum. I have seen engine compartment temps influence fuel and intake manifold temps and the dramatic drop in the horse power readings on the dynamometer as these temps go up.

[sammyphsyco]

There is an optimum timing for any given engine combo.Once that is established use whatever octane fuel is needed to prevent pre-ignition. Any more and your wasting money.
_________________

[MUD&GUTS]

I read an article concerning this and when I find it again, I'll post it, but what it said was that the VW book states an octane rating of 91 RON. We use a different system in the US and 91 RON is equal to our 87 Octane. What ever the RON rating is, you subtract 5. Like I said, when I find the article again I'll post it. I hope this helps, as I am a newbie to VW's.
_________________
MUD&GUTS
U.S. Army
'68 Baja Bug
'06 Toyota Tacoma
"Show me the mud!"

[Jimbug57]

Optimum timing from a book and optimum timing pulling an 11% grade at 10,000ft are two diferent figures. Thats why I bump my timing up and run high octane gas.

[vwdub04]

I run 91Oct on a stock engine. Only upgrades are 009 & Alt.
I brought the car from a VW mechanic with 20 yrs exp, he told me to use nothing but 91oct. Of course I tried to be 87 or 89 in it. The result were that is ran shitty. The engine was a fresh rebuid when I got it.

I called another shop in the area with over 20yrs exp, and asked them about gas and oct. The guy told me the they were built to run 95oct but 91oct it the best we can do now a days.

[John M.]

[KillerTux]

[vwdub04]

I dont what to waste money on 91oct of I don't have to but...what should I do. I'm confused, because my engine run well with the 91oct. If I go down to 89 or 87 I use to get what sounds like a fart/puff from the carb with my old carb. Now I have a new carb that is only about a year old. So I guess I should try to go down.

What does a ping sound little and how will I know my engine is pinging if it does. I don't want to mess up my car.

I've talked to my uncle about this and he told me to run what the engine likes. He's a VW mechanic with about 25yrs exp. He runs 87 in his bugs also.
He said if I can run it off 89 or 87 without the engine pinging then it's all good.

I'm almost on empty now and need to fill up on the way home today.

[vwdub04]

You guys are right, I've been wasting money. I found the following link.
Those other mechanic's are smokes something other then plain green.
Glad my uncle knows his shit, along with the right of you guys.

http://en.wikipedia.org/wiki/Octane_rating

It's states that 91RON (Euro) is 87Oct (US).
With that said today I will but about 3 gallons of 89Oct in my tank and see how it runs.

Will I have to make a carb adjustment or other adjustments now that I'm going down in Oct?

[74bug]