What's The Best Gasoline Engine Compression Ratio For RTW Travel?

[nicholastanguma]

I think it's been pretty well established on ExPo that the petrol a round-the-world traveler is forced to buy in developing countries is often suspect, at best. Especially in places where the fuel is being sold in old plastic Coca-Cola bottles. :Wow1:

So then, for a carbureted gasoline engine that will be forced to ingest such turpentine, what would actually be the highest usable comp ratio? 7.5:1? 8.0:1? As high as 8.5:1 maybe?

 

[javajoe79]

Depends on more than just compression ratio. Ignition timing, chamber design and temperature too.

 

[lugueto]

People sometimes exagerate some aspects of travel. Sure, poor planning might lead to buying gas from Coke bottles but I find it hard to believe you absolutely have to. Considering engine compression as a deciding factor in vehicle purchase for travelling is, IMHO, an overreaction.

I suppose it depends on where you're going to travel. You know, it doesn't get much more third world than my country (at least not in the Americas) and I've never had trouble with fuel. We've traveled 90% of it with the most remote places with only one issue so far (thank God). Dirty fuel or water pollution has never been an issue, even when some pumps you see on the road look like a scene from The Walking Dead.

The one issue we had was when a tanker truck operator accidentally dumped Diesel fuel in the Pump's Gasoline reservoir, mixing the two. Our convoy was made up of three vehicles, all three died without leaving the pump. There were a few other vehicles that filled up that day, but once the issue was known the pump was shut down. We had to bleed the fuel lines, drain the gas tanks back into the Pump's reservoir,fill up on lower-grade fuel (same thing, really) and we were on our way. Not a hickup since.

My advice would be to install one or two fuel filters, or a water-fuel separator, if you want peace of mind. Fill up exclusively on gas pumps. Avoid buying gas "from Coke bottles" whenever possible and enjoy your travels.

 

[GoinBoardin]

As stated, octane required depends on many factors. Aluminum heads vs iron, dome design, ignition timing, engine load (light car or heavy truck with big tires and poor gearing?), quench, and so on.

Example: I run 85 octane in a 9.3:1 iron headed 5.8L Ford without issue. I set it up for tight squish, to ensure good quench. Stock timing it's good on 85, if advanced +5° it needs 91 octane but does run a bit better. It replaced an 8.3:1 engine with crap heads, that someone set up with very loose squish, so there was no quench, and that engine eventually died from detonation (broken compression ring, melted piston).

I had a snowmobile engine with similar experience. Poor dome design, high loads, 91 octane, and it was on the ragged edge of not detonating. Warm day, not as good of fuel, lost the engine to severe detonation (damage is a lot faster on a little 2 stroke at 8500rpm). Rebuilt it, used better head dome design, little higher compression, never had detonation again.

The only times I've had detonation, is under very heavy loads. Pulling a little ignition timing can help if needed, or slow down.

 

[doug720]

I agree with most of the above, and have one more suggestion. Find a vehicle with 2 or more fuel tanks, or add a second tank.

By keeping one tank - or at least keep a partially tank of known good fuel in reserve, you have options. You can switch supplies, dilute to make crappy fuel usable, continue if get a load of bad fuel or a tank is damaged/leaks.

Primary fuel filtering can be added just out side the tank, so you have redundancy. Plus, and likely most importantly, the second tank extends range! They are also safer than cans, don't take up valuable cargo space, are typically mounted lower for better handling, have skid plates, and generally easier to use.

Just another idea.

 

[nicholastanguma]

Since you are using a carbie motor, I assume breakerpoints too ?
Get or make a 'dizzy whats advance is adjustable via external knob. One can dial up or down its advance as fuel quality of each tankfull dictates. My old 'Landy has this. Its made for 3rd world conditions of 50 years ago.

Cool idea. The engine in question is an air cooled, carbed, kickstart-only, single cylinder motorcycle mill with magneto ignition. Morris Magneto makes custom mags for any application, and their current offerings range from manually actuated timing to snap-ring automatic timing, so I'll look into what can be done for this specific application.

 

[nicholastanguma]

Okay, I think I better understand, now. Thanks for your help, everyone.

 

[comptiger5000]

On top of what everyone else has said, some research on fuel availability in areas you plan to go will help. Based on that, you may be able to plan enough tank / jerry can capacity to avoid needing to pick up super-sketchy fuel and be able to stick to stuff of at least known quality, even if it's not high octane and requires you to dial the engine back a bit.

 

[doug720]

I have done many long distance off road motorcycle rides where refueling is difficult or impossible. One thing we do is carry 1 gallon jugs of fuel to extend our range. But to make this manageable, we pour the contents into the tank as soon as possibl. This makes the ride much more enjoyable.

Good luck.

 

[rontaki]

What about Mr. Funnel?

The Mr. Funnel is supposed to remove water and some contaminants from fuel contaminants.
http://www.mrfunnel.com/Mr._Funnel/Home.html

I thought I first heard about it on this site, but did not find it in a search. I have no experience with these, does anyone here?

 

[DiploStrat]

Overthinking a Bit?

After over twenty years of living in the Third World, I will opine that you are overthinking this a bit.

Build your vehicle with a minimum range of 500 miles/800 kilometers, be sure that you have one or two good filters in your fuel line, and fill up whenever you can and you will be fine.

There are a few anomalies - gasoline sold at high altitudes in the Andes is very low octane and will knock at sea level (a real pain when trying to return to altitude) but that is about the only real problem that I know of. Do change those filters regularly, especially if you do end up buying from a drum by the side of the road, but that is simply common sense.

Remember. no one else is buying a special low compression engine.

 

[Dan Grec]

I think it's been pretty well established on ExPo that the petrol a round-the-world traveler is forced to buy in developing countries is often suspect, at best. Especially in places where the fuel is being sold in old plastic Coca-Cola bottles. :Wow1:

I strongly believe this is a myth perpetuated since the "exploration" days of the 80s.

I have driven a petrol engine Jeep from Alaska to Argentina, and now down the coast of West Africa - which hundreds of people said could not be done.

I have bumped into many people doing so in petrol engines vehicles, and met many that have been round the world.

This is not something you need to stress about in the year 2017 and beyond.

-Dan