4x2 SUV’s - what’s their purpose?

[XJ Junky]

My son has the XV and I looked at the Forester. The XV is lighter so performs better. At the coast the 2.0 is fine but in jhb it needs to be revved. It could really do with a turbo. It's tow rating is also poor. But it is still great car with excellent value for money and features.

I looked at the XV as an option instead of the Duster. I liked the funkyness & the features, but it’s biggest draw back was the boot size.

[Dwerg]

Yip. I thought so. The Subaru’s symmetrical system is indeed brilliant & they are very premium with loads for features.

How do you find the engine power on the 2.0?

I am generally a slow driver so for me power is fine but I don’t tow and when we go on holiday it’s me my wife and two dogs. But like said above, if it ran the same up here as it does at the coast it would’ve been perfect

[Dwerg]

I looked at the XV as an option instead of the Duster. I liked the funkyness & the features, but it’s biggest draw back was the boot size.

I was dead set on the XV too but took the forester for the boot plus the visibility

[hunter26]

I am generally a slow driver so for me power is fine but I don’t tow and when we go on holiday it’s me my wife and two dogs. But like said above, if it ran the same up here as it does at the coast it would’ve been perfect

You would get more power due to coastal oxygen increase. Old days one would have to change carburetor jet and retune when going from coast to inland and visa versa.

[IcePick88]

I have 2013 Nissan X-Trail 2x4.

It has taken me to Maphelane (rough road with some deep ruts and climbs) and it did it. Just because I picked some good lines.
It has towed a Gypsey Regal since 2014 without issue. Drakensberg twice. Kruger Park 3 times. Down the south coast plenty of times. Too much to mention.
It has been to nature reserves many times where the added height compared to a platkar is great for game viewing.

And we are a family of 4. Always packed and the car performed exceptionally. To this day.

So I never needed 4x4 where I went. But the added height, bigger tires and massive boot makes it much better than a low platkar for our purposes. And it can tow a heavy load. We are always in the game parks, camping or whatnot. So a SUV (be it 2x4) makes a lot of sense.

P.S. The fuel consumption on that 2.0dCi is fantastic!!

[Fluffy]

Well you can do Atlantis Dunes in an AWD softie but not a 2WD SUV.

[Skylark]

I have 2013 Nissan X-Trail 2x4.

It has taken me to Maphelane (rough road with some deep ruts and climbs) and it did it. Just because I picked some good lines.
It has towed a Gypsey Regal since 2014 without issue. Drakensberg twice. Kruger Park 3 times. Down the south coast plenty of times. Too much to mention.
It has been to nature reserves many times where the added height compared to a platkar is great for game viewing.

And we are a family of 4. Always packed and the car performed exceptionally. To this day.

So I never needed 4x4 where I went. But the added height, bigger tires and massive boot makes it much better than a low platkar for our purposes. And it can tow a heavy load. We are always in the game parks, camping or whatnot. So a SUV (be it 2x4) makes a lot of sense.

P.S. The fuel consumption on that 2.0dCi is fantastic!!

That Xtrails done it's duty, decent tires at the right pressure and some careful driving can get you far even without 4x4.

Though 4x4 is a nice peace of mind when you get into sand or mud, especially up an incline.

[mvcoller]

You would get more power due to coastal oxygen increase. Old days one would have to change carburetor jet and retune when going from coast to inland and visa versa.

NOT TRUE.....

At worst, you had to alter the ignition timing but not jets.

Normally this different timing for different altitudes, ultimately was not because of performance, but rather because of hard starting and because of pinking (pre-ignition). Just changing your fuel grade between 93 and 98 octane achieved similar results.

In the 70s and my folks lived in Margate, I lived in Joburg. I used to go down to Margate once a month and to get the best performance a slight advancement or retardation of the ignition timing was all that was required.

At the time I drove Alfas (owned many of them) and Weber or Dellorto side draught carbs have about 8 fuel and air jets, so 16 jets on twin side draughts.

To have to change jets would not have been practical and totally impossible for most people.

[Fluffy]

hmmmmm - On a NA car you can change jets and timing till the cows come home, but you will still get about 17% more power at the coast than reef altitude.

Or the opposite, 17% less power at the reef compared to coast.

Timing was changed because the Octane rating was changed, not because of altitude. It's a side effect of changing Octane because of Altitude.

[jelo]

NOT TRUE.....

Sadly it is true: your Reef tuned car will run lean at the coast. So be careful. I burned valves that way on my Essex V6 and also on my Yamaha.

[Francois Theron]

Timing was changed because the Octane rating was changed, not because of altitude. It's a side effect of changing Octane because of Altitude.

Please explain

[Fluffy]

Thankfully modern 4x2 SUV's and AWD Softies have fancy electronic systems that don't care a rat's behind what altitude you are at or what fuel you are using.

[Fluffy]

Please explain

As you are aware, at altitude you have less oxygen. With less oxygen the extra octane rating is just wasted. So they reduce the octane rating for fuel used at altitude to reduce costs. The timing is adjusted to accommodate this.

It amounts to the same thing, but it is about the cause/effect relationship.

Like standing on a burning coal. It burns because it is hot, not because it is a burning coal.

[mvcoller]

You change Octane rating (higher at the coast) because of the more oxygen being available at the coast, which could burn the fuel better and actually take advantage of the higher octane rating.

You could put the higher octane fuel into the tank upcountry, but because of the lower air pressure, but did nothing for you performance as most people thought it would. That is also why your car would pink (or knock - more modern term) up country if it was correctly tuned for sea level.

Because of the lower air pressure here, there was relatively less air in the combustion chamber when ignition took place and this cause pinking. To cure this, you had to retard your timing (for ignition to take place) until there was more air (oxygen) in the chamber.

Ait to fuel ration's best combustion/performance ratio is 13.1 parts air to one part fuel. That is how you have to get it for your car to perform at its peak. That did not change, irrespective the altitude. So once you have the correct air jet vs fuel jet combination, YOU NEVER CHANGED IT. You could then fiddle with the pump/spray jets, idle jets, intermediate jets etc, that would give that extra spurt of fuel when sudden acceleration was required.

To fine tune a petrol engine that has got the correct jets to give you 13.1 to 1/air/fuel ratio, you played around with ignition and camshaft timing

Today knock sensors do that for you, via an onboard computer

[mvcoller]

Timing was changed because the Octane rating was changed, not because of altitude. It's a side effect of changing Octane because of Altitude.

Exactly....

So you would fill up in Jhb, and maybe again in Estcourt or Pietermaritzburg, by which time you filled up with 89 octane. So the higher octane rating caused the car to pink, (Pre-ignition) and to stop the pinking, you had to retard the timing.... Those days mechanics were mostly friendly honest guys, and would happily do it for free to most passing motorists, who stopped and as them to look at this funny noise the engine was making.....

I know of nobody who drove around their car with a spare set of jets (the correct size?!!) when going to Durban and change jets when they got there.... That would be beyond of the capabilities and expertise level of about 99% of motorists (remember it will require a complete re-tune of the combustion process).

Of Course, the inverse was also true. The Durbanite would arrive in the Transvaal and refilled at Villiers or Heidelberg. By the time they got to Johannesburg or Pretoria, would feel a distinct lack of performance. He would ask around and maybe stop at a local workshop where the mechanic would check and rest the vehicle's timing according to the altitude...

I did the above myself many a time. Jets would remain the same and roughly the same for fuel consumption, depending on the weight of the right foot during the trip....

[Francois Theron]

You change Octane rating (higher at the coast) because of the more oxygen being available at the coast, which could burn the fuel better and actually take advantage of the higher octane rating.

You could put the higher octane fuel into the tank upcountry, but because of the lower air pressure, but did nothing for you performance as most people thought it would. That is also why your car would pink (or knock - more modern term) up country if it was correctly tuned for sea level.

Because of the lower air pressure here, there was relatively less air in the combustion chamber when ignition took place and this cause pinking. To cure this, you had to retard your timing (for ignition to take place) until there was more air (oxygen) in the chamber.

Ait to fuel ration's best combustion/performance ratio is 13.1 parts air to one part fuel. That is how you have to get it for your car to perform at its peak. That did not change, irrespective the altitude. So once you have the correct air jet vs fuel jet combination, YOU NEVER CHANGED IT. You could then fiddle with the pump/spray jets, idle jets, intermediate jets etc, that would give that extra spurt of fuel when sudden acceleration was required.

To fine tune a petrol engine that has got the correct jets to give you 13.1 to 1/air/fuel ratio, you played around with ignition and camshaft timing

Today knock sensors do that for you, via an onboard computer

Exactly....

So you would fill up in Jhb, and maybe again in Estcourt or Pietermaritzburg, by which time you filled up with 89 octane. So the higher octane rating caused the car to pink, (Pre-ignition) and to stop the pinking, you had to retard the timing.... Those days mechanics were mostly friendly honest guys, and would happily do it for free to most passing motorists, who stopped and as them to look at this funny noise the engine was making.....

I know of nobody who drove around their car with a spare set of jets (the correct size?!!) when going to Durban and change jets when they got there.... That would be beyond of the capabilities and expertise level of about 99% of motorists (remember it will require a complete re-tune of the combustion process).

Of Course, the inverse was also true. The Durbanite would arrive in the Transvaal and refilled at Villiers or Heidelberg. By the time they got to Johannesburg or Pretoria, would feel a distinct lack of performance. He would ask around and maybe stop at a local workshop where the mechanic would check and rest the vehicle's timing according to the altitude...

I did the above myself many a time. Jets would remain the same and roughly the same for fuel consumption, depending on the weight of the right foot during the trip....

Malcolm, at the risk of me sounding like I'm trying to take you on, please do read both your posts again, carefully. I am actually astounded by your posts!

[mvcoller]

Sorry, yes....Thank you Francois

Got the advance and the retard a bit mixed up there...

Retard timing down at the coast with upcountry fuel
Advance timing up country with coastal fuel...

[dirtshark]

Only on a two stroke do jets help, very evident on a boat.

[Peter1949]

I remember it well.
Dual Weber, Stromberg, etc carburettors ... all we ever had to do was to re-set the timing at the destination.
That's it.
We filled up with whatever octane fuel was available at the station along the way.
If fiddling with the carbs then some serious re-balancing needed to be done ... so "do not touch this" at the time.
Today, with onboard engine management and computers in the vehicles - no need.
I guess I am showing my age.
But those twin SU Carbs could produce some "oomf".

That was towing caravans at the time.

[HugoNotte]

The amount of oxygen in the air is the same at higher elevations as at sea level, it is 21%.
However, at sea level the air density is higher and therefore you get a greater mass of air into the engine. With more air mass in the engine, the total pressure inside the cylinder during the compression stroke is higher, the oxygen and fuel molecules are packed closer together and the combustion is more rapid. That's why one would use a higher octane petrol at lower elevations or altitudes in high compression engines. At higher elevations the opposite is true, the total pressure inside the cylinder during the compression stroke is lower and the speed of the flame is slower. Since the compression (not the engine's compression ratio) is lower, a high octane petrol is not required, which was probably the reason why it wasn't available in those places, at least in Namibia.

And it is true, that a conventional carburetor tuned to run at the right mixture at sea level would cause the engine to run rich (thanks Francois!) at higher elevation / altitude. It is not necessarily all that noticeable if the difference in altitude is a few hundred meters, but it certainly is noticeable between seal level and e.g. Windhoek or Johannesburg elevation. Carburetors for piston aircraft engines have a mixture control lever which one adjusts when climbing or descending.
It was therefore a good idea to have the car's carburetor adjusted if one would stay at a different elevation for a longer period of time in order to avoid running the engine too lean or too rich.