Thread: Why??

All the busses (Volvo,Mercedes, Nissan, Toyota and Hinos of several types/sizes) I drive show the same trend climbing particular hills... I get further up in winter before changing down, than in summer. Especially when loaded.
They're bricks on wheels, but since we're well under 80km/h aerodynamic drag is of academic value only.
All my previous vehicles gave same or better mpg in cold weather. Can't honestly say what the Classic does hot./cold. Reckon it's about the same (insatiable,.....)

Originally Posted by isuzurover

We are talking about a comparatively tiny difference in density and viscosity, while holding everything else equal. The overall REAL difference in drag will be tiny (either way).

10% density change from 0C to 30C is tiny? Nope.
That 10% change fits very well with the observed fuel economy change too.

As I said, I'm 100% certain of my figures and the physics backs it up exactly.
Cummins, Nasa, & Massey are all in perfect agreement with me.

Skin friction and air viscosity are such minor players they are completely ignored in vehicle aerodynamic drag.

Originally Posted by Baggy

Have to agree with isuzurover

Any difference in vehicle performance or efficiency across the span of temperature is 99.9% due to combustion efficiency, rather than drag.

Cold induction is based on cold air promotes the improved burning of the air - fuel mixture in the combustion chamber so I would also assume that this would apply equally to a cold day vs hot day.

With drag anyone who purchases a RRC will notice nothing else but drag (on their wallet) as you try to acelerate a vehicle (which is as air dynamic as a brick) weighing 2.5 tonnes with (small) 3.5 V8 engine to reach road and highway speeds through the air.....with todays fuel prices

For me tuned carbs + good spark + tyre pressure + gentle right foot = better fuel economy on the road, but off road is where the 3.5 V8 excels even in stock form


Cheers

Baggy

Originally Posted by superquag

All the busses (Volvo,Mercedes, Nissan, Toyota and Hinos of several types/sizes) I drive show the same trend climbing particular hills... I get further up in winter before changing down, than in summer. Especially when loaded.
They're bricks on wheels, but since we're well under 80km/h aerodynamic drag is of academic value only.
All my previous vehicles gave same or better mpg in cold weather. Can't honestly say what the Classic does hot./cold. Reckon it's about the same (insatiable,.....)

Both you guys are talking about engine performance (i.e. delivered power/torque).
That does indeed increase with colder temps (until your diesel waxes up, but that's a different story).

But we're talking about wind resistance, which increases with colder temps because the air gets colder, denser and is harder to push out the way because of that.
It's a completely different discussion to power/torque and engine efficiency.

Anyone who thinks wind resistance doesn't matter under 80km/h needs to spend some time pedalling a bike.

Actually I reckon we're talking about the same thing, the lightness of our wallets.

Wind resistance increases exponentially, and yes, you notice it on a bike as you increase velocity. Doubly (or 4x..) if you're on the portly side.

But do you notice it at minimal speed?- Nope. At a gentle pace, maybe yes, you become aware if you think/obsess about it...but only when you get seriously quick do you see the benefit of streamlining (lycra)

Same with a vehicle, brick or Citroen DS. At low speeds the net effect is sweet stuff-all. Double the speed and you've got FOUR times the drag. Like WOW
But since we've started at 10 km/h, and are now hurtling along at 20 km/h with heaps more drag.... it's gone up to 'stuff-all'. My old Holden V8 used to idle itself up to 20k's if left long enough, hardly a huge drag-load.
Double again from 20 to 40 and it become worth measuring. Do it again from 40 to 80 and behold! - We've got figures worth thinking about!!!
Which all means that we need progressively smaller steps to give us exciting figures to play with once we've reached a threshold of interest...
The relative differance in temperature - driven (sorry, could'nt miss that one) density and hence additional/less drag is going to change the numbers, but not, IMHO, reverse the result of thermal efficencies.

Fuel seems to co$t about the same summer/winter driving, the car is windows-up with A/C working... windows down in winter (less streamilned), but with the added slippage of wet roads.....

Maybe your service station pumps are not properly calibrated for temperature ....

My 2 cents worth as I wait on subbies to ring back and avoid working on the Great Bathroom Reno....

When you've only got 0.2 kilowatts pushing your bike along, even stuff-all drag becomes a big problem.
Your holden idling was probably putting out 10kw (50 times the power of an average pedaller).

Given the old Rangie I have here is running a a ****load better, and I'm only crusing around town.... at 60km/h I can't see how aerodynamics has anything to do with it myself

It's definitely mixtures.

seeya,
Shane L.

Shane,

In my quest to source the special tool to adjust mixture on my CD175 carbies I came across (somewhere ...but can't find it now) how you can tell if the mixture on your carbies is adjusted correcty.

I'm not sure if it's right and would like to get feedback from those more knowledgeable than I although I have tried it and it indicates my carbies are running rich.

Basically you get the engine to operating tempreture, and normal idling speed, remove air cleaner so you can get to the air piston that rises in each carbie on accelleration.

With the engine running and a thin bladed screwdriver you lift the air piston on one carbie, if the engine immediately revs when raised it indicates that the mixutre is rich.

Alternatively if the engine revs immediately drop or stalls can indicate lean mixture.

The article said that most CD175 carbies tend to run rich, and mine definately smell that way ......now only to find where I can puchase the adjusting tool needed to fix that issue.

Cheers

Baggy

Originally Posted by Baggy

Shane,

In my quest to source the special tool to adjust mixture on my CD175 carbies I came across (somewhere ...but can't find it now) how you can tell if the mixture on your carbies is adjusted correcty.

I'm not sure if it's right and would like to get feedback from those more knowledgeable than I although I have tried it and it indicates my carbies are running rich.

Basically you get the engine to operating tempreture, and normal idling speed, remove air cleaner so you can get to the air piston that rises in each carbie on accelleration.

With the engine running and a thin bladed screwdriver you lift the air piston on one carbie, if the engine immediately revs when raised it indicates that the mixutre is rich.

Alternatively if the engine revs immediately drop or stalls can indicate lean mixture.

The article said that most CD175 carbies tend to run rich, and mine definately smell that way ......now only to find where I can puchase the adjusting tool needed to fix that issue.


Cheers

Baggy

Interesting, it looks like it's just a simple mixture screw to adjust the mixtures (surely this would only be idle mixture though ?)....

Balancing twin Zenith Stromberg carburetors by ear on a TR7 - DragTimes.com

This is interesting too...
Land Rover Owner • View topic - How to Balance SU carbs

I really can't understand why anyone would fit K&N filters .... I can only see negatives from them myself on just about all vehicles.

Mines an '85 ... right when the "emissions" caper was in full swing and they struggled to get any carby engine to meet regulations. I bet it's set to run lean as possible heavily impacting performance. No doubt they would have gone to injection within a year to meet the '86 standards.

seeya,
Shane L.