Thread: Improving fuel efficiency v8i

You must eat alot!! Pat

That'll give you some idea of my taste in bikes.
Bet they are italian.
My son bought an Aprilia Mille , against his dad saying" Don't buy an italian bike, they are unreliable"
Well after about 6 months of uncompleted rides he finally completed one a few weeks ago without the bloody thing breaking down. They wanted $700 for a clutch master cylinder, but luckily the dealer was able to bodge it up using Honda rubbers.
Regards Philip A

Originally Posted by PhilipA

That'll give you some idea of my taste in bikes.
Bet they are italian.
My son bought an Aprilia Mille , against his dad saying" Don't buy an italian bike, they are unreliable"
Well after about 6 months of uncompleted rides he finally completed one a few weeks ago without the bloody thing breaking down. They wanted $700 for a clutch master cylinder, but luckily the dealer was able to bodge it up using Honda rubbers.
Regards Philip A

I think he means lazy pushbiker, downhill

Originally Posted by POD

Fuel is not 'sucked into the engine' by manifold vacuum, in a carburettor engine fuel is drawn from the carby jets by venturi effect, this is a product of air flow. Less vacuum means more airflow which means more fuel drawn through the metering jets in the carby. On those old vac guages, the 'economy' end of the scale is where the lowest pressure is; low pressure = high vacuum.

Back to the topic, I think it's unrealistic to hope for decent fuel economy from a 2 tonne V8 with constant 4wd. I'm planning on fitting the closed-loop mod to my EFI system, haven't got around to it yet but that is one of the few mods that may help economy.
Pete

Only problem with your theory here is that Vacuum is only a term used in this situation for a low pressure area.

In reality atmospheric pressure pushes the fuel through the metering jets and atmospheric pressure forces the air in to fill the low pressure area after the throttle butterfly.

Your not wrong, just your terminology is wrong for the sake of the discussion.

What Dougal is saying is 100% correct in most cases but in N/a engines atmospheric pressure can make huge changes to where the most efficient range is.

Not so much with forced induction engines but altitude may due to air density etc nut im not entirely sure there.

I dont think anybody is talking about seriously lugging an engine as this will only create a situation where the load exceeds the power available but drive within a range that you keep your speed with a large enough throttle opening to reduce negative pressure behind the throttle butterfly.

So Tank......your both right IMHO.

Interestingly enough (to me anyway), apparently that is a reason why modern engines have EGR as well as Nox reduction.
The EGR adds inert gas to the input charge , therefore needing a larger throttle plate angle to produce equivalent power to no EGR, therefore reducing vacuum or increasing pressure, thus giving better economy.
Regards Philip A

Originally Posted by PhilipA

Interestingly enough (to me anyway), apparently that is a reason why modern engines have EGR as well as Nox reduction.
The EGR adds inert gas to the input charge , therefore needing a larger throttle plate angle to produce equivalent power to no EGR, therefore reducing vacuum or increasing pressure, thus giving better economy.
Regards Philip A

That and the inert gas cools the combustion, reducing NOx formation.

Originally Posted by Rovercare

I think he means lazy pushbiker, downhill

Nah, sold my DH only bike a year ago, so now I have one hardtail (commuter), one medium duty trail bike (6" of suspension each end) and one heavy duty trail bike (6/7" of suspension, heavier wheels, bigger tyres etc). Can do the downhill duty but can still be pedalled up.

Running costs are low, but it's the "upgrades" that cost the money. Two of my bikes are insured for more than my rangie.

Quote
"However this theory has absolutely nothing to do with and is completely incompatible with what they are trying to apply it to. If you "spin" air or water down a pipe or tube etc, you INCREASE the amount of contact area it has with the pipework, taking longer to get down the pipe and significantly increasing the frictional loss through the pipework resulting in less flow.


This is fluid mechanics, refrigeration companies spend gazillions of dollars in research to do exactly what you said. The inside of some evaporators and condensers have a sort of cross hatch in it to create that swerl effect, you are completely right, it is there to increase the surface area contact, which in basic physics has to slow the the fluid down


Fluid mechanics gets very complicated very quickly and I dont profess to be an expert but I work on what the engineers and designers spend years developing. Swerl effect in refrigeration = good, swerl effect from a stationary propeller before heap bends etc = come in spinner

Pun intended

Blythe

Originally Posted by Dougal

That isn't going to save fuel. If you've ever seen a BSFC map you'll know why.

Engines are most efficient with the throttle most of the way open (just before they hit enrichment) with lower rpm.

Going down a gear raises the rpm (more frictional losses) and results in a bigger pressure drop across the throttle (more pumping losses).

The best fuel economy is found with the tallest gears your engine can pull. Making sure the auto stays in lockup will help greatly too.

I am not going to argue any technicalities HOWEVER I have found that on my regular drive to work every day which involves 1 very steep hill, If I try to tackle it in 5th which I was doing for many weeks I would use more fuel than I do now days by always dropping it back to 4th.

As I become more familiar with my vehicle (D1V8Man) and learn a more efficient driving style I have found that that lower revs and labouring is not more efficient than higher revs and getting the right torque band. If it should or should NOT is merely academic, proof is in the pudding. I am rather anal about keeping records on these things.

If fuel economy is such a big issue then don't buy a V8 FULL STOP!

But if having a cost effective fun 4 x 4 is your desired goal then read my previous article:

Running Cost V8 D1 Petrol a winner for me

Thommo
Having Fun with my V8
Got to love the current petrol prices, I paid 96 cents a litre last week (Hmmm how much was diesel?) I'll make the best of it whilst it lasts