19 replies to this topic

[AlexM]

How would you create the ultimate economy A-series engine?

What choice of cam, final drive etc?

[sheepo]

i would imagine that a lot of it would depend on the driver and what sort of journeys you were doing. if you were motorway driving then a final drive to keep the revs down at motorway speeds would obviously be desirable.

i could be wrong but i'd have thought that the best state of tune for economy would be standard out of the factory and make sure it is all functioning correctly on a rolling road.

Failing that, keep the engine off and cut a hole in the front foot-wells and give it large a la Flintstones stylee!!

[Sprocket]

No more than a 266 cam, 274 for the injection, everything else the same as you would for power, a 2.9:1 diff and a light right foot

Its all to do with increasing the VE ( volumetric efficiency) the bigger the VE the the engine makes better use of the fuel and therefor economy increases. As a result so does the power, which requires a good control of the accelerator aplication

Its not just the engine that provides 'economy' tyres, brakes and the gearbox all play a part.

Edited by Mini Sprocket, 20 August 2006 - 02:01 PM.

[AlexM]

My fuel economy increased after fitting a vacuum gauge, as i was more aware of how much load the engine was under etc.

A smaller engine capacity does not necessarily increase fuel economy so ive been told. My dad drives a 523i and a friend also owns a 545i, the friend with the 545i gets better mpg than my dad does with his car. sounds kinda strange but the theory being that a large enine in not put under as much load so does not have to work so hard and concequently burns less fuel on average. I knew a guy who owned both a 1600 capri and 2.8 and the 2.8 always got better economy....

Would things like head modification be beneficial to economy? Ive heard that fitting a stage 1 kit will increase economy as the flowed conomponants mean the engine does not have to work as hard to draw in the same volume of air/fuel etc.

[sheepo]

yeah, i heard that about the stage 1 too, my 998cc is certainly more economical after a stage 1 and a tune on the rollers.

there must be loads of factors, as sprocket says. things like, weight of the car/components in the engine, transmission and such. Also the weight of the driver!!!

a big one which is hard to measure without loads of expensive equipment is aerodynamics. the more aerodynamic it is then the less power i.e. fuel is required to move it forward.

[AlexM]

If you had

998 with single point fuel injection (minus the emmissions control)
modified head, inlet + airbox
Freeflow manifold and exhaust
266cam
2.9finaldrive
vacuum gauge
10inch wheels

That would surely be an economicall car, minimum interior and a steady right foot. A fuel injection system being preferable as it would give greater control over fuelling and cthings like cut off on overrun etc (do carbs do this?)

[Sprocket]

Injection cam 274

10" wheels less efficient than 12s, less rolling resistance on a 4.5x12

Edited by Mini Sprocket, 20 August 2006 - 03:44 PM.

[AlexM]

Also no wide arches as they would increase drag.

[1984mini25]

If you want to stream line the car for less drag, you could remove the arches, wipers, wing mirrors, aerial (if fitted) and tape over all the panel/trim joins at the front, like the bonnet, headlamp rings etc. to try and make it a smooth as possible.

[sheepo]

is that accurate about the 12x4.5s giving less resistance than the 10s??

i can't see this myself, surely the 10s are lighter, plus does it not have more to do with the tyres you have on there, i.e. what profile, condition, tread pattern etc.

Not so seriously: how about rubbing the car down so there is less paint ie weight on it and then covering it in grease to make it slippery!!!

[AlexM]

is that accurate about the 12x4.5s giving less resistance than the 10s??

i can't see this myself, surely the 10s are lighter, plus does it not have more to do with the tyres you have on there, i.e. what profile, condition, tread pattern etc.

Not so seriously: how about rubbing the car down so there is less paint ie weight on it and then covering it in grease to make it slippery!!!

I think they did something like that on the Porsche GT3, the paint was too heavy so they applied as little as possible, and the porsche badge on the front was just a sticker!

[Sprocket]

http://www.hud.ac.uk...ns/btac2002.pdf

Lower the side wall and contact patch and the rolling resistance is less, increasing the tyre pressures also reduces the resistance

10 x 4.5 against a 12 x 4.5 has a slightly higher rolling resistance due to its larger side wall.

[sheepo]

roger dodger!! i stand corrected!

is there some sort of a trade off between rolling resistance and weight though, or is less rolling resistance more important than weight in this context?

[Sprocket]

weight affects the available power to drive the car, not accelerating, not decelerating. What that means in simple terms, the lighter the car, the less power used to drive it, the less fuel used to produce that power.

the whole fuel economy thing consists of all the efficiencies of all the compnents, tyres weights, transmitions, CV joints, aerodynamics, engine VE and so on. Improve one or all and fuel consumption will get better.

it still comes down to the driver in the end.

Yes fuel injection will increase the feul ecomomy due to the fuel cut and stoichiometric corrections of the lambda sensor

[sheepo]

so for the layman (sorry mate, i don't understand the 'stoyca meters' ) it's a combination of a load of factors and striking the correct balance.

what wouild you say is the most important factor, surely it is a toss up between weight and resistance.