Economy tech discussion

[cambridge]

Sales of tigras and 1.3cdti engines will shoot through the roof

mind you, I'd sooner take the mild eco hit and keep the fun of a vx220 chassis + minimal mods needed to get it better... ie that sodding great mouth for the flat mounted rad can be tweaked im sure.

[chip]

Id be looking at weight loss (yeah I know, I should do ) more than aerodynamic changes personally, as thats going to make a more significant difference for everything except constant speed motorway work.

[alistairolsen]

Originally Posted by dhdev

Closing off the area around the headlights, by creating some perspex headlight covers
specific to your car due to the polo lamps? I assume these will be no different to original nova lamp shape?
Sealing along the edges of the bonnet and dropping it back down to the standard position
you run a raised bonnet? Id imagine even if you go as basic as taping the gaping shuts int he nova front end....
Flat floor from front to back underneath beam, extending out to a large diffuser (chopping back panel and rear bumper)
loggyboy on RB experimented before with a lotus elise diffuser under his, never got ver far I dont think. Id be wenting to go fromt he step in the shell in front of the tak (where the tank straps join onto) right back to an elise style shape at the bumper for a start. gets rid of the beam and the big apron formed by the bumper/rear panel.
Sideskirts to prevent air migration from the sides to underneath the car.
Straight square slab style! If it wasnt so difficult/ugly, extending the rear arches like old citoens to hide as much of the rear wheel as poss would also help
Vented front wings to prevent lift and drag
not so sure I get what you mean by this one
Vented bonnet to promote airflow over the car and reduce under bonnet lift and drag (may allow smaller grill opening)
Just to try and stop pressure buildup under the bonnet, and that air then being forced under the car?

I would too stuart, if I was anywhere near affording a vx220 :P but that goes back to your earlier comments ont he first page!

chip, indeed mate, hence choosing the tigra over the calibra despite slightly higher drag. As tesco say tho, every little helps!

[Giles]

Originally Posted by dhdev

I put a post up on here shortly after getting my calibra, as I wanted to reduce drag etc. It seems they were originally fitted with an undertray at the front, but very few remain,

Keep an eye on the for sale section and my posts as I'll be selling one.
They are rare as rocking horse though.
They were on astra GSi's and Cav Gsi's too.

Usually got smashed off or taken off and not put back on.

[lethal]

I notice some of these 'Aero' officianodos are moulding in their rear wheel wells ala the Citroen DS / Honda Insight.

I don't think you could do this easily on the calibra; IIRC the wheels are outside the bodyline?

You could probably make it happen on a Tigra tho.


While I'm at it, is that back window normal glass on a Tigra? It must weigh a ton!

[chip]

No calibra wheels arent outside of the bodyline that im aware of, and even if they were, it wouldnt stop you doing it, you just need a very mild sweep out past them, be careful with aerodynamics, things arent always as they seem.

There are some key angles that if you go past, things change dramatically.

Take a taper towards the rear as an example:
If you have parellel sides, and taper the rear in a degree, it gets better
taper it in another degree, it gets better
taper it in another degree, it gets better
taper it in another degree, it gets better
taper it in another degree, it gets better
taper it in another degree, it gets better
taper it in another degree, it gets better
taper it in another degree, it gets better
taper it in another degree, it gets better
taper it in another degree, it gets better
taper it in another degree, it gets better
taper it in another degree, it gets dramatically worse, so much so its worth than when they were parellel


(think thats the right number of degrees anyway, but if not the point is the same)

[dhdev]

1.Specific due to the polo lamps yeah, and yes basically the shape of nova lights
2.I run a raised bonnet to clear the reservoirs for my brake m/cyl's I'm sure I can do some relocation, to allow the bonnet to close
3.I'm planning a lot larger than the elise items, but yes it will start from infront of the beam and swoop up and hang out the back somewhat.
4.Either straight slab style or something like the sport optional extras the ones that jut out (hard to explain)
5.Vent the wings, a bit like a cossie, letting the high pressure air out the back end of the wing.
6.under bonnet region generally has a region of high presure, due to large frontal openings and all the engine and ancillaries restricting the exit of the air, an exit scoop/vent would help the air to escape and go over the car (rather than going out the bottom). This would increase the airflow over the car and provide a reduction in lift. The airflow out of the vent could be aided by a large scoop attached to the back of the rad (I think the jap boys use this on their V-mount intercooler set-ups)

[dhdev]

Originally Posted by chip

No calibra wheels arent outside of the bodyline that im aware of, and even if they were, it wouldnt stop you doing it, you just need a very mild sweep out past them, be careful with aerodynamics, things arent always as they seem.

There are some key angles that if you go past, things change dramatically.

Take a taper towards the rear as an example:
If you have parellel sides, and taper the rear in a degree, it gets better
taper it in another degree, it gets better
taper it in another degree, it gets better
taper it in another degree, it gets better
taper it in another degree, it gets better
taper it in another degree, it gets better
taper it in another degree, it gets better
taper it in another degree, it gets better
taper it in another degree, it gets better
taper it in another degree, it gets better
taper it in another degree, it gets better
taper it in another degree, it gets dramatically worse, so much so its worth than when they were parellel


(think thats the right number of degrees anyway, but if not the point is the same)

take it you were aiming for the 12deg golden rule? i believe this applies to blunt changes in direction, so if it is a curve rather than a chamfer the flow can stay attached for longer.

Giles - I'll kep my eyes peeled

[alistairolsen]

yeah, if its a chamfer then more than 12 degrees will make it break off the edge rather than follow the surface and keep flowing. effects also vary with speed.

Oli, all sounds good. Shame there is no real way to measure the difference, be good to do it all in a car with a fuel computer and measure the average at a set speed (I imagine even if innacurate these are repeatable?)

[chip]

Originally Posted by dhdev

take it you were aiming for the 12deg golden rule? i believe this applies to blunt changes in direction, so if it is a curve rather than a chamfer the flow can stay attached for longer.

Giles - I'll kep my eyes peeled

Yes mate, thats the one, it also applies to radius of curve as well but less simply so.

[alistairolsen]

which is exactly how spoilers work


(NB. spoilers, not wings)

[dhdev]

Originally Posted by alistairolsen

Oli, all sounds good. Shame there is no real way to measure the difference, be good to do it all in a car with a fuel computer and measure the average at a set speed (I imagine even if innacurate these are repeatable?)

One way of ascertaining whether improvements have been made is to do top speed runs (in both directions and take average to reduce headwind affects) before and after mods. Obviously many variables like changes in engine power due to temp etc, but would give a decent enough comparison.

[alistairolsen]

ensuring same local humidity, temperature, atmospheric pressure, tyre pressures.......

I agree tho in principle that this is probably going to be the best measure

[djivesp]

for more tigra gen, yes the back window does weigh a ton (don't know the exact weight, but my boot lifters have gone and you almost have to use both arms to open it ), a lot of weight to be saved there, at the expense of creating turbulence if you go for a mr2 style 'flat' back. If you go for the same swept perspex/polycarb design you retain the shape and save quite a lot of weight, someone should weigh one see exactly how much it weighs!

I put a glass fibre engine undertray on mine and didn't notice any difference in fuel consumption. Guess for a low car it doesn't make alot of difference

[lethal]

Originally Posted by dhdev

One way of ascertaining whether improvements have been made is to do top speed runs (in both directions and take average to reduce headwind affects) before and after mods. Obviously many variables like changes in engine power due to temp etc, but would give a decent enough comparison.

Wouldn't 'coast-down' tests from a given speed in either direction be more accurate?

[alistairolsen]

now youre onto something, that takes engine breathing out of the equation completely and just measures drag, so long as you were on a dead smooth surface and lifted in the same place.

50mph and clutch out at the eigth mile mark at pod then compare terminals?

[cambridge]

you'd have to do some sub 50mph tests like that to work out rolling resistance, and assume its linear, then do the high speed coastdowns to work out drag.

I had to play about with tests like that for my disertation for rolling friction tests, but had to keep below 54mph otherwise aero drag would have been included and lashed up the test results.

[alistairolsen]

cool, what was your dissertation mate? Is it online anywhere?

[chip]

Originally Posted by cambridge

you'd have to do some sub 50mph tests like that to work out rolling resistance, and assume its linear, then do the high speed coastdowns to work out drag.

I had to play about with tests like that for my disertation for rolling friction tests, but had to keep below 54mph otherwise aero drag would have been included and lashed up the test results.

You dont have to at all surely if its just a before and after test to see if aerodynamic changes have worked? as all the other losses can be assumed to be constant?

[a2lt16v]

there could be some interesting looking cars soon lol

[dhdev]

Originally Posted by chip

You dont have to at all surely if its just a before and after test to see if aerodynamic changes have worked? as all the other losses can be assumed to be constant?

Well the mods I have planned should increase downforce/reduce lift so rolling resistance would increase (although I doubt this would be too significant)

P.s. Just adjusted up the handbrake on the calibra and noticed that the rear bumper-to-tank tray is missing as well as the front tray...bring on the MPG when they're fitted lol!

[chip]

sod the handling of something with deliberately decreased downforce just for the sake of 0.1mpg

[cambridge]

Originally Posted by alistairolsen

cool, what was your dissertation mate? Is it online anywhere?

It was for a generic self calibrating (or semi ai lol) traction control system. Unfortunately the only electronic copy is on a HDD that is refusing to do its thing and I've only got one hard copy sat on my desk lol.

Chip, good point, the losses in that respect would be "constant" so aero mods would show the difference, didnt have my thinking hat on

[Colonel K]

I know the undertrays on senators are known to make a good 3-4mpg difference when cruising. Shame I smashed mine to pieces really!