David_Wallis

What speed rating is for 180+ Possibly touching close to 200???

David

ozzy

All the tyre companies seem to publish ZR @ 300kph or 186mph.

Interestingly, these are fitted to the SL55 AMG which is good for 202mph

Stefan

FASTER MIKE!!

did`nt think scoobs went that fast

David_Wallis

mine will

carl

Not unless you seriously sort the aerodynamics, it won't

Hoppy

Agree with Carl. You'll never get anywhere near that in a Scoob. Ever. Remember the 1000bhp Supra that 'only' managed 196mph on the A1M a couple of years ago, courtesy of Max Power? And the nutter had several goes at it before being arrested (Read about it again in next month's FHM, plus the 188mph??? Evo.)

More importantly, also check out the Damian Harty thread in the Suspension forum about high-speed lift. I know what my Scoob feels like at very high speed and it doesn't inspire confidence. Probably lethal at the sort of speeds you're looking at

Don't do it David!

Richard.

Fuzz

I'd be looking at removing the rear bumper David and making up some suction channels out the back, (forget proper name) aka nismo skyline. I'm pretty sure no more than a 15 degree slope should be used (air turbulates and you lose all good effects)
and a bloody deep splitter and / or seriously lower the car
Also get the underside as flat as poss.

tyres errr dunno

Andy

Pavlo

I think W.

David will be doing over 190 I suspect, yes really that fast.

Might be time to get making some undertray parts...

Paul

Hoppy

How?

carl

Aerodynamics is not simply a matter of 'making some undertray parts'.

1) I doubt the Impreza shape is slippery enough to ever do over 190 mph
2) I doubt you could keep it on the ground at that speed.

The trade-off is between downforce (or absence of lift) which keeps you on the ground (but induces drag) and 'slipperiness' which makes you go faster. The ratio of the two is the aerodynamic efficiency. I reckon a Scoob needs completely different bodywork to go that fast.

[Edited by carl - 3/15/2003 11:34:47 PM]

David_Wallis

Stop doubting and start reading...

http://bbs.22b.com/ubb/Forum25/HTML/000101.html

Gets interesting about page 3..

New engine will be about 600bhp..

Wagon can do 165 allready... so what do you need to get more speed??

Remove the rear bumper???

Interesting..

Car will be sat on its bumpstops if I have my way..

Carbon bonnet ordered... p1 front bumper.. and plenty of weight savings...

Im not saying Ill do 200mph but my gearing is good for 194.. and I have the power...



So what tyres??

David

Pavlo

With enough power, anything is possible.

Efficiency and lift eh? Given that an aeroplane generates mucho lift (a 737 weights aroung 70tons) does that make it grossly inefficient?

Seriously though, an Impreza can go that fast.

Carl,

Are you referring to wing/aerofoil efficieny? That is a measure of downforce vs drag, but overall for a car, the cd and frontal area are all that define maximum speed limited by power. I'm not saying an impreza will be the model of stability at 190+, but it can certainly get there.

paul

ozzy

Well, not really, but it isn't as efficient as it could be. It's all a comprimise between how fast the plane needs to travel and just how economic it has to be. If it was just built for speed, then it's very inefficient. Even a 737 has a top speed.

Stick a jet engine on a home-made go-kart and you'll hit 200mph easily. Unfortunately, power isn't everything.

I've no doubts an Impreza (or almost any car) is capable of hitting those speeds, but you need to consider drag unless your happy to simply throw money and BHP at it.

The undertray's and wings are all for downforce to aid stability, but these produce more drag, so you need even more power to keep the car accelerating.

Perhaps one of the boffins at Prodrive would provide some real-life advice.

Good luck,

Stefan

Pavlo

A 250cc racing kart can hit about 160mph with 80hp on the main straight of Silverstone full circuit, so I doubt a jet engine is required.

Not quite. An undertray can easily reduce drag an increase downforce at the same time. You get lift overall on a car due to the greater distance travelled by the air going over the top of the car compared to under the car, so it acts very much life an aerofoil (except the flow is very 3 dimensional unlike a traditional wing).

What an undertray and diffuser do is to encourage air to flow under the car. Yes you read that right, and no I'm not off my rocker. What is required is good quality airflow with high velocity, the high velocity causes a drop in the air pressure. Where it can go horrible wrong (like the Mercs at Le Mans in 99) is the air going under the car can't flow properly, stagnates and the pressure goes up.

The bonus of all this, is you can reduce lift and drag at the same time. And obviously the smoother underside in general will reduce the cd of the car.

WRT fitting a rear wing on a saloon or hatchback car, you can reduce drag and lift again. It's not uncommon to get a seperation point about 6" below the rear roofline (often lower on fastback style rear end), after which there is just a low pressure wake The wake causes lift on the boot lid and drag on the rear of the car in general. But if you put a high(ish) spoiler on you can get the flow to reattache to the top surface of the wing. This reduces the area of the low pressure wake and there for drag, but at the same time the surfaces of the wing can be used to generate downforce. it can also enhance high speed stability due to having a enforced seperation point (end of wing) rather one that can oscillate up and down the rear surface of the car.

Paul

Fuzz

Diffuserthat's the proper name of it, couldn't think earlier.

Yes David, Removal of rear bumper and make up a "diffuser"
see I'm not nuts either.

Andy

edit to add :
can't have you taking off now need you around next year as competition


[Edited by Fuzz - 3/16/2003 6:19:19 PM]

Dutch Scooby lover

iTrader: (3)

Didnt the YUN Impreza do 201 mph.
I know ive found a vid that shows it flying by but i cant seem to find it any more (found it on the old i-club forum)

Hoppy

Great thread And I would seriously, honestly, love to see a 200mph Impreza

The 22b link is full of the usual theorists spouting calculations, but let's get back to the real world.

How many Imprezas can produce a reliable 600bhp, even for a few miles sprint? Who, where? We seem to be getting there, but not there yet.

That small detail apart, the problem with 200mph is not the weight of a carbon bonnet or a lardy passenger, but aerodynamic drag and, most critically, lift and stability.

Suggest MAJOR work on the latter first.

Not trying to pi55 on anyone's fireworks, but over 170 a brick-like Impreza will need much more aerodynamic help than bhp. Work on a super-slippy shape with good aerodynamic stability and anything could be possible. It would be the fastest Calibra look-alike on the planet

Good luck!

Richard.

Fuzz

"600HP Impreza WRX STI 309KM/H!!!"

I've got a vid as named above 10,000kb so don't ask me to post it up as I'm only on 56K .
<mumbles ******* BT ****s>

I got it off kazza, I'm sure it'll still be there, especially if i'm online

Just had a quick butchers at it, great big deep front spoiler splitter. apart from that looked normal ride height.

Andy C

Pavlo

That will be me then, you ignorant gobsh1te.

I think you will find the real world can be readily characterised by such theories, which happen to so far be correct in the real world. I put much more weight in those than some idiot spouting "can't be done".

What happens at 170mph? What makes the Impreza so different? What makes you think the cars weren't still accelerating at Elvington for TOTB and not actually topping out? Of course a lower cd or frontal area will reduce the bhp requirements for a given speed, but the Impreza isn't as bad as you seem to make out.

Hoppy, If you would like to stick the real world, please be so kind as to provide some evidence for your claims.

Paul

David_Wallis

Whats the cd of a p1 due to the fact that I will have a p1 front bumper / splitter..

David

Pavlo

David,

Not that simple. Although I would expect a splitter to reduce the cd if anything, and defintely improve front lift (ie reduce it).

I think I saw a cd of 0.35 and A = 2.09 m^2, sen cd quoted as low as 0.32.

I would very surprised if an on the road Calibra managed to get the advertised cd, it's not unknown for manufacturers to test with things like mirrors, radio ariels, door handles and the like (using models).

David_Wallis

may look at sti rear top spoiler??

David

Pavlo

it would be worth asking around (prodrive?) if they did any testing on the wagon.

My thoughts are an undertray and diffuser could be good and possible. Avoiding the diff is a pain, and leaving the exhaust suitably cooled too. Possibly have a gap in the middle with a small lip on the edges. Once behind the rear diff, it's quite easy ( on my legacy anyway).

What to make such a thing from? GRP with thin foam core would be easier for DIYness, 16gauge Al isn't stiff enough.

paul

David_Wallis

Im not quite understanding this yet...

whats 16 gauge in mm??

How far under the car does the thing have to run??

David

carl

Prodrive won't have done any testing at 200mph! The aerodynamics of the car are design for, say, 140 tops (112 in Japan). Any of the rally stuff will be designed for 120 tops and going sideways (rally cars' aerodynamics still 'work' at substantial deviations from the straight ahead -- unlike an F1 car which loses all its aero, causing a spin, as soon as you get it a bit out of shape). Your best bet would be to contact someone who was involved in the running of the JGTC car.

BTW running as low as possible won't be ideal either, as if you are low the suspension will have to be stiff. Then unless you're running on perfectly smooth surfaces you'll find you spend a substantial amount of time with not much rubber on the ground (and bouncing around will screw the aero too...)

BTW Pavlo you're right in that frontal area and drag coefficient (effectively CdA) will be the only things affecting top speed, but introduction of aerodynamic devices e.g. wings and venturis will increase the Cd. Look at all supercars -- 0.35 is a very low coefficient of drag for one of those because of the downforce (or anti-lift, if you like) that they have to run. OTOH 0.35 is a crap Cd for a normal family saloon or coupé.

Flat underbody would be a good idea (make it from CF), but TBH unless you can run really low ride heights then venturis and diffusers will have little effect. IIRC the Ferrari 355 was the first road car to have underfloor 'ground effect' tunnels, but in reality all they do is smooth out the airflow as it rides far too high for any sort of ground effects.

[Edited by carl - 3/17/2003 11:10:40 AM]

David_Wallis

Plan is to wind the coilovers right down for the high speed run..

David

carl

TBH the problem with aero is that you can't just 'suck it and see'. If you have some highly experimental kit in your engine to get (say) 650bhp, the worst that can happen is you blow it up. If you try to bodge together some aero, the worst that can happen is that you end up upside-down at 180mph

ozzy

I remember seeing an article on a US website showing just how good/bad the airflow was on a US-spec 99/00 saloon. They had the usual bits of wool stuck all over the bodywork and some pics showing where all the turbulance was.

From what I remember, there was loads of turbulance on the rear screen due to the MY99/OO spoiler. Don't think the bonnet scoop would help matters either.

Removing the spoiler completely maybe the solution, but I suspect the back end might be a bit loose at those speeds. I can see a Fast 'n Furious spoiler being required or a good diffuser.

Stefan

David_Wallis

Hmm..

Wasnt really planning on suck it and see... and the engine isnt experimental... mental maybe

David

carl

This has got to be a wind up now
TBH I don't see why companies like Mercedes et al spend a shed load of money on R&D, wind tunnels, etc. when they could just make a bluff-nosed shed of a car with a decent engine (e.g. AMG V8), put an STi 6 spoiler on the back and wind the coilovers down