The infamous ultimate supercar thread.
- Thread starter mPWRD
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- England, Warwickshire
- GTP_Sigma
Agreed, the first thing you that really needs considering when designing this supercar, is what are the aims of the car. Its no good simply trying to build a good car, an objective is require.
mPWRD are you aiming for luxury, top speed, track performance? what are your objective for this sportscar.
I'm not daftI'm aware that downforce is a requirement, but at the same time, a Cd figure isn't necessarily relative to the amount of downforce the car has. Beyond a certain limit sure - as with the F1 car you mentioned - but when even something like a Nissan GT-R as a CdA of 6.08, almost two points less than the Veyron, yet
I know this is far from the point you are trying to make, but to be fair to the Veyron, it has little need for such an efficient CdA. The engine still has more in the can, its limited electronically rather than by aero limitations, only high end acceleration is really effected but that's hardly a slouch.
Again this brings back to the point of the supercar, if the objective of the car is simply high top speed then downforce can take a hike to reduce drag.
176 pounds of downforce @186 isn't exactly that much. efficient body sculpting can reduce lift and drag too, but to get significant downforce you are going to have to sacrifice your CdA, Wings aren't really an ideal way of producing downforce as the cost a lot in terms of drag. For a track car the positive outweighs the negative in terms of lap times. Its worth mentioning that diffusers increase downforce and reduce drag. Infact if you want a high downforce car without all without the drag problem then groundeffects FTW. That said, I wouldn't drive one, the tendency for groundeffects too lose all downforce instantly is a huge risk.
mPWRD, really you need to decide what you want from your car before you can even begin to speculate on your aerodynamics.
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True, but at the same time it's not bad at all for a car with such a low Cd and a reasonable CdA. And of course, that's very different from simply making a high-drag shape and expecting it to have downforce just because the Cd figure looks high. As I pointed out, you can find plenty of cars with a low Cd and high downforce characteristics, and plenty with a high Cd and little or no downforce 👍
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Is it just me who thinks Cd is a pretty redundant figure in comparison to CdA. I mean Cd tells us how efficient a shape is, but that makes sod all difference if its offset by a large frontal area.
CdA tells us pretty much all we need to know about how aerodynamically efficient a vehicle is, whereas the Cd doesn't. I am not saying Cd is unimportant or not useful rather, far from it.
Its funny because like you said: high drag =/= high downforce. Yet at the same time , more often than not, High downforce = high drag.
CdA tells us pretty much all we need to know about how aerodynamically efficient a vehicle is, whereas the Cd doesn't. I am not saying Cd is unimportant or not useful rather, far from it.
Its funny because like you said: high drag =/= high downforce. Yet at the same time , more often than not, High downforce = high drag.
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Good point. A first gen Honda Insight and an 04 Toyota Prius both have a similar Cd figure of 0.25 and 0.26 respectively, but the Insight is much smaller frontally so achieves a CdA of 5.10 next to the Prius' 6.24. Which is incidentally a higher CdA than the Nissan GT-R mentioned earlier - which highlights how impressive the apparently brick-like Nissan is aerodynamically.
Cd is a relevant figure when comparing like to like (a medium hatchback to a medium hatchback, for example), not so much when comparing one thing to something completely different (a Veyron to a Suzuki Hayabusa, for example - the bike will have a higher Cd, but a much lower CdA).
Its funny because like you said: high drag =/= high downforce. Yet at the same time , more often than not, High downforce = high drag.
Well spotted. It works much more one way around than it does the other!
Eric.
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- Ebiggs
Its funny because like you said: high drag =/= high downforce. Yet at the same time , more often than not, High downforce = high drag.
All rectangles =/= squares, however, all squares = rectangles.
ROAD_DOGG33J
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- holyc0w1
- holyc0w
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- Banbaria.
- GTP_Venari
The square law for aerodynamic drag is good, but not good enough. 384hp might get you sor in a perfrect world. But, then you have turbulence, extra drag from lift/downforce effects... so my 400-450 is probably closer to the mark.
But hey, like the rest of this thread, it's only talk, right?
But hey, like the rest of this thread, it's only talk, right?
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Plus wasn't the M3 basically the core part of the supposed supercar? It seems everything he talked about involved it, from his experience working on cars to his engine choice of two M3 engines.
- 924
It's not a top speed car. If it was, then I would be taking the Veyron comparisons a lot more seriously. This is what I'm going for: track-oriented, but usable on the street. ~ 800 hp, 2800 lbs, 200 mph top speed, 0-60 in 3.2-ish. Those are just the goals - this thread is about how to get there. I have lots of ideas, but I've learned some tips from others.
And then after you take aerodynamics into consideration, there's all the power sapped by the car's systems. Exhaust backpressure, drivetrain components, friction... I would say around 480-500 actually. A 500-hp Exige... sounds fun.
*Sigh*... no, it isn't. Please don't get into that mindset. The Elise scenario is purely hypothetical, though.
One thing I don't get - even though I probably won't use it - is variable geometry turbos. I mean, I know how a turbo works and the principle of a VGT, but what kind of system is used to extend/withdraw (for lack of better words) the vanes?
the Interceptor
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- theInterceptor77
There is a set of small adjustable vanes that lead the air into the turbo. With altering those vanes, the airflow and -amount and thus the turbo characteristics can be changed. I'll see if I can find a picture.
EDIT:
vanes closed (not totally)
vanes open
Try Google. Took me a minute.
Wiki talks about how they are being operated:
Wiki
EDIT #2: more: http://www.autospeed.com.au/cms/A_108916/article.html?popularArticle
Last edited:
- 2,587
A bit of a quick wiki revealed this link at the bottom. http://www.autozine.org/technical_school/engine/tech_engine_3.htm#VTG
As far as I can tell, It appears that at low RPM's the way the vanes work is by funneling the air towards the center of the turbo at a faster rate, essentially making it a smaller turbo, thus reducing the lag. At higher RPM's the vanes open up to make it act like a regular turbo would.
EDIT Tree'd sorta. My post is still worth a read right?!
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- gtp_jimprower
http://paultan.org/archives/2006/08/16/how-does-variable-turbine-geometry-work/
aaaaand I got treed too.
aaaaand I got treed too.
mafia_boy
(Banned)
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Twincharging has been out since the early 90's on major manufacturers (Nissan Super March for example) but the main problem for twincharging now is that turbo turbine technology is so much better than it was 10-15yrs ago. Now VTG has cured one side of the problem which was the lack of response and also better turbine housing matching to allow the motor to boost in a more efficient way and to burn excess gases more thoroughly.
The emissions argument is pretty null-in-void now because as soon as you're adding boost, you're increasing pressure and the motor works overtime anyway because it's over atmo conditions. Lowering the compression helps to a point, but there's times when too little compression is worse than too much, and makes it an absolute pig when it comes to streetability and doesn't run as smoothly or cleanly then. I know from MY twin turbo car (this is personal experience) that I've got a decent amount of compression (about 8.5:1) which makes it good for off-boost driving and prevents it from being a laggy thing when turbo 1 starts spooling up. And I wouldn't change it's setup for the world, going super/turbo would just be a disaster for my car!!
- 87,648
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- GTP_Famine
Hmm, that sounds familiar...
Famine
Ah yes!
Though you need to go back FAR more than "the early 90s".
Rrrrright.
Let's let Volkswagen handle that one, shall we?
Mk5 VW Golf Range, 2004-2008
(Model - Power - Performance - CO2 emissions)
1.4 GT Sport TSI 5d - 138hp - 8.5s/127mph - 169g/km (39mpg)
2.0 GT FSI 5d - 147hp - 8.6s/128mph - 187g/km (35mpg)
That's a small-engine mated to a twincharger set up with about the same power and performance as a larger Nasp engine and significantly improved economy/emissions (in fact the 170hp variant of the twincharged 1.4 TSi matches the 147hp 2.0 Nasp for economy/emissions).
Small engine + forced induction almost always betters a larger, similarly-powered Nasp engine in the field of fuel economy (and thus emissions as they are presently measured).
Trust me - VW may be the pacesetters here, but you're going to see more and more super and twincharged cars as car manufacturing begins to be driven by punitive "emissions" measures laid in place by the EU.
mafia_boy
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This is going to be a case of agree to disagree. The things that BMW are doing with Twin Turbo technology on both their petrol AND diesel engines is starting to show the world that turbos don't = lag.
And more boost = more fuel, and the twincharged VW's aren't the most boost-friendly of cars, reports I'm reading from different sources are quoting from 25psi. to 36psi. depending on load and rev range!!
If I was running 36psi., I'd be wanting 600hp not 160hp!! 
To think it only uses that much fuel (7.2L/100km) with THAT MUCH BOOST is amazing really. 👍
And more boost = more fuel, and the twincharged VW's aren't the most boost-friendly of cars, reports I'm reading from different sources are quoting from 25psi. to 36psi. depending on load and rev range!!
If I was running 36psi., I'd be wanting 600hp not 160hp!! To think it only uses that much fuel (7.2L/100km) with THAT MUCH BOOST is amazing really. 👍
Eric.
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- GTP_Eric
- Ebiggs
This is going to be a case of agree to disagree. The things that BMW are doing with Twin Turbo technology on both their petrol AND diesel engines is starting to show the world that turbos don't = lag.
And more boost = more fuel, and the twincharged VW's aren't the most boost-friendly of cars, reports I'm reading from different sources are quoting from 25psi. to 36psi. depending on load and rev range!!
Did I just read that as the little 1.4L twincharged motor having 25-36psi of boost stock? Because there is no way that can be accurate.
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Well, if it's direct injection...then again, I don't know why they'd have a spark plug with that much boost!
Rotary Junkie
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The Autozine link from Bergauk also says 2.5 bar for the VW... Which is utterly insane considering how weak it is in terms of power for its size. Massive exhaust recirculation is all I can come up with.
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Low end and direct injection.
Direct injection allows you to run crazy amounts of boost at a compression ratio that, ten years ago, you wouldn't even think of throwing 10 psi at.
And 36 psi of boost would likely come on at low rpms, only, tapering off at the top end, as most new turbos do.
That way, the power output stays within the torque-handling capabilities of the engine/drivetrain and you never have more air than the engine can deal with, yet you have the most power possible under the curve.
+1 on modern BMW turbos... they're awesome... but note... BMW still goes twin-turbo for their really powerful units... there's only so much a single VGT turbo can do, since the vanes only help spool up to a point... sure, the VGT is much more flexible than a standard turbo, but if you want it to spool up quickly, there's a limit to how big you can make it.
So, for that extra kick (even on their four-cylinders), BMW needs another turbo sized for high rpm power.
So... there's still room for twin-charging... you just have to bring the packaging costs down.
Heck, even plain old superchargers could come back into vogue. Some of these new superchargers have very little parasitic losses, and can give the same benefits as a more complicated VGT system.
Direct injection allows you to run crazy amounts of boost at a compression ratio that, ten years ago, you wouldn't even think of throwing 10 psi at.
And 36 psi of boost would likely come on at low rpms, only, tapering off at the top end, as most new turbos do.
That way, the power output stays within the torque-handling capabilities of the engine/drivetrain and you never have more air than the engine can deal with, yet you have the most power possible under the curve.
+1 on modern BMW turbos... they're awesome... but note... BMW still goes twin-turbo for their really powerful units... there's only so much a single VGT turbo can do, since the vanes only help spool up to a point... sure, the VGT is much more flexible than a standard turbo, but if you want it to spool up quickly, there's a limit to how big you can make it.
So, for that extra kick (even on their four-cylinders), BMW needs another turbo sized for high rpm power.
So... there's still room for twin-charging... you just have to bring the packaging costs down.
Heck, even plain old superchargers could come back into vogue. Some of these new superchargers have very little parasitic losses, and can give the same benefits as a more complicated VGT system.
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I'm not so sure this is entirely accurate in the particular instance.
Our frie...., associate, the prevaricator is trying to make a high performance vehicle with a suitable high performance engine, and trying to eke out the last bit of horsepower from an engine will generally change the emissions and fuel efficiency of an engine.
Otherwise I agree with you.
mafia_boy
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Sequential turbos have been around for hhhhnnnnages - take the Supra MkIV, for instance (1993?). But I'm not saying twin/paired turbos aren't fuel efficient solutions - I'm saying twinchargers are. Note:
Famine
Superchargers and turbos are both forced induction so... where's the issue?
Yes, but I'm comparing the FI cars to similarly-powered Nasp engines. Does the 1.4 TSi use more fuel than the less-powerful 1.4 FSi? Of course - it's the same engine with more power courtesy of a pair of turbines fitted to it. Does it use more fuel than the slightly-more powerful 2.0 FSi? No, it uses less. Why - because a small engine with forced induction outstrips a larger, similarly-powered Nasp one in this department.
Seriously, in the culture we now have of "CARBONZ = PLANET DEATH!", and manufacturers being fined if their emissions aren't below a certain level across the range, we're going to see fewer and fewer non-force-induction engines as they can make the same car with the same power and better fuel economy with FI. That includes supercharging, turbocharging, twinturbos and twinchargers.
neanderthal
Problem is there's very little we can do a comparative test on. We'd need to find a supercar with an FI engine and then another engine from the same manufacturer with as much unblown power and find fuel economy figures
I reckon it'd still stand, but no-one would actually care
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I'm almost positive that I read somewhere that the wing on the Countach does something besides look cool.
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It was a joke. Countach with a wing had a Cd in the low 5s or so.
mafia_boy
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Yeah, all I'm saying is the way that BMW has integrated their TT system into their diesel range is what sets them apart from most of the other manufacturers at the moment. And we all know sequential TT's have been out for aaaages, the most famous early example being the R32 GT-R (the JZA70 Supra Twin Turbo R of the same era was simultaneous twin turbo).
No issue there Mr.Indigo.
Not exactly. Things like the Alfa JTS system are showing there's still life in the good old NA motor yet, providing huge power boosts over other NA's with better fuel economy and improved emissions.
Problem is there's very little we can do a comparative test on. We'd need to find a supercar with an FI engine and then another engine from the same manufacturer with as much unblown power and find fuel economy figures
I reckon it'd still stand, but no-one would actually care
We can.
Ferrari F40 vs F50. Now, the F50 does produce only 30hp more and is almost double the F40's size, 2.9L v 5.7L but it's applicable I think....it runs along the lines of what you're suggesting but the result makes for horrific reading for NA.F40 Fuel Economy
F50 Fuel Economy
From that result, you (as usual) are right.
*NO NEED TO QUOTE THAT!! *Similar threads
