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MAX Speed

Joined
22 June 2007
Messages
215
Location
St. Petersburg, Russia
Y'day we have a trial to test a max speed...

Well I was on HRE 18/19' combo + my NSX 3,0 (5)MT NA1 92'
was accelerating only on 4th gear, on 5th gear she was not accelerating at all. on 4th (and 5th) gear max speed was 242 km/h - rougthly 150 mph on 6200 rpm@5th gear. Even I drove 30-50 seconds she did not show me any ability to accelerate further. Today I will change my wheels for 17/18 Rays TE37 and will try again - maybe be that's the reason?

Or the spoiler is too havy?
Any idea?
 
18/19 is much too fat for max speed. Try it with 255/35/18 in the rear.

Lesson learned: The bigger the wheels the slower the car in any way.
 
18/19 is much too fat for max speed. Try it with 255/35/18 in the rear.

Lesson learned: The bigger the wheels the slower the car in any way.

There is also a gearing benefit to be had from a larger diameter wheel; many people feel the nsx is more gear-limited than anything, once you dramatically increase the power, and add subtle aero enhancements.

With a 275/35/18, the nsx is geared to reach a maximum of 201mph, while without it, it is only geared to go 196mph (these figures are based on a US-spec 5spd transmission).
 
TCS was off..

Today was thinkin to try 18 TE37 on rear, but the offset +40 for the front 17 71/2 rays was too small to clear the BBK. Shit, onlt few mm are about. Whells start to scratch the caliper. Will check spacers...Thenafter will start again.

I've got Rear spoiler GT500 and diffusor from Taitec. So aero will be not a prob. Sonn will have front GT2000 and Marganhills sidesteps.

belive 5th gear ratio does not enougth for 19' wheels. The torque (i.e. power) equail to the front air resistance
 
I've got Rear spoiler GT500 and diffusor from Taitec. So aero will be not a prob. Sonn will have front GT2000 and Marganhills sidesteps.

belive 5th gear ratio does not enougth for 19' wheels. The torque (i.e. power) equail to the front air resistance

This is a problem, I had the GT500 taitec wing, and it was a boat anchor, you could feel its adverse effect at speed.

Put your stock wing back on, or find a more-efficient GT wing, I have the esprit rear wing now:

2.jpg


but for a high speed run, even this would lower top speed.
 
Ok, now I see the real problem: aerodynamics. Don't be surprised to lower your topspeed with a big-ass-wing and other goodies. :D If you want to go fast remain stock.

There is also a gearing benefit to be had from a larger diameter wheel; many people feel the nsx is more gear-limited than anything, once you dramatically increase the power, and add subtle aero enhancements.

With a 275/35/18, the nsx is geared to reach a maximum of 201mph, while without it, it is only geared to go 196mph (these figures are based on a US-spec 5spd transmission).

I don't get your point here. The topspeed will always be reached in 5th gear in a 5-speed. With stock sized tires at about 7.1k rpm at 168 mph for a 91. At these rpm you could still go faster but TCS or drag is limiting you. As for my case (short gearbox and small tires) I had 7.5k rpm at 168 mph and from this point on there is no more power from the engine available unless you tuned it to make more. :wink:

Also think about this one: Big, wide wheels have quite a big roll resistance than stock ones which eates up very, very much hp going to the road surface. But your problem is aerodynamics.
 
Any other clues?

I'd also guess the problems are aerodynamics and gearing.

The 2002 NSX-R has a bigger rear wing than a standard NSX and as a result, it has 6.7% more wind resistance than a standard 2002 NSX. A GT500 rear wing is a lot bigger again than the NSX-R wing, so it'll give you a lot more wind resistance. More downforce, too, but a lot more drag.

With larger wheels, your engine may be at a lower RPM at any given speed. If the RPM no longer get up to where maximum horsepower are produced, you'll lose top speed because of that, too.
 
I don't get your point here. The topspeed will always be reached in 5th gear in a 5-speed. With stock sized tires at about 7.1k rpm at 168 mph for a 91. At these rpm you could still go faster but TCS or drag is limiting you. As for my case (short gearbox and small tires) I had 7.5k rpm at 168 mph and from this point on there is no more power from the engine available unless you tuned it to make more. :wink:

My nsx is turbocharged, the point I am making, is if greenberet was able to reach 189mph with minor NA modifications (headers, exhaust, cams) and aerodynamic underpanels, then at my power level of 430rwhp, with similar aerodynamic undertrays (I have cf underpanels extending to the fuel tank), my greatest limitation will be gearing.

In this case, the larger diameter of a 275/35/18" tire, will increase the maximum speed attainable; using a gear ratio calculator, 201mph should be possible with this larger tire, compared to a maximum speed of 196mph with a standard 17" rear tire (approx 0.5" of diameter difference).
 
Y'day we have a trial to test a max speed...

Well I was on HRE 18/19' combo + my NSX 3,0 (5)MT NA1 92'
was accelerating only on 4th gear, on 5th gear she was not accelerating at all. on 4th (and 5th) gear max speed was 242 km/h - rougthly 150 mph on 6200 rpm@5th gear. Even I drove 30-50 seconds she did not show me any ability to accelerate further. Today I will change my wheels for 17/18 Rays TE37 and will try again - maybe be that's the reason?

Or the spoiler is too havy?
Any idea?

Some cars are regulated not to go beyond ~150mph. Nsx is everyday super car so it can happen. I recall BMW does this. Also, depends the countries they are sold. Just a thought.
 
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Yankee, I just stumbled across something here that may answer the question as to where your top speed went. It seems there is a maganize called Options 2 that tested the effect of a GT500 rear wing on the top speed of a Nissan Skyline.

No wing
drag coefficient: 0.28
top speed: 310 km/h

With wing, adjusted to lowest angle
drag coefficient: 0.46
top speed: 260 km/h

With wing, adjusted to medium angle
drag coefficient: 0.48
top speed: 257 km/h

With wing, adjusted to steepest angle
drag coefficient: 0.50
top speed: 249 km/h

Based on that, the 242 km/h you got up to look about right with the wing you have mounted on your NSX.
 
Yankee, I just stumbled across something here that may answer the question as to where your top speed went. It seems there is a maganize called Options 2 that tested the effect of a GT500 rear wing on the top speed of a Nissan Skyline.

No wing
drag coefficient: 0.28
top speed: 310 km/h

With wing, adjusted to lowest angle
drag coefficient: 0.46
top speed: 260 km/h

With wing, adjusted to medium angle
drag coefficient: 0.48
top speed: 257 km/h

With wing, adjusted to steepest angle
drag coefficient: 0.50
top speed: 249 km/h

Based on that, the 242 km/h you got up to look about right with the wing you have mounted on your NSX.

thank you very much. I know it will affect the performance. I did not know middle angle will better accelerating than lowest angle.
 
My NSX struggled to pass 147mph (250kph) with an APR GT500 wing at a medium angle mounted low.

A big-ass wing makes downforce from air resistance. Air resistance makes top speed slower. Simple equation.

You're generally trading speed for control with a wing.
Not exactly, pressure differences between the top and bottom of the wing generate lift/downforce, not air resistance. The goal is to provide as much lift as possible with minimal resistance - efficiency. The way you worded it made it sound like increased downforce is created only by increased air resistance/drag -which isn't necessarily true although more resistance is usually a byproduct of increased lift (but not always).
 
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I lost 6mph in the 1/8th mile with the wing installed. ET's improved however, traction increases? Wing was adjusted to it's steepest angle.

I've also noticed that the car takes 1 second longer per gear above 2nd gear to accelerate through that gear, all the way up to high 160mph. 5th gear lasted 1.5 seconds for this run before a deer ran in front of me half a mile down the "track". I shut it down early to avoid a very nasty mess.

I tagged the 8400rpm rev limiter once with 315/30/18s rear tires and the GT500 wing installed, but unfortunately the log corrupted during download :( The speedo was well past the 190mph tick mark.

Oh...650RWHP at the time...

The car felt absolutely planted with the wing. I'd rather sacrafice a little bit of speed for the rock-solid stability that the wing gave me. The next time I go to a road course with an average speed above 60mph, I'm going to install a wing.
 
just fyi- the drag created by the wing is directly proportional to the downforce created- as far as cars are concerned we can assume those two factors are equal.
 
On my NA2
I achieved 172 mph with OEM setting (from San Francisco to Los Angeles with almost no wind). 163mph with Type R wing (It was really windy in Portland Oregon that night).
 
just fyi- the drag created by the wing is directly proportional to the downforce created- as far as cars are concerned we can assume those two factors are equal.
Downforce = drag is NOT true

But there is a relationship between downforce and drag.

If you take a given wing, and adjust it's angle to make more downforce it will also make more drag, call that wing A

You could make a better wing, wing B, that makes more downforce than wing A with less drag than wing A but, wing B will still have the same basic property: when you increase the angle, you increase both drag and downforce


But no, downforce doesn't = drag

Take a wicker for example, big increase in downforce, small increase in drag



0.02
 
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Isn't "Swerve an Aero-Engineer? :biggrin: I probably wouldn't go head to head debate with him when it comes to aero dynamics :wink:

My .02
 
There are two types of drag. Induced drag and Parasitic drag.

Induced drag is a byproduct of lift or in this case down force.

Parasitic drag is caused by the friction of the air moving over the surface. This can further be broken down into form drag, skin friction and interference drag.

Induced and Parasitic drag meet at a spot where in the case of airplanes is the Max Coefficient of Lift. On a car wing this would also be the "sweet spot" of where you would get max down force with the min of parasitic drag.

Drag_Curve_2.jpg


Stuntman is not technically correct in that "down force does not equal drag". Induced drag is a byproduct of the down force, but as he pointed out there are ways of creating down force while minimizing the parasitic drag thus reducing total drag. A wicker as he said is one way. The under panels such as the NSX-R are another. Diffusers, splitters, rake, etc. What the engineers are trying to accomplish is accelerating the air without using a wing. And according to Bernoulli's Principle, when you accelerate a fluid the pressure drops.... thus you create down force.

fig2-10.jpg


Flip this upside down and you have one of those big ass Fast and Furious Wings you like to put on the back.

image001.jpg
 
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there you go.

btw, my statement was based on the lack of sophistication in design and adjustment capability of 'car wings'. for most part they are 'bricks in the wind'. obviously this thread and discussion does not, and should not, involve the example of f1 or indy as they are, in fact, able to find that 'sweet spot' as mentioned in the post above.
good job flyboy
 
Wings will generate the most downforce, but also the most drag. Splitters, underbody panels and diffusers will generate less downforce but can also decrease total drag (parasitic drag). This why you do not see big ass wings on Audi R8, GTR, Gallardo or F360/430s they all use underbody and diffusers to create downforce.

speedlab_ferrari_5.jpg


Note - these also create some drag (Induced drag) because of this downforce but the net result of smoothing the flow and reducing turbulence is an overall reduction of cD (coefficient of Drag). SO YOU CAN GET DOWNFORCE AND NET REDUCTION OF cD.

So why do you see Big Ass Wings on race cars?

23200685241343_Image1.JPG


Because they need the extra downforce on the rear to be able to put the power down earlier coming off the turn exit. They also have access to wind tunnels and testing time to find the best trade off for that particular track (top speed vs handling). They use both wings and undertray/diffusers.

I have a recent video (may try to get a screen capture) of me behind (and passing) a 944 Race car on the track with the biggest wing I have ever seen. It looked like a picnic table.


So... back to the topic at hand. If you are going for top speed - NO WING.
 
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there you go.

btw, my statement was based on the lack of sophistication in design and adjustment capability of 'car wings'. for most part they are 'bricks in the wind'. obviously this thread and discussion does not, and should not, involve the example of f1 or indy as they are, in fact, able to find that 'sweet spot' as mentioned in the post above.
good job flyboy


Additionally, you said drag was "proportional" not "equal" to lift/downforce :)
 
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