Top speed. What does it take....

[TURBO2GO]

A standard geared 6-speed NSX reaches 203 MPH at 8000 RPM's in 6th.

Does anyone have any idea what it would take in terms of power to actually reach that, given standard 2002+ bodywork aerodynamics (which I believe is lower cd than pop up cars)...

Any ideas or educated guesses?

 

[NetViper]

I think around 550 crank hp.

 

[TURBO2GO]

Is this just your best guess Dave? Cd was reduced from 0.32 to 0.30 in 2002 on the stock body. Top speed according to Acura was increased from 168 to 175. So how much more does it take to go from 175 to 203. That's the question. 550 crank is about 480 at the wheels.

 

[NetViper]

Is this just your best guess Dave? Cd was reduced from 0.32 to 0.30 in 2002 on the stock body. Top speed according to Acura was increased from 168 to 175. So how much more does it take to go from 175 to 203. That's the question. 550 crank is about 480 at the wheels.

Yeah, just a guess. Looking at top speeds of similar cars and their horsepower. Like a ford GT.

 

[CL65 Captain]

Ask Greenberet. I think he has more top speed runs than anyone. In his NA1 with 5 spd he is gear limited hitting red line at 186 mph.

 

[TURBO2GO]

Yeah I saw those posts but I think that was maybe speedo error? He didn't have FI, and the factory says 168 so 186 is way beyond that. I can see intake and headers good for maybe another 5? 10? But 186? That wasn't GPS or radar AFAIK.

 

[CL65 Captain]

Yeah I saw those posts but I think that was maybe speedo error? He didn't have FI, and the factory says 168 so 186 is way beyond that. I can see intake and headers good for maybe another 5? 10? But 186? That wasn't GPS or radar AFAIK.

yes it was GPS and a run in both directions.

"

NSXGermany 3 years agoNo, it's not stock. It has a foam air filter, polished intake manifold, ported heads, high lift camshafts, headers, and a sports muffler. But it is still a naturally aspirated 3.0 with a stock bottom end and a stock 5-speed transmission. And yes, that was 299 km/h in one direction and 301 in the other."
​

<iframe width="560" height="315" src="http://www.youtube.com/embed/W5EmrML3p1U" frameborder="0" allowfullscreen></iframe>

 

[greenberet]

A 2002+ NA2 should need about 450 crank hp at 8000 rpm to reach 203 mph.

According to Honda, a stock 2002+ NA2's top speed is 175 mph. If the car hits 203 mph at 8000 rpm with stock gearing, its engine should be spinning about 6900 rpm at 175 mph. According to this chart from Honda, an NA2 puts out about 287.5 crank hp at 6900 rpm. To increase the speed by 203/175 = 16%, you have to increase the horsepower by about 1.16^3 = 56%, so from 287.5 crank hp at 6900 rpm to about 450 crank hp at 8000 rpm. Assuming Honda's published top speed and horsepower data are accurate, of course.

... I think that was maybe speedo error?

Yeah, speedometers are often inaccurate. I've found Audis to be especially optimistic. That’s why I measured my NSX with GPS. The only good measure of a car's real top speed is a two-way run like the one CL65 Captain linked to because that compensates for wind and slope. Still pictures can show how fast a car was going at a certain instant, but that may have been influenced by a tailwind or going downhill. Still, they take less time to watch so here are a couple: example 1 and example 2.


Edit: come to think of it, you could go 203 mph in a bone stock NA2 with 290 hp if you have enough of a tailwind or drive down a hill. If you download this little spreadsheet and remove the ".pdf" ending, you can play around with how steep of a hill you need to reach various speeds.

 

[TURBO2GO]

Man that was an informative post. Thank you Greenberet. Where did you get that 1.xx^3 formula? Is this a commonly known thing that takes into account wind resistance? What about the coefficient of drag? It doesn't seem to be in the formula.

So how did you manage 186? What was your HP?

- - - Updated - - -

450 crank doesn't seem that high. A CTSC car with 350 WHP is probably close to 400 at the crank. And most of the turbo cars are probably at 450+. I know for most NSX's it's gearing that becomes an issue, but theoretically a 6 speed with the stock 4.06 final drive will be at 203 at 8K RPM's. So maybe it's not so hard for an NSX to break 200...

 

[greenberet]

Yes, it’s a standard formula that the increase in horsepower you need to overcome wind resistance is the cube of the speed increase. And the increase in force (torque) you need is the square of the speed increase. You can find that in just about any physics textbook.

At top speed, wind resistance is the major thing you have to overcome. There’s also the resistance of the oil getting squished between the transmission gears, the rolling resistance of the tires, etc. and not all of the resistances go up in lock step. The rolling resistance of the tires is actually a complex topic because standing waves develop in the sidewalls so the resistance is hard to calculate. To find the true top speed, you have to test it. But if you assume the power needed to overcome overall resistance goes up as the cube of the speed increase, you’ll get a good estimate.

You can calculate the top speed based on the drag coefficient, frontal area, air density, rolling resistance of the tires, the engine’s power curve, etc. However, all of those factors already flowed into our first data point, namely that a 2002+ NA2 can hit 175 mph, assuming Honda’s data are correct. If you already know the drag-limited top speed and the horsepower the engine is putting out at that speed, it’s easy to calculate the power needed at other speeds. If you change factors such as aerodynamics, drivetrain losses, etc. then you’re going to have to start from scratch with the complex formula based on the drag coefficient, frontal area, etc.

Since I changed the aerodynamics of my car, it should require less horsepower than stock to reach a given speed. So I don’t know how many horsepower it requires to reach a two-way average of 186 mph. Since my engine is modified and dynos usually aren’t calibrated, I don’t know how many horsepower my engine is really putting out, either.

It seems that CTSC’d NSXs have a lower top speed than stock based on what we’ve seen here in Europe. During extended top speed runs the engines seem to heat soak, causing the engine management computers pull ignition timing, resulting in a top speed of about 160 mph. If the engines wouldn’t heat soak and lose horsepower while running at 8000 rpm and full throttle for a few minutes at a time, the cars would go nice and fast. A pop-up headlight NSX with 350 whp instead of a stock 235 whp (+49%), should then be able to increase its top speed by 14.2% [1.49^(1/3)] from 168 mph to 192 mph, given proper gearing.

 

[nsxtasy]

Yeah I saw those posts but I think that was maybe speedo error? He didn't have FI, and the factory says 168 so 186 is way beyond that. I can see intake and headers good for maybe another 5? 10? But 186? That wasn't GPS or radar AFAIK.

It's NOT speedometer error. He was doing 186 at redline. The stock car with a five-speed calculates out to 186 mph at redline. The reason the stock car tops out at 168 is because it's drag-limited, not rev-limited. IOW when a stock car tops out at 168, it's not at redline; it's somewhere around 7225 RPM. So the difference between 168 and 186 is due to his added power enabling him to rev past 7225 RPM up to redline, not due to speedometer error.

Speedometers are not always accurate, as he indicates above. The NSX speedometer is generally pretty darn accurate, even at high speeds, unlike most cars. But there are always variables. Just to cite one variable, the difference in outer diameter between a tire that is brand new and one that is worn down to the treadwear indicator bars is around 2 percent. That won't affect the speedometer reading at any given RPM, but it will affect your actual speed (and therefore the speedometer accuracy).

 

[TURBO2GO]

Greenberet, are your mods basically intake and exhaust?

 

[davidf]

I would'nt trust just any tire at that speed. Not even for a single pass. Maybe I'm paranoid.:redface:

 

[UnhuZ]

Hi,

Guys, the advertized Honda top speed of 168mph (270 km/h) IS NOT the maximum a
stock NSX can do.

The thing is, if you have TCS on, then you hit a wall at 168mph, if you disconnect it
(using the button just below the cluster), you can pass that limit.

When i cutted fuel in 5th on my NSX, in long subtle down hill, i only had:
- no cats
- KN on stock air box
- CF side vent scoop

And when i'm going to do top speed with the TCS on, then at 168mph it
seems that the car hesitates and it just remains there.... and if i just lift
my foot and press the TCS to get it off, then floor it again, then when it
reaches the same 168mph it just get over it and continue to go faster.

So, as the TCS is ON by default, then a stock NSX is ALWAYS limited to
168mph until you get it off.

Nuno

 

[TURBO2GO]

Hi,

Guys, the advertized Honda top speed of 168mph (270 km/h) IS NOT the maximum a
stock NSX can do.

The thing is, if you have TCS on, then you hit a wall at 168mph, if you disconnect it
(using the button just below the cluster), you can pass that limit.

When i cutted fuel in 5th on my NSX, in long subtle down hill, i only had:
- no cats
- KN on stock air box
- CF side vent scoop

And when i'm going to do top speed with the TCS on, then at 168mph it
seems that the car hesitates and it just remains there.... and if i just lift
my foot and press the TCS to get it off, then floor it again, then when it
reaches the same 168mph it just get over it and continue to go faster.

So, as the TCS is ON by default, then a stock NSX is ALWAYS limited to
168mph until you get it off.

Nuno

If that's the case then it might take even less than 450 to reach 203? Just doesn't sound right.... LOL... Will the cd of a car drop if it's lowered? It must have some mild effect...

 

[docjohn]

hmmm are you gonna start a group buy for 201 mph Dave?...

 

[UnhuZ]

Hi,

If that's the case then it might take even less than 450 to reach 203? Just doesn't sound right.... LOL... Will the cd of a car drop if it's lowered? It must have some mild effect...

don't minimize what a slight long down hill can do to help you on a top speed run :biggrin:

and one other thing.... and this is highly subjective, but in all these years of very high
speeds, i find that the more a car does top speeds, the easier it gets for it to do it.

If i don't do top speed runs and only daily drive it for long periods, then i notice that it's
harder to reach speeds i used to (in the same places).

Dave, send me your car with the stock wing, give me a month or 2, and i'll show you what
speed i can do with it :biggrin::biggrin:
(although the blower can "blow" my attempts due to heat soak....stock NA would be better)

Nuno

 

[goldNSX]

Will the cd of a car drop if it's lowered? It must have some mild effect...

In theory, yes but I'm not sure if you can see the effect in practice as it's very low.

More over this, lowered cars very often have wider rims an wheels. That lowers you mph much more than you gain with lowering the whole car.

Nuno, I agree, the car feels pretty stronger right after a high-speed run. I guess it has to do with de-carbonization.

 

[greenberet]

Greenberet, are your mods basically intake and exhaust?

When my avatar picture was taken, the car got up to an indicated 8000 rpm in one direction on the Autobahn and 8050 in the other with 245/40 17 rear tires. At the time, my car had the following horsepower modifications: Comptech airbox, Unifilter foam air filter, Extrudehoned intake manifold, Comptech ported and polished cylinder heads milled for a bit more compression, Comptech high lift camshafts, Comptech headers, HKS muffler, and an engine management chip for the PGM-FI custom programmed by Autothority on a dyno. When the video CL65 Captain linked to above was shot, ceramic-coated Cantrell headers had replaced the ceramic-coated Comptech headers, which had rusted through. In addition to those modifications, my engine now has a Science of Speed bored-out throttle body, Comptech adjustable cam gears, a Power Enterprise timing belt, and an ATI harmonic damper/crankshaft pulley. Before doing more top speed runs I’m going to install RDX injectors and get the engine management chip for the PGM-FI reprogrammed with the car on a dyno and 100 RON fuel in the tank (which is available at public filling stations over here).

As Nuno said, don’t underestimate the impact a slight hill can have on your top speed. Play around with that spreadsheet I linked to above and set it up for a stock NA1 five speed – a top speed of 270 km/h (168 mph) with 238 rwps (235 rwhp) and a weight of 1368 kg (3015 lbs). On a 4.1% downhill grade, that car should be able to get up to 300 km/h (186 mph) due to the additional force pushing it downhill.

And a tailwind will increase your top speed as well. That’s why you need to do a two-way run if you want to determine the car’s “real” top speed. But for the thrill of driving fast, run with the wind or drive down a hill and enjoy the fact that you own a sports car and that life is good.

 

[TURBO2GO]

Guys FYI.... I ran my CTSC car last night to about 158-160 and at that point it was pulling HARD, and can tell you for sure I could have broken that by at least 30 MPH. A friend with a CTSC also contacted me and said he has been close to 180 before deciding to slow down and the car had more. I can tell you at least in both our cases, there seems to be no "160 limit due to heat soak" thing happening. I was accelerating at a very hard rate at that speed.

 

[NA1MT]

It was only 15 degrees out last night

 

[TURBO2GO]

And I also don't want to do that again but the car was remarkably stable and drama free at that speed.

- - - Updated - - -

It was only 15 degrees out last night

My spot was about an hour away from me. An hour of hard driving with the engine hot as can be. I did not pit stop. The blower was hot enough to burn my hand even after cooling. My friend lives in a hot climate.

 

[NA1MT]

I would almost say without a doubt that if you were to duplicate last nights adventure in July you will have quite a different result.

 

[TURBO2GO]

I would almost say without a doubt that if you were to duplicate last nights adventure in July you will have quite a different result.

Perhaps slightly slowe, I'm not saying there is nothing there.... but if you're going to bet me cash that we get up to 140 with an NA car and my CTSC car on a hot day and we pull... and that the NA will out-pull me, I would take that bet everytime. I'm not saying heat soak is not an issue that in an extreme case can weaken the car. I'm saying to state that a supercharged car won't break 160 as a blanket statement is inaccurate. Not that greenberet said that.

 

[NA1MT]

I don't doubt that you can hit 160 and pull on a NA car. I just doubt there would have been any real heat soak last night....especially since you stated no stopping. As far as running the car goes, you might not like the outcome, that is if I ever get it back.