As it says in my signature 185mph via GPS and I was about 50rpm from hitting the rev limiter. Flat road no wind no aero improvements. If the car has a soft limiter then that is where I was.
Top Speed
- Thread starter JW
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I've been to the event with both worn and new tyres - very little difference. I would be surprised if a standard 02+ car would do the claimed 175mph
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I would trust laser timing equipment over GPS. Maybe it is just the 02+ cars that have optimistic speedos
if the tyre diameter reduces by just 2% that is exactly what the difference in speedo readings will be. 2% at 170mph is 3.4 mph error. "Very little" maybe, but definitely significant if aiming to measure top speed.
If that claim is the Honda claim I have no doubt the car can do it. It's a matter of making sure car is in perfect condition / trim with proper tyre pressure and diameter etc. Oh and don't forget to arrange a perfectly flat and very long straight... (~5 miles) on a closed road and with no traffic ... that's often the trickiest part.
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I hit 170 with the windows down in a mall parking lot. It was a blast. Of course, the car was super charged so it got to max speed quickly.
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What I don't understand is why all the road tests in the UK (with the exception of the 2002 car - which seemed to have a special engine), topped out at ~160mph on the Millbrook bowl, which equates to ~165 mph on the flat. How is it that customer cars are that much quicker?
My car (and the other 02+ car) were in near perfect condition - both been dynoed recently, tyres checked (as one would do before a high speed test).
Highest average speed over 57 miles on a two-lane public highway was 163 mph. Highest top speed was over 180 mph, with a radar clocked speed of 175 mph. Next month the plan is to average 160 mph over 90 miles on that sinuous high desert public road. Of course, all of this in sanctioned events in Nevada with the road closed, fully fenced, fully observed, with safety planes and emergency vehicles positioned.
1992 NSX with SoS-built engine, 6-speed, larger diameter tires, competition suspension (lowered), supercharger with intercooler, Driving Ambition supplied full roll cage, fire suppression system, safety fuel cell, plus full harnesses, HANS, arm restraints, full face helmet, full Nomex, etc. The car is gear limited at about 196 mph.
1992 NSX with SoS-built engine, 6-speed, larger diameter tires, competition suspension (lowered), supercharger with intercooler, Driving Ambition supplied full roll cage, fire suppression system, safety fuel cell, plus full harnesses, HANS, arm restraints, full face helmet, full Nomex, etc. The car is gear limited at about 196 mph.
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I'm not familiar with Millbrook bowl.. do other cars (not NSX) achieve their claimed top speeds there (after correction factor for flat road)?
And what speed did the 2002 record?
Are you saying you ran at the bowl ? If so what speed did you get? Is this higher or lower than the speeds mentioned above for "road tests in the UK" (which I took to be tests by CAR magazine or similar)
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I think Millbrook gets a bit tricky as the speeds go up, but I don't think 160 is pushing it that much.
The 2002 NSX achieved 171, which is around 180 on the flat. The reason I am suspicious of that car (similar to the US 1998 0-150 example) is that it did the standing kilometre in 22.8 seconds @145mph.
The road tests are taken from here
http://www.amazon.co.uk/Ultimate-Po...8873/ref=sr_1_1?ie=UTF8&qid=1334581435&sr=8-1
(mainly Autocar)
We did our testing at Bruntingthorpe (a disused RAF runway) which allows you to come onto the straight at around 80-90 and accelerate for ~1.7 miles before crossing the timing beams. As standard, the car was hitting around 161-162, with intake and exhaust (an extra ~17hp at the hub), it got 164-165. Acceleration in 6th when the car was standard was glacial - I just can't see the extra ~13mph happening
For comparison, a well sorted (and not that many are) E46 M3 SMG got around 165-166, and earlier NSXs around 159-160.
This was me in 5th a few mph before changing into 6th
If your 02+ speedo shows 164 mph at about 8000 rpm in fifth, that sure looks optimistic. With standard six speed gearing and stock tire sizes, the car should be going several mph slower than that. And if you can go another few mph faster in fifth without your rev limiter cutting in, either your rev limiter cuts in well after 8000 rpm or your tachometer is optimistic, too. If you’ve ever had your car on a dyno that measured the engine speed from the tachometer pickup loop in the engine compartment, do you know what at what revs the limiter actually cuts in?
Sparky, can your MATLAB model estimate Noel's top speed on a long straight given that he needed about 1.7 miles to get from 80-90 mph to 161-162 mph when his 02+ NSX was stock?
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I think we TDI (hub mounted dyno) measured the limiter at a tad over 8000rpm - will check.
Thanks! At least back in 2008 I believe TDI measured the hub speed and calculated the engine speed from that. Since measuring at the hub does away with any inaccuracies due to tire sizes, wear, and slip, the calculated engine speed should still be accurate as long as TDI entered the gearing correctly. When you check your engine speed, please also have a look at the power at the wheel. When the power doesn’t develop smoothly with increasing rpm anymore but rather spikes up or varies up and down, you’ve probably just hit the rev limiter.
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8080rpm - as you say, that assumes they have their gearing number right.
I drove through the timing beams at VMAX on the limiter in 5th and the speed shown on the timing gear was 160mph which ties in with the number on this site.
Tire size has no effect on the relationship between revs indicated on the tachometer, and speed indicated on the speedometer. It only affects the accuracy of the speedometer (the difference between indicated speed and actual speed).
Your point is correct, though; when at redline (8000 RPM), fifth gear in the six-speed should be going 160 mph, as noted here.
1.7 miles is not nearly enough to achieve top speed, even with a 90mph head start. Have a look at the graphs attached (from my NSX performance model in MATLAB) one for NA2 6SP the other NA1 5SP (JDM and US).
From standstill the NA2 gets to 90mph well short of 1/5th of a mile, then it takes another 2 miles to hit 170 and then ANOTHER 2 MILES to get near 175mph.
It's not that far out. Using a standard rear tyre diameter (644mm) 8000rpm for a 6SP changing into top gear is 162.7mph. That's the sort of minor speedo error usually seen in an NSX with everything standard.
That's a fast 02. The last graph attached shows a standing kilometer for NA2 6SP should take ~24secs. But I should emphasis the hard part for my MATLAB model is the first second getting off the line, where wheel spin & clutch slip are so variable. So it's possible to improve by half a second or even more. Maybe that NA2 driver just nailed that first second :smile:
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With a .914:1 fifth gear, 4.062:1 final drive ratio, and 255/40 17 rear tires (that have a diameter of 635.8 mm, right?), I calculate 160.46 mph at 8000 rpm if the tires had 0 wear and 0 slip. The tires have to slip a little to generate friction and they were probably worn at least a little when you were at Bruntingthorpe. If your rev limiter kicks in at 8080 rpm and that was a true 160 mph through the timing lights, the numbers seem to fit together very well. Your speedometer and to a lesser extent your tachometer just look a bit optimistic.
To find out your car’s real top speed, you could get a decent GPS device (not your cell phone), hop over the channel, drive through the Netherlands, and enjoy the A31 right after the border. Car magazine ranked that as one of the best stretches of Autobahn there is for pure speed. From England, you could drive over on a Saturday, enjoy some high speed driving Sunday morning, and head back home in the afternoon. Posers aside, almost every sports car owner in the world would probably enjoy spending a weekend like that at least once in their lives. And just as a note, the highway death rate per 1000 miles driven is lower in Germany than it is in the US, despite the higher speeds driven.
Edit: you mentioned that your speedometer reads about 179 mph when the timing lights measure you at an actual 164. So your speedometer overreads by about 9.1%, right? Based on that, when you’re actually going 160 at the rev limiter in fifth gear, your speedometer should be showing a hair under 175 mph. Does that sound right?
In the picture of your instrument cluster in post #84, your tachometer shows about 8000 rpm at an indicated 164 mph in fifth gear. So if your speedometer indicates 174.5 mph in fifth, your tachometer needle should be hovering around 8500 rpm. If that’s right, I guess your speedometer and tachometer are more than just a bit optimistic. If the speedometer overreads by 9.1% and the tachometer by 6.4% and they show 175 mph and 8500 rpm when you’re actually going 160 mph at 8080 rpm, that's actually quite a lot of difference.
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There is no way my car as standard would hit 170 in an extra 0.3 miles of runway - 165 maybe.
According to sparky’s “6SP velocity vs distance.pdf” chart in post #91, a six speed NSX should be able to accelerate from 85 to about 166 mph within 1.7 miles. To get up to its top speed of 175 mph, it’ll take about 4 ½ miles, however. Even if those numbers don’t quite match up with what you’ve seen in real life at Bruntingthorpe, the take-away is that the last 10-15 mph come very slowly and you need a really long straight to max out your car.
Noel, I'm hoping to convince you your car is actually performing very close to an ideal NA2. The subtleties needed to do top speed and the fine tolerances that each make a difference in reported speed mean it's a real engineering challenge to set the car up and then accurately measure the run . For example here are just a few factors that would need to be resolved to explain the 5-10mph differences you seem concerned about:
1) if you entered started the 1.7mile runway "at around 80-90" .... was it 80? or 90? or 84?
2) is the runway really exactly 1.7 miles, or is it 1.67 miles? or 1.72 miles?
3) when exactly did you start braking, 300 meters before end of strip? 200m? 100m?
4) what was total weight of the car and driver etc? Are you heavy driver? did you have a full tank or empty? (my model uses 1410kg)
5) did you change gear at the ideal rpm point for maximum acceleration? (not necessarily 8000rpm)
6) how long did each change take? (my model uses 0.25 secs)
7) was your fuel perfect with no minor impurities? (commercial fuel is not always as pure as we think)?
8) was their a headwind or crosswind?
9) what was the air temperature and density (model assumes 20 degrees C and 1.210 kg/meter cubed) ?
10) is your car completely stock? for example even wider tyres can worsen the coefficient of drag
11) how accurate are all the measuring sensors and devices being used?
I could go on but that should be enough to get the idea. I'm not suggesting you answer all these questions.
Once I understood these ideas and especially the reality of how long it takes to get from 165 to 175 mph, I realised my cars performance (in similar tests to yours in the outback roads of the Northern Territory down here, when there were no spped limits :smile: ) was actually damn good - the small differences could be explained.
Note I did not list "engine not performing to specification" which is another the obvious possibility, but the one we tend to blame first!
The one thing I do know is that Honda engineers would have taken all these ideas into account, plus many more factors, before testing, measuring and publishing the top speed of the NSX.
Are you convinced ? :smile:
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I don't doubt my car is close to an NA2 (although not as powerful as the early 3.2s it would seem). I just don't think a standard 02+ will do 175 - I estimate that requires ~230bhp at the wheels which mine doesn't make (when standard) at 7000rpm.
1. It makes very little difference to the speed between the beams. Some cars stopped at the start of the runway to do a check and they were only few mph slower.
2. Around 1.7 to the timing beams - depending on how fast the other cars are - some are very quick! Total length around 2 miles.
http://www.evo.co.uk/news/evonews/251362/9ff_gt9r_crash.html
3. After the timing beams
4. Weight makes very little difference at those speeds - it's all about drag - my car when standard was 1350kg with 3/8 tank of fuel (we used a whole tank over the day), and I'm around 100kg
5. The optimum gearchange is as close to the limiter as possible for my car (4th to 5th just slightly shy) based on dyno and gear ratios
6. Sometimes flat shifting - that gave me an extra 1mph!
7. Same fuel as when car was dynoed, and the other 02+ NSX got similar speeds
8. We've been on more than one occasion - weather varies.
9. See 8
10. It was completely stock when I was getting 161-162mph.
I'll try and take a datalogger next time (even though car is now not standard), and we should be able to get an idea of how the car accelerates once in top. I'm not sure how flat the runway is - you definitely go over a slight crest around the 150mph mark.
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that's a damn good estimate, the model reports peak power at wheels of 231.69hp @ 7,330 rpm. But that's based on my drive train efficency figure of 80%, meaning 20% losses. I've read others claim only 19%, but I've found 20% gives 0-100kph and 1/4 miles times that match official Honda figures. I have to say ... 230hp at the wheels doesn't strike me as unlikely for a stock NA2.
True for top speed, but weight is relevant for the standing km times, e.g. that ’02 NSX may be extra light, hence explaining much about that fast 22.8 sec run.
:smile: :smile:
Sounds good, let us know how it goes
Maybe you can get a run each way, to average out slope factor ?
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