NSX Mods.

[Khuang]

ang

Originally posted by biophase:
OK, Im late to this thread but I'm also confused here.

If you have 2 NSXs with identical trap speeds in the 1/4, why can't they both get the same ET (or at least close) if both are launched the same?

Nsxtacy, you mention that the CTSC probably took 2 full seconds off the 1/4. Are you saying a stock 91 NSX does 15.1 and a stock 93 does 14.4? I thought the 13.1 time was a little slow for a CTSC NSX.

The six speed with R&P will accelerate out of the hole alot quicker and will be in the power band longer (1-2 shift) thus the 0.7 seconds faster in the 1/4 mi. It will cover the first 300 feet in less time but the trap speed will be similiar. Take a stock Mustang and put gears in it, it probably drops 0.3 seconds yet the trap speed is the same. I have missed second gear in a Supra TT and ran 13.9@117 mph and when I ran it through the gears perfectly, it ran 13.1@117mph.

 

[nsxtasy]

you mention that the CTSC probably took 2 full seconds off the 1/4. Are you saying a stock 91 NSX does 15.1 and a stock 93 does 14.4? I thought the 13.1 time was a little slow for a CTSC NSX.

According to the numbers in http://www.nsxprime.com/FAQ/Performance/gears.htm the stock 5-speed reaches 110 mph after 15.66 seconds, and 112 mph after around 16 seconds. Khuang reported reaching the same speed in 12.4 to 13.1 seconds.

I should not have said that the SC improves the time in the quarter mile by two seconds, but rather, that it improves the time to that speed (112 mph) by two seconds (or more). Sorry.

As far as quarter-mile times, the magazine tests at http://www.nsxprime.com/FAQ/Technical/performancenums.htm show the stock 5-speed doing the quarter in high thirteens at 103 mph, give or take, and that is consistent with the numbers in the FAQ chart.

Look closer at the chart and you can see that it predicts a gain in the quarter-mile of more than a full second from adding 20 hp (much less hp than the supercharger adds), and virtually no gain from changing the gearing. My guess is that most of the difference between the 12.4-second quarter-mile cited above and the 13.1-second figure was simply due to either (a) differences in power from one car to another*, or (b) a better launch on one try than on another. The numbers in that analysis show that gearing by itself just isn't capable of accounting for that big a difference.

* For an example of differences from one NSX to another, check out http://www.nsxprime.com/FAQ/Performance/measure.htm Two different stock NSX's were dynoed with a difference of 13 hp between them. Other dyno tests of similarly-equipped NSX's have shown that this is not unusual.

 

[1BADNSX]

Ken (nsxtsy) wrote:

"Look closer at the chart and you can see that it predicts a gain in the quarter-mile of more than a full second from adding 20 hp (much less hp than the supercharger adds), and virtually no gain from changing the gearing. My guess is that most of the difference between the 12.4-second quarter-mile cited above and the 13.1-second figure was simply due to either (a) differences in power from one car to another*, or (b) a better launch on one try than on another. The numbers in that analysis show that gearing by
itself just isn't capable of accounting for that big a difference."

I agree with a portion of this post and since I did the numerical calculations quoted, I need to reply. The "numbers" chart in the FAQ doesn't list 1/4 mile time and I assume nsxtsy is trying to estimate it by looking at the time it takes to reach a given speed, which you can not do. Time to distance needs to be integrated over time and I did this in the new "numbers" chart that was published in the latest NSX Driver Newsletter. But it is not currently in the FAQ (I should give Lud the new table). The new chart also gives the 6-speed comparison with and without the 4.55, and the calculation was improved by using actual dynameter data.

Because the amount of time it takes to reach a certain distance is propotional to the square root of acceleration, while the time it takes to reach a given seed is directly proportional to acceleration. This forces you to make big performance improvements to impact 1/4 time significantly. For intance, if you doubled your acceleration rate, your zero-to-100mph time would be cut in half, while your 1/4 mile time would only decrease 29%. You can see this effect just by comparing the 1/4 mile time of a Civic to the NSX. Percentage wise the 1/4 mile time doesn't drop much compared to the acceleration. Well after all of that, how much should a horsepower increase or gearing change help the 1/4 mile time with all things being equal.

My calculations show a stock 91 NSX to have a quarter mile time of 13.67. Not counting reaction time or anything like that, just a straight comparison between cases. Adding the 6-speed and 4.55R&P reduce that to 13.36 seconds. Adding 15 HP, but not changing the gearing yields 13.35 seconds. So I do agree with nsxtsy that the gearing change by itself wouldn't make 1 second improvements and there are certainly other factors to explain the example above. But I think a 0.31 second improvement in 1/4 mile time and 0.57 second improvement in 0-60mph time is pretty good for a gearing change and if I had the money I would do it!

Bob Butler

 

[nsxtasy]

I think a 0.31 second improvement in 1/4 mile time and 0.57 second improvement in 0-60mph time is pretty good for a gearing change and if I had the money I would do it!

I didn't mean to imply that the gearing changes do nothing to acceleration, only that they pale in comparison with a supercharger.

Keep in mind how gearing changes work. They improve acceleration at certain ranges of speed by keeping you in the powerband. However, they also hurt acceleration at other ranges of speed because they force you to upshift sooner, at which point you're in a higher gear. The stock five-speed does have a flat spot (wide gap) after the 1-2 upshift caused by a drop in revs out of the VTEC powerband. Using the six-speed or the short gears with the five-speed does indeed eliminate this flat spot and improve acceleration in the 40-60 mph range. Those gearing changes do hurt acceleration (compared with the stock five-speed) by introducing an upshift at a lower speed, because the stock five-speed is still in the VTEC powerband of second gear from, say, 70 to 80 mph while the six-speed or short gears have upshifted to third and thus have poorer acceleration (torque at the wheels) due to the gearing change introduced by the earlier upshift from second to third. That's why 0-60 time is improved by a third of a second but 0-80 time is not.

As Bob points out, the improvement from gearing is similar to adding 15 hp to the car. A supercharger adds 60 hp to the car - four times the hp, at much less than four times the cost. So the supercharger has more "bang for the buck".

OTOH, if the cost is not an issue, you can always do both.