Bruntingthorpe today 156mph

[simonprelude]

I guess this must be an NA2 then as it says it's in 5th gear ??

click for pic

[ctrlaltdelboy]

Posted by John McCain Racing NA1 6 speed. This car has a list of mods.

including the same gearbox, LSD & R&P as me

[NSXGB]

....another :?: ....what effect would it have on your top end speed by installing the 4.44 R+P?

[ctrlaltdelboy]

NSXs with std sized rear tyres - 225/50/16 91-93 and 245/40/17 94-01, which do 811 and 816 revolutions per mile respectively are geared to theoretically achieve the following:

91-93 = 189.0 MPH
94-96 = 187.8 MPH
97-01 = 201.1 MPH

whilst the car may be geared to be able to reach these speeds, the limiting factor is the wind resistance or drag, which increases on an exponential curve to rather massive amounts at these higher speeds, and the actual limiting factor is that the car does not have sufficient power to push through this opposing force.

this is the reason that better results are obtained downhill and/or with a following wind, both of which help to push through the drag a little bit.

of course by increasing the power that the car can put out you can make further inroads towards these potentially attainable higher speeds, but remember, when you look at a power curve you will see that peak power is usually a few hundred rpm below the redline, so since you really need all that power to get through the drag, and as soon as the power begins to wane you will stop accelerating through it, the real world figure to use for RPM is not in fact the max of 8000, but wherever your peak power is being made.

example dyno maps (showing wheel horsepower) are shown here:

first an N/A NSX, then a Turbo, then a Nos'd





you'll note that all 3 see power drop away after 7800 rpm, so the real world acheivable top speed should be measured from 7800 rpm despite the car being geared to achieve a greater speed in a world without wind resistance or the need to generate the power to overcome it.

at 7800 the speeds acheivable on std tyre sizes assuming that we can overcome drag are:

91-93 = 184.3 MPH
94-96 = 183.1 MPH
97-01 = 196.1 MPH

but as you increase the size of the rear tyres (and lose acceleration and handling) you increase theoretical top speed

e.g. my rear tyres are 255/40/17, which have a revs per mile figure of 806, so if my final drive were standard my theoretical top speed (TTS) would be 185.4 at 7800 rpm.

however my final drive is 4.4:1 (std is 4.062:1), so this changes my TTS to 171.2 MPH at 7800, or since air resistance is much less at this speed I might be able to push on through towards 8000rpm for a speed of 175.5 MPH

the resources you need to work out your theoretically achievable speed at any given revs in any given gear are as follows:

chosen RPM - just pick one
ratio of chosen gear - see ratios chart below
ratio of final drive - select as appropriate
revolutions per mile of your rear tyres - work it out here


gear ratios:

Japan 3.0
1st = 3.071
2nd = 1.952
3rd = 1.400
4th = 1.033
5th = 0.771

rest of world 3.0
1st = 3.071
2nd = 1.727
3rd = 1.230
4th = 0.967
5th = 0.771

all 3.2's
1st = 3.066
2nd = 1.956
3rd = 1.428
4th = 1.125
5th = 0.914
6th = 0.717

final drive ratios:
all std NSXs = 4.062:1
JDM Type-R = 4.235:1
OS Giken = 4.4:1
Comptech = 4.55:1


the equation to use is this:

divide your rpm by your gear ratio
divide the result by your final ratio to get wheel revs per minute
divide the result by your tyre's revs per mile to get mile per minute speed
multipy the result by 60 to get MPH

if anyone is still awake after all of that, I knocked up an excel spreadsheet with all the formulae pre-populated for you - you just have to enter the variables specific to your chosen/desired setup and the TTS will be displayed - you can download it from here

EDIT - REVISED VERSION NOW AVAILABLE - CLICK HERE TO DOWNLOAD

[Lankstarr]

~Judging by the sppeds I have had out of mine in 4th and the general 30mph in each gear pattern I see goin up through 2nd, 3rd and 4th I woudl say that 180+ would be reached in my 3.2 -if only I had the roads to take it there!

Had an interesting race with a Ducatti 999s, was up my ar5e all the way but didn't take me.. maybe he could have if he weanted to!?

[ctrlaltdelboy]

well there are 2 photo's of it happening further above in this thread and a comprehensive explanation of the theory just above also, so I can't see why not.

I've only seen 165 MPH in mine in std configuration at 7000rpm (uphill!) before I bottled and eased off - checking that against the spreadsheet the numbers are bang on (164.3 MPH actually). the car was still pulling strongly when I eased off and I felt confident that it would have made it to the redline ok, which would have placed it at 187.8 MPH if I had kept my foot in.

having discussed in person the speed shown in the 2nd photo above with the owner who took the photo, I have every confidence in the credibility of that being an accurate indication of the speed achieved in an UK 3.0 NSX.

[ctrlaltdelboy]

this link might be useful for those interesting in the more technical aspects of this thread

clicky the wiki

and in case you didn't notice my edit on the previous page, my gear ratio calculator has been updated and can now be downloaded from here

http://darrenferneyhough.com/ratios.xls

[trackdemon]

I think that another reasonably fair method of extrapolating the NSX's real top speed (I still stand by 165mph) is to compare to other cars of similar power...

3.0 & 3.2 NSX's have under 300bhp as standard (270-286bhp, depending what you read), the fastest 300bhp car I can think of is probably the Porsche Cayman. A Cayman S with 295bhp & better aero (than NSX) has a top speed of 171mph, a '97 993 with 285bhp 167mph. A 997 with 325bhp is quoted at 177mph, and the base 997 is a very slippery shape..... so you see I can't understand how an NSX can do the 180mph+ that some are claiming.

[sportyking]

I took my old 3.2 down the Autobahn at Easter and it made an indicated 174mph and though it was moving very slowly in the up direction, holding a car on WOT for long periods is not my cup of tea, so that was effectively top speed for me. It was never going to make 180 without the help of a good gradient.

I reckon the speedo is reasonably accurate but I never had my B2 in the car for comparison. I Assumed it was really somewhere approaching 170, which I feel is about right for the car.

[ctrlaltdelboy]

trackdemon - where oh where to begin my dear boy...

....it is true that a Cayman has a Cd figure of 0.29 which is better than the 3.2 of the early NSXs and also better than the 3.0 of the facelift version. (Although interestingly this applies only to the manual version - the tiptronic is 3.0)

however, drag is not measured by the cd figure alone;
the formula for air drag is Cd x frontal area

for the NSX, which has a frontal area of 1.78 sq.m, the air drag coefficient is:

1991-2001 models - 1.78 x 0.32 = 0.5696
2001+ models - 1.78 x 0.30 = 0.5340

compare this with the air drag coefficient of the Cayman with it's frontal area of 1.98 sq. m:

1.98 x 0.29 = 0.5742

so the air drag of the Cayman S is marginally higher than the early NSX and significantly higher than the late NSX, so has to work harder to punch through it at higher speeds than our baby

of course, it's weight of 1415kg compared to 1392kg on the early coupe's and 1340kg on the later ones is another disadvantage it's available power has to overcome on the way to reaching it's top speed, which the manufacturers spec sheet puts at 171MPH

at 295hp the Cayman S has basically the same amount of power as the NSX actually has, although the 'gentlemens agreement' means the NSX's stated figure is 276hp (280PS).

so we have established the following:

1. the Cayman S has roughly the same power as the NSX
2. the Cayman S has greater air drag to overcome than the NSX
3. the Cayman S has more weight to move than the NSX

so the chips really are stacked against the Cayman S in acheiving a higher speed than the NSX as the above demonstrates, but what of the Cayman's gearing?

well, it has a 6th gear ratio of 0.82 and a final drive of 3.88. with the driven wheels wearing 265/35/19 rubber (767 revolutions per mile) and peak power at 6250rpm.
the speed at this point would be 153MPH and through the remainder of the rev range up to the redline of 7200rpm it is making less power than it's earlier peak of 295hp (back at 153MPH), so it really is quite an acheivement to get to 171MPH with the power dwindling from 153 onwards.

so, when the Cayman is making it's peak power (whether you believe it is more than an NSX makes or not), it is doing so at a time when it is not needed (in terms of best overcoming air drag), and at the time when it does need the most power it can make, it is already spent

conversely, because of our lovely VTEC engine, the NSX is making peak power (lets call it 290hp eh?) at 7800rpm, where it's gearing allows for acheivable speeds in the 3.0 and 3.2 of 183MPH and 197MPH respectively.

whilst I can't see the 6-speed getting to 197MPH without serious power upgrades, the 5-speed seems to have it's ratios and power delivery matched perfectly to allow the driver to maximise all the potential behind and under him, and with a following wind and/or downhill run possibly keep on accelerating beyond the peak power delivery at 184MPH to the maximum geared speed at redline of 187+ (of which there are 2 pieces of photographic evidence posted in this very thread).

so the NSX has:

1. more power (at the appropriate speed/revs)
2. less weight to carry
3. less drag to overcome

than the 171MPH Cayman S - is it any surprise that it has a higher top speed?

not to me

I'm sure you can see why the NSX is so often underrated and underestimated by those who do not fully understand how the numbers work together, as it is very easy to see certain numbers which look better in isolation but in a practical application still add up to less.

for those who might want to crunch the numbers, you get speed from gears/tyres by the following equation:

engine revs / gear ratio / final drive ratio / tyre revs per mile x 60