How to tell what R&P you have?

[burnmacs]

Last night (on non public roads) I reached an indicated 170mph and that put the needle to a hair over 8000rpm. I recently purchased the car and it seems to rev high at highway speeds ~4000rpm at 80~85mph indicated. This seems pretty high so I was wondering how you can tell if you have a non stock R&P. The car is a 1991 with 275/35/18 rear tires. I am pretty sure it has NSX-R gears since the 1->2 shift puts me at a little over 5k.

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Mike
'91 NSX

 

[Larry Bastanza]

Mike,

Go here: http://www.nsxprime.com/FAQ/Performance/gears.htm

It sounds like you have short 2/3/4 and standard R&P, but that was just from a glance at the data.

HTH,
LarryB

[This message has been edited by Larry Bastanza (edited 13 September 2002).]

 

[Ojas]

Sounds like you have short gears AND non-stock R&P. The short gears give you the ~5000 rpm shift point from 1-2. From what I've read, fifth gear ratio is the same, but your hair over 8000 rpm at 170 mph (indicated) seems high for stock R&P. I don't have the numbers in front of me, but it sounds like it might have Comptech 4.55 R&P.

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ojaspatel.com/nsx

 

[Ojas]

I just noticed... Are the redline speeds in the FAQs correct????

The redline speeds for each gear with various gear sets is at follows (in MPH):

Stock US (5-speed): 45, 81, 114, 144, 186 (theoretical - top speed is of course drag-limited below 186)
Japanese "short" gears (5-speed): 40, 65, 90, 124, 166.
Stock US six speed: 46, 72, 99, 126, 155, 168

It says the numbers for "Stock US" are theoretical top speed. Is the same true for short and six speed? It does not look like it...

...Since theoretical top speed for short should be same as US (since 5th gear is same) and 6spd should have theoretical top speed in 6th gear since it has 0.72 ratio vs. 0.771 ratio (of US 5spd).

Does not make sense to me (or maybe I am just reading this chart wrong).

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ojaspatel.com/nsx

[This message has been edited by Ojas (edited 13 September 2002).]

 

[Gerard van Santen]

Hi Mike,

I am sure you don't have stock R&P.

I did 190 mph at 8,200 rpm (German highway)

Gerard

 

[tmeekins]

Most speedos read higher than the actual speed.

If you really want to calculate your R&P, use lower gear. In the top gear at those speeds, air resistance is a big factor. Just drive around in 2nd or 3rd gear and pick a speed and note what RPM you were at. As long as you know the gear ratio and your tire diamater, you should be able to calculate the R&P. I don't have the formula handy, but search the web for gear ratio calculator or something similar. There's a number of Java apps out there where you can just plug in the numbers. The result won't be perfect because your tire diameter will change with the temperature and your speedo probably isn't quite right. But with only three (?) R&P's available for the NSX, it shouldn't be hard to figure out which one. When I switched to th 4.55:1 R&P I lost nearly 20mph in 4th gear.



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Tim Meekins
1997 Yellow NSX-T
http://tmeekins.com

 

[matteni]

What private road in Florida can you do 170?

What was it like? I have done 140 several times at the track but have never done a bonzi run like that. I would have been sweating bullets...

 

[anvil]

Okay,

So somebody has to volunteer to ask the dumb questions, and I guess it is my turn.

In my misspent youth all the cars had a speedometer pickup in the transmission prior to the differential. Changing the ring and pinion gear would *not* change the indicated speed at a given rpm any more than a bigger tire would. So ....

1) Does the nsx have its speedometer pickup between the differential and the wheel?

2) Or does it pickup from a front wheel?

3) Or does it have some really sexy gps gizmo borrowed from James Bond?

I'm hoping for 3), but I'll bet it's much more ordinary than that.


anvil

 

[the nsxnut]

I have an OEM 5-speed and CT 4.55 R&P. At 4K in 5th gear, I'm indicating about 82 mph. This is consistent with what you are also describing.

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Mark H.,Atlanta
[email protected]
'91, Sebring Silver, BBSC and more...

 

[anvil]

Lud,

Years ago the standard practice was a cable attached between the speedometer and the transmission. When they went to electronic read outs, front wheel drives and mid/rear engine designs they probably changed the practice. I haven't kept up with speedometer technology.

Is the sensor on a front wheel or rear wheel?

anvil

 

[burnmacs]

Originally posted by the nsxnut:
I have an OEM 5-speed and CT 4.55 R&P. At 4K in 5th gear, I'm indicating about 82 mph. This is consistent with what you are also describing.

That's exactly what I was hoping to hear.

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Mike
'91 NSX