5-Speed or Automatic?

[dswartz]

Keep in mind that acceleration is the result of torque. The torque curve of the automatic is actually slightly better up to 6600 rpm's then the 5-speed. By better I mean that the cams are designed to provide more low end torque. Hence the power peak is lower (6600 rpm) for the auto then the (7100 rpm) for the 5-speed. As a result the automatic potentially produces greater acceleration up to 6600 then the 5-speed.

 

[nsxtasy]

Keep in mind that acceleration is the result of torque.

Yes, acceleration is the result of torque at the wheels - which is torque at the crank multiplied by gearing.

I think there's something we've been missing here: The gear ratios are much TALLER with the automatic than the 5-speed. And taller gears mean poorer torque at the wheels, which means slower acceleration. The reason that the top speeds in each gear are similar (despite the taller gearing) is that the automatic can't rev as high (7500 vs 8000). So even though the automatic has the same peak torque as the 5-speed (210 ft-lbs), it suffers a gearing disadvantage, which means a disadvantage in torque at the wheels. The power disadvantage (252 vs 270 hp) and the gearing disadvantage are really the same concept, since they are both result from the inability of the automatic to apply the same torque at revs as high as the 5-speed.

Yes, the peak torque in the automatic occurs at a lower RPM than in the 5-speed. But it's the same amount of peak torque, and the torque curve is relatively flat. Equal torque, combined with a gearing disadvantage, results in poorer acceleration.

I still don't understand how a Level 10 transmission can change this fundamental disadvantage without changing the actual gearing. What am I missing?

 

[dswartz]

nsxtasy,

You missed part of my previous remarks. A 5-speed has a 4.06 ring & pinion while the automatic has a 4.43. The torque multipliers in 1st, 2nd, and 3rd are, therefore, 12.47, 7.01, and 4.99 for the 5-speed and 11.56, 6.49, and 4.53 for the automatic. The speeds at optimum shift points are 45, 80, and 110 for the 5-speed and 47, 78, and 117 for the automatic.

As you can see, the torque multipliers and speeds in each of the first 3 gears are similar. However, at engine speeds below 6600 rpm the automatic has slightly more torque. Therefore, a lower engine speed in each gear the automatic will have slightly greater acceleration, while at higher engine speeds in each gear the 5-speed will have slightly greater acceleration. So, as I said, up until 117 mph there's little advantage for the 5-speed. That is why, by the way, that “Car Test” shows the 0-60 times only .1 seconds different.

Now, regarding high stall speed torque converters. These provide a sling shot affect that actually amplifies the torque multiplication factor at low engine speeds in each gear. The result is faster off-the-line acceleration, as well as, during up shifts.

All that said, the potential acceleration of any car can be determined by calculating the area under the torque curve. While the 5 speed torque curve tapers off later, the automatic torque curve starts sooner resulting in almost identical acceleration potential. This potential is exploited through gearing and diminished by losses in the drive train. It is the drive train loss that has the greatest affect on the automatics performance. A Level 10 upgrade can minimize these losses resulting in equal acceleration to the 5-speed.

One more quick point about my practical experience with this theory. For 25 years I owned and raced a 71 Corvette with a Fairbanks 3 speed automatic and a B & M Torque Converter. This combination never proved to be a disadvantage on the Drag Strip or Road Race Course. Furthermore, in autocross events, it was unbeatable.

I hope I’ve answered your question.

 

[nsxtasy]

I hope I’ve answered your question.

Yes, I think it's starting to make more sense. Also thanks for figuring out the torque multiplier numbers - they are helpful as well.

Does this mean we should all abandon our 5-speeds and get automatics?

 

[hejo]

Well I had a chance to check the web while in Italy and found this has been a very informative thread for me.

Without real data I could not back up what I was finding in driving my 95 auto NSX. Like I said I've always owned manuals and had to switch to the auto because of my hip problem. I think manuals are more fun but I've been really impressed with my SportShift. It seemed to me on my spirited drives that the auto had pretty close to the same punch as the manuals. Where it lacks isn in taking off but it sounds as though the Level 10 mod will fix this problem.

The guy who drives me to the airport actually is into race cars and has been pushing me to get the level 10 upgrades. He has a reissue heavily modified AC Cobra from the factory in So. Cal. with a Jericho trany. I think he told me that it's pushing around 700hp. After getting a ride in it I'd say that trany is not for general street driving. Big clangs when shifting and whinny noise.

He told me that he's used Level 10 and that it does make a big difference. The last quote I got was about $3k for the mods. After reading this thread I'm starting to think it may be worth it. I just need to get my son through college before I can pop for my mods.

Thanks everyone for answering my questions however do you think we answered the question for the original post?

------------------
Hal Jones
Lake Oswego, Oregon
95T Blk\Blk SportShift

[This message has been edited by hejo (edited 10 May 2001).]

 

[jag]

Well,
I just took delivery of my 95 NSX-t SportShift. I had previously owned a 95 NSX-t 5 speed that I sold 3 years ago. I was hesitant to purchase an "automatic" but did so anyhow without ever driving one.

Now I know that I've only put on 200 miles or so but I am pleasantly surprised by how much I like it. In fact, I love it... the SportShift works wonderfully. I can time the shift from 1st to 2nd without any delays and the "hard" shift to 3rd or 4th is very positive.

In response to the original question, I did make the decision to purchase a "SportShift" because it was a great deal... 95 NSX-t, 11,500 miles, very low 40's. I am not disappointed!

FWIW
[I think the "SportShifts" are under rated and often badly maligned.] JMO

jag
95 NSX-t, SportShift




[This message has been edited by jag (edited 14 May 2001).]