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Re: Question.
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Posted by PGAero [Email] (#1143) [Profile/Gallery] (more from PGAero) on Fri, 17 Apr 2009 15:25:50 Share Post by Email
In Reply to: Question., moeman, Fri, 17 Apr 2009 14:36:49
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Can you find a pdf or something of the V6 torque/HP curves? And, can you get the gear ratios for me?

Those two things would allow for some quick "back of the napkin" calculations which could support or discount your hypothesis.

It would be different for each gear, since the ratios between gears are not all the same.

A quick look for the 9000 Aero (5spd):

1st gear at 5500 RPM (Red line in that engine) means the tires are spinning at:
5500/3.61/3.38 = 450.7 RPM
Let's check to see that this makes sense...(450.7 RPM*(24"/12)*pi*60/5280=32.2 mph - Checks out with reality)

Once you shift into 2nd, 450.7 RPM at the wheels...
450.7*3.61*1.76 = 2911 RPM

At 2911 RPM, the car is making maximum torque, so that's good.

So, in second gear, the car can "pull" with 1639 lbs.

But, how much was the car pulling in first? What torque would be needed for first gear to be the preferable option at 32 mph, even at red line? For that to be the case, first gear would need to be creating more than 1639 lbs.

1639 lbs = 3.61*3.38*Torque --> Torque = 119 lb*ft

The torque at red line must be below 119 lb*ft for second gear to be preferable to first at red line for the 9000 Aero, under full load, shifting from 1st to 2nd. While my 9000 Aero certainly doesn't make 258 lb*ft at red line, I happen to know that it makes more than 119 lb*ft.

What about 2nd-3rd gear shifts?
2nd gear at 5500 RPM --> 3rd gear at 3688 RPM.
3rd gear produces 1099 lbs of "pull"
What torque must 2nd gear produce at red line to be preferable to 3rd gear at the same speed?

1099 lbs = 3.61*1.76*Torque --> Torque = 173 lb*ft
Does my 9000 Aero make 173 lb*ft at red line? I think it does... I've seen dyno results for stock 9000 Aeros. I found one with a google search, but I can't post the link here.

You can do the same analysis for each gear. So, shifting at red line makes sense for my 9000 Aero. You can't say much about your V6 9-3 Aero without some more info. That being said, though, I'd be curious to know what its torque curve and gear ratios look like. You might be right about where to shift to optimize the force accelerating the car.

You certainly have given me food for thought. Thanks!

~Peter
'93 9000 Aero, 5spd, 105K

posted by 71.140.0... 
_______________________________________
Past:
'06 9-5 Combi, AT, Polar/Black
'04 9-5 Aero Wagon, AT, Nocturne/Granite
'03 9-5 Aero Wagon, 5spd, Polar/Black
'03 9-5 Aero Wagon, AT, Steel/Charcoal
'00 9-3 Viggen, 5D, Silver/Black
'93 9000 Aero, 5MT, Cirrus/Black (Owned this one twice... my favorite)
'86 900 SPG, Edwardian/Buffalo Grey
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