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1987-1991 Parley with regards to your 1987 to 1991 Bonneville, Olds 88 or Buick Le Sabre Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 09-05-2004, 12:35 PM   #1
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Even after I got my tranny rebuilt I still think there might be a problem with it, or something.

Does anyone know what my RPM should be in final gear while doing 110kph on a level streach of highway?

I have the GX3 with 3.33 final drive ratio.
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Old 09-05-2004, 01:11 PM   #2
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Not awfully sure for 110... I do it at 2100, maybe. Haven't checked my RPO codes lately; junk in the trunk and I'm lazy to move it... the last time I looked, I didn't know to look for GX3.

100km/h is done at 1950-2000rpm (at or a *hair* below 2k).

One time, neither me or dad noticed we had it out of overdrive as we went on the highway... 100km/h is done at 2500rpm pretty much on the dot in 3rd gear. OD was engaged after that, because 2500 brings a very audible exhaust resonance... that, and 1700-1800rpm. But I digress.
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Old 09-06-2004, 11:53 AM   #3
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Thimk my cars have a 2.97. 1425 @50 mph, almost exactly 35 mph/1000 rpm. 3.33 will be 10% slower - 31.5 mph/1000 rpm. Tire size will also be a factor.
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Old 09-06-2004, 12:00 PM   #4
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I know there is some math that can figure it out.. but as always I don't know the equation. I am sure someone here would know.


-justin
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Old 09-06-2004, 12:10 PM   #5
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I'm pretty sure the tire size is stock... but I'll 2x check today.

As for conversions... (for you Americans)
90 kph = 55.9234073 mph
100 kph = 62.1371192 mph
110 kph = 68.3508311 mph
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Old 09-06-2004, 02:33 PM   #6
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I have the math to figure it out....
What'* your tire size? 225/60R16?
I'm just gong to assume the 4T60 has the same ratios as the 60-e and 65-e.
68.3508311 mph eh? That'll take a bit.
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Old 09-06-2004, 03:08 PM   #7
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Stock is 215/60R16 in the SSE. Though I'll be getting some 225/60R16'* before winter.
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Old 09-06-2004, 03:50 PM   #8
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215/60R16'* are 82.17614799389994596986536 inches in circumference so you should be doing:

5825.1391840930560989062429099365 rpm in first
3126.9490724607709562084864391039 rpm in second
1994.2277247836549465615347175408 rpm in third
1405.9305459724767373258819758662 rpm in fourth

at 110 kph = 68.3508311 mph

That'* figuring no load, basically cruising with the tires at full pressure. And it doesn't account for transmission wear, fluid viscosity... It'* just purely tire size and gear ratio.
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Old 09-06-2004, 04:16 PM   #9
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Ok... tire sizes are stock....

Here'* the results from my latest run...
2000rpm @ 90 kph = 55.9234073 mph
2250rpm @ 100 kph = 62.1371192 mph
2400rpm @ 110 kph = 68.3508311 mph

Somethings of note.... OD does not kick in until 75kph (75 kph = 46.6028394 mph)
RPM is 2300 @ 70kph, just before OD kicks in.
RPM is 1900 @ 75kph when OD kicks in.

Do these numbers sound right? or are the RPMs high... I'm thinking the RPMs are high.
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Old 09-06-2004, 04:23 PM   #10
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That can't be just tires. Something is wrong. (it'* not my numbers)
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