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quote:

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Originally posted by Camaro_Woody:
He wants to but in different rear gears. What is the top speed for 4.10 and 3.73 gears. also what has the fuel economy,

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I'm assuming that if he's considering 4.10s then the car is a 6MN...
A 6MN LS1 F-body will achieve a limited top speed of 160 mph in 5th. It can't pull its top end in 6th with the 0.50 ratio. 160 mph is reached at approx. 5300 RPM with the stock 3.42 rear gears. According to the gears chart, 160 mph would be hit at 4300 rpm in 6th with the 4.10s, with a 4 mph increment after that for every 100 rpm.
Now I know the STOCK vehicle won't pull anywhere near 4300 rpm in 6th - but it will pull 5300 rpm in 5th to reach 160 mph. So I'm thinking if that's the case, then a car with the 4.10s ought to pull 4300 rpm in 6th, based on overall drive ratios.
stock vehicle = 3.42 X 0.74 (5th) = 2.53 (overall which allows the car to reach at least 5300 rpm)
4.10 equipped vehicle = 4.10 X 0.50 (6th) = 2.05 (this is a 19% reduction in the overall ratio)

So if the stock vehicle can reach 5300 rpm in 5th (limited), and 6th with
the 4.10s is a 19% lower ratio, then I'm gong to extrapolate a 19% rpm reduction in 6th, with the 4.10s before the stock limiter kicks in. So 5300 RPM, less 19% = 4293 RPM. And 4300 RPM in 6th with the 4.10s = 160 MPH.
Theoretically (and I say this because I haven't tried it yet), I don't think you lose any top end with the 4.10s with this reasoning.
I haven't done the numbers with 3.73s, but i'm guessing they're not too far off.
As far as fuel economy is concerned, it is virtually uneffected - provided you can resis the temptation to keep your foot out of it!!
When I went to the 4.10s, I went from 32.5 MPG (Canadian gallon) to 30.5 MPG at 60-65 MPH with the cruise on. In the city, there is no difference because the engine isn't turning over any faster since you are just in the next higher gear at any given speed. There will be a need to shift a bit more, but this can be countered (if desired) by simply skipping a gear. Very frequently, I'll start in 1st, shift to 3rd and go to 5th at 40 MPH. A 3.42 car will go 1-2-3 and end up cruising at 40 MPH in 4th.
If anybody has differing thoughts or experience at 4300 rpm in 6th, please post and let's hear it from somebody who's been there!

Best regardSS,

Elie

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98 Camaro SS #C079
... a few mods
http://www.geocities.com/sselie
SSOA/TFbM/OMSC

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quote:

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Originally posted by poSSum:
What Elie said.

160 MPH in 5th is about 5300 RPM with 3.42's, 5800 RPM with 3.73's and 6300 RPM with 4.10's. So top speed in 5th with 4.10's is rev limited to about 150 MPH.

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... or 164 MPH with a 6500 rev limiter...

Best regardSS,

Elie

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98 Camaro SS #C079
... a few mods
http://www.geocities.com/sselie
SSOA/TFbM/OMSC