rear end suggestions
10-30-2018, 02:06 PM
#1
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Join Date: Oct 2018
Posts: 2
rear end suggestions
hi everyone i have a 1998 Camaro Z28 LS1 fully stock with posi 2.73 ,i would like a better launching power ,so im thinking of going to a 3.42 or a 3.73 ,l don't mine spending the extra coin on fuel, i just don't want to over rev and damage the engine in any way or a lot hum when lm on the highway. This is just a cruising car ,no track maybe a 1 1/2 hour max on the highway at one time . your suggestions or opinions will be greatly appreciated
10-30-2018, 05:02 PM
#2
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Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
Posts: 70,645
Re: rear end suggestions
You aren't likely to get responses to "tech" questions in the "CamaroZ28.com Podcast" forum - that's why it says "PLEASE do not post" here. The Podcast was discontinued several years ago.
I'll move this to "General 1967-2002 F-Body Tech" forum, where you will get more help.
With regard to the rear axle ratio, you have three choices - 3.23 (gears that came with the LS1 V8 if it has the GU5 "performance rear axle option"), 3.42, or 3.73. There's also a 4.10, but most auto trans owners do not go there. The changes in "launch" and the changes in RPM at highway cruise are simple math:
LAUNCH
The rear axle ratio multiplies the torque available at the rear wheels. Torque is what moves the car forward. The increase with each ratio, compared to your current launch with 2.73 gears, is:
3.23 gains 18% (3.23 / 2.73 = 1.18)
3.42 gains 25% (3.42 / 2.73 = 1.25)
3.73 gains 37% (3.73 / 2.73 = 1.37)
That's how much harder it's going to pull from a standing start.
CRUISE RPM @ 60 MPH in Overdrive
Approximate - This assumes stock 26" tire diameter
2.73 - 1,475 RPM
3.23 - 1,745 RPM
3.42 - 1,845 RPM
3.73 - 2,015 RPM
None of these ratios will damage anything. You will lose a bit of fuel MPG, and cruise RPM will be higher, but will not damage anything. Most auto trans owners looking for max performance settle on the 3.73 gears. You may find the car traction limited, and need stickier tires with 3.73's.
You currently have a 2-series carrier in the rear axle assembly. To run anything above 3.08 you either need to buy a thicker gear set specifically made for the 2-series carrier, but a ring gear spacer for gears made for a 3-series carrier, or you need to buy a new 3-series limited slip carrier.
You will also need to have your PCM reprogrammed with the new rear axle ratio, or your speedometer and odometer will no longer be accurate, and the programming for the auto trans shift points will be messed up.
I'll move this to "General 1967-2002 F-Body Tech" forum, where you will get more help.
With regard to the rear axle ratio, you have three choices - 3.23 (gears that came with the LS1 V8 if it has the GU5 "performance rear axle option"), 3.42, or 3.73. There's also a 4.10, but most auto trans owners do not go there. The changes in "launch" and the changes in RPM at highway cruise are simple math:
LAUNCH
The rear axle ratio multiplies the torque available at the rear wheels. Torque is what moves the car forward. The increase with each ratio, compared to your current launch with 2.73 gears, is:
3.23 gains 18% (3.23 / 2.73 = 1.18)
3.42 gains 25% (3.42 / 2.73 = 1.25)
3.73 gains 37% (3.73 / 2.73 = 1.37)
That's how much harder it's going to pull from a standing start.
CRUISE RPM @ 60 MPH in Overdrive
Approximate - This assumes stock 26" tire diameter
2.73 - 1,475 RPM
3.23 - 1,745 RPM
3.42 - 1,845 RPM
3.73 - 2,015 RPM
None of these ratios will damage anything. You will lose a bit of fuel MPG, and cruise RPM will be higher, but will not damage anything. Most auto trans owners looking for max performance settle on the 3.73 gears. You may find the car traction limited, and need stickier tires with 3.73's.
You currently have a 2-series carrier in the rear axle assembly. To run anything above 3.08 you either need to buy a thicker gear set specifically made for the 2-series carrier, but a ring gear spacer for gears made for a 3-series carrier, or you need to buy a new 3-series limited slip carrier.
You will also need to have your PCM reprogrammed with the new rear axle ratio, or your speedometer and odometer will no longer be accurate, and the programming for the auto trans shift points will be messed up.
10-31-2018, 04:10 PM
#3
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Join Date: Jul 2005
Location: Euclid,Ohio
Posts: 424
Re: rear end suggestions
^^^ that.
From many threads here and on ls1tech,accumulated MPGs averages for freeway use.
2.73-25.9
3.23-24.5
3.42-24.0
3.73-23.0
4.10-22.2
4.56-21.5
MPG is not inverse proportional to gear ratio as it was in the past with carbureted cars. Our computers do a good job managing MPG.
I'm running 4.56s with an A4 and use it for long distance travelling.
One thing 'Injuneer' didn't bring up is a torque convertor. Better performance with no change in freeway MPG.
From many threads here and on ls1tech,accumulated MPGs averages for freeway use.
2.73-25.9
3.23-24.5
3.42-24.0
3.73-23.0
4.10-22.2
4.56-21.5
MPG is not inverse proportional to gear ratio as it was in the past with carbureted cars. Our computers do a good job managing MPG.
I'm running 4.56s with an A4 and use it for long distance travelling.
One thing 'Injuneer' didn't bring up is a torque convertor. Better performance with no change in freeway MPG.
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