Paper weights are worth more now
- Thread starter pagrunt
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15 years ago, my favorite gears of all time in my 2+2 were 2.50's. Zero to 60 sucked and I burned out multiple clutches driving it around... but from 110 to 160 it was faster than a C5 Z06 and bus lengths ahead of Camaro/Mustangs at mile events, because it could run 170 mph without shifting into OD. That shift into OD was a killer.
I paid $100 for the 2:41 7.5 I'm using. But I do have the 3:73 open that came in the car, also a 7.5... if anyone is feeling needy and generous.
How much $ are parts to rebuild a diff and what's it cost to change the ratio? What ratio options are available for the various OE ratios? Is it cost effective to install a new posi unit while changing the ratio? Is there a website with any of this?
I anticipate no more than 350 whp behind a 4L60E and street tires; am I right that a 7.5" should be adequate?
Inquiring minds want to know.
Cheers - Gary
I anticipate no more than 350 whp behind a 4L60E and street tires; am I right that a 7.5" should be adequate?
Inquiring minds want to know.
Cheers - Gary
Bearing kit and gears can be had for well under $200. Gear choices are based on the series carrier - 2 series, 3.08 and numerically lower and 3 series, 3.23 and numerically higher. There are spacers and various gear sets that can be purchased to run 3 series gears on a 2 series carrier, but step one is determining what gear ratio you want based on your transmission top gear ratio and tire size. Most transmission's top gear ratio are in the .65-.72 area which doesn't equate into much of a difference, so the next factor is tire size. Stock G-body 14" tires are dinky, hence the high gear ratios. Installing a tire 3-4" taller creates the bulk of the issue, hence the need for a rear gear ratio change. Couple this with a trans swap to an OD transmission and the gear change is an absolute must. All of this, coupled with your engine's 'happy spot' in rpm range, will decide the gear ratio that will best suit your need.
Where is your engine's 'happy spot' and what size tires are you going to be running?
Regarding your question of durability for a 350HP build, yes it will be adequate without an issue.
Where is your engine's 'happy spot' and what size tires are you going to be running?
Regarding your question of durability for a 350HP build, yes it will be adequate without an issue.
A 2.40 gear with a TH350 and a loose, lockup converter (3000 stall) would be a good street combo. No the converter wouldn't be $200 like a non lockup 3000 stall and 3.42 gears would be a would be .3 second quicker at the track (then you'd have to buy better tires), but you could use a cheap TH350 and still get reasonable gas mileage @ 70 mph on the highway.
For a low budget driver build, I would pick a 2.40 gear posi over over a 3.73 geared non posi.
For a low budget driver build, I would pick a 2.40 gear posi over over a 3.73 geared non posi.
Unless someone was "powering out of a corner" at 140 mph plus, I can't imagine any timed, circuit event where any 2 series rear would be better than Every 3 series rear. 3 series FTW in every case.
It really is a balancing act and there is some math involved but thanks to the wonders of the interwebz, there are plenty of calculators available.
For instance, my Cutlass was born with a 305/TH200/2.29 open. I played with the calculators a bit and ended up with the same 305 but now with a 200-4R in front of a 3.42 posi. My cruise RPM and MPG are still exactly the same but it felt like I added 100 horsepower at the stoplights.
There's no way that 305 will ever break the 7.5 but I'm the kind of guy who likes to keep spares around. They aren't making these rearends anymore and a complete one, especially with a posi, for a couple hundred bucks isn't bad to have in the corner of the garage.
For instance, my Cutlass was born with a 305/TH200/2.29 open. I played with the calculators a bit and ended up with the same 305 but now with a 200-4R in front of a 3.42 posi. My cruise RPM and MPG are still exactly the same but it felt like I added 100 horsepower at the stoplights.
There's no way that 305 will ever break the 7.5 but I'm the kind of guy who likes to keep spares around. They aren't making these rearends anymore and a complete one, especially with a posi, for a couple hundred bucks isn't bad to have in the corner of the garage.
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