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· Registered
1,590 Posts
Discussion Starter · #1 ·
What are some things to look for when purchasing a new diff?
I'm in search of a 3.27 rear and found a couple for sale.

I came from the mustang world originally and we just changed gears, not the entire rear diff.

Thanks in advance.

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· Registered
3,019 Posts
why only 3.27 and not 3.45? 3.27 is not much from 2.92.

Going to do the Janetty Posi Mod? Keep from peg legging

· Registered
3,019 Posts
Fair enough. FWIW, with my 3.45, got 25+MPG on 500Mile trip last weekend if gas is a concern to you.

Yeti has a DIY write-up in this board that is fine. Can be done in < 3hrs with one person. Two folks would make it easier for sure. FWIW, while some say you can do it all by flopping only one spindle loose and then shifting the diff to pop the 2nd axle, I found it easier just to flop both spindles. Make sure you mark to arm locations to avoid having to do a alignment afterwords.

May want to look into new bushings. there is much chatter about noise (whine) with the firm bushes. I have the pedders (with holes) that work fine for me. Perhaps the softer BMR would do the same.

Posi mod is here.

You should change the oil, I went with GM oil with FM already in it.
I suggest you head over to camaro5 for additional install / bushing comments. I see you in the sale section already.

PM me your email and I'll send a .doc I used

· Registered
3,019 Posts
For all intense purposes, tire smoke is independent to diff ratio. If you only drive it like you stole it, no tire will last.

IMO, there are two reason to change ratios:
1. 1320 guys - they usually go with a ratio optimized for power band, 60ft times, tire diameters and holding a gear and at the end.

2. DD /street fun. It's apparent GM put the 2.92 to eek every little MPG out to avoid gas guzzler tax. Car still drives great. Going to a different ratio makes the car "feel" lighter when on a roll and nailing it. May make you bit quicker for the short run but not in the 1320 as documented in a few posts.

While the camaros are lighter, but not much, they come with 3.27, 3.45, 3.91 ratios. Not sure if trans ratios are different, but the "sportier" models have higher ratios.

The conventional wisdom for ratio change is the if less than 0.5, not worth it.

I went 3.45 and have no regrets. MPG may have dropped 1 or 2, but it's much more fun. And yes, tire smoke comes easier. If you are going to floor it, better have a plan before doing. In all honesty, I drive very light throttle 90% of the time. FWIW, my wife has not noticed any change in the car at all.

For me, it's the best of both worlds.

That all typed, if I was planning FI, I'd wait as the additional power may be useless as you would not hook at all...or you may have the time of your life going sideways.

Finally, if purchasing used, carefully vet out the unit. For example, if one is for sale on camaro5, do a search on the owner and read about his adventures. You may be surprised it has only 12K miles but saw 50 passes on a car with FI.

as always,
caveat Emptor

· Offshore Prositute
1,149 Posts
As I said before in another thread, depending on your mods and power levels, and what you are using it for, would depend on what you want.

It seems the OP takes it to the track, so he needs to figure out if he wants more power or not before he decides on gear ratio. I personally think at 3.45 first gear is useless.


I hope that FB link works.
Anyway, both of those are G8s I am on the right, my friend is on the left. I have the 6.2 LS3 he still has the L76 6.0. I have ported heads, 3.27 gears, and a mild cam, compared to his more aggressive came, ported and milled heads, and 3.45 gears. I am on stock 18s with 275/40/18 NT05s in the back compared to his CCW drag pack with drag tires. We both did gear swap within a few weeks of each other and it was our first time racing with the near gears. Before this race, I was at 12.1 to 12.2, he was at 11.8 to 11.9.

With the new one, I am at 11.83 and he was at 11.80, his best time. He even admitted, he should have waited on finding a good 3.27 gear as he had too much gear for first, but not enough to start in 2nd. 1st gear ratio is 4.07 (if i remember correctly)
4.07 x 2.92 = 11.88
4.07 x 3.27 = 13.31
4.07 x 3.45 = 14.04

Now lets compare it to say, a 94-97 Fbody M6, such as my brothers car
rear diff is 3.42 and 1st gear is 2.66
2.66 x 3.42 = 9.10
2.66 x 2.92 = 7.77
2.66 x 3.27 = 8.70
2.66 x 3.91 = 10.4

Look at those numbers. going from a 2.92 to a 3.27 would not be worth it, and a 3.42 which is stock is still lower than our first gear ratio stock. even the 3.91 gears are not even up to our stock gear ratio in first gear.

I really think you need to think why you want the gear change, if you want to just smoke your tires at 45 mph on the freeway, yeah go with the 3.45. If you want more usable power and a lighter feeling car, and a gear ratio.

Here is the final thing I will say though, If you like to drag race, you will have to think at what gear you will be in. If you are tuned and changed the shift point to say 6600 rpms, 3rd gear tops at 113, and 4th at 150. Well more than enough to get some power mods and not be in OD.
3.27s it is 101 and 134, Still good enough for me to never top out at 4th (i think even if I do supercharger, I will be in the high 120 mph). At 3.45 3rd is 95 and 4th is 127 mph. Right now, if I was at 3.45 I will be near the top of 4th, and going straight into OD with any power adder.

Anyway, it is up to you, but don't let people say, it isn't worth it on the 3.27s, I picked up 5mph and dropped .3 on the ET. Worth the 1k I spent on buying and paying shop labor.
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