Join Date: Nov 2007
Location: Whitmore Lk., MI
05 6 sp. with 4.56 gears, ZR1 clutch, Edelbrock intake, Lunati cam, Crane rockers, C6 modified pan
Rear Axle Gear Swap Info
This subject seems to come up again and again and again. This past week there have been two threads dedicated to this subject, and that is about typical over the past several years. My thought here is that maybe we can consolidate a lot of pertinent info into one place, then direct questions to it, rather than constantly repeating part #s, opinions, etc.
The question most frequently asked is, which is the "best" gear for the SSR. First of all, though we all own one, there's actually three different models to consider. They all share the same basic platform, with similar base weight and identical 3.73/1 axle ratios. All the automatic models have a .70 4th gear which converts to, a 2.61/1 final drive ratio. Couple that with 29.3" drive tires and you can understand why the automatics are lazy, off the line. The stick versions have a .57 6th gear which converts to a ridiculous 2.13/1 final drive ratio - it's no wonder they're hard on clutches! At 2000 rpm in high gear an automatic ( with no convertor slippage and no tire growth ) would be going around 66.5 mph. A stick, at the same rpm, would be going around 81.5 mph. To me, the stick is very poorly geared and demands a change. Getting back to the 3 models, the two different engines can influence your gear choice also. The LM4 makes 300 hp @ 5200 rpm, while making 331 #ft. @ 4000 rpm. The LS2 makes 395 hp @ 5700 rpm and 405 #ft. @ 4000 rpm. So, the LS2 has 74 #ft. additional torque at the same rpm as the LM4 - that's significant. With the 03/04, if it's increased performance that you're seeking, I believe the 4.56 is the best choice. The best compromise ratio would be a 4.30, with the 4.10 giving the least bang for the buck. If you get into blowers or convertor changes, then it's another story entirely. The 05/06 autos, with their increased torque, would probably handle the 4.30 real nicely. After 5 yrs. on my 4.56s, in my 6 sp., I wouldn't consider anything else.
Here's a few part #s to start the list:
MGR-GM9-5-456. That's A Motive Gear 4.56 for the 9.5" stick axle, from Summit. It's been in mine for 5 yrs. and 40k miles with no issues.
MGR-GM10-430. Motive Gear, 4.30 for the 8.5" axle, also from Summit. One of the forum members, that I talked with, went with that ratio and picked up around a half second in the 1/4 mile in his 04.
Feel free to add good and bad part #s along with recommended installers, and people to stay away from. Good installation has a LOT to do with the outcome.
If you want to play around with some #s, this old formula works well:
MPH = RPM x tire diameter x 2.96 divided by gear ratio x 1000.
"Strive for perfection in everything. Take the best that exists and make it better. If it doesn't exist, create it. Accept nothing nearly right or good enough."
Sir Henry Royce, of Rolls-Royce