Rear Axle Gear Swap Info

Topspin · 06-03-2011, 08:56 PM

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.

Cash · 06-03-2011, 09:49 PM

2006 6sp - I installed Yukon GM9.5 456 gears.
American Axle 4.56's were not available for the 6sp and as I was going to be the "novice" installer I wanted to give myself the best chance of having quiet gears. By that I mean I bought the most expensive gears with the best reputation I could find so that if they were noisy 99% chance it would be the installers fault. Fortunately they are quiet as can be and I am quite pleased with them.

JOHN317 · 06-03-2011, 11:08 PM

Topspin, I had a feeling you were lurking back somewhere with the straight dope as usual.

xs-cash · 06-04-2011, 09:11 AM

great post topspin!!
i agree that 03-04 nedd 4.56 , mine have been in mine for 4 years.

Topspin · 06-04-2011, 10:24 AM

Hey, Thanks guys, though John your choice of the word dope gives me pause?!

I've noticed some guys, when thinking of changing gears, relate back to the 60s and 70s and remember how miserable the 4.11s were on the street. Consequently they're very leery of sticking 4.56s in their R. The two situations are not very comparable because of two distinct differences. Back in the day, all the popular auto and stick transmissions had no overdrive - simply 1 to 1 high gear. Also, the popular F70 wide oval tires were just 27" in diameter. Now, using the 2000 rpm from my first post, here's how they compare in high gear. An old 70 Mustang with 4.11 gears and the F70-15 rear tire would be going 39 mph ( in high gear ) compared to my R with 4.56s going 66 mph in high gear. An auto. equipped R, with 4.56s, would be going 54 - 15 mph faster! Obviously, the overdrive trans. and the tall drive tires minimize the cruising impact of the gear change in our rides! The stock gearing in the early muscle cars tended to be around 3.5, and even that was worse than our Rs with 4.56s. That same Mustang with 3.5s would be going 45 mph in high gear. I guess my point is, don't be afraid of a gear change in our cars, as it's nothing like the " old days ".

Cash · 06-04-2011, 10:45 AM

My 4.56's are such a dramatic improvement over the 3.73's and I really like them but I can't help but wonder if something like the 4.30 might be the ideal for the average driver that isn't necessarily wanting to haul azz. I have not driven anything but the 3.73 and the 4.56 so certainly can't judge the options in between. With the 4.56's I often find myself in 4th gear at times when it seems real odd to be in that high of a gear.

Topspin · 06-04-2011, 11:42 AM

$, I don't believe the 4.30 is an option for us stick guys. I've only seen it offered for the 8.5" axle, unfortunately. As far as doing a lot of cruising in 4th gear, that's a real good thing as the transmission is most efficient in 4th when it's not "driving" the cluster or countershaft.

Topspin · 09-08-2011, 08:02 AM

Bump for Team Tall.

Cash · 09-08-2011, 01:34 PM

From Post #1.
Here's a few part #s to start the list:
MGR-GM-5-456.

Hey Topspin, I think you might have done a typo. Pretty sure (but not positive) that should be MGR-GM9.5-456.

Topspin · 09-08-2011, 02:38 PM

Right you are $, skipped the 9 - Thanks, will correct post #1.

shakemyhand · 09-08-2011, 04:31 PM

Quote:

Originally Posted by Topspin

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.

Hi Ken, After just reading your thread I'm still not sure what gear to use. I know for sure that I'm not going to go with the 4:10 like I was going to do. I'm really leaning towards the 4:30's now. I have a 2004 and I don't see me ever spending the money to put a Magnacharger on it, so whatever I go with will stay in it. But I still think about the 4:56's most of my driving is around town, but I don't want to limit myself to that. If I decide to take a trip back to Michigan I want to be able to run 75 and 80 without my engine screamin with high rpm's. What do ya think? Thanks, Ken.

TEAM TALL · 09-08-2011, 04:50 PM

Thanks for the bump with Topspin, haha! With my auto and considering I do 99% highway driving the 4.30s would probably be my best choice or do I need another bump? Would that not make my final drive ratio pretty close to a 6sp with 4.56s?

xs-cash · 09-08-2011, 06:31 PM

Quote:

Originally Posted by shakemyhand

Hi Ken, After just reading your thread I'm still not sure what gear to use. I know for sure that I'm not going to go with the 4:10 like I was going to do. I'm really leaning towards the 4:30's now. I have a 2004 and I don't see me ever spending the money to put a Magnacharger on it, so whatever I go with will stay in it. But I still think about the 4:56's most of my driving is around town, but I don't want to limit myself to that. If I decide to take a trip back to Michigan I want to be able to run 75 and 80 without my engine screamin with high rpm's. What do ya think? Thanks, Ken.

80 mph=3000 rpm,just drove 3000 miles, not an issue for me.
i'm still in flagstaff & have 2000 miles to go home.

Topspin · 09-08-2011, 08:49 PM

Hey Mike, how's that new knee doing? My feeling is that the 4.30 would suit your needs perfectly. Final drive @ 3.01 would give you 79 mph @ 2750 rpm - not excessive by any means. I always like to keep my cruise rpm under 3000 rpm, for no really good reason other than it has a more comforting sound to me.

Team Tall, tell me about your name - b. ball or v. ball perhaps? I was surprised, when I did the math, that the two combos weren't as close as expected. My 4.56 stick final drive is 2.60, while the 4.30 auto combo is at 3.01. Doesn't sound like much, but the stick goes 8 mph faster @ 2000 rpm in high gear. I still like the 4.30 as the best compromise ratio, for the auto guys.

TEAM TALL · 09-09-2011, 09:22 AM

Thanks Topspin, I will add a Magna one day and I think the 4.30s are my best choice, you agree? I see you are a Detroit fan, good team to be cheering for the last couple of decades. I am unfortunately a Canuck fan but Boston is my eastern team as I went to school with Cam Neely, so the Cup Final was bitter sweet last year. The name came from my old crotch rocket buddies as I am 6'8" and yes was forced to play b.ball and v.ball back in high school and college. I would have a 6sp if my legs were not so long which makes the clutch very cramped to use. As for football, unfortunately I am a Seahawks fan as my dad was as season ticket holder and I had my first beer in the Kingdome. Cheers!

abadssr · 09-09-2011, 10:54 AM

So just for $hits and grins what are the 04 s getting with 4.10,4.30,4.56 gear ratios for fuel mileage on th city and highway with all other variables being in stock form

sprooney · 09-09-2011, 11:59 AM

I too would be most interested to see what mileage people get with the different gear ratios

Topspin · 09-09-2011, 12:58 PM

Yep T.T., I agree that 4.30s would be a nice fit for your ride. Only other thing worth mentioning is that speedo corrections are somewhat challenging for the 05/06 models. Custom tuning is needed to accomplish that.

I'm sorry, but somehow I just can't imagine 6'8" on a crotch rocket??!!

As both a Wings and hockey fan, I'm saddened by the plane crash in Russia. Both Ruslan Salei and Brad McCrimmon were with the Wings last season. Quite a few other former NHL players were also lost!

I don't know your age, but you playing any v. ball still? I'm still playing some tournaments @ 62 and, all things considered, feeling pretty good.

Topspin · 09-09-2011, 01:04 PM

Having a six speed, obviously I can't comment on the auto's mileage. But, mine with 4.56s does slightly better, at highway speeds, than with the stock gearing. I no longer find myself downshifting into 5th on the slightest grade. If you're going 80 mph or slower it sure won't hurt mileage any!

Topspin · 10-18-2011, 08:10 PM

Bump for Kevin

xs-cash · 10-18-2011, 08:39 PM

Quote:

Originally Posted by sprooney

I too would be most interested to see what mileage people get with the different gear ratios

as for mileage, no real differece in mine, all i will say is if anyone out there has an 03-04 and wants more performance, put in the 4.56 & a tune!!! you will not be dissapointed!!
then anything else you decide to modify at a later date will just be enhanced by the gears!!
i've had my gears in mine almost 5 yrs now, best thing i've done to it, and i drove to flagstaff at 75-85 mph,i dont keep track of gas mileage, but if i had to guess i'd say 20-22 mpg.

ZoomAddict · 10-18-2011, 11:54 PM

Recently changed to 4.10 in the manual '05. Thought the mileage would drop but it is close to the same (about the same on the highway and one mpg better in the city). More nimble & fun to drive with this ratio, IMO it should have come from the factory with 4.10 or 4.30.

Topspin · 10-19-2011, 07:45 AM

Hey Zoom, I totally agree with you that 4.10s should have been the stock ratio for the 6 sp. for certain and probably for the autos, too. I know when I ordered mine the 4.10 was listed as an option and I tried to order it, but was unsuccessful.

true520 · 10-24-2011, 02:22 PM

I put the 4.56 in my 05 6spd. I am really pleased with the difference too!

I looked up the info for another guy the other day too and

I found the order slip from where I got my 4.56 gears.

Ordered them from Summit Racing at 800-230-3030
Part# MGR-GM9-5-456 GM R&P 14 Bolt 9.5
RAT-429k BASIC INSTALLATION KIT

the shipping label didnt have the prices...but it seems like it all was around 300. I ordered the gearing and the installation kit.

Misterdiggs · 10-25-2011, 06:11 PM

Guys, I changed my 3.73 gears to 4.30 Motive in my 05 automatic. I'm turning 2000 rpm at 60 mph. The gas mileage with a 93 octane tune went from 17 mpg to 20 mpg on the highway and 18 to 19 when playing around with it. Topspin is right. The gear change is the best modification for the money you can make to the R. The gear cnange really made it come alive at bottom end. I also installed headers with high flow cats and have the check engine light. Can anyone tell me who I can get to turn off the down stream oxygen sensors and calibrate the odometer. Thanks Topspin for the information you posted that led me to the gear change. Good job.

Topspin · 10-25-2011, 08:41 PM

Mr. D, Thanks for the feedback, and I'm glad the thread was of some benefit to you. Your mileage #s should reinforce how beneficial a gear swap can be! Don't know of a tuner in your area, but Bryan Herter @ PCM4less can certainly do the needed corrections.

Steve Guy · 10-25-2011, 08:48 PM

Topspin,
The information the past couple of days has been great. Have an 06 with auto. tranny, ordered the 4.30 today from Summit (those guys probably owe you a commission). Know of any one in the Wichita, or Denver area that has worked on R's? I would be interested in a cam and assorted necessaties, and also a tune after we get the 4.30's installed.

Misterdiggs · 10-26-2011, 03:18 AM

Topspin, Thanks for the information on the corrections.

eric-mpd · 10-26-2011, 06:40 AM

Lot of insight here for when I start doing the mechanicals on my SSR. Thanks.

Topspin · 10-26-2011, 07:49 AM

Steve, I really like the way you think - commission huh?!

Man, I really don't know who to steer you toward out in your area, but you can send your ECM to PCM4less and Bryan can do a good remote tune on it. I sent mine to him and he did the speedo correction, rev limiter adjustment, altered the fan temp. on/off points, altered the throttle delay and torque management, along with a modified general tune for my cam swap. It ran perfectly when I re-installed the ECM. By the way, Welcome to the site!

Eric, Thanks for the kind words and I'm really pleased to see you're getting an R, after all the terrific parts you've designed and produced for them. It's about 3 yrs. now, on my MPD rear spoiler, and it still looks perfect!

When are you pulling the trigger or have you already?