Chevy SSR Forum banner

1 - 20 of 36 Posts

·
Senior Privileged Member
Joined
·
4,100 Posts
Discussion Starter #1
I just fed the 05 gear ratios into my modeling software, and I can't believe I was given the right numbers.

Does an 05 6-speed SSR really only turn 1284 rpm at 60 mph??? If so, that's INSANE for this engine that:
Makes peak torque at 4400 rpm
Makes peak power at 5400 rpm
and
Redlines at 6500

Is this for real or was I given the wrong ratios?
1st = 2.66
2nd = 1.78
3rd = 1.30
4th = 1.00
5th = 0.74
6th = 0.50
Final drive ratio (stock) = 3.73

Is this is for real, then you can change to a 4.56 rear end and STILL only be doing 1570 at 60 mph, AND still have a 1st gear that goes to 46 mph!

If these ratios are correct, run don't walk to your nearest EXPERIENCED rear axle mechanic and get that 4.56 in there. We are talking 0.66 second off your 0 to 60 time and about the same off your quarter mile time. But most important of all, a truck that actually ACCELERATES in 6th gear.

Seesh. There outght to be a LAW against the kind of abuse that 1284 rpm at 60 on this engine represents. That's breaking its back. And a stock first gear that goes to 57 mph on a vehicle this heavy is laughable.

If you are by nature incredibly conservative, I could understand if you can't bring yourself to go beyond 4.11, but that will STILL get you 4/10ths off the 0 to 60 and 1/4 mile time. You just should NOT use 6th at 60 mph if you have ANY mechanical sensitivity in your heart.

No wonder GM isn't selling more of these. They put cement overshoes onto this baby with that just-shoot-me-and put-me-out-of-my-misery gearing.

By the way, the above quoted numbers are for the vehicle in Bob A's posting that makes more power than stock because of its Supermaxx headers, hi flow cats, aftermarket exhaust, and dyno tune. A STOCK SSR woulkd do proprotionately BETTER in terms of DIFFERENCE in 0 to 60 and 1.4 mile times, because proper gearing has even more impact as the power to weight ratio decreases (on my own 04 SSR with a lower power output than the 05 and with my portly weight, the difference was over a full second).

If you haven' done it, darn it, DO it! There's absolutely NO better way to spend about $850.

The engineers that let that factory gearing out the door should be put up on felony charges.

And this is the last time I sugarcoat it . . .

Jim G
 

·
Resident Rocket Scientist
Joined
·
11,997 Posts
Actually it's more like 1430 rpm at 60 in 6th gear.
4.56 bumps it to 1750 rpm.
This is based on a rolling diameter of 26.25" for the rear tire for which I did a physical check at home..

The remaining issue os getting the gear ration changed in the computer so everything else operates properly.
 

·
Registered
Joined
·
189 Posts
Jim,

That is almost correct, less than 1500 on the tach at 60 MPH. I believe 80 is still around 1800! The thing does not have enough torque at that RPM to get out of it's own way when the RPM's are that low!

BTW, is there any manufacture of after market software that can be specifically mentioned by name so that the new gearing can be programmed into the system? I for one would have the gears installed tomorrow but would like the computer corrected at the same time?

Regards,

Rob
 

·
Senior Privileged Member
Joined
·
4,100 Posts
Discussion Starter #4 (Edited)
The correct tire diameter is 29.2 inches for stock tires (unless they have changed the stock tires for the 05??).

The computer change is indeed going to be the glitch for an 05. It's easy on an 03 and 04 using either a microcomputer or one of the tuning software package/cable combos, but no one is yet shipping an 05 microcomputer or software package.

However, the Tech II that every GM dealer has for diagnostics and reflashes will be able to do the job, so you need to ask your friendly Chevrolet dealer service rep or mechanic how much he would charge you to go in and make that one change. The entire procedure, if it's anything like the software package / cable combos, will take under 10 minutes of work. The paperwork, driving in, and driving back out takes longer than the work.

Some dealers might not be willing to do it. If so, note that Chevrolet itself offers axle ratios up to 4.11 for most of its pickup trucks (normally for trailer towing), so ask how much for a package deal that includes the 4.11 GM gears, installation by an EXPERIENCED rear end mechanic ( :) , and changing of that one field in the PCM software. You might then even have a real GM warranty on the new gears!

Jim G
 

·
Premium Member
Joined
·
30 Posts
Why are you concerned by the low RPM?

For me the question is, what speed will I have if I'm at the max RPM for 6th gear.

"Evil-Twin" annoyed me last night on the highway, as it hit the RPM limiter at 263 km/h = 163 mph. ;-(

Looking forward to my SSR which should be over here in a few weeks.

Best regards,

Stefan
 

·
Resident Rocket Scientist
Joined
·
11,997 Posts
Jim,
Stock tire is the same. I could have likely hit the wrong key when putting that number into my spreadsheet since my typing skills suck..
 

·
Registered
Joined
·
541 Posts
Is this what you mean?

I was looking at Summit and they have exactly one listed for an 05 with the 6 speed - which has the 9.5", 14 bolt Torsen rear axle.

Linky

That still doesn't get the PCM corrected and I'm not sure I want the folks at my Chevy dealer in the software. They had a hard enough time getting the speaker wiring problem fixed. I have a very good local speed shop that has done work on my other truck, so installation is not a problem. Hmmmm, I wonder if he has a Tech II....

Diggs
 

·
Senior Privileged Member
Joined
·
4,100 Posts
Discussion Starter #8
Stefan: As I have explaained vefore in other posts, how a vehicle has been geared by the factory has very little to do with its actual top speed potential these days. ]

This is because the factories are gearing to get the last little bit of extra miles per gallon, instead of gearing for performance.

That modified (not stock) 05 whose dyno Bob A provided will hit the following top speeds once the speed limiter (hwoich is based on tire rating) has been disabled:

Stock 3.73 gearing: 170 @ 5385 rpm (Remember, this is a MODDED 05, not stock)
4.11 gearing: 170 @ 5934 rpm (identical speed, just at higher rpm)
4.56 gearing: 166 @ 6428 rpm (rev limited by the 6500 rpm redline, and most Americans would give up 4 mph to get 0.66 seconds off their time to hit freeway speed)

The problem with low rpm at highway speeds is that you have no appreciable actual POWER available at 60 mph. An SSR won't even gracefully accept lots of throttle at under 1500 rpm. To get ANY appreciable power, you have to be turning at least 2000 rpm, and even then this modded 05 has only 123 hp available, and a stock 05 would have LESS. And, with the stock gearing, you don't even get to 2000 rpm until about 90 mph! At that speed, 123 hp, after subtracting the power needed to overcome air and road drag, leaves you precious little power to actually ACCELERATE.

So, with the crappy stock gearing, you are forced to downshift to get power, as though you had one of those pesky high rpm Japanese eggbeaters. That's not why you buy a vehicle with a V-8! You want to be able to just hit the gas and GO.

It is also VERY hard on an engine when you force it to try to accelerate under load from low rpm. The analogy I always use is imagine two men shoveling sand from a pile into a bin. One of them is a husky guy who moves slowly, 6 shovelfuls per minute (SPM :) ), but lifts 20 lb with each shovelful. The other guy is a much smaller built "high revver" who lifts only 10 lb with each shovelful, but does it 12 times per minute.Both men move identical amounts of sand per minute, but do it completely differently.

The husky guy is your Chevrolet Silverado equipped with diesel engine. The high revver is your Chevrolet Silverado equipped with the LS2 engine you have in your SSR - which came from a SPORTSCAR.

Everything is fine until the boss tells the high revver to lift 20 lb per shovelful at 6 SPM, rather than 10 lb per shoveful at 12 SPM. He'll soon fatigue himself, and may strain his back. That's what you are doing to the LS2 when you ask it to accelerate, or even just hold steady speed up a hill or into a strong headwind. It's abuse.

It is ironic that GM builds "abuse management" into the PCM of every SSR, so that we can't abuse it, but then equips the 6-speed LS2 with this gearing.

Jim G
 

·
Senior Privileged Member
Joined
·
4,100 Posts
Discussion Starter #9
Diggs: Yes, that brand is one option. Other brands available include:
Motive Gear
Yukon
 

·
Senior Privileged Member
Joined
·
4,100 Posts
Discussion Starter #10
hdflstf: I mistyped too! :) It's actually 29.2 inches diameter. I corrected it above just now using the edit capability!

Jim G
 

·
Premium Member
Joined
·
30 Posts
Jim,

I understand your analogy. My EVO II has an RPM range to aprox 9300 RPM. The meter does not give any detail below 4000 RPM. And depending on the hill climb chalange, I install the apropriate rear differential.

So what do I have to do to get decent Autobahn performance out of my SSR over here?

What rear-axel?
What software mods?
What other mods?

thanks,

Stefan
 

·
Resident Rocket Scientist
Joined
·
11,997 Posts
Diggs said:
I was looking at Summit and they have exactly one listed for an 05 with the 6 speed - which has the 9.5", 14 bolt Torsen rear axle.

Linky

That still doesn't get the PCM corrected and I'm not sure I want the folks at my Chevy dealer in the software. They had a hard enough time getting the speaker wiring problem fixed. I have a very good local speed shop that has done work on my other truck, so installation is not a problem. Hmmmm, I wonder if he has a Tech II....

Diggs
Just a clarification. As I understand it, the rear is an Eaton not the Torsen. Whatever the case it looks like you found the right gears for it.
 

·
Senior Privileged Member
Joined
·
4,100 Posts
Discussion Starter #15
stfallet: The answers to your questions are not easy or trivial. Before even addressing them, I would need a known accurate and typical dyno cruve for an 05 SSR. I currently don't have one.

Piddler: The automatic has entirely different ratios than the 6-speed, AND a torque converter that multiplies torque whenever transmission shaft rpm is less than engine rpm.

hdflstf: You were wise in poitning out to prospective modders that the rear axle on the 05 SSR 6-speed is NOT the same axle as used on the automatic. The automatic uses the 8.6 (not 8.5) rear axle that includes traction control AND Torsen features. The 6-speed uses a larger and stronger Eaton rear axle that does NOT include traction control, and also does NOT include the wonderful Torsen differential, but rather in its place a plain old limited slip differential.

The ring and pinion sets used in the 2 different axles would NOT be the same. Be sure to get the correct one for your configuration of vehicle.

Jim G
 

·
Senior Privileged Member
Joined
·
4,100 Posts
Discussion Starter #16
There's something very wrong with "almost 1500 rpm" at 60 mph with the Tremec. And, because I am detail oriented, it has been bothering me. So, I did the calculaton manually.

It IS 1284 rpm, not anything higher, at 60 mph.

Here is the mathematical proof:

Overall ratio = primary ratio x 6th gear transmission ratio x rear axle ratio
Overall ratio = 1.0 (no primary gears) x 0.50 x 3.73
Overall ratio = 1.865

60 mph = 5280 ft/minute
But tire diameter is 29.2 inches = 2.433 ft
So tire circumference = pi x diameter = 3.14159 x 2.433 = 7.645 ft
So 60 mph = 5280 ft/minute / 7.645 ft/revolution = 690.69 rpm at the rear axle
Multiplying that by the overall ratio, we get 1.865 x 690.69 = 1288 rpm
(Ok, so I have so rounding errors, so it doesn't EXACTLY match 1284)

How are you guys getting the higher readings?

Or, is the tachometer simply optimistic? That MUCH?

Jim G
 

·
Registered
Joined
·
541 Posts
Service Information Home

hdflstf said:
Just a clarification. As I understand it, the rear is an Eaton not the Torsen. Whatever the case it looks like you found the right gears for it.
According to the CDs, the rear axle is Torsen. It does not mention the Eaton and does not differentiate between the 8.6" and the 9.5" on the description page.

I do not doubt Jim's information. Anyone that has been into the thing like he has would have the right info. At least you know why I made the statement I did above.

Diggs
 

Attachments

·
Resident Rocket Scientist
Joined
·
11,997 Posts
The CD is correct in that the standard axle is the Torsen. The catch is that the 6 speed is an option and part of that option is a different rear axle that comes with it. I'm not familiar with the CD but I would bet there is a section on options that would detail the "optional" rear axle.
 

·
Senior Privileged Member
Joined
·
4,100 Posts
Discussion Starter #20
The 05 brochure I have makes it clear:

You can choose the automatic transmission with Torsen and traxction control,

OR

You can go with the optional 6-speed with Eaton axle, limited slip diff (instead of the Torsen) and NO traction control.

Jim G
 
1 - 20 of 36 Posts
Top