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Discussion Starter · #1 ·
Some of you know that I have been contemplating a change in rear axle ratio on my 04 SSR to improve nimbleness.

I may also have mentioned to a couple of you that I run a small Internet business in which I use custom performance modeling computer software to determine for my clients what re-gearing they might do, to their cars or motorcycles, to optimize the performance for THEIR target use. Naturally, I applied the normal modeling process I use for my clients to my own motorcycles, and now to the SSR.

As it turns out, the modeling software predicts pretty impressive results in the case of the SSR.

To review a bit first, the stock 3.73 axle ratio in the SSR sounds impressive, but only until you remember that this is a 4800 lb vehicle BEFORE you add fuel, driver, passenger, and other load. In addition, the SSR, like all other vehicles made to sell in the United States, is geared from the factory to try to optimize fuel mileage for a better corporate average, rather than to optimize performance. Finally, we all have different target uses and preferences for our vehicles, and I suspect that maximized fuel mileage is not high on the priority list for the typical SSR owner, if it interferes with throttle response performance.

My own preferences and target objectives are a little sporty but pretty sensible overall:

1. I never cruise, for more than a few minutes, at speeds above 78 mph (I try to stay under 5 mph over the posted limit, which on the fastest freeways is 75 mph, to make myself an unworthwhile target for a police officer to paint with radar)

2. I DO like the periodic blast up to 100 mph or so, but only on deserted country roads where “there is no one in the forest to see or hear the tree fall”.

3. I do like carving along windy, hilly, narrow country roads at speeds that are “brisk” but not anywhere near pushing any boundaries

4. I don’t ever “race”, or really “speed”, on the street or anywhere else. I value my skin and bones, my low insurance premium, and the safety of my fellow drivers too much

5. I like satisfying throttle response in the 0 to 90 mph range, WITHOUT needing to force the automatic to downshift to get it

6. I normally like lightweight vehicles, so the heavy SSR is an exception for me (I fell for the retro styling and the untypical boldness for GM!!), and the deadened throttle response caused by the weight warrants addressing

7. I LIKE the sound of a higher revving engine – it makes any vehicle more exciting, and in the case of the SSR, that sound is pretty nice – like the sound of a Ducati motorcycle engine is!

I used these criteria to do some iterative performance modeling in my software, assuming MY weight and 13 gallons of gas, and learned a few things. I have found in the past that the quick shorthand way of best expressing what I learned, without the normal 9 to 15 page modeling results report, is by giving you some 0 to 60, 0 to 100, and ¼ mile times.

My stock SSR with the 300 hp GROSS / 250 (dynoed) hp NET hp 5.3 liter and stock 3.73 ratio, 160 lb driver, and 2 gallons of fuel:
0 to 60 mph:7.61 sec
¼ mile:15.84 sec at 90 to 91 mph.
0 to 100 mph: 19.39 sec

With ME and 13 gallons of fuel aboard (a more reasonable approximation of my SSR’s actual loading, those numbers become:
0 to 60: 7.86 seconds
¼ mile: 16.04
0 to 100: 20.10

Changing from the 3,73 to a 4.11 axle ratio, but keeping everything else the same:
0 to 60: 7.43 (0.43 sec better)
¼ mile: 15.76 (0.28 sec better)
0 to 100: 19.38 (0.72 sec better)

Changing from the 4.11 to a 4.56 axle ratio, but keeping everything else the same:
0 to 60: 7.03 (0.83 sec better than stock 3.73)
¼ mile: 15.54 (0.50 sec better than stock 3.73)
0 to 100: 18.60 (1.50 sec better than stock 3.73)

Then, I looked closely at the stock internal ratios of our 460 automatic (this is for 03 and 04 SSRs, remember – the 05 auto transmission is different I believe). The internal ratios are NOT designed for performance, but rather for flexibility and the EPA mileage test. There is a HUGE drop in rpm between gears, and a particularly disastrous one on the 1st to 2nd shift, that drops the rpm from redline down to only 3200 rpm. You can imagine how low the power output is at that rpm!

So, I tried upping the rev limit from the stock 5900 to 6200. That knocked 0.15 seconds off the 0 to 60 time, regardless of which gearing I modeled. With the 4,56 gearing, that dropped the 0 to 60, even with my portly body and 13 gallons of fuel, down to 6.9 seconds (a lighter driver with 2 gallons of fuel aboard would be appreciably quicker).

So, to summarize, if I go to 4.56 gearing, and also raise the rev limit (via LS Edit at the local tuning shop), I get the following improvements:
0 to 60: -0.96 sec
¼ mile: -0.65 sec
0 to 100: -1.65 sec

That’s a HUGE improvement.

The gear swap will be done at a well respected speed shop (Lamar Walden Automotive in Atlanta, where I am apparently going to stay on a temporary contract assignment for a year or so!). That shop has done lots of rear end changes and knows the subtleties of setting the clearances RIGHT (don’ t try this at home as an amateur). Done by these pros, it will cost $850.

Now, let me ask you, where else can you get -0.96 sec in 0 to 60 time, -0.65 sec in ¼ mile time, and -1.65 sec in 0 to 100 time for only $850 parts and labor TOTAL? THIS is the performance mod bargain in the array of choices.

Yes, the rpm at highway speeds does increae by 22%. That still only means:
2198 rpm at 60 mph
2564 rpm at 70 mph
2858 at 78 mph (my absolute highest cruise speed for more than minutes at a time)
These are acceptable. Check out the rpm at 60 mph for other performance oriented cars. This is higher than many, but not as high as some with engines of comparable capability and features.

Don’t sweat the fuel mileage either. If you haven’t yet read my earlier posting on fuel mileage on this board, you might want to check it out (“Incredible but true – gas mileage vs gear ratio test”).

I think this might be THE killer “bang for the buck” mod for 03 and 04 SSRs.

Or, if you feel more conservative, go with the 4.11 ratio. It’s still pretty good results!

Naturally, a duno tuning session at the same time is a reasonable idea. Lamar himself HAS an 03 or 04 SSR, and got his up to 270 hp via a simple dyno tune.

Feedback, opinions, and criticisms?

Jim G
 

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Some very good information but I think that by increasing the gear ratio will improve tq output thus causing the tq managment to work even harder. The 4l60e is not a strong transmission to start with.


Traction permitting I think the tq managment will hurt your truck even more with the gear swap.

I turned mine off today to see what diffrence it made..HUGE but the shift was crap... Back on it went and I played with the shift pressures and speed along with top mph and rev limiter... Truck feels allot better...
 

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Discussion Starter · #3 ·
Boosted: One of the neat things about this mod is that it does NOT increase the load on the transmission at ALL.

The extra torque multiplication is occuring at the rear axle pinion and ring gear, not at the tranmission.

The engine is NOT feeding any extra torque to the transmission (we aren't changing the engine except when we do the dyno tuning in ADDITION to the gear swap).

Under FULL throttle, the transmission gets no worse torque loading to handle than before, but the rear axle needs to handle more (22% more).

Under NORMAL driving conditions, the loading on the transmission is as follows:

POWER loading, and thus heat production, is the same, since the same amount of work is being done to move the vehicle down the road.

TORQUE loading (i.e. actual twist forces on the transmision clutches) is REDUCED, since both the engine and transmision are spinning 22% faster than before the rear axle ratio swap, and power (which is the same as before) =
torque x rpm x a numerical factor.

Since rpm is increasing, and power stays the same, torque loading on the transmission DEcreases.

Jim G
 

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Hey Jim,
I think I'm going to solve my acceleration issues with about 10psi of boost from a turbo
kit from Hahn Racecraft...................available soon !

It's amazing how a turbo ''shortens'' even the tallest gears !
 

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feed Back Only

I Would Decrease My 1/4 Mile Time By 2/3 Of A Second if I Pay $850 For A Gear Ratio That Increases Engine Rpm By 22% Which Will Turn The Power Steering Pump,air Conditioning Compressor, Water Pump And Alternator 22% Faster , Decrease Fuel Mileage , Loose The Function Of Transmission Kick Down Sooner ,hassle Of Recalibrating The Speeometer, Increased Engine Noise And Exhaust Noise On The Highway.

For Me It Is Not "the Killer Bang For The Buck", But Please Take This As Feed Back Only.as It Is A Different Scenario For Each Of Us,but We Bought Ours To Cruise In And Reducing Our 1/4 Mile Time By 2/3 Of A Second Isn,t A Biggy To Me.
 

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Discussion Starter · #6 · (Edited)
41chevycoe: Most of what you list is technically correct, except the "hassle of recalibrating the speedometer" and the transmision kickdown.

Our SSR's onboard computers have a data field into which you specify the axle ratio. As soon as you change that value from 3.73 to 4.56, the speedometer, and everything else that depends on the axle ratio, is automatically recalibrated.

The transmission kickdown is also programmable, and the shop doing the install will adjust the va;ues for me as part of the job (I asked). In fact, I WANT the SSR to, among other things, hold lower gears longer (i.e. shift at higher rpm than stock) for better response AND nicer sound!

Then, you also need to look at the impacts of the accessories spnning 22% faster:

Because the water pump is spinning faster, we might actually reduce the tendency of our SSRs to run a little warm at times.

Because the AC compressor is running faster, we might cool faster and better.

Because the alternator is spinning faster, more recharging current is supplied to the battery, and battery recharging after a cold start occurs faster, so short trips at low speeds are less likely to run the battery down. (In Canada, where you live and where I am from, this is a significant plus, especially in Winnipeg where the winter temperatures are COLD!!)

The reduced fuel mileage IS partially a result of these accessories spinning faster at highway speeds. That's why the mileage does fall a bit (but as I found and explained in my other posting, probably not more than 8 to 10% with the 4.56 ratio).

I agree wth you that each of us has different objectives. In my performance modeling business, I find that very few client reports, even for riders of equal weight riding identical model motorcycles, are even close to being the same in the recommendations. Everyone has a different set of target speeds, usage, and constraints. It is what makes individual vehicles like the SSR even MORE individual.

Jim G
 

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Discussion Starter · #8 · (Edited)
Yeah, personally I like a positive displacement supercharger better than a turbo. I just like the more instant response at any rpom.

BUT, there is a HUGE difference in cost. Like $6500 minimum versus $850 . . .

Jim G
 

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Jim,
I currently own six GM vehicles that are turbocharged, in the past I played with vehicles
with roots blowers, screw type, centrifugal and by far like the turbos best. A properly
sized turbo and intercooler is tough to beat, at 8psi on a small v-8 a turbo will typically
have 100 lb. ft. of torque more. I had a 2003 Cavalier on 12psi, manual shift, in the lower gears
tach. could not keep up, absolutly no lag what so ever. We will be dynoing a twin turbo
new GTO this week, will see 500+ rwhp at only 6psi. SSR kit will be a single tuned for low end power, will not have heat soak problems like the Magnusons do.
 
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Rear End

Jim Your modeling and logic are very impressive. Can't wait to hear how the actual swap out will work. The poof is in the pudding. So we shall wait and see if the computer modeling matches the real thing! :seeya
 

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Hey, Rcik

Can the SSR handle the exhaust plumbing required? I really like the idea of putting headers on the SSR - Turbo and headers are incompatible. Does the turbo system include a better than stock exhaust?

Ray
 

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Boosted said:
Some very good information but I think that by increasing the gear ratio will improve tq output thus causing the tq managment to work even harder. The 4l60e is not a strong transmission to start with.


Traction permitting I think the tq managment will hurt your truck even more with the gear swap.

I turned mine off today to see what diffrence it made..HUGE but the shift was crap... Back on it went and I played with the shift pressures and speed along with top mph and rev limiter... Truck feels allot better...
Just used my Diablosport Predator tonight for the first time. Very impressed for what I changed "performance tune" for premium fuel and then part throttle shift firmness. What I can't seem to improve to my liking is the speed and firmness of the WOT shift. Is this related to what they show under the "torque management" parameters and what you mentioned here above. I was hoping to be able to get a real nice firm crisp 1-2 shift while under WOT. It sounds like you have experience with these functions and I'm interested in some suggestions if you can help. I have an 04 SSR with just over 375 miles.

Thanks,


Del
 

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Jim:
I'm wondering if you could run the same numbers for an 05 with the bigger motor, using just the stock gears?? I am interested in exactly how much faster the 05 is... Relating the figures for the stock 03 & 4 to my 94Z28 I find the SSR would be slower - a totally unacceptable progression - (new vehicle always has to be faster than the one it replaces). I suspect many other people would also be interested in that comparison. Thanks in advance. :seeya
 

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Discussion Starter · #15 ·
Blue6T9: It's not a trivial exercise to do this modeling.

Setting up any new vehicle for the first time is very time consuming, as I have to feed EVERY individual variable in power vs rpm curve, transmission gear ratios, weight disribution, etc into a software database first, and then run the actual iterative modeling.

The 05 power curve is completely different than the 04, and of course the 05 comes with either stick or automatic (and are the 05 automatic ratios same or different than 04?). Furthermore, I would need to find a reliably accurate and representative 05 NET actual dyno curve (not the gross factory curve).

Then, there's the actual iterative modeling to find the best 2 or 3 gearing options, and then the process of assembling the results into readable report pages that enable intelligent comparison.

It's a lot of hours of work.

Most of my current database is for motorcycles rather than cars, because I started with motorcycles first, and I only generally invest the time and effort to set up data for higher sales-volume, frequently modified vehicles where there is a reasonable chance of recovering the time and effort via multiple modeling sales.

I did the 04 SSR because I have a personal intent to do the gearing mod myself (And have now ordered the gearset)! I didn't mind sharing the results (although anyone considering the mod should remember that their actual specific results will vary by driver weight, amount of fuel aboard assumed, etc). I'm not sure I want to go through the whole exercise again right now for fun for a low volume vehicle that I don't own! It's NOT a "5 minute" exercise!

Jim G
 

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hpdjv --- Lets start a new thread on the Diablo Sport Tuner under the tech section, This way we will not hijack Jim's thread.

Sorry Jim.
 

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Discussion Starter · #17 ·
Boosted: no problem. I just subscribed to your Predator posting. Looks REALLY helpful.

Jim G
 

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You might have to worry about the power steering pump. It has an upper speed limit that you might exceed with 4.56. You definitely will have higher temperatures in the power steering fluid. Therefore, a larger P/S pulley should be used.
 

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Discussion Starter · #19 ·
freezer: I appreciate the heads up on the power steering pump!

One thing that encourages me is that I did a fair bit of research on OTHER models of Chevy trucks using this same 5.3 L engine, as part of my preparations. Chevy actually offers as a factory option a 4.11 axle ratio just for the asking, on their pickups, for use in trailer towing. The 4.56 axle is only 11% higher than the 4.11, and I`m sure the safety factor on that power steering pump is at least that high.

Jim G
 

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Jim do you plan on running the motor past say 6200 rpm? If not I would not worry about the power steering pump. It was desgned by GM to run at max rpm from the factory..

Now if you are going to try and turn this motor to say 6500 I would then worry about it...
 
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