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I broke down and got a G-Tech RR so I could get a bit more quantitative in assessing SSR mods. It seems to have shown that the cagnge from the 3.73 rear axle ratio to the 4.56 was a GREAT idea.
To refresh everyone on the factory statistics, Chevrolet claims:
0 to 60 mph: 7.6 seconds
Quarter mile: 15.9 seconds at 90 mph.
Of course, unless Chevy did something way different than what is industry normal, those numbers are attained with a 160lb driver and 2 gallons of fuel in the tank.
Then, there’s the matter of vehicle weight. Sometimes, the factory specs are honest, and sometimes they are from a planet with less gravity.
The first thing I did was take my SSR to a CAT certified truck scale (They defend a trucker in court if he gets an overweight citation, so I guess they must be pretty confident of their accuracy). I was surprised, and delighted, to find that the SSR, me (way above that 160 lb “average” at 235 lb dressed for the street), and 14 gallons of fuel (86 lb), totaled to only 4960 lb. Working backwards, you can see that my particular SSR therefore weighs 4639 lb without me or gasoline, which is LESS than the factory spec. This is GOOD, as the SSR is a very heavy vehicle, and every 100lb saved makes a BIG difference (as you will see below).
Then, there’s the mattr of the shiftpoint. Yes, our 2003 and 2004 5.3 liter engines are factory redlined at 5900 rpm, but guess what, the automatic transmission starts its upshift at only 5600 rpm! (Something that the G-Tech proved beyond any doubt).
If you computer model an SSR’s acceleration as I have done, and substitute me and 14 gallons of fuel for the 160 lb factory driver and 2 gallons of fuel, you find that the statistics for a stock SSR become:
0 to 60 mph: 8.02 seconds
Quarter mile: 16.15 @ 89 (Excess weight DOES affect terminal speed as well as time)
I have had my rear axle changed from 3.73 to 4.56, and naturally wanted to know reasonably quantitatively how much it has changed the performance (seat of the pants says it has changed it a LOT).
It’s not easy to find a SAFE place to use a G-Tech, and it’s also darn hard to make certain that the section of road you are using is ABSOLUTELY flat. The problem with flatness is that it is very hard for humans to accurately judge, and even a little elevation gain or loss will hurt or help the acceleration performance a LOT, especially when the vehicle weight is such a big factor to begin with (Most “performance” vehicles are 1000 to 1500 lb lightr than an SSR, or looking at it another way, our vehicles are 29 to 50% too heavy for this engine to be able to qualify as “performance” ready).
To show you the magnitude of the problem, a 5% grade on a freeway is considered VERY, very steep. 2% is very noticeable. 8% is a mountain pass type grade. But, when you run the math (which gets a little tedious so I won’t bore you with it), it turns out that a 2% downhill grade will affect the 3rd gear performance of an SSR significantly, as it artificially adds almost 14% “acclerating force” to what the SSR is producing itself after deducting the force used to counter air drag at 3rd gear speeds. How much would that change a 0 to 60 time and a quarter mile time? I’m glad you asked, because I did the tedious modeling to find out, and it’s a big effect. Turns out, it reduces 0 to 60 by almost 0.4 second and quarter mile time by about the same amount. I mention this not out of academic interest, but because it will loom significantly below. Remember, the difference between 2 acceleration runs, one taken accidentally on a 1% upslope (pretty undetectable by a normal human), and the other accidentally taken on a 1% downslope, is 2%.
With all that preamable, I found what appeared to be 3 spots this morning that LOOKED flat and seemed safe. The 1st run turned out to be a bad run, as I got a bad launch AND had to shut down pretty early when a vehocle appeared out of nowhere (when at full throttle, I want NO vehicle anywhere within ¼ mile of me). The 2nd run seemed good, and I was able to complete an entire quarter mile. The 3rd run, in the opposite direction, went even better (too well, looking at the results?)as I started to get the hang of launching without too big a bog. The results are below:
Statistic / 1st run / 2nd run / improvement over 3.73 gearing
0 to 60 mph / 6.99 / 6.48 / 1.03 to 1.54 seconds
Qtr mile / 15.48 at 89.9 mph / 14.99 at 96.9 mph / 0.67 to 1.16 sec and 1 to 8 mph
I was of course deeply suspicous of the differences between the 1st and 2nd runs. The differences were pervasive throughout the the 2 runs, and so could NOT be explained as a betetr launch for example. The 2nd run showed better acceleration everywhere. I checked the wind reports for that time of day. 3 mph or so, so should not have been a factor. I have to assume that there HAD to be a grade difference between the 2 runs, even though they both LOOKED “flat”.
My post-run computer modeling verifies that a 2% differential between the 2 runs would be all that is needed to create this kind of difference between the 2 runs. I apologize for an obviously inadequate sense of levelness.
The computer model predicts that the difference between the 3.73 and 4.56 runs, using the actual 5600 rpm shift points (instead of the ideal “as high as possible” with this “wideratio” set of gearbox ratios) should be about:
0 to 60: 1.12 seconds difference
Qtr mile: 0.67 second and 2 mph
So, I am right in there in terms of actual results, with the 1st run being much pretty close, and the 2nd a little “too” good.
Even in the absence of precision, a few things are clear:
- The improvement in performance is BIG
- On a bang for the buck scale, this is awesome
- You CAN get an 03 or 04 SSR 0 to 60 time into the 6’s
- The regeared vehicle feels WAY better than the raw numbers even suggest. It actually feels “nimble”!
Jim G
To refresh everyone on the factory statistics, Chevrolet claims:
0 to 60 mph: 7.6 seconds
Quarter mile: 15.9 seconds at 90 mph.
Of course, unless Chevy did something way different than what is industry normal, those numbers are attained with a 160lb driver and 2 gallons of fuel in the tank.
Then, there’s the matter of vehicle weight. Sometimes, the factory specs are honest, and sometimes they are from a planet with less gravity.
The first thing I did was take my SSR to a CAT certified truck scale (They defend a trucker in court if he gets an overweight citation, so I guess they must be pretty confident of their accuracy). I was surprised, and delighted, to find that the SSR, me (way above that 160 lb “average” at 235 lb dressed for the street), and 14 gallons of fuel (86 lb), totaled to only 4960 lb. Working backwards, you can see that my particular SSR therefore weighs 4639 lb without me or gasoline, which is LESS than the factory spec. This is GOOD, as the SSR is a very heavy vehicle, and every 100lb saved makes a BIG difference (as you will see below).
Then, there’s the mattr of the shiftpoint. Yes, our 2003 and 2004 5.3 liter engines are factory redlined at 5900 rpm, but guess what, the automatic transmission starts its upshift at only 5600 rpm! (Something that the G-Tech proved beyond any doubt).
If you computer model an SSR’s acceleration as I have done, and substitute me and 14 gallons of fuel for the 160 lb factory driver and 2 gallons of fuel, you find that the statistics for a stock SSR become:
0 to 60 mph: 8.02 seconds
Quarter mile: 16.15 @ 89 (Excess weight DOES affect terminal speed as well as time)
I have had my rear axle changed from 3.73 to 4.56, and naturally wanted to know reasonably quantitatively how much it has changed the performance (seat of the pants says it has changed it a LOT).
It’s not easy to find a SAFE place to use a G-Tech, and it’s also darn hard to make certain that the section of road you are using is ABSOLUTELY flat. The problem with flatness is that it is very hard for humans to accurately judge, and even a little elevation gain or loss will hurt or help the acceleration performance a LOT, especially when the vehicle weight is such a big factor to begin with (Most “performance” vehicles are 1000 to 1500 lb lightr than an SSR, or looking at it another way, our vehicles are 29 to 50% too heavy for this engine to be able to qualify as “performance” ready).
To show you the magnitude of the problem, a 5% grade on a freeway is considered VERY, very steep. 2% is very noticeable. 8% is a mountain pass type grade. But, when you run the math (which gets a little tedious so I won’t bore you with it), it turns out that a 2% downhill grade will affect the 3rd gear performance of an SSR significantly, as it artificially adds almost 14% “acclerating force” to what the SSR is producing itself after deducting the force used to counter air drag at 3rd gear speeds. How much would that change a 0 to 60 time and a quarter mile time? I’m glad you asked, because I did the tedious modeling to find out, and it’s a big effect. Turns out, it reduces 0 to 60 by almost 0.4 second and quarter mile time by about the same amount. I mention this not out of academic interest, but because it will loom significantly below. Remember, the difference between 2 acceleration runs, one taken accidentally on a 1% upslope (pretty undetectable by a normal human), and the other accidentally taken on a 1% downslope, is 2%.
With all that preamable, I found what appeared to be 3 spots this morning that LOOKED flat and seemed safe. The 1st run turned out to be a bad run, as I got a bad launch AND had to shut down pretty early when a vehocle appeared out of nowhere (when at full throttle, I want NO vehicle anywhere within ¼ mile of me). The 2nd run seemed good, and I was able to complete an entire quarter mile. The 3rd run, in the opposite direction, went even better (too well, looking at the results?)as I started to get the hang of launching without too big a bog. The results are below:
Statistic / 1st run / 2nd run / improvement over 3.73 gearing
0 to 60 mph / 6.99 / 6.48 / 1.03 to 1.54 seconds
Qtr mile / 15.48 at 89.9 mph / 14.99 at 96.9 mph / 0.67 to 1.16 sec and 1 to 8 mph
I was of course deeply suspicous of the differences between the 1st and 2nd runs. The differences were pervasive throughout the the 2 runs, and so could NOT be explained as a betetr launch for example. The 2nd run showed better acceleration everywhere. I checked the wind reports for that time of day. 3 mph or so, so should not have been a factor. I have to assume that there HAD to be a grade difference between the 2 runs, even though they both LOOKED “flat”.
My post-run computer modeling verifies that a 2% differential between the 2 runs would be all that is needed to create this kind of difference between the 2 runs. I apologize for an obviously inadequate sense of levelness.
The computer model predicts that the difference between the 3.73 and 4.56 runs, using the actual 5600 rpm shift points (instead of the ideal “as high as possible” with this “wideratio” set of gearbox ratios) should be about:
0 to 60: 1.12 seconds difference
Qtr mile: 0.67 second and 2 mph
So, I am right in there in terms of actual results, with the 1st run being much pretty close, and the 2nd a little “too” good.
Even in the absence of precision, a few things are clear:
- The improvement in performance is BIG
- On a bang for the buck scale, this is awesome
- You CAN get an 03 or 04 SSR 0 to 60 time into the 6’s
- The regeared vehicle feels WAY better than the raw numbers even suggest. It actually feels “nimble”!
Jim G
