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Most of you know that I had my SSR over at MTI Racing in Atlanta earlier this spring, while working on a contract assignment in Atlanta. That work was interrupted when the assignment ended early, so Reese Cox and his crew at MTI were only able to do the “exhaust” portion of the program we had planned. The results from that were themselves pretty impressive, but we knew we could get much more if we moved on to the intake side, as the dyno graphs clearly showed we were runing out of air.
Recently, Reese, his partner Paul, and I talked again about me coming to Atlanta to complete what we started, and with me going to the SSR Homecoming, and Atlanta being on the way, things finally worked out to get me back to MTI!
There was one important constraint though: Reese couldn’t start the work until Monday 8-15, and I needed to be out of the shop no later than Wednesday night, in order to be able to drive the 720 miles to Detroit and get there by 6pm Thursday. This was so I could attend the special GM Heritage Museum tour that GM arranged for SSR Homecoming participants for Thursday evening. That gace us 3 work days.
What we wanted to do was replace the extremely mild cam in the LM4 5.3 liter engine in my SSR with the much more vigorous GM LS6 cam – the same cam used in the 2002 and 2003 Corvette Z06, and now used in all Corvettes. Reliable information I had obtained suggested that this cam would give us at LEAST 39 more horsepower at peak (as you will see below, we actually beat that by a CONSIDERABLE margin!).
There were a number of other changes that would need to be made along with the cam (details will be in my book “The SSR Experience”), plus Reese and his guys also recommended other mods that they felt would be either necessary or desirable.
In changing the stock cam to the LS6 cam, we would need to install new longer Z06 pushrods, as the LS6 cam has a smaller base circle in order to enable its higher lift. Many of the valvetrain components, including valve springs, retainers, etc. needed to be changed to provide the valve control needed at the higher rpm that the LS6 cam is capable of supporting.
Since I am running a 4.56 rear axle, which spins the engine about 22% faster than stock for any given highway speed, we also wanted to install a 25% underdrive crankshaft torsional dampener. This would reduce the rpm of the various accessories attached to the front of the engine back down to approximately stock, so that they would not be an unnecessarily high parasitic load at high engine rpm. In addition, the underdrive dampener is a beautiful billet part, and weighs 7.25 lb versus 10.25 lb. for the stock one!
Reese also strongly recommended changing the timing chain. The stock chain is a puny single row design. The Corvette uses a chain with much beefier sideplates, and that was one option. But, Reese really encouraged me to go to the aftermarket double row chain that MTI offers. It has the thick plates but also has a DOUBLE row construction (see photo below that shows stock, better, and double row chains!)
Doing all the above might not SOUND hard, but it actually is very time consuming. In fact, the former head of GM Performance Parts Division recommends pulling the engine entirely out of the vehicle to do this kind of work! This is because there is “insuffficient” clearance in front of the engine, even with the radiator and AC condenser removed, to slide the long cam forward out of the engine and remove it. It is also technically “impossible” to replace the timing chain without removing the oil pump, which requires gaining access to the retainer that holds the oil pickup to the pump, and that retainer supposedly cannot be removed without dropping the oil pan which is as much work on the Gen III engine as pulling the engine! (The retainer setup is different than the easier Corvette one).
Reese and his guys are magicians though! They got the cam out by unfastening the engine mounts and judiciously manhandling the engine, and Reese personally developed a secret extremely clever way of handling the oil pickup retainer issue.
We were all worried Wednesday morning when the entire front end of the engine was still outside the car, along with the radiator components!
Reese and the guys volunteered to stay late, and actually buttoned up the vehicle late Wednesday evening, and finished dyno tuning and testing at 9:38pm!!
The results were spectacular – MUCH better than we had dared hoped for.
Remember that the total mods to my car before 8-15 were:
4.56 rear axle ratio versus stock 3.73 (which depresses reported dyno horsepower on an inertia dyno, as the engine is forced to accelerate the entire drivetrain much more quickly when using a stiffer ratio, and the physics of that dictate that much more power is being diverted to spinning up that drivetrain.
Dynatech Supermaxx headers with hi-flow cats
MTI Dual Shotgun true dual exhaust system
Rush air filter (NOT K&N)
Dyno tune
Between Monday and Wednesday, we added:
LS6 cam replacing stock cam
Z06 pushrods
Z06 valvetrain components
Double row timing chain
Underdrive crankshaft torsional dampener
The results are all shown in the graph posted below! Note the following:
The original exhaust mods got us an AVERAGE torque increase across the entire rpm range of 23 ft lb. The gain in the critical 3500 to 5000 rpm range was much greater than that – well over 30 ft lb.
The original exhaust mods got us 21 more horsepower at peak. The gain here was “modest” compared to the torque numbers simply because with the stock cam, we were running out of air! Nevertheless, the 273 peak horsepower at 5250 rpm translates to about 329 hp before driveline losses, versus the 300 stock hp rating.
The SSR with the 4.56 gearing and exhaust mods was MUCH more fun to drive than the stock configuration!
The second set of mod though REALLY woke things up compared to stock configuration!
Now we have an AVERAGE of 66 ft lb. more torque at the rear wheels!!!
Our gain in peak torque is 55 ft lb.!! And, the point of peak torque changed from 4000 rpm to 4750, showing how much better the engine is now breathing!
The new torque peak of 321 ft lb at the rear wheels translates to 387 ft lb at the engine before driveline losses, versus a tock rating of 335 ft lb.!!
Our AVERAGE gain in power across the entire rpm band was 45 horsepower.
Our peak rear wheel horsepower hit 331 hp!!! This is stronger than an 05 SSR with automatic, from an engine that is 13% smaller than an 05!!!
Our power peak moved from 5250 rpm to a BROAD peak that starts at 5900 and is still RISING at 6500 rpm!!! Take a good look at the red horsepower line in the graph below. The power at 6500 is 330.9 hp, actually a tiny bit higher than it is at 5900, where the curve first levels out to a value around 330.5 hp. What this tells me is that the 5.3 liter displacement and this particular set of mods is one of those “magical combinations” that performs better than it “should”. Note that at 6000 rpm and above, the gains in horsepower exceed 100, and at 6500 rpm, the gain is 123 horsepower.
This is incredibly beneficial in an SSR with the automatic transmission, as the ratio difference between 1st gear and 2nd gear is severe enough that when you shift at the stock setting of 5600 rpm, you hit only 3000 rpm in 2nd, where the stock engine is produing less than 140 hp at the rear wheels. With my new power curve, and able to shift at AT LEAST 6250, and maybe 6500 (I have the Z06 valvetrain, remember), I will hit 3400 rpm in 2nd and have at LEAST 190 horsepower available at the rear wheels – a 36% improvement!! If I can shift at 6500, I get 3500 rpm and 200 horsepower after the shift!!
Although this already spectacular, I need to point out that it gets even better. The dyno results were obtained under AWFUL conditions: 94.8 degrees temperature, high humidity, and low barometric pressure! Although dyno results are always “corrected” to “standard conditions”, the reality is that engines in real life do NOT perform as proportionately well under these kind of conditions as they do under better conditions. They ALWAYS dyno better under ambient conditions that are close to the standard ideal conditions. So, if anything, these results are understated.
In fact, on the street sinc ethe work was done, the engine performs even better than the dyno curve shows. It wants to rev like a motorcycle engine! If I don’t have cruise control on, and take my eyes off the speedometer, my 65 to 75 mph speed quickly turns into 85 or 90. Fuel mileage on the 700 mile trip from Atlanta to Detroit averaged 19.6 mpg, and that included very hilly country in Georgia, Tennessee, and Kentucky.
Yes, I AM understandably delighted.
continued below . . .
Recently, Reese, his partner Paul, and I talked again about me coming to Atlanta to complete what we started, and with me going to the SSR Homecoming, and Atlanta being on the way, things finally worked out to get me back to MTI!
There was one important constraint though: Reese couldn’t start the work until Monday 8-15, and I needed to be out of the shop no later than Wednesday night, in order to be able to drive the 720 miles to Detroit and get there by 6pm Thursday. This was so I could attend the special GM Heritage Museum tour that GM arranged for SSR Homecoming participants for Thursday evening. That gace us 3 work days.
What we wanted to do was replace the extremely mild cam in the LM4 5.3 liter engine in my SSR with the much more vigorous GM LS6 cam – the same cam used in the 2002 and 2003 Corvette Z06, and now used in all Corvettes. Reliable information I had obtained suggested that this cam would give us at LEAST 39 more horsepower at peak (as you will see below, we actually beat that by a CONSIDERABLE margin!).
There were a number of other changes that would need to be made along with the cam (details will be in my book “The SSR Experience”), plus Reese and his guys also recommended other mods that they felt would be either necessary or desirable.
In changing the stock cam to the LS6 cam, we would need to install new longer Z06 pushrods, as the LS6 cam has a smaller base circle in order to enable its higher lift. Many of the valvetrain components, including valve springs, retainers, etc. needed to be changed to provide the valve control needed at the higher rpm that the LS6 cam is capable of supporting.
Since I am running a 4.56 rear axle, which spins the engine about 22% faster than stock for any given highway speed, we also wanted to install a 25% underdrive crankshaft torsional dampener. This would reduce the rpm of the various accessories attached to the front of the engine back down to approximately stock, so that they would not be an unnecessarily high parasitic load at high engine rpm. In addition, the underdrive dampener is a beautiful billet part, and weighs 7.25 lb versus 10.25 lb. for the stock one!
Reese also strongly recommended changing the timing chain. The stock chain is a puny single row design. The Corvette uses a chain with much beefier sideplates, and that was one option. But, Reese really encouraged me to go to the aftermarket double row chain that MTI offers. It has the thick plates but also has a DOUBLE row construction (see photo below that shows stock, better, and double row chains!)
Doing all the above might not SOUND hard, but it actually is very time consuming. In fact, the former head of GM Performance Parts Division recommends pulling the engine entirely out of the vehicle to do this kind of work! This is because there is “insuffficient” clearance in front of the engine, even with the radiator and AC condenser removed, to slide the long cam forward out of the engine and remove it. It is also technically “impossible” to replace the timing chain without removing the oil pump, which requires gaining access to the retainer that holds the oil pickup to the pump, and that retainer supposedly cannot be removed without dropping the oil pan which is as much work on the Gen III engine as pulling the engine! (The retainer setup is different than the easier Corvette one).
Reese and his guys are magicians though! They got the cam out by unfastening the engine mounts and judiciously manhandling the engine, and Reese personally developed a secret extremely clever way of handling the oil pickup retainer issue.
We were all worried Wednesday morning when the entire front end of the engine was still outside the car, along with the radiator components!
Reese and the guys volunteered to stay late, and actually buttoned up the vehicle late Wednesday evening, and finished dyno tuning and testing at 9:38pm!!
The results were spectacular – MUCH better than we had dared hoped for.
Remember that the total mods to my car before 8-15 were:
4.56 rear axle ratio versus stock 3.73 (which depresses reported dyno horsepower on an inertia dyno, as the engine is forced to accelerate the entire drivetrain much more quickly when using a stiffer ratio, and the physics of that dictate that much more power is being diverted to spinning up that drivetrain.
Dynatech Supermaxx headers with hi-flow cats
MTI Dual Shotgun true dual exhaust system
Rush air filter (NOT K&N)
Dyno tune
Between Monday and Wednesday, we added:
LS6 cam replacing stock cam
Z06 pushrods
Z06 valvetrain components
Double row timing chain
Underdrive crankshaft torsional dampener
The results are all shown in the graph posted below! Note the following:
The original exhaust mods got us an AVERAGE torque increase across the entire rpm range of 23 ft lb. The gain in the critical 3500 to 5000 rpm range was much greater than that – well over 30 ft lb.
The original exhaust mods got us 21 more horsepower at peak. The gain here was “modest” compared to the torque numbers simply because with the stock cam, we were running out of air! Nevertheless, the 273 peak horsepower at 5250 rpm translates to about 329 hp before driveline losses, versus the 300 stock hp rating.
The SSR with the 4.56 gearing and exhaust mods was MUCH more fun to drive than the stock configuration!
The second set of mod though REALLY woke things up compared to stock configuration!
Now we have an AVERAGE of 66 ft lb. more torque at the rear wheels!!!
Our gain in peak torque is 55 ft lb.!! And, the point of peak torque changed from 4000 rpm to 4750, showing how much better the engine is now breathing!
The new torque peak of 321 ft lb at the rear wheels translates to 387 ft lb at the engine before driveline losses, versus a tock rating of 335 ft lb.!!
Our AVERAGE gain in power across the entire rpm band was 45 horsepower.
Our peak rear wheel horsepower hit 331 hp!!! This is stronger than an 05 SSR with automatic, from an engine that is 13% smaller than an 05!!!
Our power peak moved from 5250 rpm to a BROAD peak that starts at 5900 and is still RISING at 6500 rpm!!! Take a good look at the red horsepower line in the graph below. The power at 6500 is 330.9 hp, actually a tiny bit higher than it is at 5900, where the curve first levels out to a value around 330.5 hp. What this tells me is that the 5.3 liter displacement and this particular set of mods is one of those “magical combinations” that performs better than it “should”. Note that at 6000 rpm and above, the gains in horsepower exceed 100, and at 6500 rpm, the gain is 123 horsepower.
This is incredibly beneficial in an SSR with the automatic transmission, as the ratio difference between 1st gear and 2nd gear is severe enough that when you shift at the stock setting of 5600 rpm, you hit only 3000 rpm in 2nd, where the stock engine is produing less than 140 hp at the rear wheels. With my new power curve, and able to shift at AT LEAST 6250, and maybe 6500 (I have the Z06 valvetrain, remember), I will hit 3400 rpm in 2nd and have at LEAST 190 horsepower available at the rear wheels – a 36% improvement!! If I can shift at 6500, I get 3500 rpm and 200 horsepower after the shift!!
Although this already spectacular, I need to point out that it gets even better. The dyno results were obtained under AWFUL conditions: 94.8 degrees temperature, high humidity, and low barometric pressure! Although dyno results are always “corrected” to “standard conditions”, the reality is that engines in real life do NOT perform as proportionately well under these kind of conditions as they do under better conditions. They ALWAYS dyno better under ambient conditions that are close to the standard ideal conditions. So, if anything, these results are understated.
In fact, on the street sinc ethe work was done, the engine performs even better than the dyno curve shows. It wants to rev like a motorcycle engine! If I don’t have cruise control on, and take my eyes off the speedometer, my 65 to 75 mph speed quickly turns into 85 or 90. Fuel mileage on the 700 mile trip from Atlanta to Detroit averaged 19.6 mpg, and that included very hilly country in Georgia, Tennessee, and Kentucky.
Yes, I AM understandably delighted.
continued below . . .
