Modifying a Corvette Grand Sport – LS is the Best Chevy V8
The LS engine platform is the best engine GM has ever had. I know there are some die hard small and big block guys out there that think otherwise – but follow along and I will show you what none of those engines could ever accomplish.
We are going to start with a new 2011 GS, while it is not a 2012, it is a brand new left over. The first dyno run was done with 800 miles on the clock. I first used this car to do some air filter testing. The outcome of that testing will have to be for another story. This particular GS was an A6 automatic. The car runs fairly well, but I did have a check engine light when I first picked the car up. A quick check of the gas cap fixed that. So now it was time to pump the tanks dry and fill up on some Sonoco 94. I do this because every brand of gas has their own blend and since we are always testing Corvette parts, I like to use the same fuel so I know that at least every tank is very close to the same fuel makeup. With the tanks full of the Sonoco, I headed out to one of my trusted dynos. We typically use several different dynos depending on what we are trying to do. This time, it was just to get some good base line numbers, so we used a Dynojet 248.
Getting a Benchmark
Once the car was strapped down it was time to hook up the scanner and get to work. The first step was to make a first run and see what the GS could do. The first pass was good with a 383.82 hp and 380.65 ft/lbs of torque. Next, we reset the fuel trims to see what she would do. I made 5 runs after this, trying to get the car back to the same engine coolant temp before each run. The best the car could do was what it did in the first pass, the closest to it was 383.06 hp but 377.35 ft/lbs of torque. Now this is not enough difference that even the best of any driver would ever feel and it falls in the +/- accuracy of the dyno. So with data in hand, it was time to head back to Zip to add some parts.
With the new design of the LS7 box with that huge Donaldson air filter in mind, we set out to make the best CAI available. The first design was by far the biggest air box that was in a Corvette and it looked awesome.
On top of the new design, the Mamba was made out of genuine 2×2 twill carbon fiber, the same stuff used on real race cars and the Team USA bobsled. Our Mamba Air Boxes are built by hand and cured in an autoclave just like they do with the Indy Car body panels. So obviously, we are a little biased, but we have seen some great numbers with it and we have also added a honeycomb airflow straightener to clean up the MAF signal and eliminate surging that was so common in the LS7 and LS3 air boxes.
The downside – if there is one – is that on a LS3, PCM calibration is required because of the increase in air flow. If you do not calibrate an LS3 car, you will end up with a WOT air/fuel ratio in the low 10’s because of the increase in airflow and the way the factory calibration is “biased” on that end of the scale, so to speak.
So with these two great parts added, the next job was to control the heat. Heat is the worst enemy of any Corvette. But you may be surprised to learn why. The GM engineers are very smart people and with that being said, they incorporated some safety into the calibration of the PCM. You have an ECT (Engine Coolant Temperature) timing retard and an IAT (Intake Air Temperature) timing retard. Starting at about 200 degrees Fahrenheit, the PCM will start to remove timing so the engine will not pre-detonate (spark knock).
This kills horsepower, depending on how much it removes. The easy way some tuners battle this is to eliminate or lower the amount of timing that the PCM removes, but this is really not the right way to handle it. The timing is there for a reason, so our philosophy is to not get the temperature there and then we don’t have to worry about it. On those really hot days, I like the added comfort knowing that it is there and that we will have no issues of damaging our motor because we sabotaged the ability of the PCM to keep us safe. To increase cooling, we installed a DeWitts HD aluminum radiator.
Keeping the Fire Lit
We also added Zip’s Hi-Performance Shielded Spark Plug Wires that are made for us with a Magnecor wire. I strongly suggest that everyone visit their website and read up on the truth about spark plug wires. For years, I had the wrong idea about what to look for in a spark plug wire until a very smart engineer friend of mine pointed me in this direction.
Our wires are shielded from the extra heat, being in close proximity of the header tubes, with DEI heat shields. Next, we also added a set of Corsa Xtreme Exhaust mufflers to finish out the package.
The Proof is in the (Dyno) Pulling
So, I’ve told you about all the parts we used and why we used them. Now comes the fun part – the results! How does 428.43 horsepower and 411.50 foot-pounds of torque sound? Needless to say, we were very pleased with how the GS turned out – what an improvement! We picked up more than 44 horsepower to the rear wheels and just shy of 31 pound-feet of torque, with relatively simple bolt-ons and a little tuning.
Now – back to the LS engine family and the hardcore early SBC and BBC crowd. I can’t think of any small block or big block that you add a couple of parts to and have that kind of power output and still be civil enough to let your mother drive it to the grocery store. You could get into this GS and take a drive across the county in traffic, if you wanted to. Having personally owned many earlier Corvettes, I can’t think of any of them that could do that and put down 428 horsepower to the ground.
Zip is not being very intrusive on what we are bolting on to the engine. The original factory engineers did a really good job on the calibration for a universal customer; however for performance-minded individuals, there are some things we need to focus on. First and foremost, we need to get the PCM to deliver what we ask it to. Part of this important process is to have the right equipment. Depending on the year of the Corvette, I use a EFILive V2 interface or the HPTuners Pro interface. They both have their pros and cons, but they both get the job done.
My most important piece of equipment is my wideband oxygen sensor. Why is this so important? This is the one sensor that all of our programming is being based off of, so accuracy is key. I use an ECM AFM1500 which has a serial output to my interface. This is what the OEM’s are using, it has an accuracy of 1% and there are different models that ECM makes that are within ½ of a percent. But you must be willing to pay for accuracy – the AFM starts at about $2000. So why not a $199 wideband sensor? Remember - accuracy is key. If your wideband is 5% +/-, that is a variance of 10%. That could easily be the difference between an engine that lives on a hot day at WOT, and one that does not.
The next tool in Zip’s arsenal is a ASNU injector flow bench. When we are doing the install of a power package or supercharger, the first thing we do is flow the injectors to make sure they are operating the way they are supposed to. It also allow us to check their flow to make sure they are within a certain percentage of each other and balance them if needed. With all of this together, it allows us to create power packages that have parts that are designed to work together and the end result is a customer that is very happy with his or her Corvette.