CorvetteForum - Chevrolet Corvette Forum Discussion - Z06 The Blue Bullet Project: My Quest for a 600-hp Street-Drivable LS7

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The results of my three-year search for 600-hp. Image: author

For the last three years, I've been consumed with having a 600-620-hp LS7 in the "Blue Bullet," my Carlisle Blue, 2012 ZO6/ZO7 1LZ. Not only did I want 600-horsepower, but I also wanted "bullet-proof" reliability and I had to pass my state's emissions test. If that wasn't enough–I wanted "good" drivability. Little did I know when I began this quest on 10 August 2017 that I'd still be working on it today.

My adventure began with ordering a "street/track" engine installation from a master engine builder in the Midwest. Since this engine shop is far from my home in the southern central-coast region of California, I drove the car there–because there's nothing I like better than a Corvette road trip–then caught a Southwest Airlines jet back home.

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"Ah...ma'am...ah, this is such a long flight. Can you get me another beer, please?" Image: Southwest Airlines

The engine was pulled, the 600-hp rebuild was accomplished, the engine was reinstalled and some modifications to body aerodynamics were made. I flew back in December of '17, picked up the car, paid the balance due on the bill then drove the Blue Bullet 2500-miles home to California, after a stop in Indianapolis for a day at the PRI Show.

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7DEC2017, the start of the first of three 2500 mile trips back to California I'd make in the next three years . Image: Author

Even before I reached home, I observed high oil consumption. I assumed this was break-in related.

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This was a view I got used to seeing in late December of 2017 and early 2018. Image: Author

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If I pulled one of the plugs, this is what I'd see. Image: Author.

In fact, the rings were faulty and my $20,000 engine continued to consume oil at an alarming rate. Several months later, after 5784 miles, oil use deteriorated to about 200 miles per quart. Additionally, the car made blue smoke out the exhaust on wide-open-throttle runs–to see video of that is shown below

In May of 2018, I shipped the car back to the Midwest engine builder for a second rebuild. But wait–this gets worse. The shop said the failure was my fault and wanted another 20-large to fix it.

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The Blue Bullet gets loaded into a Pilot Transport hauler. Pilot Transport has reasonable rates, nice trucks and drivers who take care of the cars they haul. Image: Author.

Fast forward to November 2018. On the 2500-mile trip back after the Rebuild-2, again, I observed high oil use which, once I was home, did nothing but get worse. After 6750-miles, I couldn't go more than 150-175 miles without adding oil. At this point, frustration had set in. I had spent two years and a shit pile of money and still had an LS7 that sucked oil like crazy.

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Shortly after I got the car back home after Rebuild-2, I took a road trip over to Nevada and back. On into early-2019, the problem got worse. Image: Author

In the spring of 2019, Blue Bullet went back to the same shop a third time, but this time, the builder paid for both shipping the car and Rebuild-3 This rebuild took longer than the first two because the engine builder decided there might be a problem somewhere and began a months-long test program to determine why the engine failed twice.

In my opinion, this shitshow was a perfect storm of mistakes: 1) at the time of Rebuild-1, the engine shop had just started using a new piston/ring combination, however, it never validated those parts in a high-performance street environment 2) the piston and ring supplier, Mahle, never tested its 1-mm/1-mm/2-mm ring package with the LS7's press-in cylinder liners and 3) the Mahle rings were used on the first two rebuilds.

For Rebuild 3, Diamond Racing Pistons and Total-Seal rings were installed–what should have been used in the first place.

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A Diamond Racing LS7 pistson. Image: Author.

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Total Seal rings were used but they were not gapless. In this case, they were "traditional" rings with gaps which, today, are the majority of Total Seal's business. Image: Author.

The car was ready in early February 2020, so once again, I hopped on a Southwest jet and flew to the Midwest to pick-up the car for another road trip back home. This time, oil consumption improved significantly. Prior to R-3, the engine was using a quart about every 150 miles. After R-3 the engine was not only making 600-hp, but I no longer had to carry oil on trips of more than a hundred miles.

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13FEB2020. Back in California after the third 2500-mile return trip from the midwest. I'm just west of the Arizona-California border. In the background is I-10 west going towards Los Angeles. Image: Author (ok...I used the self-timer on my Nikon)

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When I got home, this was what I saw when I pulled the dip stick after the 2500 mile trip. Wow. What a difference, eh? Image: Author.

At this point, in late summer 2020, with almost 7000 miles on the engine since Rebuild-3, oil use has averaged a quart of Red Line 0W40 every 1840 miles in a mix of highway driving, chassis dyno testing and wide-open throttle runs to the top of third gear.

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Image: Red Line Synthetic Oil Corp.

While I'd like that to be closer to a quart every 3000 miles, 1840 miles-per-quart in that duty cycle is acceptable for a forged piston engine. Finally, I had a street high-performance LS7 with acceptable oil use. The Midwest engine builder and I worked out a deal where they refunded half the cost of Rebuild-2.

So...that's how I got to where the Blue Bullet is, now. For the rest of this thread, I'm writing about living with a professionally built, street/track engine–the good, the bad and the ugly.

The good: the engine makes great power. I have PS Cup 2s on the car and it's spins the tires easily in first and second and sometimes in third. The engine uses much less oil and has far less knock retard because it's burning a lot less low-octane oil vapor. More good news is that the engine passed the emissions test in my state.

The engine shop has a number of engine dynamometer cells in which every customer engine is tested. When mine was run after Rebuild-3, there was a mistake in the dyno set-up which resulted in inaccurate data that was not discovered until after the engine was off the dyno. Rather than putting it back on and retesting; they decided that, while the error was unfortunate, I'd just have to get over it.

In cases when engine removal and replacement was done by the builder's "car shop," finished cars are run on a DynoJet chassis dyno. After Rebuild-3, at the rear wheels, Blue Bullet made 537.64-hp @ 6700-RPM and 485.17-lbs/ft torque @ 5200-RPM, SAE-corrected. C6 manuals using synthetic lubricants in the driveline, the correction factor to derive flywheel power and torque varies between 8 and 13% depending on lubricant type, lube temperature along with tire type, condition and temperature. Using those conversions, at the flywheel, the engine is making between an estimated 584 and 618-hp and between an estimated 527 and 558-lbs/ft torque, SAE-corrected.

Once I was back home with my thrice-rebuilt LS7, I decided to verify the engine builder's chassis dyno test with one of my own. I took the car to Full Throttle Kustomz in Fillmore CA. "FTK" is an automotive fabrication and service business, specializing in high-performance street, hot rod and race car builds. It bills itself as being "...for those who live their life at red line." That's my kinda place. Their techs can handle just about any enthusiast car build or maintenance task you want to throw at them. In addition, FTK's owner, Ray McClelland, is a renowned Southern California tuner.

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The Bulle Bullet, strapped onto FTKs Mustang dyno. Image: Author.

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FTK owner, dyno operator and calibrator, Ray McCelland. Image: Author.

I drove the Blue Bullet 140 miles to FTK and back for some runs on their Mustang chassis dyno. In that session, at the tire, the car made 546.8-hp@6545-RPM and 510.5-lbs/ft torque@5276-RPM, SAE-corrected. Using the conversions listed above, that was between an estimated 594 and 629-hp and between and estimated 555 and 587-bs/ft torque SAE-corrected at the flywheel.

Averaging the two chassis dyno sessions works out to between 589 and 623-hp @6600-RPM and between 541 and 572-lbs/ft torque@5238-RPM. Ok. The engine is making power consistent with the original, 600-horsepower goal I set.

Now, to fix some problems.

During Rebuild-1, the stock crankshaft damper was replaced with an ATI Super Damper. I had a couple of problems with that. First, it was a $450 expense I did not order, but that I could have been persuaded to purchase–had I been asked. Plus, it uses a shorter belt, so all my spares were now useless, but, wait–there's more. After I arrived back in California on December of '17, I found the HVAC compressor drive belt had no tension. While it was around the crank and the compressor, it was not running under the tensioner. Good think I didn't need A/C on the trip, eh? The belt likely came off during chassis dyno testing and no one thought check anything after testing.

For the next couple of years, the engine pitched the A/C drive belt with regularity when it was above about 6500-RPM. I learned that, after it came to market, ATI's "standard" Super Damper for LS7s earned a reputation here on the Corvette Forum for throwing the A/C drive belt. The problem was common enough that, according to CF threads I read, ATI revised the design of the standard LS7 damper to increase the height of shoulder at the rear of the A/C belt grooves. This made it harder for the belt to slip off the rear of the pulley, however, according to an ATI customer service representative I spoke to by phone, the design of the under-driven part was never changed, thus, LS7s with "ten-under" Super Dampers spit out compressor belts on a regular basis.

Between rebuilds, I experimented with two different belt tensioners from GM and Dayco, but neither changed anything. After Rebuild-3 and three more spit belts, I decided to try another new tensioner but, this time, I'd add a shorter belt figuring the two together might increase belt tension enough to end my LS7's belt tossing habit.

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Continental's Aftermarket Automotive Catalog lists belts, hoses, tensioners and timing belt kits for 1950-2020 cars and light trucks. It lists by application, has crossover data from OE and aftermarket part numbers and listings by dimensions. It was easy to find a Continental belt for the main accessory drive. I read the part number off the shorter belt installed by the engine builder, consulted the catalog's crossover and found a Continental Elite, six-rib Poly-V belt (PN 4060790), one of the original applications for which V8 fourth-generation Camaros. I installed the Elite belt and kept the other as a spare. The shorter A/C belt was a little more difficult. Normal for the compressor drive on an LS7 is a Continental 4040417, meaning it's a 40-series product having four grooves and a 41.7-inch length. After consulting the Continental catalog, I tried a half-inch shorter (41.2-in.) belt, however, even with the tensioner fully retracted, I could not get it on. I tried another Elite belt (PN 4040415), which is a main accessory belt on some import four-cylinders. At 41.5-in, it was longer than the first one, but still a bit shorter than stock. If I retracted the HVAC tensioner all the way, I could just slip the belt on. Hopefully, that modest increase in belt tension will be enough to keep the belt on at 7000-RPM. I got all these Continental Elite belts from RockAuto.com.

With the front end on jack stands during my quest for a shorter A/C belt, I also changed my LS7's coolant. Each time that midwest engine shop completed a rebuild, I drove the car back to California during Winter–once in mid-December '17, a second time in mid-November '18 and, the third time, in early February '20. Because of that, for three years, the coolant was a 50/50 mix of Dexcool and water. Where I live in California, it rarely gets below freezing. Once every few years, we might see a few winter nights where it gets down to 30°–maybe even 29°, but we have plenty of hot weather in the summer, especially, if I'm road-tripping across the deserts of southeastern California and southern Nevada.

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"RLWW" can improve cooling for engines with cylinder head coolant passages which have trouble with nucleate boililng. It also contains the necessary coolant additives for engines which use low/no antifreeze coolant mixes. Image: Red Line Synthetic Oil Corp.

Since water absorbs more Btu's per-gallon than antifreeze, coolants with low or no antifreeze cool better a 50/50 mix. Now that I was confident there would be no more rebuilds, I went back to my normal "California" coolant mix of 7-10% Dexcool mixed with distilled water and a bottle of Red Line "Water Wetter" (RLWW). Once you go below 30% antifreeze, there are not enough anticorrosive, antifoaming and pump lubrication additives in the coolant for good cooling performance and durability. Water Wetter has all of those additives to replace what you loose when you reduce antifreeze. Lastly, the 7-10% antifreeze/water/RLWW coolant must be changed every couple of years, regardless of mileage.

I slid my drain pan under the car. The Blue Bullet is a ZO7, so it has the C6 ZR1 all-aluminum radiator which has a pipe plug screwed into the radiator drain rather than a drain cock. I put my socket on the plug and the ratchet turned with almost no effort. "That's not right," I thought. I used my fingers to remove it and, lying there while the coolant drained, I wondered, "If the drain plug was so loose, how the hell did it stay in place for 6350 miles?" Once I got the plug out in the light and looked closely, I could see RTV sealer on the threads. Those putting the engine back in the car smeared some RTV on the drain plug threads as a back-up sealing measure. Then, they screwed it in with their fingers, but never tightened it. I was only a couple of threads away from the plug blowing out. Thankfully, enough RTV was on the plug such that, once it cured, it kept the plug from loosening. The only thing that saved me from that plug coming out while driving, was a some RTV.

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Image: Author.

While working under the front end, I noticed that wiring and power steering plumbing, running cross-car in front of the engine and on top of the steering rack was loose and too close to the crankshaft damper and accessory drive for my taste. After inspecting the wires, hoses and pipes, I discovered the plastic, toothed clamp which goes around the steering rack and holds the power steering hoses in place had never been tightened. I tightened the clamp and the problem was solved.

Now that some of the little mistakes were corrected, I was ready to confront one of the car's bigger challenges: idle speed and stability along with poor low-speed/light-load drivability. The symptoms were: high idle speed, idle speed oscillation, low-speed surging and bucking and occasional stalling. All were a disappointments from an expensive engine package marketed for high-performance street use as well as occasional tracking. Correcting these problems required calibration (or just "cal") changes with HPTuners' "VCM Suite" software, but first...the backstory.

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Image: HPTuners

I am a self-taught, DIY calibrator. When I started tuning a dozen years ago, I didn't know crap. Fortunately, I didn't fall for the myth: "Tuning? No problem. Learn from the Internet." The trouble with the Internet is beginning tuners don't know if what they read or watch is correct information. Tuners acting upon bad information can result in cars that drive like crap or even blow up engines. I think people wanting to learn to tune are better off getting some legitimate instruction from experienced calibrators before they start taking what they read or see on the web seriously.

I installed HPTuner's "MVPI Pro" hardware interface, which connects between the USB port on my Panasonic CF-31 Toughbook laptop PC and the car's diagnostic link connector (DLC). I loaded HPT's two VCM Suite apps, "VCM Scanner" and "VCM Editor" onto the Toughbook's SSD. I've run HPT's apps under both Windows 7 and 10.

VCM Scanner is the application used to log engine controls data from the DLC. VCM Scanner also has the ability to record additional data like information from a wideband oxygen sensor. VCM Scanner saves the data to your PC's disk drive or SSD. You use the scanned data to make decisions as to what calibration changes you make.

Next, I obtained some "credits," from HPT, one or more of which are required to calibrate a vehicle's ECM. This is how HPTuners makes its money and the number of credits required for a given ECM depends on HPT's development costs in supporting that particular engine controls platform. To do a cal for the GM E38 in the Blue Bullet costs two credits at $49.99-each. Credits can be purchased direct from HPTuners or from HPT retailers. Once you have some credits loaded into your interface, VCM Editor is what you use to change the calibration. Once you have a new calibration file written, you "flash" it into the ECM's EEPROM which is non-volatile "flash" memory containing all the data necessary to calibrate the ECM's operating system in a manner that it can properly control the engine.

I took home study classes on calibrating from two different sources. "The Tuning School" offers a wide variety of classes on use of HPTuners software from good old-fashioned books. "Calibrated Success" offers instruction on either CDs or, just recently, streaming video. Both instructional resources have been invaluable to me, especially back in the late '00s, when I was starting out and only knew enough about calibration to be dangerous. Yeah, these classes aren't cheap, but when I considered that good training would help me to avoid future problems and would save time and stress, the cost was warranted. Even today, I go back my Tuning School books and Calibrated Success CD-ROMs for occasional "refreshers". In addition, both those companies, offer classroom instruction at various locations around the country. See their web sites for more information.

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My tuning home study material. At left are some Calibrated Success CDs. At right are some of the Tuning School's books. Image: Author.

Once I began working on my thrice-rebuilt LS7s cal challenges, I found another excellent source of information in the "Gen4 Idle Tuning Guide." This is a very long thread on the HPTuners Forum about tuning modified Generation 4 V8s (LS2, LS3, LS7 and LS9, as well as non-Corvette Gen4s) for improved idle quality and better light-throttle/low-speed drivability. That tuning guide is a gold mine of information, however, some of the information there will be easier to digest if readers already understand calibration basics.

Three times, the engine shop flashed its own cal file in to my ZO6's E38 ECM and each time idle and slow speed drivability were not where I wanted them. The first problem was idle speed. Most cars registered in my state have to pass an emissions test every two years. I was concerned that a 900-RPM idle might be too close to the test's idle speed limit. Plus, while the engine had an aftermarket camshaft, its profile (220°/244° duration at .050-In lift, 116° lobe separation and no overlap above .050-in lift) was not that radical, so a 900-RPM idle was unnecessary. First, I reduced it to 800-RPM and then once I had it running ok there, I dropped it to the 700-RPM I wanted. At lower idle speeds, "Idle stability," which can be affected by misfire, surging, oscillation, idle spark advance and a host of other qualities, can be difficult to get right. Demonstrative of that is the above listed "Gen 4 Idle Tuning Guide" which runs 13 pages and 260 posts. I've visited that thread a number of times in the last few years and almost every time I find something helpful.

Why are modified engines with good drivability the exception rather than the norm? 1) Some folks will spend enough to get the wide-open-throttle fuel and spark right, but pass on the greater sum it often costs to have better drivability. 2) Some tuners lack the skills to calibrate for drivability and it's difficult for customers who are not tuners themselves to gauge a tuner's skill and 3) Some owners have unreasonable expectations–for example: a ZO6 owner who installs a cam with, say...250° intake duration and 110° lobe sep, then expects the engine can be calibrated to idle "like stock" which, of course, is so not going to happen.

My quest for idle quality took a lot of on-road tuning sessions. In a perfect world, I'd have done some of that work on a load-bearing chassis dyno which can offer a higher level of control and accuracy than does on-road tuning. Unfortunately, with the nearest chassis dyno at FTK, 70 miles away, I didn't have convenient access and, even if I did, it would have cost a substantial amount of money in dyno time.

To get idle quality improved over what it was when the car left the engine builder had me using HPTuners' "VCM Editor," to alter numerous "tables" in the Blue Bullet's calibration file. I changed various idle speed tables, idle spark settings, high and low octane base spark tables in the idle and light-load speed-vs-airmass cells and adaptive idle spark settings. I also worked with proportional idle, integral idle, base running air flow and throttle follower settings, all of which affect throttle opening under idle and low speed/light load conditions. Minor tweaks were done to the virtual volumetric efficiency (VVE) tables and that effort was to improve low-speed/light-load drivability when the engine controls are in closed loop.

Once I had improved drivability, I took a look at WOT fuel and spark. While that Midwestern engine builder supplied chassis dyno data after every rebuild, its data lacked air-to-fuel ratio information. I did have air:fuel data from my session at Full Throttle Kustoms and it showed the engine running a bit rich at wide open throttle, between 0.81 and 0.84 lambda from 2000-7000 RPM. My next step was to confirm that data from the FTK session with additional information.

As early as 2015, right after I installed an MSD Atomic Air Force intake manifold, I was doing wide-open throttle cal changes to the Blue Bullet. To log wide-open throttle fuel:air ratio, requires a wideband oxygen sensor, so I had a sensor bung installed in the exhaust just ahead of the driver side catalytic converter. Then I acquired a Bosch LSU4.2 wideband sensor and an Innovate Motorsports LC-1 sensor controller.

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The Innovate Motorsports LC-2. Image: Innovate Motorsports.

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The LC-2 "kit" includes the controller, a Bosch LSU4.9, a sensor bung and various cables. Image: Author.

Later, I upgraded to a Bosch LSU4.9 sensor and an Innovate LC-2 controller. In both cases, I connected the controllers to the serial port of my Panasonic CF-31 Toughbook laptop PC which is, these days, one of the few laptops which still has an RS-232 serial port because they are still widely used in industrial communication devices such as wideband controllers. If your PC doesn't have a serial port, Innovate widebands can also be connected to the HPTuner interface which then transmits WBO2S data via its USB connection.

After the FTK chassis dyno session, I reinstalled my wideband sensor and my Innovate LC-2, but then ran afoul of Murphy's Law. A year or so ago, HPTuners introduced its second generation hardware interface, the MPVI2. Before doing more LS7 WOT cal work, I finally decided to upgrade, but it requires the user to return his/her original MVPI interface to HPTuners so their techs can transfer data from the old interface to the new unit. There was a glitch on HPTuners' end of this process which took several weeks to solve. Plus, about the same time, my five-year old Panasonic CF-31 died and I had to ship it to a Panasonic repair facility.

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HPT's MVPI2. It's cordless and transmits its data via Bluetooth to your PC. Image: HPTuners.

Those delays allowed me time to pull my engine's MSD Atomic Air Force intake manifold and send it to Tony Mamo at Mamo Motorsports for porting and other procedures that optimize its performance. Mamo Motorsports is in Valencia, California. Its specialties are the ultimate LS7
heads/cam package, ported MSD intake manifolds and ported Gen 4 and Gen 5 throttle bodies. Tony is also "one of us". He owns a C6 ZO6.

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Tony Mamo and his ZO6. Pretty cool how he stores it into his shop in Valencia. Image: Author.

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Tony Mamo is best known for his cylinder heads. Here he does finish work on a Mamo LS7 head on his shop's Newen CNC valve seat and guide machine. Image:Author.

Delays caused by obtaining an MVPI2 and getting my Toughbook fixed also gave me some time to do an exhaust system upgrade to OE '11-'13 mufflers which were modified for increased exhaust flow.

Once I have my MVPI2 in hand, my laptop fixed, my Mamoized MSD back in place and my muffler mod'ed exhaust in place. I'll post the final part of this story.