June 26, 2007
The Sled From Hell (June 2007)
OK so my 2007 Corvette, when I first got it, started with a chugga-chugga-puUuUuUuUuRrRrRrR… just a nice smooth loping, purring idle. It cruised wonderfully at 1,500 rpm down the highway at 65 mph, getting 30 mpg easy, purring quietly and smoothly, giving great mileage and providing an excellent environment for listening to music on it’s really quite amazingly good sound system. As well, punching the throttle, the smooth purr built smoothly into a wonderful, smooth rrroooOOOOAAAARRRR as the engine surged smoothly to 6,500 rpm.
It was truly perfection.
Which is to say, obviously, that it was not enough.
Because, after all, if GM can deliver 10 joy-units for $60,000, then maybe, with aftermarket modifications, I could INCREASE that to 15 joy-units!
After all, the smooth roar builds up to a PERFECT wave of sound at 6,500 rpm, so if we could tweak the engine up to 7,000 rpm, then that would make it even BETTER!
So, a phone call or two later and I am touch with Mike, an energetic guy here in Columbia who modifies Corvettes in all sorts of ways. My first question: Can we tune that engine up to 7,000 rpm to really feel and hear even MORE roar at high rpm, and get even MORE power up in the high-rpm range?
Mike’s answer should be pretty obvious to anyone schooled in automotive engineering: “Sure, we could tweak the chip up to 7,000 rpm no problem, but we won’t get any more power, because the intake and exhaust systems are not QUITE set up to handle the higher airflow, and the cam is tuned for the low-rpm side, and will keep you from getting any more POWER at high rpm!”
Remember how the cam works: It causes the valves to open and close at certain times in the revolution of the engine. The cams in any production car are optimized for low-rpm, in-town driving. They have the valves opening and closing at just the right time for perfect airflow for a smooth idle. There is a price to pay for this, though: As the engine speeds up to high rpm, the valves are clearly opening and closing at the wrong time for the new hi-speed airflow, causing the intake, combustion, and exhaust events to move out of phase from ideal, and causing the engine to ‘run out of air’… unable to move air in, burn it, and move it out fast enough to keep the power flowing optimally at high rpm. The result is pretty simple: as the rpm builds up too high, the engine starves for air and the torque falls off!
Obviously, there is a solution to this: You can get a cam for your Corvette that is optimized for high-rpm rather than low rpm. This cam will have the valves opening and closing at just the right times to optimize the production of power at REDLINE rpm.
Obviously, there is a price to pay for this: The engine is barely able to idle, feeling like it is mis-firing or something as it goes whop-whop-whop at idle, barely able to run with all the combustion events clearly happening at the wrong time, resulting in a knocking, barely-running, NASTY engine with a severe attitude problem. You have heard this any time you watch a top-fuel dragster pull up to the line for it’s race: The engine clearly is NOT happy at low rpm as the exhaust sputters and flickers unevenly out of the stacks and racer rocks from left to right under the engine as the engine struggles to keep an even beat with power-strokes that are clearly not in the right phase to make smooth power. Of course, when the hammer comes down and the rpm goes where it’s supposed to, the whole thing just comes alive.
So, Mike made it clear that just bumping up the rpm with the rev-limiter would NOT help with power: A new cam optimized FOR this higher rpm would be needed if I actually wanted to GO any faster.
My answer to him was obvious: “Well, while you have the engine opened up, we might as well go all-out, right?”
“Sure.. I can do anything you want while I’m in there.”
“What else can we do for more power and sound?”
“We can go for a new intake system to let in lots more air. New headers to let out more air. New heads for a higher compression ratio to get more power per stroke. New high-lift cam to let more air in and out at higher rpm. New under-drive accessory pulley so the air conditioning and generator aren’t dragging you down as much. New programming on the engine to balance it out with all this new stuff is a requirement for sure or that computer won’t know WHAT is going on… if we do all that, we will be looking at 525 horsepower at the flywheel. (base Corvette is 400) But are you sure you really WANT all that? You will really feel that power at idle!”
“Oh yeah! Bring it on! I want it ALL! And take out the sound-proofing too! How much weight will that save?”
“20 pounds. It isn’t worth it. I don’t recommend it.”
“How about a new exhaust system? More flow! More noise!”
“I don’t recommend it. The new headers will help flow, but the catalytic converters aft are great in the stock Corvette… you don’t need to change them. General Motors did just fine with their basic system. It will handle the flow just fine.”
“How about turbo-charging? Super-charging? Nitrous Oxide!?”
“I don’t recommend it. You will run out of tire traction before you run out of power, and you just don’t need it.”
Well, Mike was trying to warn me of going too far, but once I started I could hardly be held back. I agreed to hold off on the supercharger, turbocharger, NO-2 injection, and cat-back exhaust system (for NOW), but charged full speed ahead on the hi-flow intake, hi-flow headers, hi-compression heads, hi-lift valves, hi-rpm cams, hi-rpm chip, and underdrive-accessories. Mike predicted 525 horsepower, but as I would soon learn when we put the car on the dyno, he was just being conservative so as not to over-promise: A 540-horsepower demon was actually in the making.
About 30 days and $7,000 later, Mike was in the driveway with my modified Vette, and it was time for me to drive it to the dyno to see the proof in the pudding.
The first jolt came with the first engine start.
Hmm.. no start. OK.
“Yeah, it can be a little tricky to hot-start… I don’t have the mixture dialed in the hot-start yet.”
Now this is interesting: Airplanes have always been tricky to start when hot, because the mixture is just not dialed in for that start condition, and the cams in the airplane are optimized for high rpm… now we were seeing the exact same thing in the CAR that I am USED to seeing in the airplane. Interesting. As well, the car had a very clunky, rattling, trembling sound and feel during the start. That was the new hi-lift cams and valves smacking open and closed, clearly audible during the simple starting of the engine.
I pushed the starter again:
AH HA! COMBUSTION! As I sat in the cockpit, the car was literally ROCKING BACK AND FORTH at idle at a fairly high frequency, like a child’s boat in a bathtub. You are literally rocking back and forth, over and over, as the engine goes WHOPPA-WHOPPA-WHOPPA-WHOPPA… CLEARLY unhappy to be turning so slow.
Hmm.. OK. Next step is try to move the car. Backing out slowly was pretty tricky, because the engine would buck and surge when asked to do any work at or below maybe 1,500 rpm. At low throttle, the engine would buck and surge and kick, and if you tried to solve that with hi-throttle, then the whole CAR would buck and surge. By balancing liberal use of gas and clutch, you could back out pretty smoothly with plenty of barking and snorting of the engine, then put it in first and sort of lurch just a little as you tried to get the unevenly-running engine up to speed as you got the car moving along with it.
Anyone within ear shot could easily tell that they were listening to a drag-racer in street-car clothing.
Going down the road at 35 mph in 4th gear is… umm… interesting. The rpm is round 1,500, which USED to be a smooth purr, but is now a bit of an urgent SURGE. The engine sort of surges and falls back, surges and falls back, as the combustion events are just not quite in sync with the turning of the engine.. the car is clearly DESPERATE to go faster.
OK, turning onto the race-track, it was time to tell what this snorting, argumentative beast would do when finally turned loose.
OH MY GOD.
I have driven the Corvette Z06, Ferrari 360, the Ferrari 360 Challenge Stradale (track version of the 360), The Ferrari 430, the Lamborghini Gallardo, an actual stock car, and a few Maseratis as well.
NONE of them EVEN COME CLOSE.
You hit the gas and the engine goes from it’s nasty, surging, argumentative clatter to a SCREAMING, HOWLING, WAIL!!!!!! The tires are spinning and screeching frantically and the tachometer races to the top of it’s travel so fast you don’t even have time to READ it before you have to shift to second… the engine barks and backfires and shouts at you for half a second as you make the shift, registering it’s complaint at having the fuel yanked away from it, and you hammer the gas in the second gear AND IT IS NO DIFFERENT THAN FIRST GEAR! The engine is screaming at a pitch several octaves higher than anything I have heard from a Corvette before as the tires continue to slide at the ragged edge of traction as the tach races to redline AGAIN under the SHRIEKING of the engine and then before you have time to really consider what the rpm actually IS, you see the tachometer racing up to redline and you have to shift to THIRD. The engine gives another angry bark at having it’s fuel taken away for a half-second during the shift and then JUMPS back into it’s shrieking wail and you are at redline in third, and my desire to avoid Imperial entanglements prohibits me from giving you the speed at this point.
I can tell you from my experience on the.. umm.. track.. that the modified Corvette now races 20 mph to 100 mph in what seems like about 6 seconds. On the.. umm.. track, the Vette screams at the ragged edge of tire cohesion clear to 100 miles per hour, the engine unleashed in a manner totally different from ANY production car. You sort of expect the car to just fly apart into a million flaming pieces like one of those X-Wings getting blown apart by a Tie-Fighter in the first Star-Wars movie. That’s what it feels like. You sort of want to scream: “AAAAEEEEEEEEEEEEEEIIIIIIIIIII!!!!!!!!” as the pieces all fly in different directions along the same general flight-path, flame exploding into the cockpit. The engine now has a much HIGHER-PITCHED sound… NOT the typical Corvette “VrroooOOOOMMMM”, but instead a high-pithced “wwhaaaaAAAEEEIIIII!!!!!!”
All the other cars on the track sort of seem to just slow to a stop as the engine howls and the speed comes through un-mentionable ranges… It is like when the Enterprise goes to warp speed and all the stars just go into a BLUR, falling behind you as the whole Galaxy just seems to be dead and motionless compared to your speed.
Any semi-sane person would quickly be overcome with fear and get off the gas. I do it, the engine snarls and barks at having it’s raw bloody meat taken away, and the Vette quickly decelerates back to ambient speed. All the other traffic comes back into focus at the same speed as the car, just like the Enterprise going from Warp back to Impulse, and I drop the precise, perfect transmission into 6th gear and with a satisfying YANK I am back in phase with the engine and the car is humming along at 65 mph, surging fore and aft slightly, at 1,500 rpm, desperately wanting to do it again.
Is this really sane?
For me, no.
I got the car Friday, it is now Sunday, and I am going to have Mike put a much less-agressive cam back in on Monday to give me back that smooth, silky lo-end performance that makes the Corvette such a friendly, wonderful car to own… but I will always remember the two days with that voracious animal that would kill me in a heartbeat, the second I let it off the leash!
I will add to this report once I have the old cam, but still the other new hardware, to tell you how it drives! (I think that will be the perfect blend)
Halltech stinger air induction
Kooks 1-7/8″ header with 3″ mid-pipes and x-pipe
GM LS-6 head pack with stage 3 porting, 2.04-1.575 valves
Dual valve springs, Viton seals, titanium retainers
cam pack with hardened pushrods, + engine bolts and gaskets
port and polish throttle body