jimgia

Here's the dyno specs on modifying my Z06/06 with a Kooks Header System, LAPD Camshaft Kits, milled the heads .020" to increase compression for measured stock 11.3:1 to 11.8:1, and fuel curve recalibration. All work performed at LA Performance Division in Chatsworth, CA, to the best quality standards. This pup is a rocketship!



©By Jim Gianatsis

I figured the 427ci engine, despite being rated 505hp at the crank, was way under tuned because of its primary use as a street car . Even Corvette was promoting it for track day use in the Owner’s Manual while retaining its full warranty coverage. Wetting my appetite for wanting more power in my Z06 was a feature article that appeared in the February 2006 issue of Hot Rod magazine where they tested an L7 crate motor with headers and two different Stage 2 and 3 optional GM Performance Parts camshafts. In Hot Rod’s test with an off the shelf, undersize 1.75 in. primary tubes / 2.5 in collector small block headers showing 510hp with the stock cam, and with the hottest Stage 3 GM cam the engine showed a 90hp peak increase (600hp total) at 6,803 rpm with a 54 ft-lb torque gain. However, both the GM Stage 2 and 3 cams showed a loss of power, torque and tractability under 3,000rpm where the stock Z06 likes to be driven on the street.

I contact my GM Performance Dealer to see about buying the Stage 3 cam kit with springs, but it wasn’t yet available. I put my performance upgrade plans on hold for a few months, until May when I took my Z06 out to a Touring Car Club track day at Willow Spring Raceway, CA, about an hour north of my home in Los Angeles. On the track, the car was a pure blast to drive, so controllable and neutral, killer brakes and really high cornering speeds. By the 3rd session of the day I had the traction control’s Competition Mode switched off and was getting down to some serious lap times.

Of all the Porsches, Vipers and Ferraris in my street group, none could run with me. Only this one British sportscar, the Noble, a 2380lb, winged, rear engine V-6 2.5 liter 352hp twin turbo supercar that was hell to stay with in the corners because it was so much lighter with more downforce, and leading onto the straights I didn’t have the power to weight ratio to out pull him. I’d have to sit in his draft down the 2 main straights at Willow, then dive inside under braking and block check him into Turn One and the 140mph sweeper into Turn Eight.
It was challenging to say the least, especially when I’d miss the 5-4 downshift going into Turn Nine, bog it in 6th, get re passed going onto onto the Front Straight, and have to do it all over again.

It was fustrating having to sit on the Noble’s rear bumber and twiddle my thumbs going down the two main straights at Willow. It didn’t seem my Z06 was putting out its full 505 advertised horsepower when I really needed it. It was then I knew the time had come for the cam and header upgrade I had been thinking about.

A lot of researching on the web and in the car magazines in May ’06 showed there still were not many performance parts available for the new Z06. GM Performance had yet to release their L7 performance cams which were tested in the Hot Rod article.

I gave a Vette tuning shop in Texas a call and ordered their complete 1.875 in dia. Primaries / 3.0 in collector Long Tube header System, complete with race cats and X pipe middle pipes to bolt up to the stock Z06’s 3in. dia. mufflers. I learned when talking on the phone to the salesman, after asking many questions, their performance header system they were selling for the new Z06 was origionally designed for the base C6 400ci L6 round port motor, that they were actually manufactured for them by another well known exhaust company back in California, but he claimed it “worked great” on the new L7 D-port engine and “made great power.”

I questioned how round port header flanges would work on the L7’s D-port exhaust ports, and their own dyno charts only showed a peak 20 hp gain. That didn’t sound right to me, since any good race header should show a good 10% (50hp gain on the L7). “These are the same headers we use on our race cars,” was his claim. And at the time, because there wasn’t anything else on the market, I placed my order and waited for them to arrive.

A week later UPS dropped off the infamous “Long Tube Headers” on my doorstep. I excitedly finished opening the huge card board carton which was partially destroyed in shipping and the tubes were hanging out (“The manufacturer ships us the header kits loosely packed in lightweight boxes tied to on pallets, and we don’t see the need to repackage them in sturdier cartons for individual reshipping to customers”).

Upon inspecting the “Long Tube Header” kits I was extremely disappointed in the quality of workmanship with rough cuts, sloppy welding, ugly tube bender marks, unfinished rough blending and matching of the tubes welded to the header flanges. Looking inside the collectors where the primary tubes were merged, and inside the midsection X-pipe, was a nightmare of rough cuts and drippy welds with no attempt to grind them clean. I measured the primary tube lengths to see if they were equal (tuned) and they were not, varying from 32 inches to 38 inches in length. If these pipes made 20 hp more than stock, then the stock Z06 headers must really be restrictive.

But I had come this far, so I jacked up my car and tried installing the infamous “Long Tube Headers” The extend long primaries tubes required relocation of the Oxygen Sensors much further back, and the kit included wiring harness extensions, which in turn required cutting on the floorboards and frame to reroute the wires not to burn on the pipes.

It was at this point, having to cut up my car to bolt on crap headers which would only make 20 hp, that I finally called it quits, repackaged the pipes and sent them back to Texas demanding a full refund. When I called the company to tell why I was returning their header system, this time a different salesman I was talking to told me, “We’ll can sell you the real racing headers we use, but the price is a lot more at $6,000!” You guys told me these were your race pipes, and that’s what you advertise. You liars.

It was now June and I was again back on the internet doing a search for Corvette Z06 performance products and this time I found a shop called Los Angeles Performance Division (L.A.P.D.) which was located just a few miles away from me in Chatsworth, CA, in the San Fernando Valley. They pictured all types of Corvettes in their shop for modifications, and they had a real chassis dyno for testing and tuning cars. I jumped in my car and I was down there in a flash.

L.A.P.D is a very low key shop, very casual, with Al Carreon the general manager and designer, and Dave the parts manager. On telling them what I wanted in the way of race quality headers, Dave pulled from his parts room a brand new set of headers just released for the new Z06 made by Kooks Custom Headers in New York.



I was immediately blown away…. Here were the L7’s D-port exhaust ports perfectly duplicated in the billet cut header flanges, matched to D-shaped primary ends, cleanly welded and hand ported to perfection. Equal length stainless steel 1.875 in primary tubes, clean tube bends without clamp marks, flowing smoothly into the 3.0 inch collectors with beautifully clean welds. Looking down into the collector ends I saw what you only see in high quality race headers: a machined tapered diffuser cone positioned in the center of the collector where the four tubes come together. The Kook’s mid-section X pipe was also a thing of beauty and certain to produce an stronger power band than the Z06’s already nice stock 3 inch mide section H-pipe. This was a true racing exhaust system for system the C6 Z06 and it was priced affordably around $1700, the same price as that other system which wasn’t worth the metal it was made out of.



I told Al about the GM Performance cam I was trying to get and he said, “Don’t worry, I’ll got my own cam for the ZO6 that will make a lot more power, and will be a lot more streetable.”

More power than a GM factory cam and more streetable? Hard to believe. But all it took was a tour of the back of their shop to see about 10 different C5 and C6 Vetttes in various stages of being modified, some with just cams and headers, some with superchargers, twin turbos, and some with full ground up suspension modifications. I was conviced I had come to the right place and I gave them a depost to order the parts.

When the Kooks Headers and Al’s new new LAPD billet cam arrived with the necessary valve springs and push rods, I brought my Z06 back to the shop for a base dyno run before leaving it for a week for the install and computer recalibration.

My stock car was strapped down on the rear wheel Dyno-Jet dyno, warmed up, then put through a run. The engine reved up to about 350hp at 5000 rpm and then the power band curve on the dyno monitor went to hell with huge spikes of mountains and valleys. Al looked at the numbers, the erratic air/fuel mixture line and figured there was something inside the car’s intake restricting the air flow. The guys pulled off the intake tunnel in front of the air cleaner and found a glued-in plastic pad had come loose and was flapping in the intake and suffocating the air cleaner. No wonder it felt down on power at the track.

We could only guess why GM had glued the pad in there (it had a GM part number on it) – possibly to dampening the harmonics inside the air intake tunnel? We pulled the pad out of there, bolted the intake tunnel back out, and fired the car up for another base run. This time it recorded 420 horsepower at 6,300, which seemed about normal, indicating a 85 hp drivetrain loss through the transmission and differential and rear tires from the advertised 505 hp at the engine’s crankshaft.

The dyno also ran with a fuel mixture probe up the exhaust pipe and it indicated the stock fuel mixture controlled by the car’s computer was very rich at around 12.5 to 1 across the power band, where 13.7 was ideal. There was more power to be found in just the stock motor by recalibrating and leaning out the computer.

A week later the parts installation was completed and I returned to L.A.P.D. to pick up my car. It was waiting for me back on the dyno for a comparison test to when I first brought it in, and to recalibrate the fuel injection computer to work with the modified parts. The first run saw the car putting out about 485 hp with the fuel mixture still very rich. Not bad. The guys then went to work on a lap top computer which had the software to recalibrate the fuel injection curve 10 rpm at a time in .10ths of a mixture point. After about 3 hours and 5 more runs the fuel air mixture was leaned out to 13.8 to 1 across the RPM range and we were now up now up to 503hp at the rear wheels.

This was a very impressive gain of around 88 hp and 70 ft. lbs of torque at 6,100 hp. Comparted to the more radical GM Performance cam trested in Hot Rod magazine which only made 66hp at this rpm, and had to spin to 6,800 to make 80 hp – which was still less then us (even less with the crankshaft measurement factored in). But even more impressive was down on bottom end under 3,000 rpm the LAPD cam was making 50 hp and 30 ft. lbs. of torque more than stock, where the GM Performance Stage I and II cams were actually loosing power to stock. Al had delivered on his promise to give me a better track and street cam than General Motors.

The total cost from LAPD for parts, labor, dyno tuning and a nice car detailing before picking up the my Z06 came out to $7,622.46

In looking at the Dyno Chart’s before / after, you will see there is a noticeable dip in the new power curve between 2,300 and 3,700. Not a big deal when the overall power gain is considered, but still not what we’d like. Al contributes this to the engine’s low compression ratio, in part to production tolerances being somewhat low on my particular motor, and to the new cam’s slightly more radical overlap.
The L7 engine has an advertised compression of 11:1, but with varied production tolerances and cam timing overlap, that compression might actually be down as low as 10.5 to 1. Most modern engines now, particularly now with knock sensors, a radical camshaft can run as high as 12.5:1 on 93 octane pump gas.

Al wants to go back now and increase the compression on my engine by about 1 point. To do so correctly and safely would require pulling the heads, measuring the combustion chamber in cc’s, checking the valve clearance, and then either reducing the head gasket thickness and/or milling the heads. A mild increase in compression from 10.5 to 11.5:1 should increase cylinder filling capacity, a.k.a. Break Mean Effective Pressure (BMEP) nearly 10% across the power band, with horsepower showing a similar proportional gain, plus it would round up that unwanted dip in the power curve.

We could have a Corvette Z06 with 50 more peak horsepower by going with a mild 1-point compression increase, and possibly gain 560 hp rear wheel / 650 hp at the crankshaft. That’s for around $9,000 compared to the rumored new supercharged 650hp Z06 Super Corvette that will cost around $100,000

The engine’s compression was never check when the headers and cam were installed, because the heads were never pulled. A few weeks later i brought the car back to LAPD to pull the heads and check the compression. Al measured the chambers at 11.3:1 which was close to stock, but he figured we could run more compression safely on pump gas with his more radiacal cam. He milled .020" from both heads, which increased the compression to 11.8:1 and then bolted it back up and sent it back to the dyno for recalibration. The car showd a very impressive 20hp and 20 ft lbs of torque power increase across the entire powerbancd from 2,000 to 7,000 rpm!

On my Z06 I am still running the stock muffler system, but with the two tail pipe valves left fully open by removing the fuse for the controller system. This fuse panel is located in a fuse panel under the front floor carpet of the passenger compartment. I am not running an aftermarket performance muffler system because they are really expensive without much of a performance gain. The Z06’s mufflers already run low restriction 3-inch pipes, and with the two stock silencer valves open they make more than enough noise with the Kooks Headers with the Race Cats and X pipe. The $1,700 spent on mufflers to gain no more power than pulling out the fuse on the stock mufflers, is better spent on the Kooks headers which might gain 30-40hp on their own.

Until some company brings out a lightweight titanium performance muffler system that will drop 50 lbs of dead weight off the rear of the car, I won’t spend my money on a shiny stainless steel aftermarket muffler that won’t make any more power than pulling the fuse that controls the stock mufflers’ noise reduction valves.

What I am waiting for are lightweight 2-piece racing brake rotors with aluminum center hats. Replacing the Z06’s heavy 1-piece cast iron rotors with 2-pieve race rotors should save about 8 pounds per wheel, 32 pounds overall. It could be a huge and very noticeable improvement in acceleration, braking, cornering and handling.


So how does the car perform? Even with the stock muffler (flapper valves open) the car sounds like a real race car, throbbing like a NHRA dragster, the hood rocking and bouncing. The car is no longer drivable under 2,000 rpm, surging and bucking, where the stock engine could be lugged at 1,500 rpm cruising on the highway in 6th gear. But once rolling over 2,000 rpm the power increase is more than obvious. With a clear road, the car in 3rd gear and hard on the throttle at 4,000 rpm where the power band crosses the torque peak and explodes, the acceleration is violent even with the traction control on. Shift into 4th and the acceleration is so hard as you hit 120mph and the power curve again, you have to back off. There’s not another supercar under $300,000 that can touch it.

I've had it out to Willow Springs on another track day and the power is really incredible. Nothing can stay with it between corners. My only limiting factor now is the stock run flat Goodyear tires which just don't have the traction to stick with full-on slick shod race cars in the corners. So a 2nd set of race wheels and tires is my next upgrade....

Sources:


L.A. Performance Division
10155 Canoga Avenue
Chatsworth, CA 91311
Ph 877 843 5373
818 998 3966
www.TheLAPD.com

Kooks Custom Headers
200 Candlewood Rd
Bayshore, NY 11706
1-866-586-KOOK (5665)
www.KooksCustomHeaders.com

NORTY

For comparitive purposes~
6300RPM...466.32HP...388.75ft.lbs....11. 47 air/fuel
Dynojet. This car is 100% stock as delivered. It had 1925 miles on it at the time of the pull. 91 octane California gas.

74.02F...29.82in-hg...humidty 44%

GoTreo

Congrats on the mods! Very nice writeup. I am curious why the throttle body, intake and exhaust ports were not ported? My research is telling me there is some significant HP to be gained by cleanig up the heads and opening up the TB.

Jeff

RadioManJ350Z33

VERY COOL .

mousecatcher

What a GREAT writeup! I hope LAPD gives you a kickback!

Where are you getting 93 octane in CA?


http://forums.corvetteforum.com/show....php?t=1523426

Brabus2

Jim,
Outstanding writeup!!! I recall seeing your car at LAPD's shop and meeting you at the Valley GTG, and you C6Z sounds & looks amazing. Congrats on your rocketship results... LAPD does TOP NOTCH work!!!

Whiteonrice

How about emissions, is that a California car?

Rick

fa63

No need to wait; there are a few companies that are making two-piece rotors with aluminum hats (Brembo and Hardbar come to my mind). Brembos are very expensive, and Gary's (Hardbar is Gary's company) rotors just look outstanding while being much cheaper. I think he is a forum vendor here so give him a call or e-mail him. Fromm what I remember, his front rotors shave off 10 lbs each. Good luck.