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Image: CHpg Staff

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In the last part of the THRS series, we had DeGroff's Cylinder Head Service build us a pair of street high-performance, 3800 Series II heads and we installed a Comp Cam and lifters.

In this part of the story, we're going to finish off the engine. Next, we're going to add some HD parts to the driveline appropriate for our modified engine's torque output and do some upgrades to the car's brakes. Finally, we'll go to the chassis dyno to validate our work to date.

Heads On

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Combustion chambers grow slightly in the valve unshrouding and polishing processes and that decreases compression ratio. To recover some of that, we ordered Cometic head gaskets (PN H1773052S, left, H1772052S, right). The Cometics are .052" thick or about .011" thinner than stock and good for about a tenth of a point more compression. Hopefully, that will bring us back up to where we were before we did the heads.

For the last decade or so, Cometic Gasket, Inc. has promoted multi-layered steel (MLS) head gaskets for street high-performance and racing applications of many engines, including the 3800. Initially, the introduction of this type of gasket generated mixed response. Some were disbelieving that a set-up of stainless steel layers with strange little bumps could seal their engine. Today, the MLS design is widely accepted by engine builders and being used in place of the typical composite and/or copper designs. it is also being use by O.E.'s in high-performance applications, such as the 620-hp LS9 engine in the Corvette ZR1.

Multi-layered steel offers benefits which cannot be attained with standard head gaskets. The stainless in an MLS gasket withstands temperatures in excess of 2000°F, about twice what a standard gasket can take. Because they are the same material throughout rather than most OE gasket's steel-fire-ring-and-fiber composition; they don’t cause as much bore distortion.

Some other benefits of Cometic's design? Since it's not limited by the size of the steel fire ring commonly found around the bores in an OE gasket, a wide variety of custom bore sizes and thicknesses are available. Need a thicker gasket to modify your compression ratio or add piston-to-valve clearance? Not a problem. Need to accommodate your strange sized overbore? Chances Cometic can make what you need with a short turn-around time.

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The 3800's cursed, torque-to-yield head bolts can only be used once, so we installed a new set of Fel-Pro head bolts (PN ES74033). A torque angle meter must be used for final head bolt tightening. It's a difficult process, but stay calm–it just takes time. Those of lesser strength may need to squat on the front stabilizer bar, between the engine and the radiator, to tighten some bolts. Use the tightening pattern listed in the factory Service Manual.

The combination of our Comp cam's smaller base circle and thinner head gasket require a 7.000" pushrod. Because we're going to buzz this motor to 6200 rpm, we ordered a dozen of Comp's Hi-Tech units (PN 7936). Made from .080" wall-thickness, seamless chromoly steel, they are 5/16" diameter and a ton stiffer than O.E. pieces. We dabbed Red Line Assembly Lube on each end then dropped the pushrods in place.

Next we reinstalled the stock rocker arm fulcrum bars and the stock roller rocker arms. Rather than GM's torque-to-yield rocker bolts, we installed INTENSE-Racing reusable bolts (PN HSH-RAB) and tightened them to 25 ft/lbs. We stuck new Fel-Pro gaskets in the valve covers and put them on.

The upper and lower intake manifolds weren't ready for installation, so we put the engine reassembly on hold and turned to some chassis and brake mods.

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Drivetrain Digest

Our eventual goal is 250-hp on the motor and, if we do nitrous, 300+. Planning for that, we needed a clutch upgrade so we called McLeod Industries' Billy Mieczkowski. He said that the stock clutch, a 9-11/16-in. unit of 1200-1400 pounds pressure, was inadequate for our needs. We drained the TREMEC T5 five-speed, removed it per the factory Service Manual, then pulled the stock clutch assembly and headed for McLeod.

Inspecting our parts, Mieczkowski advised that, while the clutch disc had plenty of material left, its damper springs and their mounts in the hub were worn, a common problem with six-cylinder discs. The stock stuff was scrap so we replaced it with a McLeod clutch (PN 360131) and disc (PN 260275). The McLeod has significantly more pressure, 1875 lbs., and its disc, with an enhanced-organic facing and HD hub and damper springs, offers better reliability and durability at our higher torque output and engine speed.

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The clutch release bearing was worn. It's a GM-only part (PN 89060001) so we ordered that and a pilot bushing (PN 24506531) from Tom Henry Racing. We installed the new bearing on the concentric clutch slave, changed the pilot, put the trans back in then reinstalled the rest of the parts removed to get the clutch out.

We filled the T5 with Red Line MTL, a low-viscosity, 70W80, ester-based-synthetic, GL4, gear lubricant. MTL provides excellent protection and improved shift feel in manual transmissions which require low-viscosity lubricants. It has the appropriate coefficient of friction for cone-type synchronizers whereas some gear oils, engine oils, and ATFs are too slippery for proper synchro function. MTL's wide viscosity range facilitates proper shifting over the full temperature range a transmission may experience. Its synthetic base stocks have a high viscosity index which insures constant viscosity as temperature changes. MTL is a 70W at low temperatures and a high 80, nearly an 85, at high temperatures. That range provides adequate viscosity to prevent wear and deaden gear noise. MTL has outstanding shear stability and oxidation stability, so its physical characteristics will change little with use.

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Working our way back, we added a Hurst Billet/Plus Shifter (PN 391-5032) which has a shorter throw and feels more precise because it eliminates the stock shifter's rubber coupler. Hurst's user-selectable “bias springs” provide the tension you feel when moving the shifter, cross-car, in the neutral gate. The default is all four springs. While drag racers like hefty centering tension, street-drivers and road racers might not. If that’s the case, remove the inner springs. Finally, we added the Hurst shift lever for a T56 six-speed (PN 2388572) which accepts the O.E. shift knob, giving the interior a stock appearance.

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The Tom Henry RS will have a higher top speed because the engine is going to have more top end and, after we installed Z-rated Goodyear F1 GS-D3s in Part 1, we raised the speed limiter to 118 mph and we may raise it again. This had us wondering about the stock driveshaft. V6 shafts become more prone to vibration at speeds beyond the production speed limiter because of the interaction of V6 firing impulses and the driveline's resonant frequencies. To address this, GM sticks a fat vibration damper on the driveshaft's front yoke. That's a cheap solution but makes for a 20 lb. driveshaft and might not be an effective fix, once top speed goes higher than stock.

We had Inland Empire Driveline Service build us a 41.5x3.0-in. driveshaft out of .120 in. wall-thickness, 6061-T6 aluminum tubing and forged 6061-T6 ends. Basically, this is an aftermarket version of the unit used by Camaros with the 1LE option but fitted with a V6 front yoke. Though it's larger, as it's aluminum and lacks the big damper, there is a whopping 50% weight reduction. At only 10 lbs, it has far less rotating mass which not only eliminates vibration at high speed but allows the car to accelerate a little quicker.

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Better Stop

Stock brake pads on later 4th Gen Camaros, the scary-expensive new units from GM, are a great choice for hi-po street use, so we kept them. If we start doing track days, we'll need a more aggressive pad, but for now; stock is good.

Brake rotors are a different story. They're a stunning example of how GM cost cutting forces use of inferior materials. Stock rotor durability, even for cars driven by people easy on brakes, is lousy.

The problem is crappy, low-silicon iron which lacks thermal stability causing thickness variation to develop. Our O.E. rotors barely made 40,000 miles before their thickness variation was so great, the car shuddered upon every brake application. The original pads had plenty of thickness left, but the rotors were junk.

We pulled the caliper assemblies, scrapped the GM rotors and replaced them with Baer Brakes' EradiSpeed Plus parts (PN 2301006, front, and PN 2302013, rear) which are more massive and made of high-silicon iron. Additionally, the fronts are a racing-derived, two-piece, reduced-weight design consisting of an iron brake disc with a more efficient cooling vent system bolted to an aluminum hat. For a trendy look, EradiSpeed Pluses are drilled, slotted and zinc-plated. These rotors eliminate brake shudder, perform better, look cool and cost only about fifty bucks more, per set, than O.E.

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Now that the THRS has good-looking, drilled and slotted rotors, we needed to tart-up the brake caliper assemblies a bit. Using Standard Abrasives BriteRite Pads, we scrubbed them with Simple Green and hot water then dried them with shop air. Using Eastwood High Temp Coating (PN 10396Z), we painted the mounting brackets silver and, using Brake Caliper Coating (PN 12070Z), we painted the calipers red.

Caliper painting takes planning. Eastwood's polyurethane paint lasts about four hours, once its reactant is added. In that four hours, give all calipers two coats with at least an hour between coats.

By the time we got around to revising this part of the project for the Internet version of the series, the brake caliper finish was nearly two years old. Eastwood's product has proven quite durable. When we wash or blow-off the brake dust, those DIY-painted calipers still look great.

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Our final brake upgrade was braided-stainless-steel-covered, Teflon brake hose assemblies. Building them with components from Eaton's Aeroquip division, in front, we used 10". Aeroquip hoses (PN FBPA0390-10) and, in the rear, between the calipers and the ends of the hard lines on the rear axle, 8" hoses (PN FBPA0390-8). Each has a straight, AN-3 fitting on one end and a 90° on the other. To connect to the calipers, we used long, 10-mm. banjo fittings (PN FCM2947) in front and short 3/8" banjos (PN FCM2949) at the rear, the O.E. banjo bolts and new copper washers. To connect to the hard lines on the frame in front and at the ends of the rear axle, we used Aeroquip AN-3 to 3/8-24 inverted-flare adapters (PN FCM2936). Aeroquip doesn't make parts to connect the chassis' hard line to the junction on the axle, so we had an 11" hose made by Orme Brothers, a hose and fitting retailer in Northridge, California. It has a 7/16-24 inverted flare connection on one end and a T, which bolts to the axle and accepts two 3/8-24 inverted flare fittings, on the other.

GM used a mix of metric and fractional inverted flared fittings on some 4th Gen. Camaros. If you make braided brake hoses for these cars, measure the fittings, first, before ordering parts. Aeroquip makes a nifty "Port and Thread Identification Kit" (PN FCM3644) for this purpose.

Motor Ready

"Extrude Hone" is the brand name for "abrasive flow machining" (AFM). Invented 50 years ago, during the Nike antiaircraft missile program, it's widely used in the aerospace and industrial fields. In the early '70s Southern California's Melendez family formed Extrude Hone AFM, Inc. and introduced the process to the automotive industry. By the 1980s, its use became popular with high-performance-street and racing engine builders. Today, it's even used by OE's for limited production, high-performance applications.

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This process removes material from the interiors of intake manifolds and other parts, leaving a smooth, polished surface behind. AFM's active ingredient is silicon carbide particles carried in a creamy polymer. The polymer is actually Silly Putty and the Extrude Hone Corporation is the world's largest manufacturer of the stuff and Extrude Hone AFM is one of its biggest customers.

The abrasive polymer is forced, or "extruded" through the part abrading and polishing all surfaces exposed to it. The amount of material removed depends on how long the part is processed, the particle size and where in relation to the point of polymer injection the abrading is taking place. This modest enlarging and polishing improves flow through the part.

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Typically, if you've fitted your 3800 with a set of ported heads, the lower intake manifold is "port-matched" using abrasive tools and traditional porting techniques. Additionally, with an induction system like that used on the 3800 Series II, there is a performance gain in porting and polishing the intake plenum, however, effectively doing that can be challenging because of the difficulty in reaching areas deep inside it.

Extrude Hone AFM eliminates these troubles while doing a more uniform job of removing material. it rounds all sharp edges and polishes all surfaces. The process is done to the upper and lower intake manifolds while they are assembled so port matching of the two parts, as might be required during the traditional porting process, is unnecessary.

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The day we visited Extrude Hone AFM to pick-up our intake and exhaust manifolds, we requested a flow test and observed while they did it. Tested on Extrude Hone's Super Flow SF600 Flowbench, air flow through the intake manifolds increased by a whopping 25% and exhaust flow increased an average of 13%.

You're asking, "What's up with cast iron manifolds?" We'll switch to headers in Part 4 of this series. For now, we want to try Extrude Honed and coated stock manifolds to see if they can be a budget-minded alternative to headers.

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We installed the lower intake manifold using a stock GM intake gasket set (PN 89017819) which we prefer because of the gaskets' metal cores. During the lower intake manifold installation, follow the Service Manual's instructions for tightening the bolts and use of a thread locking compound is required.

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Because the ports in the two intake parts have been enlarged, the gasket between them must be trimmed to enlarge its port openings. We laid a Fel-Pro upper intake manifold gasket (PN 95746) on a piece of plywood then used an Xacto knife to enlarge its port openings by trimming the fiber material right up to the RTV silicon sealing bead.

We had the upper intake manifold powder-coated silver by Extreme Performance Heat Coatings then installed it on the engine. Many of the upper intake manifold fasteners are smaller than you might expect. Tightening them requires an inch-pound torque wrench. Observe service manual torque specs and its tightening pattern.

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Extreme Performance Heat Coatings applied a silver metallic-ceramic coating to the outside of the exhaust manifolds and a thermal barrier coating to the inside. Extreme uses raw materials from Techline Coatings, one of the top suppliers in the performance coating business. As a result, the manifolds look better, radiate less heat and can be used without their stock heat shielding.

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Next, a final beautification project: we painted the crankshaft balancer, brackets, housings and some pulleys on the front of the engine, the lower intake manifold and the valve covers. For this we used Eastwood Co. products, Extreme Chassis Black (PN 11175Z), Chevrolet Orange (PN 10016Z) and Stainless Steel High-Temperature Coating (PN 10364Z).

It Runs!

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We sent our fuel injectors to RC Engineering cleaning and testing. In tuning our mod'ed V6, we'll start with 19 lb/hr., stock injectors but, if it needs more fuel than they can provide; we'll step-up to RC's 21.5 lb/hr. units. After RC's test, we stuck the injectors back in the fuel rail and reinstalled it.

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We got the ignition system up on the bench to install MSD Blaster Two-Tower Coil Packs (PN 8224) for the GM "waste-spark", distributorless ignition systems used on 3800s. The MSDs put out up to 40kV which, when they're used in an inductive ignition application like the THRS V6, is only slightly more than the OE coils. Where the Blasters are an advantage is during high-load operation at engine speeds beyond where the stock coils normally operate. Our project's engine is soon to get a rev limit higher than stock and future mods, such as nitrous oxide injection, will put a higher load on the ignition. Better materials, such as higher-quality copper wire, and more robust construction means the MSDs will be more reliable when the combination of higher rpm and higher ignition loads typical of a modified engine are present. These coils, along with MSD Super Conductor plug wires installed previously, give us a performance margin we like.

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We installed a fresh set of Denso Iridium Power IT20 spark plugs. We've used the IT-20 since the beginning of the Camaro Performers magazine version of this project in 2005 and always have had good results. It is a heat range colder than stock and its iridium tip is more durable but has less resistance than platinum. Its small, 0.4-mm center electrode and tapered ground electrode give the spark maximum exposure to the incoming, air-fuel charge. In short, we think the IT-20 is the best spark plug choice for 3800s in street high-performance and mild racing applications.

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Oxygen sensors are critical to drivability. We replaced the Camaro's, O.E. sensors with Densos (PN 234-418, front, 234-4087, rear). The Denso "O2S" is better because its aluminum-oxide "trap layer" covers the sensor element and resists damage to its platinum electrode and a porous, PTFE (Teflon) filter on the sensor's atmospheric side prevents moisture or contaminants from degrading accuracy.

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Finally, we reconnected the exhaust, coolant plumbing and wiring. To reduce the air bubble in the cooling system until the thermostat opens, with the 'stat out and the water outlet off, we filled the engine with a gallon of Dexcool antifreeze, a bottle of Red Line Water Wetter and distilled water. We reinstalled our Stant, 180° 'stat. A 160 was tempting, but running that cool sets code P0182 for excessive coolant warm-up time. Custom reprogramming can fix that and we'll do that later, then try the 160.

We double-checked everything, then lit the motor. For a few seconds, lifters clattered, then the engine settled to a somewhat less-noisy, but unstable idle. We connected our Bosch Mastertech scan tester to read engine data. While idle speed fluctuated, the engine was not stalling, no codes set nor were idle air control (IAC) counts or fuel trims way out of line. We used Mastertech's IAC function to temporarily raise idle to 1000 rpm and the engine smoothed-out. Once the thermostat opened, we opened the cooling system bleeder until we saw coolant, then topped-off and capped the radiator. We shut the engine off and checked for leaks.

A drive around the neighborhood showed that, while we lacked idle stability below 1000 rpm, at light-to-medium load, the car ran ok to our temporary, 4000 rpm rev limit. On a longer, weekend test drive, not only did we have a funky idle but we also observed knock retard ("KR"). We weren't sure if this was "false" knock retard, due to valve train noise, or real detonation, resulting from a whacked-out fuel map too lean for our camshaft/cylinder head package.

After changing the oil filter, we did another 300 miles of easy driving to 1) break-in the new parts and 2) do additional Mastertech data logging to learn more about KR.

Cal Challenges

In Part 1, we used a Hypertech Power Programmer for minor changes in the engine computer calibration, however, the more aggressive Comp Cam, bigger Manley Valves, better flowing DeGroff heads and Extrude Honed manifolds we've added pose a challenge the Hypertech was never designed to address. No way could we continue to use it.

While there are a number of aftermarket tuners having experience with 3800 Series II calibrations for racing and non-emissions-legal, street applications, the aftermarket has done little with "cals" for seriously-mod'ed, street-legal V6es, so we knew a calibration which exhibited good drivability, exhaust emissions compliance in California and other states with stringent emissions tests as well as a performance increase would be a challenge.

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We retained, Z-Industries of Temecula, California, a top aftermarket cal specialist. Z-I's owner, Ron Zimmer, told us that the computer for the later V6s has programming as complex as that of GM's latest stuff for the C6 Vette. The cal for our project was a arduous task, even for a pro like Zimmer.

On our first visit, Z-Industries made progress on idle quality, worked on knock retard strategy, revised wide-open throttle fuel and spark function, changed the fans-on temp to 185°F and reset the rev limiter to 6200 rpm. This took several reflashes of THRS's ECM followed by road tests with Zimmer riding shotgun, watching ECM data on his Bosch TECH2 scan tester.

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While putting more fuel to the engine had us using our mods to near their full potential; we still had knock retard. Our Mastertech now showed some "KR" under load, typical of detonation rather than "false knock". We added five gallons of Rockett Brand 100-oct. unleaded racing gasoline, road tested and saw less knock retard, but it still wasn't eliminated.

Since Part 1, Green Filter revised its Camaro air filter (PN 2021) with "custom fit tabs" on its edges. "Going Green" is a good thing, so we dropped an updated filter in the air box base. We added a Whisper Motorsports, carbon fiber air box lid (PN CFLid-6-99/02) which eliminates the baffles and fins inside the stock lid. The Whisper Lid replaces the silly, plastic intake resonator, attaches the stock rear air duct and relocates the intake air temperature (IAT) sensor. By using carbon fiber in this Lid, Whisper Motorsports stiffens the assembly, reduces it weight and vastly improves the appearance of the underhood. Plus, the Whisper Motorsports air box works well on a modified V6.

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Back at Z-Industries, a week later, we had Zimmer back-off the spark a scosche and add a bit more fuel. He, also, spent several hours tweaking idle programming. When we left his shop, idle stability was improved and the best we could expect considering our cam profile. We decided we were, finally, ready for Westech's Super Flow SF840 chassis dyno.

What Kind of Power Does it Make?

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Several days later, Rockett Brand Racing Fuel's, Tim Wusz, Ron Zimmer and we reconvened at Westech. Dyno Technician, Ernie Mena strapped our car to the Super Flow and made two baseline passes. Darn knock retard was present under load, so Tim Wusz supplied some more of his fine 100-oct. unleaded for us to mix with the 91-oct. pump gas already in the tank, then Ernie made several more passes during which Ron Zimmer tweaked the fuel and spark tables. This put our air-fuel ratio at WOT at an ideal 12.8:1 and further improved idle stability, however, we still had a slight KR issue. Nevertheless, we signaled Ernie that we were done fooling with the cal (for now) and to go for the money shot.

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Bottom line: we're making progress with the Tom Henry RS. Eight passes at Westech averaged, at the wheels, 206.0 horsepower (SAE-corrected) at 5350 rpm and 218.0 pound/feet torque at 4600 rpm. That equates to about 250 hp SAE net at the flywheel or around a 25% improvement over stock. Since we are already at the 250-hp goal set back in Part 1 and we've got plenty of tuning to do and a few more modifications, we're raising our power goal to 270-hp. Now that's what we're talkin' about!

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When the THRS comes back in Part Four of this series, hopefully, we'll have the knock retard issue solved, turn-in some good performances on straight pump gas and add some more modifications.

Yella Terra Rocks

The first version of this series, in Camaro Performers magazine back in 2006, reused the SLP 1.8:1 rocker arms from Part One. During preparation of the last part of the magazine series, we found the SLP rockers were not compatible with our Comp camshaft. The result was valve float above 5800 rpm and that was in-spite of SLP's Chief Engineer at the time insisting the 1.8 rockers would work with our cam.

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The solution was two fold. First, as told in the last part of this series, we replaced the Comp Cams valves springs we used at first with springs (PN PSI-LS1511) having slightly more open pressure which we sourced from Katech, Inc., the Michigan firm which runs the engine program for GM Racing's C6.R road race Corvettes.

Secondly, we installed a different 1.8:1 rocker arm design which was lighter. With a little investigation, we learned the manufacturer of the SLP rocker was an Australian company called "Yella Terra". Via email, we contacted Mark Conner, Yella Terra's Technical Sales Manager, and explained our problem to him. Conner responded quickly explaining that the 1.8 SLP rocker was the company's first aftermarket rocker design for the 3800. He, also, confirmed that it had been intended for stock cams and was not compatible with aggressive aftermarket profiles at higher rpm.

Conner went on to say that Yella Terra had designed the SLP rocker several years ago but had since discontinued that part. The SLP 1.8s were 16% lighter, per rocker, than the O.E., 1.6:1 stockers. Yella Terra has since further developed its 3800 Series II rockers by such that it was an additional 8% lighter yet had the same level of strength as the first design. The new Yella Terra rocker is called "Ultralite" and not only is its overall weight less, its reciprocating mass is reduced even more by revising the part's structure, especially at the valve end of the arm. Mark Conner agreed to ship us two sets of the Yella Terra second design rockers, 1.7s and 1.8s. Because the Yella Terras have higher pushrod seats we had to change pushrods so we ordered a set of 7.350" Hi-Tech pushrods (PN 7950) from Comp.

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Several weeks later, when the Aussie rockers arrived, we put their support bars on the heads, dropped in the longer Comp pushrods, lubed the pushrod and valve stem tips with Red Line Assembly lube, oiled each rocker with Red Line 10W30 then installed all those parts. We retorqued the rocker bolts, then replaced the valve covers and other parts removed to change the rockers.

In Part Four of the Tom Henry RS project, we'll add headers, do some additional tuning then run on the chassis dyno, again.