Dawson Racing Headers' Mario Avila at work welding-up our headers. Dawsons are made from 16-ga. (.065" wall), 1010 mild steel tube stock. They have 3/8" flanges, 1 5/8" primaries and 2.5" collectors. Tubes are mandrel bent. Most joints are tungsten inert gas (TIG) welded, however, typical of high-end race headers, the outside of each pipe-to-flange joint is TIG, silicon-bronze brazed.
The Heads-Up on Headers
While the Extrude Honed, stock exhaust manifolds installed in Pt. 3 improved flow on a per-manifold basis, the manifolds had flow differences between each primary pipe. In addition, the right manifold's #1 and #3 primaries intersect sharply and we felt there was turbulence and restriction at that point. While modified stock manifolds are good if you're on a tight budget, because nitrous increases exhaust flow; it was time to put headers on.
We headed for Dawson Racing Headers in Nuevo, California. Owner, Tom Dawson, has 25 years experience and does premium headers for everything from Top Fuel cars to tractor-pullers, including Camaros-all of 'em, from '67 to '02, street or race, and with just about any engine.
Dawsons for a 3800 Series 2 V-6 are a "mid-tube" design. Their oxygen sensors (we use Denso PN 234-4018) are in stock locations and the headers are designed with easy access to header bolts and our Denso IT-20 spark plugs. The system includes a 2.5"-into-3" y-pipe with a bolt-up connection which must be welded on to the stock catalytic converter. We sent our Dawsons to Extreme Performance Coatings then installed them using Fel-Pro gaskets and Stage 8 Locking Fasteners.
Inside the right exhaust manifold in the area circled is where we believe there is exhaust flow turbulence and restriction.
A month later, on a brutally hot day in early September, the FV6 Project Team met at Westech Performance Group for another chassis dyno session. First, Z-Industries,' Drew Zimmer, updated our computer programming, then, because air temperature inside the building was 91 degrees Farenheit, we mixed Rockett Brand 100-oct unleaded racing gasoline, 1:2 with the pump gas already in the car and went for the money on Westech's SuperFlow.
Fast Victor Six peaked at 212.9 SAE horsepower at 5800 rpm at the rear wheels. Not only is that a slight improvement over the last test in Pt 3, but that peak moved higher and the power curve extended to about 6000 rpm whereas, before, it dropped-off past 5500. All this came in spite of a milder camshaft and an air temperature 20 degrees warmer than our last test. No doubt-Dawson Racing Headers work very well!
On the downside, in the 3000-5000 rpm range, we're down as much as 10rwhp from our last session, most likely due to the second cam's less duration on intake.
Dawson Racing Headers for a '99-'01 GM 3800 Series II V-6.
Ready to Rock-Not
A rocker ratio increase might have been a way to get back the mid-range we lost. Since the DeGroff heads, installed in Pt. 3, support up to .550" valve lift, we tried a set of 1.8:1 aluminum roller rocker arms from SLP Performance Parts (PN 51116) which increase valve lift to .549".
We whipped off the valve covers, stock rockers, fulcrum bars and pushrods. SLP's 1.8s have a higher pushrod seat so a longer pushrod is required. We unboxed a set of Comp Cams 7.350" pushrods (PN 7950-1), applied some Red Line Assembly Lube to each and dropped them in place. On went SLP's fulcrum bars and rockers with some more Red Line Assembly Lube followed by a set of INTENSE Racing Reusable Rocker Arm Bolts (PN HSH-RAB), torqued to 25-ft/lbs.
The headers had been in once already for a fit check prior to coating. After going to Extreme Performance Coatings for its "Extreme 1600 Degree Coating System," which goes on the inside the outside of the headers, they were shipped back to Dawson's for Mario to do that final installation.
On Westech's chassis dyno, it was bad news: 1) the 1.8 rockers did nothing for our mid-range and 2) they cause valve float above 5700 rpm-in spite of the most robust Comp Cams valve spring available (PN 26918-130 lbs. seat pressure and 318 lbs. at .600" lift). With the stock 1.6es, the motor would run to its 6200 rpm rev limit. Sadly, the 1.8 rockers are incompatible with aftermarket camshafts such as our Comp Cam.
The upside: below our new, valve-float-induced rev limit of 5700 rpm, a 1.8 rocker improved performance by 7.4 hp to 220.3hp at the wheels at 5680 rpm. Had they not floated the valves, the rockers might have been worth 10hp at our previous power peak.
Until we can keep the valvetrain stable past 5700, after this article; the 1.8 rockers come off, because, when combined with an aftermarket cam, in a 3800 V-6 turning above 5700 rpm, their effect on reliability/durability is unacceptable.