First, I order up a set of Hedman headers, part number 68290, from Summit Racing. These are mild-steel painted headers with a standard port shape (i.e. not D-shaped), a 1/4" flange, 1 5/8" primaries, and cost under $100 for a set. According to Summit's application chart, they're listed for 1971-1991 B-bodies. I soon found out why they're not listed for later B-bodies - they interfere with the brace that ties the lower control arm mount to the frame. On my '92 Roadmaster wagon, this brace is bolted in place (it needs to be removed to swap starters, as I've personally discovered), while it's welded in place on my '96 Impala SS. The interference was such that it wouldn't be possible to "ding" the header tubes enough to fit them into place. I had the engine mount bolts out, the engine jacked up about 2", the steering shaft removed, and the oil cooler lines bent up a lot before I figured out that they weren't going to fit my car.
Option #2 was a set of Dynomax headers, part number 85001. Once again, these are mild-steel painted headers very similar to the Hedman parts, but with a slightly different routing of the primary tubes. They do indeed fit with a bit of hammer work on one of the primaries on each side, as shown below in a very poor photo (you can see the ding on the #5 primary - do the same on the corresponding primary for the other side).
So, with a bit of work with the ball-peen hammer, removal of the stock AIR tube that runs under the front of the engine (it interferes with the right-side header), the removal of the OEM oil cooler adapter (I fitted a F-body filter adapter to my car), removal of the stock plug-wire brackets that run under the valve cover, and some rerouting of the AC lines, the headers drop into place. They don't include any attachments for O2 sensors, EGR, or the AIR pump, though.
I bought Hooker O2 bungs from Summit and welded them into the flanges that I attached to my new Catco 3" cats (also purchased from Summit - part number CTO-8007). As I found out later, I could have modified a set of 18mm spark plug "anti-foulers" (available at most parts stores under the "Help!" product line) at considerably lower costs (those Hooker bungs were nearly $9/each!). The primary disadvantage to this is that I need to make sure I've got a good seal at the header flanger, or else the resulting exhaust leak will cause major errors in the O2 sensor readings. You will also need to find a way to extend the sensor harness on both sides. With this setup, though, I can switch to the Jet-Hot coated Dynomax headers (part number 86001) later and not worry about welding problems with the coating.
I simply deleted the EGR and AIR functions. With my ZZ3 cam, the EGR isn't required due to the cam overlap. The AIR pump can be removed due to the new GM TSB. I reprogrammed the PCM using my copy of LT1_edit to lean out the fuel mixture and remove timing when the coolant temp is less than 44 degrees F. I also changed the EGR on/off points to prevent the PCM from attempting to enable it under any conditions. If one wishes to retain these functions, they will need to weld the appropriate fittings onto the headers.
Below are some poor pictures of the headers
as installed in the car (which I hope to update soon).
Watch out for the AC line clearance on the right side! I managed to burn a line, which is a real bummer. Proper clearance can be obtained - just be patient, unless you want to remove the headers to replace a line. On the left side, I had a problem with the #5 plug wire, as it wasn't quite long enough to route properly. I grabbed a #6 plug wire off a spare set in the garage and used that instead with good results.
I used 3" collector flanges to hook up the
aforementioned Catco 3" cats. If I was doing this for a NA 350, I
definitely would have used 2.5" cats, but I'm building the exhaust to handle
a 396 on nitrous oxide so I went for something with sufficent flow.
I continue with 3" pipe to the Dynomax Bullet mufflers, and then exit with
2.5" pipe. You can see my setup below - it's not bad with respect
to ground clearance on my stock-height car, but I'd be very careful about
using it on a lowered vehicle.
If there's any questions, please contact
me at eric@bryantperformance.com
This is certainly not the easiest way to
put headers and hi-flow exhaust on your car, but I'm rather pleased with
my results and the money that I saved (which, compared to purchasing one
of the commercially-available header/cat/cat-back packages, is enough to
buy a set of LT4 cylinder heads!). Good luck!
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