Ported and Polished Manifold
as you can see from the pictures above, clearly there's a lot of work to do--and a lot of opportunity for improvement. the soot line is anywhere from 1/8" to 1/4" inside the interior casting line of the pipe. these pipes were sourced from eastcoastscoobie for a very good price. for these header inlets i took it back to the gasket line. if the exhaust ports are slightly smaller than the gasket then i will end up with a small antireversion step.
these are some slightly blurry picures of the interior showing the completion of the rough cutting. this portion is done exclusively with carbide bits. the carbides cut quickly, and do not clog or wear out. properly cared for they will last a very long time. due to their extraordinary hardness they are fragile, however, so you must be sure not to drop or otherwise shock them. a good source for carbides is http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=38692
after a LOT of careful bulk removal with the carbides, i then switched over to a stone. the stones are a bit less aggressive and are useful for an intermediate smoothing, since the carbides can leave a mottled or grooved surface. using stones will make the final smoothing with flap wheels MUCH quicker, as well as preserving their lifespans. a good source for the flapwheels is http://www.caswellplating.com/buffs/flap_wheels.htm the flapwheels are great for a final smoothing over since they conform to the surface. the highest grit i went to on the manifold was 80, starting at 60.
i also removed all of the heatshield mouting tabs and standoffs that were cast into the manifolds. i started with a sawzall and a metal cutting blade to remove the bulk of the material, then switched to the carbide bits, then a 4.5" rigid disc sander/grinder to feather them into the rest of the exterior. the tabs were removed so that the wrapping of the exhaust would be easier, and they represented extra weight and thermal inertia that was unnecessary.
the final exterior smoothing and shining was accomplished with a flap disc in the angle grinder. the smoothing was done for two purposes: 1) to increase the heat-holding ability of the pipe by increasing reflectivity, 2) to prevent the next layer of fiberglass exhaust wrap from getting cut. a quick pass with the flap disc was all that was necessary. i also cleaned up the flanges, including the mating surfaces. be very careful when cleaning the flanges as any metal removed will directly affect their flatness... you just want to clean them, and not round out any of the edges.
some of these pictures illustrate how far down i tried to feather in the metal removal. everything i could find--like casting buttons, slag, rough casting artifacts, protrusions--i smoothed over and faded in as best as i could.
the one port i did NOT open up to the gasket line was the RH collector to up pipe port. even though there was a WIDE soot line inside this port, when i compared the gasket to an oem up pipe i had laying around, the inlet diameter of the up pipe was much smaller than the inside gasket diameter. as a result i left a step at that junction. i COULD have tried to widen the bottom of the up pipe but i did not have access to the one that was still on the car, and the spare one i had had not been gutted, and probably won't be for some time. so the manifolds i had in hand would be going on a gutted but otherwise virgin up pipe, and i decided to err on the safe side... always better to have a step UP in diameter than a step DOWN.
the other two pipe to pipe junctions were gasket matched. these included the two ends of the crossover pipe, and the ports which interface to the crossover pipe on both LH and RH collectors. the crossover pipe, since it is a welded rolled steel pipe, had a few welding beads as well as a couple of steps at both ends. these were removed and/or feathered in to be smooth, and the metal was removed to the soot mark, on both the crossover pipe and its matching ports on the collectors.
here the heatshield has been removed from the crossover pipe. the accordian style flex joint can be seen. on the inside of the pipe, however, the inlet pipe continues to prevent a direct flow of exhaust gas from having to navigate through the rough accordian section. it is a good design for a flex section--the only drawback is interior diameter, which is a bit on the small side.
it is VERY IMPORTANT to let your exhaust wrap soak well. this accomplishes a couple of things: 1) it makes the wrap softer and more pliable, 2) it cuts down a lot on the dust and shards of fiberglass which invariably get released while working the wrap, 3) the wrap stretches slightly when wet and thus will shrink slightly as it dries, making a nice tight wrap.
the wrap has been applied to the crossover pipe, and the metal heatshield is being reinstalled. the heatshield holds the wrap from unravelling (no clamp needed), as well as provides a very sturdy mechanical shield to protect it from abrasion and water. finally by creating a vapor barrier it increases the insulating quality of the wrap. notice there is no "sealant" on the wrap--it is unnecessary. the small bent metal bands which previously kept the pipe centered in the shield are also left off since the exterior diameter has been increased by the wrap.
the LH collector has a pair of casting buttons opposite one another that are ideal for the EGT bung. an 11/27ths inch drill bit should be used along with a 1/8"npt-27tpi tap. when tapping, start carefully perpendicular to the hole and proceed slowly, go a half turn right and a quarter back left, and use plenty of oil.
after that was tapped i placed a spare brass hose barb fitting into the hole to keep it located and prevent the wrap from covering it. two layers of wrap were used, "up and back" the length of collector, then fastened with a stainless hose clamp. the clamp's extra length was removed with a cutoff wheel in a dremel.
the RH collector was more complicated to wrap, but turned out well with some work. again, two layers were used throughout, with some portions getting a third layer of wrap due to topological issues. make sure access to the front o2 sensor port is left while wrapping.
to protect and seal the wrap i chose to use some heavy aluminum tape from home depot. this tape is typically used for HVAC ducts. it's pretty durable. i went through the different options at HD and picked the heaviest duty i could find. there is an adhesive backing on the tape, but i am unsure how well it will hold up to the high temperatures developed in the exhaust manifold. the couple of layers of wrap will certainly keep surface temps of the pipe lower than egt temps (1600 farenheit), but it will still get good and stinking hot. even if the adhesive burns off, i am banking on the relatively thick metal tape tending to stay on the pipes. i will keep checking it as the time progresses and see how long it will make it.
if it has decent longevity, the advantages of the foil are many: it is cheap--i used less than a quarter of a 13 dollar roll to do both cast manifold portions. it is a vapor barrier which cuts down on convective heat loss. it is a reflective surface which cuts down on radiative heat loss. it is physically tough which will prevent the wrap from being abraded. it is also very water resistant which will prevent the wrap from becoming wet in all but the most extensive of soakings.
i am planning on retaining the oem splash shield on the car, at least until i can get an aluminum sheet and bend it to make a nice skidplate. that should reduce the wear and tear on the collectors and foil. time will tell!
i've also been busy on the vf23...