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More on Bill Boyle's 400
rebuild... The (stock for this engine) 6X-4 heads were machined to
94 ccs and the intake bowls blended to improve flow to work better with
the lift and duration of the 270H Competition Cam [.470" lift (intake
and exhaust)]. The heads also received a 3 angle Pontiac competition valve
job. [Note: several people have asked whether the
intake ports were gasket matched. The answer is "no" they were
not. I choose not to do this because I wasn't sure what effect enlarging
the ports would have on emission testing. It is something reserved for the
future when my car doesn't require testing.] Overall, lift with the Competition Cam's Magnum roller rockers (1.52 ratio) is .476". ARP 7/16" studs are used with 7/16" poly lock nuts. Crower valve springs provide the tension to accommodate the lift. Intake valves were all shimmed .060" for proper installed height. Shims were used to get the proper installed height and spring tension. A valve job usually alters the location of the valve on its seat that may require the use of shims to get a good installed height. The spring seat or pocket needed no machining because Crower springs were used instead of the Comp Cam 995s that required cutting into the base. The stock chrome valve covers were modified because the oil drippers made contact with the rocker arms. The drippers were flattened. There is sufficient clearance using Fel Pro valve cover gaskets. [NOTE: This engine rebuild was not without minor complications.
The biggest problem I ran into involved two main caps that were fractured
near the dowel pins. Consequently, the two bad main caps were replaced and
the mains align honed to make everything true. By the way, all the main
bearings were in excellent shape when the engine was disassembled and inspected
for this rebuild. Hmm, What caused the broken caps then? My guess is that
both caps were damaged years ago when I spun the # 1 rod bearing. The damage
probably went unnoticed by the shop that did the The entire reciprocating mass was balanced and a new stock damper was installed to ensure vibration free movement. The old damper was coming apart so it was replaced with a new GM part. The original timing chain housing was also scraped and replaced because it was cracked near the lower right bolt hole. After degreeing in the camshaft, and ensuring the TDC mark was correct on the new damper, a discrepancy was discovered with TDC and the replacement cover timing marks. The two were not in alignment. The cover was off by 3 degrees. Initial timing of this stock HEI unit is 10 degrees for normal cruising. There is no detonation problem (still low compression) and the engine purrs on 89 octane gas. The engine runs around 190 degrees F on the highway. (A little higher in city traffic.) The engine is mated to the stock Borg Warner T-10 . Nothing trick with the transmission, or Safe T-Track 3.23: 1 (posi-traction). However, the OEM replacement Borg Warner pressure plate and clutch did not perform well under track conditions. To eliminate the terrible amount of slip experienced in each gear, I replaced the OEM set up with a no kidding around Centerforce Dual Friction system. The stock WS6 suspension and brake system on the TA 6.6 remains untouched--the front brake pads are still original. |
Comments or ideas--email me at bboyle@boyleworks.com This site created, maintained,
and hosted on Apple Macs. Copyright © 1997-2001, Bill Boyle. All rights reserved. |
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repairs for
me. I guess I was lucky that nothing more serious occurred prior to my rebuild.]