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427 Rebuild and performance

June 28 2010 at 12:39 PM
Randy  (no login)


Response to Nice dissertation Tom

I am just wrapping up the rebuild on the original 427s from my 1969 38' Commander Sedan. I had one break a connecting rod at the end of last season, so they both got pulled out for an overhaul. I will be starting the first one in the next couple of days. I am a 427 purist, but also wanted to get the most power and efficiency out of an already great package and be ready for the E-15 to E-20 fuels, which I hate.

I did a lot of research before starting this project, including talking with Gessford Machine. They were helpful, but hey are definitley catering to high end car guys. I eneded up keeping the original heads and intakes because of how well their specifications fit the purpose. They actually have fairly large valves and ports compared to other FE hardware and should breath plenty well at 4,000 - 4,200 RPM. I went with new valves, springs, and hardened seats. I had both cams re-ground by Erson for use with hydraulic flat tappet lifters. I kept basically the same cam specs for low RPM torque, I just tweaked them a little for a new stroke and displacement. I had the blocks sonic checked and bored 0.020" to clean and true things up since the blocks had been honed once already and had a taper to the bore. I had custom 9.0:1 pistons made by Diamond to match the cams and heads and fitted them to a fully balanced Scat rotating assembly with a 4.125" stroke. The displacement is now around 470 cid, but they should have the same low end torque characteristics as the originals. These engines can safely rev to the 4,800 - 5,000 RPM range if desired because of the balancing and decent stock shaft-mounted rocker assemblies. I build and race a 1/4 mile drag boat with a 496 cid cast iron block burning methanol at 16.5:1 compression using the same cranks and rods. It regularly runs 7,300 - 7,500 RPM with no problems. I won't be doing that with these 427s, but I am hoping to let them rev a little higher with the same reduction gears and props.

I also welded plates in the intake manifolds to block off the exhaust cross-over to help keep the intake manifold charge cooler. I fitted them with Holley 950 programmable throttle body fuel injection systems (700 CFM progressive linkage, four injector throttle bodies) with programmable timing control. I can program the base fuel and timing curves based on a combination of an O2 sensor and an exhaust gas analyzer inserted in the port in the exhaust manifold for the choke heat tube. With the O2 sensors, the ECMs can correct the fuel-air ratio if conditions change.

Any comments? I will post some pics shortly.


 
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