04-03-2012, 03:29 PM
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CC Member
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Join Date: May 2006
Cobra Make, Engine:
Posts: 140
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Plans, Drivetrain
Waiting for the Cobra to arrive is good time to plan the drivetrain.
The engine will be based on a new Boss block, stroked to 347 C.I. (3.250 stroke, 4.125 bore) with Air Flow Research (AFR) 185cc heads. A mild cam with 112 degree lobe separation will be used to keep the car street friendly and compatible with Webers. Induction will be Weber 48 IDAs. The engine will hopefully be an aesthetic clone but with significant updating.
The displacement of 347 C.I. followed a bit of research. There are reports of the Boss block having reliability issues when stroked to 3.400 due to the short length of the cylinder sleeves. If stroked to 3.400 with a bore of 4.125 the displacement would be 363 C.I. Many have done that with success, but we prefer to take a more conservative approach and avoid any possible issues.
Once could reach a 347 C.I. displacement in two different ways: bore of 4.030 and stroke of 3.400, or bore of 4.125 and stroke of 3.250. We chose the latter since the shorter stroke avoids the potential problems associated with the short skirts.
Mahle pistons and a Scat Crank are planned. Rods will be 5.40
Engine details, like the valve covers, original style distributor (with Petronix internals), proper plug wires, proper appearing coil, etc. will be fabricated or acquired. The MSD electronic ignition will be buried where it will not be seen.
The transmission will be at TKO 600. An offset shifter attachment should make it fit like a top loader. The first four gears will match a top loader, but that 0.82 fifth gear will be better suited for highway cruising.
The clutch will likely be McLeod, based on prior good experience with the brand. Although an internal clutch slave is recommended, an external slave will be explored. The latter is much easier to repair or replace if there is a problem. We are leaning towards a Quicktime rather than Lakewood bell housing.
Horsepower should be north of 400, which is more than needed for a street car, but preserving the option of taking it to the track where it may prove useful. With a mild cam and tune we will forfeit some power to assure a good streetable Cobra.
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