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Original Message
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| The cam is the key difference. |
| By Dave Shoe - 03/09/2003 1:10:29 PM; IP 216.243.176.34 |
The 390GT motor, available from 1966 thru 1968, was a hot-cammed version of the 390 4-barrel engine. It also got a Holley carb and neato air cleaner, but was saddled with the restrictive exhaust manifolds found in all 390 Fairlane/Mustang cars. Note that 390-2V, 390P-2V (hi comp), and non-GT 390-4Vs were also available in the Mustang/Fairlane.
The 390GT cam was later used in the 428PI, the 427Hyd, and the 428CJ/SCJ, so it was a very nice cam. Naturally, stiffer valve springs and stronger valve spring retainers were needed with the cam, but a standard hydraulic lifter was used with the GT cam.
Otherwise, the engines are approximately identical, though the exhaust manifold bolt pattern was drilled differently, and various calibrations, such as the distributor curve, was modified. The head castings, block castings, intake castings were the same.
The original 335HP rating was probably correct on the dyno using Galaxie log-type exhaust manifolds, but once installed into the car, with restrictive Fairlane/Mustang exhaust manifolds in place, it's likely the power was down a bit from this advertised number. It's likely that customer complaints drove the 1967 advertised number to be adjusted downward.
Stricter emissions laws in all 50 states in 1968 forced the addition of Thermactor to all 390GT engines in 1968. Prior to this, only California 390GTs needed Thermactor. The 390 was still available in 1969 Fairlane and Mustangs, but the 390GT engine was gone, replaced by the lower-cost 390IP, as the 428CJ had taken top honors for 1969, and only the CJ was allowed to run the expensive Thermactor option, an option which allowed the GT cam to pass emissions in the CJ.
Your lifter clatter is a real concern. I'd advise hooking up a mechanical oil pressure gauge and characterizing the pressure curve to get a feel for what it looks like under varying conditions. It might be time for a simple tear-apart, inspection, and reassembly, just to be sure nothing has gone haywire in the 30-some years since the engine was built.
JMO,
Shoe. |
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