Shelby could be both a genius and a fraud!
When he had to build 500 GT-350s in order to race them he did not have them done, so he put 500 cars in a parking lot, the first 3 rows were GT-350s, the rest were just plain jane Mustangs ... but he passed the inspection!
The GT-350 package transformed the Mustang into a real performance car, everything was better! But most of the GT-500s were kind of a fraud (except the KRs).
The early 428s had 390 heads on them. They could barely feed a 390 with a 4 barrel, they had no chance of properly feeding a 428 with 2 - 4 barrels. The later KRs had 428 heads and were true performers. A lot of folks thought he was putting 427 Ford motors in them (as were in the 427 AC Cobras) but only a few experimental ones were built that way.
390, 427 and 428 are all FE Ford motors, but 427 Medium riser heads have valves too large for the smaller bore 428 or 390. A 428 CJ head has 427 low riser valves and combustion chambers, but 427 Medium riser ports.
Bore size for 390 + 410 Mercury is 4.05
Bore size for 406 + 428 is 4.13
Bore size for a 427 is 4.23
390, 406 + 427 all have the same stroke and are internally balanced. The 410 and 428 have a longer stroke (both use an externally balanced 428 crank).
The 427 Ford engine was a racing motor and only installed in a very limited # of street cars (never in a Mustang). It was much more expensive to produce due to the larger thin-walled bore, cross bolted mains, and side oiler block. The piston pins were also dead on center, instead of being a bit offset to facilitate a smooth idle.
When he had to build 500 GT-350s in order to race them he did not have them done, so he put 500 cars in a parking lot, the first 3 rows were GT-350s, the rest were just plain jane Mustangs ... but he passed the inspection!
The GT-350 package transformed the Mustang into a real performance car, everything was better! But most of the GT-500s were kind of a fraud (except the KRs).
The early 428s had 390 heads on them. They could barely feed a 390 with a 4 barrel, they had no chance of properly feeding a 428 with 2 - 4 barrels. The later KRs had 428 heads and were true performers. A lot of folks thought he was putting 427 Ford motors in them (as were in the 427 AC Cobras) but only a few experimental ones were built that way.
390, 427 and 428 are all FE Ford motors, but 427 Medium riser heads have valves too large for the smaller bore 428 or 390. A 428 CJ head has 427 low riser valves and combustion chambers, but 427 Medium riser ports.
Bore size for 390 + 410 Mercury is 4.05
Bore size for 406 + 428 is 4.13
Bore size for a 427 is 4.23
390, 406 + 427 all have the same stroke and are internally balanced. The 410 and 428 have a longer stroke (both use an externally balanced 428 crank).
The 427 Ford engine was a racing motor and only installed in a very limited # of street cars (never in a Mustang). It was much more expensive to produce due to the larger thin-walled bore, cross bolted mains, and side oiler block. The piston pins were also dead on center, instead of being a bit offset to facilitate a smooth idle.