quote:Originally posted by PanteraDoug:
... I don't know if the NASCAR engines used the modification either (exhaust port plates) ...
... there was an issue with valve spring failure in long races like the 500 mile races NASCAR ran ...
... Getting specific details of the Detomaso Gp4 factory race engines now is a bit difficult and sometimes the details are sketchy ...
Yes NASCAR Fords used the exhaust port plates until the rules made them illegal.
Valve spring failures were not an oil-cooling issue, folks intentionally limited the amount of oil flowing to the valve train; valve spring failure was mostly due to the choice of springs. Valve springs in the 1970s were mostly of poor quality. The Ford springs were unreliable for racing, as were Crane springs and a bunch of others. In my little part of the world folks used Vasco Jet springs. Traco is another brand of "good" spring that comes to mind. Holman Moody and Reed cams both sold springs which were choice quality stuff, they were probably sourced from Vasco Jet or Traco. It seems there's another brand I'm forgetting (my memory isn't what it used to be). But even the "good" springs from that era are junk by today's standards. Another cause of valve spring failure was the camshaft lobes. Some cam grinders had better lobes than others, lobes that put less stress on the valve train, Reed cams comes to mind as an example.
The earliest Group 4 Pantera engines are not something anyone should copy, they were unreliable; the best thing you can learn from them is what NOT to do. The original engines were supplied by Bud Moore Engineering (BME) in the US. The motors were built in late 1971 or early 1972. Bud Moore was the first US engine builder to be considered a 351 Cleveland expert ... because he had raced Boss 302 Trans Am Mustangs equipped with Cleveland cylinder heads for 3 seasons (1969, 1970 and 1971). The problem was, his experience racing the 351 Cleveland short block at that point in time was nil, his team didn't actually race a 351 Cleveland in NASCAR until the 1972 season! PLUS he had no idea what the race courses in Europe were like. The Group 4 Pantera race engines were unfortunately Bud Moore's guinea pigs!
The Panteras were dominant in their class during the 1972 and 1973 seasons, but the motors were unreliable which often prevented the Pantera race entries from finishing races. When the motors didn't fail the Panteras usually won! The motors BME delivered to DeTomaso were equipped with a single plane Ford intake manifold, Holley 1050 cfm Dominator carburetor, GTS style tri-y headers, titanium valves, 12:1 compression ratio and a wet sump style racing oil pan. These motors came in two states of tune, rated first at 470 bhp and later at 440 bhp. They failed one by one during the 1972 racing season.
Problems were pretty typical of the stuff you expect from a 351C circa 1972, cylinder wall cracking, rod bearing under-lubrication, head gasket failure and valve train component failure (springs and fulcrums). On top of that, at least one engine threw a slug of Mallory metal (that had been used to internally balance the crank) through the oil pan! Bud Moore's engine shop had drilled the holes for the Mallory metal on the edges of the crankshaft counter weights instead of through the sides of the counter weights. Then, instead of welding the Mallory metal in place, the holes in the counter weights were merely peened to hold the slugs of Mallory metal. As Homer would say, "DOH"!
Disillusioned by the experiences with the motors supplied by BME DeTomaso began developing in-house expertise for building 351 Cleveland based racing motors in 1973. In fact DeTomaso's engine shop became the only engine shop in Europe with 351C expertise. This occurred in a period of time in which DeTomaso and Ford had parted ways.
DeTomaso's engine shop upgraded the induction and exhaust systems with individual runner induction employing Weber 48 IDA carburetors and 180 degree, bundle of snakes style headers to improve volumetric efficiency. The power increase was substantial. The compression ratio was lowered to 10.5:1 to avoid cracking cylinder walls, a dry sump lubrication system replaced the factory wet sump system to prevent oil starvation of the connecting rod bearings (I'm not sure about lifter bore bushings) and the cylinder heads were sealed to the block with O-rings to resolve head gasket failure. Crane Cams camshafts and valve train were employed instead of the stuff Bud Moore had installed. The DeTomaso engine shop's motors achieved reliability while producing 475 to 500 bhp at 7000 rpm; that was considered the motor's limit for endurance racing employing the thin wall production cylinder block casting.
Its unfortunate that the Group 4 Panteras were forced to compete with production blocks, because Bud Moore had in his possession a stock of thick wall racing blocks referred to as "366 blocks" or as "Bud Moore's blocks". The NASCAR displacement limit for the small engines was 6 liters in 1972, i.e. 366 cubic inches, hence the name 366 block. They were cast and machined in the US. They had cylinder walls that were so thick there was no gap between adjacent cylinders in the water jacket (i.e. siamesed). The thick cylinder walls allowed Bud Moore and others to bore the cylinders to 4.080" thereby achieving 366 cubic inches. The bulkheads at mains #1 and #5 were thickened on their internal sides, but left "stock appearing" on their external sides; this gave the block the external appearance of a production block. The 3 central bulkheads were thickened on both sides. It is rumored that approximately 200 "good" copies of this block had been cast between 1969 and 1972 (Bud Moore's first season in NASCAR was 1972). These blocks preceded the racing blocks cast in Australia and were available at the time Bud Moore built the racing motors for the Group 4 Panteras.
As the years went by and improved parts were made available the DeTomaso 351C endurance racing motors were equipped with heavy duty NASCAR blocks (the ones cast in Australia), steel crankshafts and Holman and Moody cams and valve train. The motors were capable of operating at higher rpm, they made more horsepower and yet they were developed to such a high state of durability they could undergo an entire season of endurance racing without failure or rebuilding. That is an outstanding accomplishment for any motor.