Diesel 350 blocks are extremely desirable as the basis for a 600+HP buildup
Before showing the differences in blocks, let’s explain why we would want a better block, and what kind of horsepower range we are talking about.
| | With the Oldsmobile V8’s, there are 4 basic “levels” of block durability.
Fourth (weakest) are the ’77 and later blocks (260, 307, 350, and 403). These were all small blocks, and all have “windowed” main webbing. This means there are 2 large triangular open holes in each of the main webs. This was done to lighten the blocks. They also have threads for ½” head bolts and 2.50" crankshaft main bearing journals. These blocks are fine for building a 300-350HP street engine. 300-350HP in a 3500lb car will get you into the 13's in the quarter mile.
Third in durability are the standard 330, 350, 400, 425, and 455 blocks. These blocks are a thicker casting in general, and do not have windowed main webs. They were produced from ’64 thru ’76, and take 7/16” head bolts. 330's and 350's have the standard 2.50" crankshaft main journals, while the 400 through 455's have standard 3.00" main journals. These blocks prepared correctly, are fine for up to 600HP. 600HP will get a 3500lb car into the low 10’s.
Second in durability is the 350 Diesel block. They were produced in 2 forms – the 350D and the 350DX block. This moniker is cast into the side of the block in very large letters. The 350D block has the common .841” diameter lifter bores, while the 350DX block has the larger .921” diameter lifter bores for factory hydraulic roller lifters. Most novices think getting the larger lifter bores is better, but all racers want the 350D block with the small lifter bores. This is because when building any racing engine, you will install solid roller lifters, NOT heavy, weak factory hydraulic roller lifters, and the aftermarket solid rollers are not available in the .921" sizes. The larger lifter bores can be reduced down to the smaller size by installing bushings and resizing them. Either way, the diesel blocks are the heaviest, thickest block you could get in a passenger car. Note in the picture how the diesel block’s main webbing is extremely thick. This is the area that racers making over 550HP have problems cracking, both in big blocks and gasoline small blocks. The diesel block is ideal for adding steel 4 bolt main bearing caps to, with some expert machine work. The diesel blocks also have the big block sized 3.00” mains, rather than the 2.50” mains like all the other small blocks. This provides several crankshaft options... a big block steel 425 crank will fit, but not without some expensive machine work (for starters, the crank counterweights must be reduced in radius by .375"). The 455 crank will NOT fit, so don't try (believe me, others have already thought of this and tried)! Some racers use main bearing spacers in the block saddles, and a 4 bolt steel main bearing cap with a reduced saddle size to use a 2.50" diameter main bearing crank.
This picture shows the differeces between a standard non-webbed and diesel small block.
All 455 blocks are similar in construction to the standard small block shown above.
|The top of the line in Olds V8 blocks is the elusive NASCAR “HP” block. This was the block that was produced by GM for the NASCAR stock car program. Unlike the Olds DRCE blocks (which are really an enlarged Chevy big block), these "real" Olds blocks fit any head, intake, crankshaft, and oil pan that would fit a factory Olds small block. They also have the traditional small block 2.50” main bearing size preferred by racers. The HP blocks were produced in two versions: siamese bore and non-siamese bore (a siamese bore means that coolant does not flow between the cylinders, allowing for a larger cylinder bore and larger displacement). According to Art Rizzi Jr. ("SPOLDS" on RealOldsPower.com), the non-siamese bore blocks are the most plentiful. They can typically be bored to 4.155", and with a sonic check sometime a little more. The more desirable siamese bore block was a low production block. Some say a little as 30 or less were made by Oldsmobile and can command a $2500 price tag for those that need the strength. These can typically be bored to 4.250". The HP block pictured at left is shown as it came from the factory - it has only a NASCAR casting number, and was finished with 2.5" mains and .842" lifter bores and the cylinders were rough bored to 3.80". Notice the main webs and oil pan rail are the thickest of all, and the entire main web surface is finish machined, facilitating installation of steel 4 bolt main bearing caps. There are racers at this time producing over 1000HP with these blocks with 4 bolt mains and aftermarket steel crankshafts.