5.0L, 305 Bare Block. 1986-Later Style, 4-Bolt Main, 1-Piece Rear Main Seal. Replaces GM #10243869

5.0L, 305 Bare Block. 1986-Later Style, 4-Bolt Main, 1-Piece Rear Main Seal. Replaces GM #10243869

New Standard bore 5.0L, 305 Bare Block. Ready to be assembled. Camshaft bearings, brass freeze plugs, and oil line plugs installed. 

• Cast-iron 4-bolt main block
• 4.000" bore
• Machined for hydraulic roller or flat tappet lifters

About our Engine Blocks

When building a small block performance or marine engine, or a replacement for a stock engine, our performance 4-bolt main engine blocks are an ideal option for your build. A much better option than using an engine core, our new blocks bring peace of mind, OEM precision, and durability that others cannot. Each cylinder block is machined to production spec tolerances and is manufactured to the exact specifications of 1986-newer one-piece RMS 878 engine blocks.

The benefit of using our in house produced engine blocks include:

• Priority main oiling system feeds main bearings first. See Figure 1.
• Siamese cylinder bores with extra thick walls resist cracking and improve ring seal for more power (minimum .275” thick with 4.185” bore).
• Open lifter valley improves oil return to pan.
• Blind head bolt holes don’t go through to water jacket.
• Billet steel 4-bolt main bearing caps on all 5 mains.

Figure 1: Priority main oiling primes the main bearings first and then to the lifters and top end instead of top down oil priming in OEM blocks allowing for peak performance at high temperatures.