New Splayed Main block using GEP 6.5L Diesel Engine Block
For Center Mount Turbo CMT applications.
Please note that this product page is primarily used to display the base engine block that has been modified to utilize splayed main caps on the center 3 main caps. This product is best purchased as an option on a Custom Engine build.
Well folks, it's finally available, and long over-due but a proper solution for the 6.5L engines that crack the main webbing. This splayed block solution provides a tremendous amount of improvement in rigidity on top of many improvements made by AM General that greatly improved upon the GM variants. This is the first time this has been offered for new engines.
About Splayed Mains
Splayed main caps have long been a go-to strength improvement to allow an engine block to produce higher power numbers. This is a widely successful and understood modification used on performance gas engines using cylinder blocks that are of the shallow-skirt design. Common examples of other shallow-skirt engine designs are most of the GM Chevrolet V-8 Gas engines like the 350 and the 454 and variants in between. This modification either converts a 2-bolt main block to a 4-bolt main block or abandons the outside bolt holes on a block that was already a 4-bolt main. The problem with 4-bolt main blocks is while it creates better clamping of a main cap to a block, the placement of the fastener threads in the block is in a weak part of the block where the cylinder bore partially intersects the main webbing bridge. Removing material to drill and tap for threads weakens the main web, then the stress of the bolt being stretched and cycled in a running engine causes stress and can eventually break the block (which is what we see in 6.2L and 6.5L Diesel engine blocks). The splayed mains address this by using a wider cap that enables the outside bolt hole to go beyond the weak spot of the main webbing and places the bolt into a more solid part of the bottom of the block where there is more material. The wider cap also helps create more rigidity. The angled bolt hole compared to the factory bolt that is installed straight into the bottom of the block also helps clamp the cap in place by having alternating angles which pull the cap outward and onto the block reducing the chance of the cap from being able to move on the block at all (cap walk eliminated).
The process implementation of splayed mains is not just for modifying factory blocks, performance race engine blocks come with them from the beginning. Even deep-skirt blocks like found on the LS-series GM engines are starting to receive splayed mains within the railings of the deep skirt block design in aftermarket blocks in an effort to further improve performance handling abilities in the block.
The Process of Installing Splayed Main Caps
To begin we start out with a new 6.5L block.
The block is loaded into a CNC engine block machine and carefully squared up in precise fixturing. Then the number 2,3,4 main caps and fasteners are removed from the block and discarded. The block then receives new parallel cut registers that are much wider than the former factory cap registers. Splayed caps are placed onto the block is their new registers. The caps receive studs in the center mounting holes, after being carefully aligned on the block. Once the caps are mounted to the engine block, the fixture holding the block is rotated to accommodate the precise angle to drill the block for angled bolts. A specific measured depth is specified from the block floor holding the cap to drill into the block bottom rail where there is material. The holes are then threaded using a bottoming tap to the end of the drilled hole. Specific numbers are used in the depth to both maintain excellent full thread engagement for the cap fastener and leave material in the block and keep the hole away from the water jacket, the holes retain material for safe blind holes.
The block then receives the hardest part of the entire process. A proper align bore has to occur to bore the new caps to specific sizes and maintain full main alignment and sizing between all 5 mains. The block receives all replacement studs and bolts on every cap. Each cap is held on with studs, adding studs to mains 1 and 5 and studs along the entire crankshaft center line. The splayed main caps receive studs in the middle and bolts on the outer holes. Everything is lined up and torqued. The block then receives a full align bore on a CNC block machine ending in a precise and repeatable housing size on each main. Factory blocks are machined by align bore only, and we are matching that process down to the final .0001" (ten-thousandths).
Unique Diesel is extremely detailed in demanding exacting standards, tremendous efforts have been accomplished to ensure that the process to create these splayed blocks either meets or exceeds an OE standard. We want it right!
Splayed 6.5L Vs. P400 6.5L
All things considered, we have worked with both variants. The Splayed 6.5L can handle the same power as the rated power level of the P400 engine. The Splayed 6.5L beats the P400 in application, availability, support-ability. The Splayed 6.5L is the replacement for the P400.
Application...
The Splayed 6.5L as an engine assembly can replace all 6.2 and 6.5 Diesel engines in their original vehicle applications. The P400 can not directly replace all variations of engines without modifications (like custom oil pan). The P400 is really only applicable to a Humvee, and does not readily install in civilian vehicle applications.
Availability and Support...
The Splayed 6.5L is currently in production because the base engine used to produce the Splayed 6.5L engine is newly available. All of the internal parts of the Splayed and production GEP engines are readily available and in production and many parts are supported by the Aftermarket.
The P400 6.5L was fully discontinued by the manufacturer back in 2023. Prior to formal discontinuation only old stock parts were being sold as the engine was long out of production. Currently, only new-old-stock versions exist at great expense, and the same can be said for the proprietary replacement parts that were discarded by the manufacturer. No support parts exist from the original source. The P400 is obsolete and creates many support and rebuild issues due to many proprietary components that are unsupported even in the aftermarket.
Splayed Block Compatibility
Block is compatible with former
6.5L block and rotating assembly components. Replacement for blocks
with casting numbers ending in 6.5L Diesel casting 141 and
506.
This block comes bare as seen in the
pictures and only comes with the 5 expansion casting core plugs, all other necessary block hardware items are not
installed including cam bearings. All the hardware block components are available as a product
option hardware kit containing the necessary items. Block comes with a
light rust preservative (why cylinder bores are dirty looking), not
responsible for rust storage issues once shipped, take necessary steps
to preserve block if not being used immediately. Recommend cylinder hone to match your specific piston usage using a torque plate.
The
block hardware kit provides all the threaded plugs, press-in plugs, oil
spray jets, dowels, and bypass valves. This is an extensive kit with
all the hard to find and hidden items.
Ordering Process
This product is a Build to Order item whereby we will order the proper block then perform the processes on that block. Typical processing time for this is 12-weeks. We may have blocks already processed on-hand, but they are only utilized for custom engine builds, ordering of this product is considered a special order.
