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Eagle Flat Top 461ci Competition Rotating Assembly Stroker Kit, for 400 Block, 4.250" str.

  • Eagle Kit 51500- Mahle -6cc Flat Top Pistons
  • New Forged Crank 4.250" Stroke
  • .035" Over- 4.155" Bore, 461 cu.in.
  • 6.800" forged 4340 H-Beam rods w/7/16" ARP 8740 rod bolts
  • Plasma-moly rings
  • Performance Main & Rod Bearings
  • All assemblies must be balanced prior to installation
Pricing: $2,549.95

Customize Your Item

- Choose your balancing option -
 * required


Forged steel crankshaft, forged 4340 H-Beam rods
7/16” ARP 8740 capscrew rod bolts (ARP 2000 & L19 available).
Forged 4032 Mahle pistons and plasma-moly file fit rings.
Performance bearings.
Designed for internal balance with no heavy metal needed.
Recommended for Street/Strip use.

All assemblies that are internally balanced will require a neutral balanced flexplate or flywheel and harmonic balancer.

All Eagle kits contain File Fit Rings

The Butler Process

All rotating assemblies sold by Butler Performance, regardless of brand, must be balanced. Our balancing service offers balancing in our shop by our experienced machinists.

We don't take anyone else's word when it comes to the parts we stand behind. We put all rotating assemblies through the Butler Process for quality and performance. Our internal balancing process ensures each part of the kit is put through a multi-step inspection process. We then weigh and pin fit the rods and pistons as needed. We computer balance the crankshaft to the rest of the assembly. This process ensures that all the parts of the assembly are matched to form a "Butler Performance" worthy assembly. We then document all weights and information on a balance card that ships with the assembly.


Cast crankshafts are an excellent alternative to O.E. Cranks. These crankshafts are new cast pieces made with modern material and casting processes to be a great alternative to 30 year old factory cranks. Recommended for use in street engines without power adders. Many factory cranks we check have stress cracks, so even though your crank has not broken yet, you may have a problem developing that could destroy your engine.

Forged Cranks offer a tremendous advantage in strength and durability over cast cranks. This is very inexpensive insurance to protect your engine and even if its not needed at your current horsepower level now. Upgrading to a forged crank to build a solid bottom end will give you the option to safely upgrade performance and increase horsepower without having to worry about costly breakdowns in the future.


Butler Performance chooses to start Bore Size options for rotating assemblies, short blocks, long blocks, and engines at .030" to .035" over. Most engines have normal wear and machining the block and honing the cylinders to .030"-.035" over will ensure that you have a good foundation to install your assembly into. This ensures the pistons and rings will seat properly and be within specs and tolerances for building an engine capable of performance, horsepower, and longevity usually found in a Butler Engine.

Std Rings- The rings are normally "Drop-In" Style rings. These still may require additional filing for your application.

File Fit- The rings are usually .005" over the desired bore size so they can be filed to fit.

Example; Total Seal CR, .030 Over, File Fit, 4.150+5 Bore
This is a Total Seal brand, Classic Race Series ring used in a .030" over bore application. The stock bore is 4.120" plus the .030" making it a 4.150" bore size. The ring will actually measure 4.155" so that there is an extra .005" so it can be filed to fit the desired ring gap.


Most rods in our rotating assembly's are high tensile 4340 Forged H-beam or 5140 Forged I-Beam. All rods are full floating, bushed unless otherwise noted.

Most rods come with stock ARP8740 rod bolts are rated at a tensile strength of 190,000 psi. Upgraded ARP2000 rod bolts rated at 220,000 are also available.


ESP Armor is a revolutionary new surface finishing process that is available only through Eagle. Similar processes exist, but ESP armor is unique because it is NOT A COATING, nor is it a chemical etching process. ESP Armor is a unique surface finishing process that results in an incredibly slick surface. This has many benefits. First and foremost is reduce bearing friction. By giving the oil a slicker surface to slide along, the bearing friction is reduced. This will also be evident in slower oil heating, reduced windage losses, and improved corrosion resistance. You will also notice that your bearings will live longer as a result of ESP Armor. The finish is unmistakable. Although it resembles chrome, it is not a coating that might flake off or wear out. Eagle is so confident in the effects ESP Armor has on our rods and cranks that we include a ONE YEAR LIMITED WARRANTY against breakage when ESP Armor is used on any 4340 steel crankshaft or H-beam rod. Many customers have tried it and all have been not only pleased, but surprised by the results. You’ve got to see it, and use it, to believe it!

Compression Calculator

Compression Calculator

Simply fill in the form below to calculate your compression ratio

*BP Flat Top pistons normally include +8cc valve pockets. When selecting dish piston from list, do not add valve pocket cc volume. Valve pocket cc is already included in the dish piston volume*

Bore: (diameter)
Cylinder Head Volume:
Effective Dome Volume:
Use (-) for Dome and (+) for Dish.
Deck Clearance:
Compressed Gasket Thickness:
Number of Cylinders:
Compression Ratio :  
Total Displacement (in.3) :  
Total Displacement cc's :  

Listed is an example of a 461 cu.in. with a 72cc head.

If deck clearance and head gasket sizes are not known, enter 0 and .040 as shown below.

*Chamber volume cc should be entered as a (+) number for dish and (-) negative for dome*

Cu. In. Chart

Pontiac Cu.In. Chart

400 Block Stroke
Bore 3.75 4.00 4.21 4.25 4.35 4.50
Stock 4.120 400 427 449 453 461 480
+.030 4.150 406 433 456 460 471 487
+.035 4.155 407 434 457 461 472 488
+.040 4.160 408 435 458 462 473 489
+.050 4.170 410 437 460 464 475 492
+.060 4.180 412 439 462 467 478 494
+.065 4.185 413 440 463 468 479 495


  • EAG-51500-4155
  • EAG-51500-4155
  • Eagle Specialty
  • New

Shipping Information

  • Item Requires Shipping
  • 130.0 lbs.

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