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Speedy Bill
Since 1952
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Forged Small Block Chevy Rotating Assembly, 421 .283 Dome, 400 Mains, 6 Rod

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Specs
Sold in Quantity:
Kit
Piston Diameter:
-
Stroke:
3.875
Main Journal Style:
400 mains
Rod Journal Diameter:
2.10"
Rear Main Seal Style:
2-piece
Wrist Pin Diameter:
.9272
Piston Ring Style:
C
Connecting Rod Length:
6.000"
Piston Weight:
427
Piston Style:
Dome
Dome Height:
.283
Piston Material:
Forged Aluminum
Garage Sale:
No
Main Journal Diameter:
2.650
Bearing Undersize:
Standard
Narrowed Bearing:
Yes
Bearing Construction:
Bi-metal
Coated Bearing:
No
Crankshaft Material:
Forged 4340 Steel
Connecting Rod Type:
H-Beam
Connecting Rod Material:
Forged 4340 Steel
Connecting Rod Weight:
634
Forged Small Block Chevy Rotating Assembly, 421 .283 Dome, 400 Mains, 6 Rod
Forged Small Block Chevy Rotating Assembly, 421 .283 Dome, 400 Mains, 6 Rod

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Details

Reviews

Q & A

What's in the Box

Speedway introduces forged rotating assemblies, with an optional balance job. Includes new 2-pc rear main seal crank, rods and pistons. Cranks are new so they use standard size bearings.

All Scat 4340 cranks are 2-piece rear main seal, internally balanced and weigh approximately 51-55 lbs.  All balancing is done with our state-of-the-art Hines balancer by race mechanics with over 30 years of experience!  A kit purchased with the optional balance job will ship in 24-48 hours. These rotating assembly engine rebuild kits may require additional charges for heavy metal.

If you are going to run this crank in a sprint car motor, you must have the crank flange turned down prior to balancing the crank to allow it to go through the motor plate. 

NOTE: A balance rotating assembly option is currently not offered for this package but the proper balancing service can be determined after your order is placed.  If you would like our balancing option service for 395 and 421 engine builds, please call 1-800-979-0122 when placing order.

NOTE: Piston rings are not included and must be purchased separately. Use Style C rings.

Application

  • 415/421-ci SBC (3.875-inch stroke)
    • Displacement: 421 ci
    • Bore x Stroke: 4.155 x 3.875 inches
    • Compression: 10.7:1
    • Rod: 6.00-inch

 

Notes

Kits feature: 

  • Scat 4340 Forged Steel Crankshaft   
    • Standard size journals
    • Straight shot and chamfered oil holes
    • Nitride hardened and shot peened
    • Lightening holes in all rod throws
    • Large radius on all journals
  • KB Signature Series Forged Pistons 
    • 2618 aluminum alloy construction
    • T-6 heat treated 
    • 4.000" bore pistons available in standard, .030, .040, or .060 sizes
    • 4.125" bore pistons available in .030 or .040 sizes
  • Speedway 4340 H-beam Connecting Rods
    • Full floating pin in silicon bronze bushing
    • Precision bolt bushings to positively locate cap
    • 6.0" lengths
    • 634 grams
    • Weight matched set of 8 rods
  • King HP Series Main & Rod Bearings
    • 0.015" thick top layer for superior macro particle embedability and conformability
    • 40 Vickers hardness to resist overlay migration and extrusion
    • 450°F heat threshold for superior protection against friction and overheating
    • Mains are 3/4 grooved for improved oiling to the rod journals
    • Bi-metal aluminum silicon alloy featuring fine micro-bore finish

You may also be interested in:

Forged SB Chevy Rotating Assembly, 350 Flat Top, H-Beam, 5.7 Rods
(Part #9151220)
                        

Speedway introduces forged rotating assemblies, with an optional balance job. Includes new 2-pc rear main seal crank, rods and pistons. Cranks are new so they use standard size bearings. All Scat 4340 cranks are 2-piece rear main seal, internally balanced and weigh approximately 51-55 lbs.

All balancing is done with our state-of-the-art Hines balancer by race mechanics with over 30 years of experience!  A kit purchased with the optional balance job will ship in 24-48 hours. These rotating assembly engine rebuild kits may require additional charges for heavy metal.

If you are going to run this crank in a sprint car motor, you must have the crank flange turned down prior to balancing the crank to allow it to go through the motor plate.

NOTE: Piston rings are not included and must be purchased separately. Use Style C rings.

Kits feature: 

  • Scat 4340 Forged Steel Crankshaft    
    • Standard size journals
    • Straight shot and chamfered oil holes
    • Nitride hardened and shot peened
    • Lightening holes in all rod throws
    • Large radius on all journals
  • KB Signature Series Forged Pistons 
    • 2618 aluminum alloy construction
    • T-6 heat treated 
    • 4.000" bore pistons available in standard, .030, .040, or .060 sizes
    • 4.125" bore pistons available in .030 or .040 sizes
  • Speedway 4340 H-beam Connecting Rods
    • Full floating pin in silicon bronze bushing
    • Precision bolt bushings to positively locate cap
    • 5.7" lengths
    • 622 grams
    • Weight matched set of 8 rods
  • King HP Series Main & Rod Bearings
    • 0.015" thick top layer for superior macro particle embedability and conformability
    • 40 Vickers hardness to resist overlay migration and extrusion
    • 450°F heat threshold for superior protection against friction and overheating
    • Mains are 3/4 grooved for improved oiling to the rod journals
    • Bi-metal aluminum silicon alloy featuring fine micro-bore finish
  • Chevy 350: 4.000" bore x 3.48" stroke
Forged SB Chevy Rotating Assembly, 350 Flat Top, H-Beam, 6 Rod
(Part #9151230)
                        

Speedway introduces forged rotating assemblies, with an optional balance job. Includes new 2-pc rear main seal crank, rods and pistons. Cranks are new so they use standard size bearings. 

All Scat 4340 cranks are 2-piece rear main seal, internally balanced and weigh approximately 51-55 lbs.  All balancing is done with our state-of-the-art Hines balancer by race mechanics with over 30 years of experience!  A kit purchased with the optional balance job will ship in 24-48 hours. These rotating assembly engine rebuild kits may require additional charges for heavy metal.

If you are going to run this crank in a sprint car motor, you must have the crank flange turned down prior to balancing the crank to allow it to go through the motor plate.

Chevy 383: 4.000" bore x 3.75" stroke

NOTE: Piston rings are not included and must be purchased separately. Use Style C rings.

Forged Small Block Chevy Rotating Assembly, 350 Dome, H-Beam, 6 Rod
(Part #9151235)
                        

Speedway introduces forged rotating assemblies, with an optional balance job. Includes new 2-pc rear main seal crank, rods and pistons. Cranks are new so they use standard size bearings. 

All Scat 4340 cranks are 2-piece rear main seal, internally balanced and weigh approximately 51-55 lbs.  All balancing is done with our state-of-the-art Hines balancer by race mechanics with over 30 years of experience!  A kit purchased with the optional balance job will ship in 24-48 hours. These rotating assembly engine rebuild kits may require additional charges for heavy metal.

If you are going to run this crank in a sprint car motor, you must have the crank flange turned down prior to balancing the crank to allow it to go through the motor plate.

Chevy 350: 4.000" bore x 3.48" stroke

NOTE: Piston rings are not included and must be purchased separately. Use Style C rings.

Forged SB Chevy Rotating Assembly, 383 Flat Top, H-Beam, 5.7 Rods
(Part #9151250)
                        

Speedway introduces forged rotating assemblies, with an optional balance job. Includes new 2-pc rear main seal crank, rods and pistons. Cranks are new so they use standard size bearings.

All Scat 4340 cranks are 2-piece rear main seal, internally balanced and weigh approximately 51-55 lbs.  All balancing is done with our state-of-the-art Hines balancer by race mechanics with over 30 years of experience!  A kit purchased with the optional balance job will ship in 24-48 hours. These rotating assembly engine rebuild kits may require additional charges for heavy metal.

If you are going to run this crank in a sprint car motor, you must have the crank flange turned down prior to balancing the crank to allow it to go through the motor plate.

Chevy 383: 4.000" bore x 3.75" stroke

NOTE: Piston rings are not included and must be purchased separately. Use Style C rings.

Forged Small Block Chevy Rotating Assembly, 383 Dome, H-Beam, 5.7 Rods
(Part #9151255)
                        

Speedway introduces forged rotating assemblies, with an optional balance job. Includes new 2-pc rear main seal crank, rods and pistons. Cranks are new so they use standard size bearings. 

All Scat 4340 cranks are 2-piece rear main seal, internally balanced and weigh approximately 51-55 lbs.  All balancing is done with our state-of-the-art Hines balancer by race mechanics with over 30 years of experience!  A kit purchased with the optional balance job will ship in 24-48 hours. These rotating assembly engine rebuild kits may require additional charges for heavy metal.

If you are going to run this crank in a sprint car motor, you must have the crank flange turned down prior to balancing the crank to allow it to go through the motor plate.

Chevy 383: 4.000" bore x 3.75" stroke

NOTE: Piston rings are not included and must be purchased separately. Use Style C rings.

Forged SB Chevy Rotating Assembly, 383 Flat Top, H-Beam, 6 Rod
(Part #9151260)
                        

Speedway introduces forged rotating assemblies, with an optional balance job. Includes new 2-pc rear main seal crank, rods and pistons. Cranks are new so they use standard size bearings.

All Scat 4340 cranks are 2-piece rear main seal, internally balanced and weigh approximately 51-55 lbs.  All balancing is done with our state-of-the-art Hines balancer by race mechanics with over 30 years of experience!  A kit purchased with the optional balance job will ship in 24-48 hours. These rotating assembly engine rebuild kits may require additional charges for heavy metal.

If you are going to run this crank in a sprint car motor, you must have the crank flange turned down prior to balancing the crank to allow it to go through the motor plate.

Chevy 383: 4.000" bore x 3.75" stroke

NOTE: Piston rings are not included and must be purchased separately. Use Style C rings.

Forged SB Chevy Rotating Assembly, 383 Dome, H-Beam, 6 In Rods
(Part #9151265)
                        

Speedway introduces forged rotating assemblies, with an optional balance job. Includes new 2-pc rear main seal crank, rods and pistons. Cranks are new so they use standard size bearings. 

All Scat 4340 cranks are 2-piece rear main seal, internally balanced and weigh approximately 51-55 lbs.  All balancing is done with our state-of-the-art Hines balancer by race mechanics with over 30 years of experience!  A kit purchased with the optional balance job will ship in 24-48 hours. These rotating assembly engine rebuild kits may require additional charges for heavy metal.

If you are going to run this crank in a sprint car motor, you must have the crank flange turned down prior to balancing the crank to allow it to go through the motor plate.

Chevy 383: 4.000" bore x 3.75" stroke

NOTE: Piston rings are not included and must be purchased separately. Use Style C rings.

Forged S/B Chevy Rotating Assy., 434 Flat Top, 350 Main Journal, 6 Rod
(Part #9151270)
                        

Speedway introduces forged rotating assemblies, with an optional balance job. Includes new 2-pc rear main seal crank, rods and pistons. Cranks are new so they use standard size bearings.

All Scat 4340 cranks are 2-piece rear main seal, internally balanced and weigh approximately 51-55 lbs.  All balancing is done with our state-of-the-art Hines balancer by race mechanics with over 30 years of experience!  A kit purchased with the optional balance job will ship in 24-48 hours. These rotating assembly engine rebuild kits may require additional charges for heavy metal.

If you are going to run this crank in a sprint car motor, you must have the crank flange turned down prior to balancing the crank to allow it to go through the motor plate.

Chevy 434: 4.125" bore x 4.00" stroke

NOTE: Piston rings are not included and must be purchased separately. Use Style C rings.

Forged S/B Chevy Rotating Assy., 434 Flat Top, 400 Main Journal, 6 Rod
(Part #9151275)
                        

Speedway introduces forged rotating assemblies, with an optional balance job. Includes new 2-pc rear main seal crank, rods and pistons. Cranks are new so they use standard size bearings. 

All Scat 4340 cranks are 2-piece rear main seal, internally balanced and weigh approximately 51-55 lbs.  All balancing is done with our state-of-the-art Hines balancer by race mechanics with over 30 years of experience!  A kit purchased with the optional balance job will ship in 24-48 hours. These rotating assembly engine rebuild kits may require additional charges for heavy metal.

If you are going to run this crank in a sprint car motor, you must have the crank flange turned down prior to balancing the crank to allow it to go through the motor plate.

Chevy 434: 4.125" bore x 4.00" stroke

NOTE: Piston rings are not included and must be purchased separately. Use Style C rings.

Forged Small Block Chevy Rotating Ass., 434 Dome, 350 Main Journal, 6 Rod
(Part #9151280)
                        

Speedway introduces forged rotating assemblies, with an optional balance job. Includes new 2-pc rear main seal crank, rods and pistons. Cranks are new so they use standard size bearings.

All Scat 4340 cranks are 2-piece rear main seal, internally balanced and weigh approximately 51-55 lbs.  All balancing is done with our state-of-the-art "hines" balancer by race mechanics with over 30 years of experience!  A kit purchased with the optional balance job will ship in 24-48 hours. These rotating assembly engine rebuild kits may require additional charges for heavy metal.

If you are going to run this crank in a sprint car motor, you must have the crank flange turned down prior to balancing the crank to allow it to go through the motor plate.

Chevy 434: 4.125" bore x 4.00" stroke

NOTE: Piston rings are not included and must be purchased separately. Use Style C rings.

Forged Small Block Chevy Rotating Ass., 434 Dome, 400 Main Journal, 6 Rod
(Part #9151285)
                        

Speedway introduces forged rotating assemblies, with an optional balance job. Includes new 2-pc rear main seal crank, rods and pistons. Cranks are new so they use standard size bearings.

All Scat 4340 cranks are 2-piece rear main seal, internally balanced and weigh approximately 51-55 lbs.  All balancing is done with our state-of-the-art Hines balancer by race mechanics with over 30 years of experience!  A kit purchased with the optional balance job will ship in 24-48 hours. These rotating assembly engine rebuild kits may require additional charges for heavy metal.

If you are going to run this crank in a sprint car motor, you must have the crank flange turned down prior to balancing the crank to allow it to go through the motor plate.

Chevy 434: 4.125" bore x 4.00" stroke

NOTE: Piston rings are not included and must be purchased separately. Use Style C rings.

Labor To Side Clearance Rods and Balance Rotating Assembly, 434 Kit
(Part #91510222)
                        All balancing is done with our state-of-the-art "hines" balancer by race mechanics with over 30 years of experience!  A kit purchased with the optional balance job will ship in 24-48 hours. These rotating assemblies may require additional charges for heavy metal.

Forged Small Block Chevy Rotating Assembly, 395 .063 Dome, 350 Mains, 6 Rod
(Part #9151267)
                        

Speedway introduces forged rotating assemblies, with an optional balance job. Includes new 2-pc rear main seal crank, rods and pistons. Cranks are new so they use standard size bearings. 

All Scat 4340 cranks are 2-piece rear main seal, internally balanced and weigh approximately 51-55 lbs.  All balancing is done with our state-of-the-art Hines balancer by race mechanics with over 30 years of experience!  A kit purchased with the optional balance job will ship in 24-48 hours. These rotating assembly engine rebuild kits may require additional charges for heavy metal.

If you are going to run this crank in a sprint car motor, you must have the crank flange turned down prior to balancing the crank to allow it to go through the motor plate.

NOTE: A balance rotating assembly option is currently not offered for this package but the proper balancing service can be determined after your order is placed.  If you would like our balancing option service for 395 and 421 engine builds, please call 1-800-979-0122 when placing order.

NOTE: Piston rings are not included and must be purchased separately. Use Style C rings.

Forged Small Block Chevy Rotating Assembly, 395 .400 Dome, 350 Mains, 6 Rod
(Part #9151268)
                        

Speedway introduces forged rotating assemblies, with an optional balance job. Includes new 2-pc rear main seal crank, rods and pistons. Cranks are new so they use standard size bearings.

All Scat 4340 cranks are 2-piece rear main seal, internally balanced and weigh approximately 51-55 lbs.  All balancing is done with our state-of-the-art Hines balancer by race mechanics with over 30 years of experience!  A kit purchased with the optional balance job will ship in 24-48 hours. These rotating assembly engine rebuild kits may require additional charges for heavy metal.

If you are going to run this crank in a sprint car motor, you must have the crank flange turned down prior to balancing the crank to allow it to go through the motor plate. 

NOTE: A balance rotating assembly option is currently not offered for this package but the proper balancing service can be determined after your order is placed.  If you would like our balancing option service for 395 and 421 engine builds, please call 1-800-979-0122 when placing order.

NOTE: Piston rings are not included and must be purchased separately. Use Style C rings.

Forged Small Block Chevy Rotating Assembly, 421 Flat Top, 350 Mains, 6 Rod
(Part #9151271)
                        

Speedway introduces forged rotating assemblies, with an optional balance job. Includes new 2-pc rear main seal crank, rods and pistons. Cranks are new so they use standard size bearings.

All Scat 4340 cranks are 2-piece rear main seal, internally balanced and weigh approximately 51-55 lbs.  All balancing is done with our state-of-the-art Hines balancer by race mechanics with over 30 years of experience!  A kit purchased with the optional balance job will ship in 24-48 hours. These rotating assembly engine rebuild kits may require additional charges for heavy metal.

If you are going to run this crank in a sprint car motor, you must have the crank flange turned down prior to balancing the crank to allow it to go through the motor plate. 

NOTE: A balance rotating assembly option is currently not offered for this package but the proper balancing service can be determined after your order is placed.  If you would like our balancing option service for 395 and 421 engine builds, please call 1-800-979-0122 when placing order.

NOTE: Piston rings are not included and must be purchased separately. Use Style C rings.

Forged Small Block Chevy Rotating Assembly, 421 Flat Top, 400 Mains, 6 Rod
(Part #9151272)
                        

Speedway introduces forged rotating assemblies, with an optional balance job. Includes new 2-pc rear main seal crank, rods and pistons. Cranks are new so they use standard size bearings.

All Scat 4340 cranks are 2-piece rear main seal, internally balanced and weigh approximately 51-55 lbs.  All balancing is done with our state-of-the-art Hines balancer by race mechanics with over 30 years of experience!  A kit purchased with the optional balance job will ship in 24-48 hours. These rotating assembly engine rebuild kits may require additional charges for heavy metal.

If you are going to run this crank in a sprint car motor, you must have the crank flange turned down prior to balancing the crank to allow it to go through the motor plate. 

NOTE: A balance rotating assembly option is currently not offered for this package but the proper balancing service can be determined after your order is placed.  If you would like our balancing option service for 395 and 421 engine builds, please call 1-800-979-0122 when placing order.

NOTE: Piston rings are not included and must be purchased separately. Use Style C rings.

Forged Small Block Chevy Rotating Assembly, 421 .283 Dome, 350 Mains, 6 Rod
(Part #9151273)
                        

Speedway introduces forged rotating assemblies, with an optional balance job. Includes new 2-pc rear main seal crank, rods and pistons. Cranks are new so they use standard size bearings.

All Scat 4340 cranks are 2-piece rear main seal, internally balanced and weigh approximately 51-55 lbs.  All balancing is done with our state-of-the-art Hines balancer by race mechanics with over 30 years of experience!  A kit purchased with the optional balance job will ship in 24-48 hours. These rotating assembly engine rebuild kits may require additional charges for heavy metal.

If you are going to run this crank in a sprint car motor, you must have the crank flange turned down prior to balancing the crank to allow it to go through the motor plate. 

NOTE: A balance rotating assembly option is currently not offered for this package but the proper balancing service can be determined after your order is placed.  If you would like our balancing option service for 395 and 421 engine builds, please call 1-800-979-0122 when placing order.

NOTE: Piston rings are not included and must be purchased separately. Use Style C rings.

King HP Series Chevy 350/400 Large Journal Engine Rod Bearings, Std
(Part #910807HP-STD)
                        
  • Bi-metal aluminum silicon alloy featuring fine micro-bore finish
  • Mains and rods are narrowed for large radius crankshafts
  • Greater rod bearing height improves bearing-to-bore contact/heat transfer and reduces spin potential at high RPM
  • 0.015" thick top layer for superior macro particle embedability and conformability
  • 40 Vickers hardness to resist overlay migration and extrusion
  • 450°F heat threshold for superior protection against friction and overheating
King HP Series Chevy 400 Large Journal Engine Main Bearings, Standard
(Part #910509HP-STD)
                        
  • Bi-metal aluminum silicon alloy featuring fine micro-bore finish
  • Mains and rods are narrowed for large radius crankshafts
  • Mains are 3/4 grooved for improved oiling to the rod journals
  • Greater rod bearing height improves bearing-to-bore contact/heat transfer and reduces spin potential at high RPM
  • 0.015" thick top layer for superior macro particle embedability and conformability
  • 40 Vickers hardness to resist overlay migration and extrusion
  • 450°F heat threshold for superior protection against friction and overheating
Total Seal Style E Conventional Style Piston Rings, .025 OS, 1.5/3mm
(Part #718CR2012-025)
                        

For years Total Seal has been leader in performance ring technology. These conventional style ring sets featuring a plasma moly ductile iron top ring, cast second and a 3-piece oil ring.  They have a 1.5mm top ring 1.5mm second ring and a 3mm oil control ring.  Fit many aftermarket piston including Mahle.

Ring Style Chart (GIF)