Sanctioning Body Specifications Handbook
Updated January 2020
*This engine was developed to compete with the 347 SR Ford Crate Engine utilizing as many of the parts used in a GM version as possible.
Displacement 350 cubic inch to 355 cubic inch
Block Dart HMS/ENFORCER
Bore 4.000 to 4.030 Plus Allowance for Wear of .005 Over Bore
Crankshaft Steel 4340 HMS/ENFORCER
Main Journal Size SBC Stock # Large Journal 2.449
Rod Journal Size SBC Stock # Large Journal 2.100
Crank Weight Min. 47 lb with Crank Gear, Flywheel Bolts and Pilot Bushing
Balance Offset Neutral
Vibration Damper 6 ¼ HMS/ENFORCER
Connecting Rod HMS/ENFORCER 6.000 Inch
Piston Forged HMS/ENFORCER
Dish or Dome Value Flat Top – 5 cc
Ring Set Any Brand Ring Set EXCEPT 0-Gap Rings measuring 1.0 1.0 2.0 mm / 1.5 1.5 3.0 mm
Compression Height 1.250
Pin Bore Diameter Minimum wrist pin diameter .927" oversize wrist pin permitted
Piston Material Forged Aluminum
Camshaft Mechanical Roller HMS/ENFORCER
Lifters Mechanical Roller Link Bar HMS/ENFORCER
Cam. Timing ***see note below ICL 104 + or – 2⁰ as Run in Engine
Camshaft Lobe Lift IN .3610 / EX .3630
Camshaft Duration @ .050 IN 230 / EX 236
Camshaft Lift IN .549 / EX .551 at 0 Lash
Calculated @ Valve with 1.52 Rocker
Valve Lash Cold .003 to .004 / Hot .008 to .010 – Recommended, not for Tech
Cylinder Head Aluminum HMS/ENFORCER
Chamber Volume 63cc + or - 2cc
Compression Ratio 10.5 : 1
Valves - Diameter HMS/ENFORCER - IN 2.0200 / EX 1.600
Intake & Exhaust Valve Stem Diameter 11/32
Valve Spring/Locators Steel
Approved Optional Springs PSI LS-1511 PAC 1218X Comp 26918
Valve Spring Installed Height 1.750 to 1.800
Valve Spring Retainers Beehive Steel HMS/ENFORCER 10⁰
Valve Lock 11/32 10⁰ STD or +/- .050
Rocker Arms HMS/ENFORCER 1.52 Ratio
Intake Manifold Edelbrock Victor Jr. #2975 HMS/ENFORCER With Any 1” Solid Aluminum
Straight Wall Open Spacer – No Lightening of the Spacer is Permitted
Push Rods HMS/ENFORCER 7.950
Timing Chain Set HMS/ENFORCER Double Roller Billet
Oil Pump M55HV
Oil Pan 7qt – 8qt HMS/ENFORCER
- Cam Spec Notification : Early HMS ENFORCER cams were ground with no advance, later cams were ground with 4 degree advance. Both Cams must run at above spec. -
Tech Specifications for Inspection
No unapproved modifications, lightening, or changes of any kind will be allowed to any of the HMS ENFORCER parts.
Max RPM 7000 – Recommended, not intended to be a CHIP Rule.
The HMS ENFORCER Head must be run as manufactured without modifications other than the following:
Head gasket surface may be milled/resurfaced for straightness and to achieve the minimum 61cc combustion chamber volume, however no angle milling of the head will be permitted.
Any valve job will be permitted with a valve seat angle of 45° only. The top cut can extend past the edge of the seat into the combustion chamber. Cutting and preparation of the valve job may not extend below the valve seat insert. All seat cuts are concentric to the valve stem centerline. Back cutting of the valves is permitted. No modifications to the cylinder head below the valve seat insert will be allowed. The opening diameter at the bottom of the valve seat insert shall not exceed 1.837 for the intake and 1.382 for the exhaust. (it is not uncommon to have machine marks on the combustion chamber walls caused by performing the valve job)
Intake manifold bolt holes can be slotted for alignment and the gasket surface may be milled/resurfaced for straightness and intake manifold sealing.
Pistons must be installed .005″ or more below the block deck surface.
Engine block may be sleeved for repairs or to correct worn cylinders. Maximum bore allowed will be 4.030″ plus up to an additional .005″ for over bore. Cylinder spacing must maintain 4.400″ cylinder to cylinder as per standard SBC specifications.
Lifter bores may be sleeved to repair damaged or worn blocks, max diameter .8477
No offset dowel pins or shifting of the head to block positioning will be permitted.
Crankshaft may be balanced, counter throws can be ground, lathe turned or drilled for lightening. If grinding or turning is used the counter throws may not be cut completely round. Adding weight for the purposes of balancing only is allowed.
Crankshaft Journals may be ground to a maximum of .010″ under on rods and mains.
Engine block can be chamfered and deburred on all corners and edges.
All engine parts laser labeled with “HMS/ENFORCER” along with the “QR-Code” the labeling must not be disturbed and must be readable at all times.
Any main or rod bearings will be allowed. No coatings will be allowed on rod or main bearings.
Any standard style cam bearings are allowed. Coatings are allowed on cam bearings.
Any engine fasteners of choice are permitted.
The only approved head gasket is Fel Pro 1043. It is allowed to enlarge the coolant flow holes, in the gasket, to reduce engine temperature, as described in the Fel Pro Installation Tips.
The only approved intake gasket is Fel Pro 1206. All other gaskets are the builder’s choice.
Only metal timing covers are allowed.
The approved oil pump is Melling M55HV and may be modified for oil pan clearance. The oil pump spring may be changed.
Optional oil pumps for Enforcer Engine: 1. Standard volume - Melling Select 10553 2. High Volume - Melling M55HV
Steel valve spring shims are allowed.
Oil restrictors, All Star Performance Part # 90072, are permitted. As noted in the Dart SHP Iron Small Block Chevy -Technical Notes, under the Priority Main Oil System heading.
The specification data on all camshafts for the HMS ENFORCER Engines are tracked through Comp Cams. This data is available, upon request, to all tracks and technical personnel.
Any Questions on Technical Specifications not listed should be Addressed with HMS, at number below
No Other Modifications Can Be Made Unless Authorized By HMS
No substitutions or modifications may be made unless authorized by HMS and listed in these rules.
Questions – Please Call 1-828-632-7835 or email
- SUPPLIER NOTE -
Due to sales of the Enforcer Engine exceeding projections we developed a substitute part to help ensure supply met demand at the time. Both are considered legal parts. Details are shown below:
The Crankshaft on the left is the original. The Crankshaft on the right was the alternate. Both will show the HMS ENFORCER logo and QR code.
The Lifter on the left is the original. The Lifter on the right is the alternate. Both will show the HMS ENFORCER logo and QR Code.
Questions – Please Call 1-828-632-7835
Picture on the left is the original markings
Picture on the right is the new markings as 10/15/19. The new markings will be on the top of piston as well as the bottom of piston.
Questions – Please Call 1-828-632-7835