What is SFI Spec. 18.1…

The SFI Foundation, Inc. (SFI) is a non-profit organization established to issue and administer industry standards for specialty performance automotive and racing equipment. The SFI Spec. 18.1 provides a set of minimum requirements for manufacturers to comply with when producing crankshaft vibration dampers. The standards were introduced to ensure safety on the track where certain racing classes require a SFI certified damper as specified by the sanctioning body.

The SFI spec 18.1 stipulates minimum mechanical properties for the steel used in the construction of the damper, the requirement that the outer inertia ring is retained and where the damper is subjected to spin test requirements of 12,500 rpm for one hour. PRO/RACE and PRO/SPORT models conform to SFI Spec. 18.1 – As a further safe guard a PRO/RACE damper was spin tested at 18,000 rpm (40% increase) however after 15 minutes the shaft bearings in the test machine failed, the PRO/RACE damper however survived !

Harmonic Balancer…Crankshaft Harmonic Damper…Torsional Vibration Damper….

The term so often used for this component is harmonic balancer, which suggests the unit “balances” the engine. In generality this statement is misleading…. a better description for this component is a harmonic damper or torsional vibration damper. This better describes the actual function of the unit.

Torsional vibration occurs in the crankshaft of engines, as a result of the combustion process. The sudden reversal of load on the piston, conrod and crankshaft during compression, followed by the ignition or firing of the compressed fuel and air in the combustion chamber. Subsequent relaxation of the load following combustion causes deflection or flexing of the crankshaft. This oscillating vibration which results from the reciprocating load changes will remain in force until dissipated by internal friction or damping. At certain rpm ranges these oscillations can come into phase with each other creating potentially damaging torsional peaks in the crankshaft.

Unless the amplitude of these torsional vibrations is controlled, major damage can occur to engine components, such as rapid wear of the timing sprockets, stretching or breakage of the timing chain, pitting or cupping of the camshaft and lifters, broken valve springs and valve train failure, reduced service life of crankshaft bearings. In extreme situations uncontrolled torsional vibrations can lead to a loose flywheel or a broken crankshaft with serious safety consequences.

Why use a tuned elastomer (rubber) damper…

Elastomer harmonic dampers have been used exclusively by Automotive OEM’s for car engines, no matter what brand of vehicle, be it local or imported. The reason is simple, they have found that a tuned elastomer damper is able to reduce destroying crankshaft harmonics more effectively and over a wider range of RPM’s than other styles of dampers.

PRO/RACE, PRO/SPORT and PRO/STREET tuned elastomer dampers are also marketed as private label models by Ford Racing, Mopar Performance and others. These groups tested a number of aftermarket dampers including fluid or viscous style dampers prior to selecting PRO/RACE and PRO/SPORT tuned elastomer dampers which provide superior dampening for rapidly accelerating, high RPM engines.

Why do racing and stroker crankshafts need to have significant damper mass or inertia…

As explained above, the higher the horsepower output, the longer the stroke, the greater the deflection of the crankshaft. The amplitude of the resulting torsional vibration in the Crankshaft must be controlled to effectively counteract these potentially engine destroying torsional peaks, mass is required in the inertia ring for the damper to perform this function. Light weight inertia rings are less capable of adequately damping out these torsional peaks, particularly for stroker crankshafts having less crank-pin overlap, generally resulting in greater torsional amplitudes.nim.

What is Dynamic Engine Balance…

The dynamic “balance” of an engine relates to the balance characteristics of the rotating assembly, i.e. crankshaft, conrods, pistons, flywheel etc.. A “harmonic balancer” cannot correct an incorrectly balanced engine assembly. All our dampers are neutral balanced (except for externally balanced models), so if balancing the rotating assembly of an engine the damper, crankshaft and flywheel/flexplate should be balanced together.

HOWEVER there are SOME applications where the “harmonic balancer” does have a mass attached to it, to “externally balance” a crankshaft (such as 400 Chev, 454 Chev, or 289-351 Ford applications). This is not to be confused with the ability of the harmonic damper to perform its’ function as an absorber of torsional or harmonic vibration.

It should be noted that all our dampers have bolt-in counterweights for externally balanced applications where appropriate. This allows a great deal of flexibility to the user and engine builder. Please refer to the removable counterweights section for further details.

When installing or replacing a new damper onto a previously dynamic balanced crankshaft, requires that the new damper be match balanced to the old damper (if material was added or removed during the dynamic balancing process). If the damper being replaced, was not modified during the dynamic balancing process, the new damper can be installed as per the installation instructions. When dynamically balancing the damper DO NOT drill or remove material from the outer inertia ring.

Removable Counterweights…

An original innovation by PRO/RACE, now a convenient feature for our entire range of Dampers, is that all externally balanced models are fitted with a bolt-in counterweight. Removing the counterweight returns the damper to neutral balance condition. Conversely you can take our corresponding internally balanced models and bolt-in a counterweight to make it suitable for externally balanced applications, for example, utilizing our 350 Chev (internally balanced) damper, bolt-in our 400 Chev counterweight and the damper will then work fine in 400 Chev Applications.

Having the counterweight within the hub section of the damper is more accurate, as it can never creep or rotate out of alignment, when compared to some other methods of externally balancing the damper. As example the GM OEM 400 Chev damper has had material removed from the outer ring – which for one isn’t as accurate and should the outer ring ever creep or rotate the engine balance is lost – this can not occur with any PRO/RACE, PRO/SPORT, or PRO/STREET models.

Supercharger Dampers…

PRO/RACE produces dampers specifically for supercharger applications to suit Chevrolet Small Block and Big Block engines as well as Small Block Ford Engines. These dampers are neutrally balanced models, however by adding our optional counterweights they can be used on an externally balanced engine. While this design is typically for blowers using Gilmer tooth belt drives, this damper can be used with any type of supercharger drive. The Chevrolet dampers include a 6-bolt pattern (on a PCD of 2.782”) that is consistent with most tooth belt blower pulleys. The original pulley three bolt pattern is also retained. These dampers have dual keyways, with the stock 3/16” wide keyway and a 1/4″ wide keyway positioned 180° from the original stock keyway. The Small Block Chev model damper features a heavier wall thickness hub to provide greater strength for the 1/4” wide keyway. This damper is supplied with a new Chicago Rawhide front timing case oil seal (CR #19215).

The SB Ford version is neutral balanced and is drilled for Ford 3 or 4 Bolt pulleys. Use solid pulley spacers which can be found in the Ford Racing catalog as may be required. A larger diameter oil seal is supplied to accommodate the increased oil seal thickness (CR #20520).

Ford V8 Engines…

General Notes relating to Ford dampers: All our Small Block Ford dampers use removable counterweights. If you are building a new engine with a neutral balanced crankshaft you may simply unbolt and remove the counterweight.

PRO/RACE #64269, PRO/SPORT #34269 and PRO/STREET #24269 – These dampers are designed to be used with Ford Small Block 289-302 engines requiring the earlier 28.4 in.oz. damper imbalance. These dampers have a dual bolt pattern to suit both three bolt and four bolt pulleys. Most early three bolt pulleys attach directly to the damper and line up correctly. Four bolt pulleys of various types and styles are accommodated by the pulley sleeve and spacers supplied. A solid spacer is recommended for supercharger drives. Note that this damper has two sets of timing marks to align with the various Ford timing pointer positions. A third position is used on some early Ford engines which is not accommodated by this damper, (use later model timing pointer).

Please Note – Some cast iron water pumps have a casting lug which must be ground off to clear damper.

PRO/RACE #64270, PRO/SPORT #34270 and PRO/STREET #24270 – These dampers are designed for ‘81 and later 5.0 engines requiring a 50 in. oz. damper counterweight. Note that the stock damper is 6.38” in diameter while our dampers are 6.61” in diameter. As a result, there are some instances where the lower water pump bolt contacts the damper and some instances where the damper may contact the pump housing and/or timing chain cover. This is usually found on ’95 covers. Spot facing the bolt pad on the water pump and some minor grinding will alleviate the interference. This damper includes a sleeve and pulley spacers. See notes above ref: #64269, #34269 and #24269 for specifics.

PRO/RACE #64272 and PRO/SPORT #34272 – Theses dampers fit 429-460 Big Block engines which have used several different timing pointer locations. Most applications have the timing pointer at the “10 o’clock” position looking at the front of the engine. These models have two keyways, a 1/4” wide and a 3/16” wide. Using the ¼” keyway will correctly position the damper on a production crankshaft (or custom crankshaft machined to OEM specifications) so a “10 o’clock” pointer lines up correctly with 0° TDC on the damper. Use the 3/16” wide keyway with Ford Racing M6303-A600 & B600 crankshaft or a component of the M-6011-A600 & B600 short block kit. The “10 o’clock” timing pointer should align with 0° TDC on the harmonic damper.

When using this damper with a Ford M-6303-A600/B600 crank, use a Ford Racing spacer M-6359-B460 for internally balanced engines and for externally balanced engines the stock spacer (Ford Racing # M-6359-D460) will need to be machined for the pulleys to line up correctly. This damper has the stock four bolt pulley pattern together with the Chev three bolt pattern which facilitates the fitment of most crank trigger setups. Pulley alignment must be checked and adjusted by machining the Ford crankshaft spacer as required.

Please Note: that the 429-460 engines are often called ‘externally balanced’, however unlike most engines, the external balance mass is attached to the spacer sleeve behind the damper. The damper is neutral balanced; however the spacer sleeve is externally balanced.

Chevrolet Small Block and Big Block Engines… Timing Marks and Timing Tabs…

The Small Block and Big Block Chev Engines have two different locations for TDC timing pointer. PRO/RACE, PRO/SPORT and PRO/STREET dampers are designed to be used with an aftermarket bolt-on timing point indicator. Our Small Block damper may vary in diameter to some factory dampers. For a range of aftermarket timing pointers, please refer to the Tavia website (www.tavia.com) on line catalogue.nim.


400 Small Block and 454/502 Big Block Chev engines use an externally balanced crankshaft, in which the damper has a counterweight attached in the back of the damper to provide correct OEM external balance. The counterweight can be removed if the damper is to be used on internally (neutral) balanced crankshaft.

Pontiac V8 Engines…

PRO/RACE #64275 – Installation of this damper on ‘65-’68 engines requires the use of a timing chain cover, water pump, pulleys, etc, from a ‘69 or later engine. These parts are available from wrecking yards or may be purchased from Year One at 1-800-932-7663 or www.yearone.com

Chrysler V8 Engines…

PRO/RACE #64277, PRO/SPORT #34277 and PRO/STREET #24277 – These dampers are for internally balanced “A” series engines, including 318 Standard and Magnum, all 273 and 340 engines with forged cranks. Not suitable for ‘72-’73 cast crank engines, due to external balance specifications, email tech@pro-race.com for further advise.

PRO/RACE #64278, PRO/SPORT #34278 and PRO/SREET #24278 – These dampers are for externally balanced “A” series engines only with a cast crank (1971-1992). This damper is not suitable for a ‘93-’97 5.9 Magnum engine, due to external balance specification, email tech@pro-race.com for further advise.

PRO/RACE #64279, PRO/SPORT #34279 and PRO/STREET #24279 – These dampers are for 383-440 internally balanced “B” series engines. It fits the 440 forged crank, 361-383 “B” and “RB” engine forged cranks (‘62-’70), and 413-426W. The damper has six bolt holes. This damper is not suitable on a 400 cast crank engine or a 440 6-bbl (or 1970-71 4-bbl) with heavy rods, due to external balance. This damper can be used on a 426 Hemi with slight TDC modification.

Contact P.A.W. at 818-678-3000 for a specially designed damper to suit early model 331-354-392 Chrysler Hemi.

Consumer Comment….

We value your consumer feedback of information, advice, etc; Please forward your suggestions to:

USA:                   PRO/RACE Tech-line, CA:          Tel: 800 977 0767          Fax: 800 803 0087

Australia:          PRO/RACE Tech-line                 Tel: (03) 9584 3522         (03)  9584 5194

Email:                tech@pro-race.com                      Website: www.pro-race.com