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Crank Pulleys- V-Belt
Pontiac V8 Crank Pulleys- V-Belt
Set the Belt Speed — Crank Pulleys- V-Belt for Pontiac V8s
The crank pulley sets the speed of everything else on the belt and it is the one the factory built as a stamped two-piece set. Billet replacements are stronger and run truer, and their deeper grooves lock the belt in instead of letting it walk. An underdrive pulley goes a step further by slowing the accessories down.
Butler stocks billet V-belt crank pulleys from Ram Air Restorations, March Performance and Butler in two and three groove versions, for 1968-70 and 1971-and-later offsets, and for both four-bolt factory and three-bolt aftermarket dampers.
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1. 1968-70 or 1971 and Later
This is the first fork and it is not about the engine, it is about where the grooves sit relative to the balancer face.
| 1968-70 | Butler's billet two groove crank pulley for 1968-70 is offered in a billet finish and in black anodize. The three groove 1968-70 pulley for A/C applications is 7.5" in diameter, locates all three grooves in the stock position, and uses a four bolt balancer. |
| 1971 and later | Ram Air Restorations' billet two groove crank pulley for 1971-81 replaces the stock stamped two piece crank pulley set, and the three groove version covers 1971-and-later A/C applications. Both use a four bolt balancer. |
| Why it matters | The underdriven pulleys are explicitly cut to one offset or the other — the 1968-70 versions share the groove offset of the 68-70 double groove pulley and want 1968-70 bracketry, and the 1971-81 versions share the 71-81 offsets and want 1971-and-later bracketry. Mixing eras puts the belt out of plane. |
2. How Many Grooves
Count the belts on the car, not the accessories.
| Two groove | The common non-A/C arrangement, driving the water pump and alternator, plus power steering where fitted. |
| Three groove | Required when the car runs A/C. Both the 1968-70 and the 1971-and-later three groove pulleys are made for that, in black anodize and polished finishes. |
| Single groove | March's 1971-79 one groove 15% underdrive pulley is the choice for a stripped-down front drive with nothing but a water pump on the belt. |
3. Three Bolt or Four Bolt: Match It to the Damper
The pulley bolts to the balancer, so the balancer decides the pattern.
| Four bolt | For factory 1968-81 balancers. Ram Air's four bolt underdriven pulleys fit all 1968-81 balancers and come with stainless attaching hardware. |
| Three bolt | For aftermarket dampers from ATI, TCI and similar. The 1971-81 three bolt underdriven pulley is a double groove billet piece with groove centers .9" and 1.65" from the balancer face, matching the 1971-81 OEM offsets. A 1968-70 three bolt version is also stocked for ATI balancers in that era. |
| The ATI catch | On an ATI balancer the pulley mounting surface sits .200" further out than stock. You use the three bolt V-belt pulley, and then you have to re-space the brackets and accessories to account for that .200" difference in damper face. Plan that in before the front of the engine goes together. |
4. Underdrive, and What Else Has to Change
An underdrive crank pulley consumes less engine power turning the accessories, which puts more of it at the rear wheels. It is a real gain, but it is not a standalone part.
| March 15% underdrive | The 69-77 two groove and 71-79 single groove aluminum pulleys are 6-1/8" and come with all mounting hardware. They require a 1968-or-newer balancer, meaning one without a V-groove, and a 1969-or-newer 11 bolt 4-1/2" water pump. |
| Bracketry era | Use 1968-70 bracketry with a 1968-70 offset pulley and 1971-and-later bracketry with the later one, so accessory alignment stays correct. |
| Belt length | A smaller crank pulley changes belt length. Measure after mock-up rather than reusing the old belt on faith. |
| Charging at idle | Slowing the alternator down is the point, but if the car idles low with a big cam and heavy electrical load, size the alternator with that in mind. |
Year, groove count, damper bolt pattern, water pump diameter. Settle those four and the correct crank pulley is usually a single part number.
Not sure what your Pontiac needs?
Call our tech team at 866-762-7527. Tell us your engine, heads, car, and power goal, and we will put the parts together as one combination that works.