Small-Block Chevy Build - Cog Drive Pulleys

To include some science in the test, we added a GM alternator, loaded it with a cooling fan, and ran the stock pulleys first. The loaded alternator cost 8 hp and 7 lb-ft versus the unloaded test, dropping the engine down to 422 hp and 473 lb-ft from the previous test performed with a V-belt-driven water pump only.

To include some science in the test, we added a GM alternator, loaded it with a cooling fa

Step Three
Millerspeed Cog Drive Pulleys
431 hp at 5,300
479 lb-ft at 3,900

We've heard claims that slowing down the water pump and alternator frees up horsepower. Since changing the intake manifold also required changing the alternator bracket, we decided to test the claim. Millerspeed, a small company out of Hermosa Beach, California, offers a set of billet brackets and cogged pulleys that reduce the water pump speed to a 1:1 ratio and the alternator to 1.92:1. We normally don't give billet a second look, but the supercharger-like cogs and high-rpm whine reminded us of an 8-71, so we gave in. Owner Alistair Miller also claims the overall design of the cog drive is more efficient because it lacks the requisite tension of a V-belt pulley, a trait that might also be worth some power.

There was really no contest between the factory iron parts and the Edelbrock aluminum. Aside from the peak gains of 74 hp and 51 lb-ft, the E-equipped engine gained an average of 42 hp and 51 lb-ft throughout the curve.

There was really no contest between the factory iron parts and the Edelbrock aluminum. Asi

The result was a 9hp gain using the 1-inch or 2-inch pulley system plus a satisfying sound that will alert the guy in front of you that you don't like his Prius. Selecting the correct system is a matter of space under the hood.

Pulley Test Results
The stock pulley test was performed with the E-Street heads, the Air-Gap intake manifold, and 500-cfm AVS carburetors. We added a GM alternator and factory-style V-belts and loaded it by spinning an electric cooling fan. The 2-inch pulleys were added for the second test using the same GM alternator loaded with the same electric cooling fan. We then tried the 1-inch-width pulleys and saw no difference.

	Stock Pulleys		2-Inch Pulleys
RPM	LB-FT	HP	LB-FT	HP
2,500	427	203	429	204
2,600	422	209	425	211
2,700	418	215	422	217
2,800	416	222	420	224
2,900	417	230	420	232
3,000	421	240	424	242
3,100	429	253	432	255
3,200	438	267	441	269
3,300	447	281	450	283
3,400	455	294	458	297
3,500	461	307	465	310
3,600	466	319	471	323
3,700	470	331	476	335
3,800	472	342	478	346
3,900	473	351	479	356
4,000	472	359	479	365
4,100	471	368	478	373
4,200	471	376	478	382
4,300	469	384	477	391
4,400	467	391	475	398
4,500	463	397	471	403
4,600	459	402	466	408
4,700	455	407	461	413
4,800	450	411	457	418
4,900	445	415	452	422
5,000	439	418	447	425
5,100	433	420	441	428
5,200	426	422	435	430
5,300	418	422	428	431
5,400	409	421	419	430
5,500	400	419	409	429