Chevy 350ci Small Block Engine - Results

Cam Specs
Cam		Adv.	Dur. @	Lift	Lobe
		Dur.	0.050	Angle	Sep.
Stock 350 H.O.	Int.	320	212	0.435	112.5
	Exh.	324	222	0.460
Comp XE268	Int.	268	224	0.477	110.0
	Exh.	280	230	0.480
GMPP Hot	Int.	279	218	0.525	112.0
Hyd. Roller	Exh.	287	228	0.525

Note that the stock cam appears to have a longer advertised duration than the Comp Cams. This is merely the difference in where GM decided to establish the opening point of the lobe. If the stock cam were checked at Comp's checking height of 0.006 inch, the duration numbers would be substantially smaller. Also, the Hot cam uses 1.6:1 roller rockers while the other two cams utilized 1.5 rockers.

Power ResultsTest 1 is the best overall power the 350 H.O. made from last month's tests. This configuration included an Edelbrock Performer RPM Air Gap manifold, Holley 750-cfm 0-4779 mechanical secondary carburetor, Hedman 151/48-inch headers, and Borla Pro XS 211/43-inch muffled exhaust. Idle vacuum measured 16.5 inches at 850 rpm.

Test 2 charts the results from the Xtreme Energy 268 hydraulic flat-tappet cam. While most longer-duration cams usually sacrifice torque at the bottom to gain peak hp increases, this combination improved everywhere over the smaller stock cam. The 268 cam also extended the power up to 6,000 rpm where the smaller cam fell off radically after 5,600 creating a wider 1,400-rpm power band between 3,800 and 5,400. Idle vacuum measured 14 inches at 900 rpm.

Test 3 illustrates the advantages of a hydraulic roller camshaft with its more aggressive lift curve. The roller offers shorter duration at 0.050 yet makes significantly more power than the flat-tappet cam making an honest 400-plus hp with stock port Vortec iron heads. This mild cam makes for a great everyday driver combination with 15 inches of vacuum at idle at 900 rpm.