Small-Block Chevy Bolt-Ons - Quick-And-Easy Bolt-On 70 HP

Next on the test schedule was a quick installation of the AFR 195 Eliminator aluminum heads. As you can see from this intake port, there is virtually a straight shot from the manifold right to the valve. Also note these are the competition versions of the AFR heads with full CNC porting of the intake and exhaust ports as well as the combustion chamber.

Next on the test schedule was a quick installation of the AFR 195 Eliminator aluminum head

The Test
After baselining the car at the track, Migletz pulled the small-block and we bolted it to Westech's SuperFlow engine dyno and began flogging it again. It was clear that the car's 107-mph trap speed indicated it was making good power, and the baseline run with open headers also saw a slight change to a Holley Street HP 750-cfm carb. We did a quick comparison of the Street HP to the vacuum-secondary carb, and at the peak, the difference was around 8 hp, so we went with the HP carb as the baseline horsepower number. As you can see, the motor made a reasonable 447 lb-ft at a torquey 4,100 with 418 for horsepower at 5,400.

Next, we had ordered a more aggressive hydraulic roller cam that would offer up a little more lift than the flat-tappet cam without necessarily adding a ton of duration. This materialized as a Comp Cams XR282HR cam with a slightly wide 112-degree lobe-separation angle to improve the idle vacuum. We also added a set of Comp Cams aluminum 1.6:1 roller rockers to bump the lift to 0.544/0.554 inch. This cam is smaller in duration at 0.050, which belies its intent to really pump up the torque curve while also adding as much lift as possible, even though it is still way short of an ideal 0.600 inch of lift. By changing to a roller cam, we also had to add a button to the end of the cam to limit cam walk, which could retard ignition timing.

Even though the cam appeared to be smaller, the combination of cam and better cylinder heads pushed the peak torque by 600 rpm and horsepower by 500 rpm. This was worth a small increase in peak torque but a major 30-plus gain in peak horsepower, which now jumped to 453 hp at 5,800. This set the stage for the last test on the engine dyno with a swap to the feature attraction AFR 195cc heads. After a short exercise with optimizing jetting and timing, Westech's Steve Brul ran the motor through a complete pull from 2,500 to 6,500 rpm, and above 5,000 was when the big numbers started popping up. At 6,000 rpm, peak horsepower came in at an impressive 490 with peak torque jumping up to 480 lb-ft at 4,900 rpm, offering up a solid 1,100-rpm powerband between peak torque and peak horsepower. Overall, with just a cam and head swap, the 395ci small-block was making a solid gain of 72 hp and 33 lb-ft.

As you can see by the flow numbers, this test began with a pretty good set of heads in the ported 461Xs. We've listed the flow numbers for similar stock 462 heads to reveal what the porting work produced. To put this in perspective, there are several 180 to 200cc aftermarket aluminum heads that don't flow nearly as well on either the intake or the exhaust side as these ported heads. The AFR heads are better yet with a 30-cfm jump on the intake and 31 cfm on the exhaust side at 0.500-inch valve lift. While everyone usually concentrates on the intake side, the large gains on the exhaust are generally what deliver good peak horsepower numbers.

By Jeff Smith

Enjoyed this Post? Subscribe to our RSS Feed, or use your favorite social media to recommend us to friends and colleagues!