Small-Block Bolt On Tests - Chevys Gone Wild, Part 2

Our once-meager junkyard mouse has turned into a real rat-eater with simple bolt ons.

Richard Holdener Oct 13, 2006 0 Comment(s)
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Our next step up the performance ladder involved the installation of aset of excellent Holley SysteMax heads. The lightweight aluminum headsoffered 68c combustion chambers, a 2.02/1.60 valve package and 184ccintake ports to maximize flow.

We liked the fact that the Holley literature promised over 400 hp from a350 Chevy using these SysteMax aluminum heads and a mild cam profile.Heck, it was worth replacing the heavy stock cast-iron heads for theweight savings alone, but we just knew the Holley heads and new camwould provide more than just weight savings over the previous combo. Inhindsight, we should have installed head studs on this small-blockinstead of the ARP head bolts, since we planned so many head swaps. Wepaid the price for this oversight after pulling the threads on one ofthe head bolt holes (in the block). Lucky for us, Steve Brule fromWestech had a Helicoil at the ready and we were back in business in notime.

Expecting a number of camshafts, we were smart enough to install atwo-piece front cover on the motor. This made changing cams on thesmall-block much easier. After installing the new Xtreme Energy Compcam, we allowed time for the hydraulic flat-tappet cam and lifters tobecome properly acquainted (at approx 2,200 rpm for 15 minutes). Thedual-pattern XE268H cam offered a 0.470/0.480 lift split, a 224/230duration split (at 0.050) and a 110-degree lobe separation angle. Onceagain, we were pleasantly surprised by the power gains offered by theHolley heads and XE268H cam. The new aluminum heads and Comp camimproved the power output from 364 hp and 422 lbs-ft to 419 hp and 444lbs-ft of torque.

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In addition to the 20-degree Holley SysteMax heads, we performed a camupgrade as well by replacing the small PE246H can with a slightly wilder(but plenty streetable) XE268H profile. The XE268H cam offered a0.470/0.480 lift split, a 224/230 duration split (at 0.050) and a110-degree lobe separation angle. Naturally new lifters were employedwith the cam upgrade.

Interestingly enough, the Holley heads and larger XE268H cam actuallyreduced the rpm where the motor made peak torque. Equipped with thePower heads and PE246 cam, it made peak torque at 3,900 rpm. Once weinstalled the Holley heads and XE268H cam, the 355 made peak torque atjust 3,700 rpm. Running a wilder cam profile, we expected a trade off inlow-speed power, but such was not the case. The ultra-efficientcombination of the SysteMax aluminum heads and Comp XE268H cam improvedpower literally everywhere.

During the Holley head and Comp XE268H cam swap, we noticed that ourfancy aluminum-headed small-block was still sporting (horror of allhorrors) stock stamped steel rocker arms. While the stock slidingrockers might be appropriate for the 229-hp, two-barrel version of oursmall-block, they had no place on our aluminum-headed performanceengine. The stock rockers have a well-deserved reputation for inaccuracyand slipping jam nuts, the later especially if taken on and offrepeatedly for the many cam and head swaps performed on our test mule.Thus far, the stock (high-mileage) rockers had been run on threedifferent sets of heads, with three different cams. It was certainlytime to swap them out for something a little more performance oriented.

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Cam swaps were made easier by this two-piece front cover from COMP Cams.

Reaching for the Comp Cams catalog, we selected a set of Comp Cams ProMagnum roller rockers. In addition to offering improved rockerstability, the Pro Magnum rockers increased the valve lift slightly byoffering a 1.52:1 ratio in place of the questionably accurate 1.50:1ratio of the stock rockers. Off came the stock rockers and on went thePro Magnums. In no time Westech's own Steve "Lightning Lash" Brule hadthe valves adjusted and our 355 was once again ready to run in anger.The Comp roller rockers improved power by as much as 10 hp, with themajority of the power gains coming at the top of the rev range. Whilethe power gains were certainly welcome, we felt better knowing we hadaccurate geometry as our motor was now running to 6,000 rpm.

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In the previous test, we had run the small-block with a set of ported882 castings and a mild PE246 cam. After swapping out the ported stockheads and Pure Energy 246 cam for the Holley Systemax heads and wilderXE268H cam, we were rewarded with a jump in power from 364 hp and 422lbs-ft of torque to 419 hp and 444 lbs-ft As is evident by the graph,the Holley heads and COMP Xtreme Energy cam improved the power outputthroughout the rev range.

After testing the roller rockers, we decided that it was time to getserious. Serious in this case meant installing our last cylinderhead/cam combination. This final head and cam package consisted of a setof Air Flow Research 195 aluminum performance heads and a healthy XtremeEnergy XR294HR cam. The hydraulic roller cam offered 0.540 intake lift,0.562 exhaust lift and a 242/248 duration split. Like the XE268 beforeit, the dual pattern XR294HR cam offered a 110-degree lobe separationangle. The cam was ideally suited to the AFR 195 heads, as theCNC-porting offered plenty of airflow right to 0.600 valve lift. The AFR195 heads have always proven themselves powerful performers, and theseguys followed suit. The AFR/Comp cam combo literally transformed the 355small-block into a pretty serious street/strip power plant.

You will remember that the two previous cylinder head/cam combinationsoffered sizable power gains, and the AFR heads and XR294HR cam continuedthis trend. In fact, the new combination stepped things considerably, tothe tune of 524 hp and 481 lbs-ft of torque. We couldn't decide what wasmore impressive, the 524 hp or the 481 lbs-ft produced by this 355. Knowthat 480 lbs-ft of torque is a healthy number for a 383 stroker, buthere was our little 355 pumping out more than 450 lbs-ft from 4,200 rpmto 6,100 rpm. It is worth mentioning that the AFR heads were milled toproduce 64cc chambers, bringing our static compression to a stillpump-gas friendly 10.0:1.

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After the installation of the Holley SysteMax aluminum heads and XE268Hcam, the power output of the 355 small-block jumped from 365 hp and 422lbs-ft to 419 hp and 444 lbs-ft. Note the use of an S&B air cleanersystem. This could make a wonderful low-buck street combo, but we wantedmore.

The final modification came from sheer greed, as our 355 small-block wasoh-so-close to 550 hp. Disregarding our own advice to readers about theimportance of the average power production, we went looking for that bigpeak number. Don't worry, we paid the price, as not only did we notreach the 550-hp mark, we managed to kill much of the impressive torqueproduction of the original combination. Our quest for peak power took usto a single-plane Super Victor intake manifold and slightly larger 750Mighty Demon carburetor. As expected, the combination netted an increasein peak power from 524 hp to 543 hp, but the cost of the extra power wasa significant drop in low-speed and mid-range torque. In fact, from5,000 rpm down, the power output was down compared to the runs made withthe RPM Air Gap and 650 Mighty Demon. Testing with the larger 750 Demonon the Air Gap showed an increase of 6 to 7 hp so the difference betweenthe Super Victor and RPM Air Gap was actually less significant since thelarger carb was responsible for some of the power gains. For our money,the RPM Air Gap and 750 Mighty Demon would be the hot set up.

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Not trusting the accuracy of the factory stamped steel rockers, weinstalled a set of 1.52 Pro Magnum roller rockers. The additional liftsupplied by the slight change in ratio combined with the consistentvalvetrain geometry added 7 to 8 hp.

Is it possible to take a stone-stock two-barrel 350 originally producingjust 229 hp and add more than 300 additional horsepower using the rightheads, cam and intake? Obviously the answer is yes, but there isactually more to the story than simple peak power numbers. Not everysmall-block owner is looking to exceed 500 hp with their build up. Whilewe ultimately exceeded 500 hp with our final combination, as always, thereal success came from the journey and not the destination. Along theway, we managed to build not just a 500-plus hp combination, but a 400hp, a 300 hp and even a 250 hp small-block. We are pretty certain thatnot many enthusiasts will want to recreate our 229-hp version, but whatabout a version that produced 278 hp and 385 lbs-ft of torque usingnothing more exotic than a stock four-barrel Q-Jet and a set of headers?

Need more? It's possible to add nearly 100 hp with a set of ported stockheads, an Edelbrock RPM Air Gap intake and a BG Demon carb. Topping the400-hp mark is a simple matter of a set of excellent Holley SysteMaxaluminum heads and a very streetable XE268H cam. For a wildercombination that will shine at the strip, the AFR heads and wild XR294HRcam are definitely the way to go. Whatever route you choose, its hard togo wrong with a small-block Chevy.

Sources

Air Flow Research
Valencia, CA 91355
661-257-8124
AirFlowResearch.com
Comp Cams
Memphis, TN 38118
800-999-0853
http://www.compcams.com
S&B Filters
Ontario, CA 91761
800-358-2639
www.sbfilters.com
Coast High Performance
Torrance, CA 90505
310-784-1010
www.coasthigh.com
Fel Pro
Ashland, MS 38603
662-224-8972
federal-mogul.com
Power Heads
Fullerton, CA 92832
714/992-4909
www.powerheads.com

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