Small-Block Bolt-Ons - Chevys Gone Wild

Making a mundane two-barrel small-block into a spicy meatball

Richard Holdener Aug 15, 2006 0 Comment(s)
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Ask any performance enthusiast, bolt ons work wonders.

Dedicated engine builds are great fun, but more often than not theycreate as many questions as answers. For instance, building a 500hpsmall-block is extremely rewarding, especially if you get some seat timebehind the wheel of the monster. While the 500hp combination mightprovide impressive acceleration, not everyone is interested in that kindof top-end power. What does the torque curve look like and (moreimportantly) can it be improved or shifted to suit a different purpose,like towing for instance? Knowing that a dedicated small-block Chevybuildup can often create as many questions as answers, we decided totake a different approach for the readers of Super Chevy. In place of asingle-minded, small-block build up, we decided to cater to as manycombinations as possible given our limited dyno time. The one consistentcomponent in the equation was the four-bolt main short block provided byCoast High Performance. After purchasing the four-bolt truck motor froma local wrecking yard, I was fortunate enough to stumble upon not onlythe more desirable four-bolt block but also a short-block that seemed tobe in pretty decent shape internally. Basically I had a usable core thatwas the perfect starting point for a series of performance tests thatwould more than double the power output of the stock motor.

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The original four-bolt short-block was in decent shaped when removed,but was taken to Coast High Performance for a quick once over. The 350small-block was treated to 0.040-over forged flat-top pistons, forgedI-beam rods and the usual array of new rings and bearings.

As with any project, we needed an official starting point. In this casethat starting point would be a bone stock small-block 350 equipped witha two-barrel carb and intake (and matching air cleaner), stock heads,and cam and even the wretched factory cast-iron exhaust manifolds. Theidea was to start with the most basic of small-blocks, in its lowesthorsepower form. Why start with the lowly two-barrel motor? Believe itor not, there were a great many more two-barrel 350s offered by GM thanthe high-performance four-barrel versions. While the 350 will end upwith a set of aftermarket aluminum cylinder heads, a hydraulic rollercam, and racey single-plane intake, not everyone wants to take theircombination that far. What happens if you just want to replace yourtwo-barrel induction with a four-barrel Q-jet? These parts cost almostnothing at a bone yard, but they actually offer impressive gains overthe stock two-barrel. Ditto for a simple air cleaner swap or evensmall-tube headers. Rather than cater to the high-end enthusiasts, wedecided to cover the basics along the way.

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The original four-bolt short-block was in decent shaped when removed,but was taken to Coast High Performance for a quick once over. The 350small-block was treated to 0.040-over forged flat-top pistons, forgedI-beam rods and the usual array of new rings and bearings.

The first order of business was to get the short block prepped and readyfor action. The small-block 350 was taken to Coast High Performancewhere the four-bolt block was bored 0.040 over in preparation for a setof forged pistons and I-beam connecting rods along with the factory castcrank. The factory crank was deemed more than adequate for our intendedpower and rpm needs and was found to be in excellent shape, requiring nomachining whatsoever. After the forged flat-top pistons (with valvereliefs) and I-beam connecting rods were installed with a fresh set ofrings and bearings, or reciprocating assembly was ready for action. Allthe short-block needed was a new factory cam, since the previous ownerhad installed a mild RV cam. A trip to a local auto parts store resultedin a stock (180hp 307 and 350 applications) hydraulic flat-tappetcamshaft. For oil pump duties, we selected a Mellings standard-volumeoil pump and new pickup along with a hardened oil pump drive shaft. Theheavy-duty oil pump shaft was only a few bucks more, but well worth itwhen rebuilding any motor. A shaft failure means no oil pressure, whichin turn means no more engine or at the very least no bearings. After aliberal dose of Lucas Oil assembly lube and a once over with the torquewrench, the Coast High Performance four-bolt 350 short-block was readyfor cylinder heads.

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We also upgraded the timing chain to double roller status.

When purchased from the original owner, the 350 core motor was alsoequipped with a set of 882 cast-iron cylinder heads. To put our heads ingood working order, they were taken to Power Heads in Fullerton,California. While the motor was running when removed, the heads weretreated to a simple (matching the factory) valve job, reamed guides anda fresh set of factory valve springs. Unfortunately for us, one of theoriginal 882 heads was cracked, not uncommon given the age and usage.Fortunately for us, the guys at Power Heads came to the rescue not onlywith a replacement casting, but also a set of ported heads for ourtesting. Obviously porting your existing heads is an alternative topurchasing expensive aftermarket heads. Power Heads went to work on the882 castings, treating them to a full port job (intake, exhaust, andchambers) designed to work with the larger 2.02 intake and 1.60 exhaustvalves. The heads were finished up with a performance three-angle valvejob. Before porting, the heads were surfaced to ensure proper sealing.The heads were not milled to increase the compression ratio, just aminimal cut to produce a straight, level surface. The pushrods andfactory stamped steel rockers were reused.

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Our original 882 heads were freshened up by Power Heads in Fullerton,California. Power heads also supplied the ported version complete with a2.02/1.60 valve package.

Before we could start our testing, it was necessary to do a littlewrecking yard rummaging. Since our 350 core motor was originallyequipped with a factory four-barrel Q-Jet intake and carb, we wentlooking to secure (of all things) a stock cast-iron two-barrel intake,carb and air cleaner assembly. Not a hot item in the wrecking yards,even the workers laughed at us when we brought it up to pay the askingprice of $20. While we all take for granted that every carburetor istopped with a free-flowing performance filter, the reality is that thereare a great many factory air cleaners still running around and we wantedto demonstrate the effectiveness of a good filter system. We enlistedthe aide of Sean Murphy Induction (SMI) to make sure that both the 2GRochester and Q-Jet were in good working condition. Though we had nointention of keeping them on the motor, we wanted to demonstrate thepower potential of the combination without fear that either carb waspoorly tuned. Both SMI carbs performed so well that it was a shame toremove them, though the after market carbs did show major powerimprovements.

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The stock 882 heads were equipped with the smaller 1.94/1.5 valves and a76cc combustion chamber to produce a static compression ear 9.0:1 withour flat-top pistons.

Before attempting to run either of the factory intakes on our freshlyrebuilt 350, they were in need of a good cleaning. The first step was totake them both to a local machine shop for bead blasting. Naturally wehated treating the factory cast-iron intakes to such expensivepampering, we just did not want them to deposit all the years of carbonbuildup (and now beading blasting material) into our new motor. Afterblasting, we also took the opportunity to grind the rivets securing theoil splash plate located on the under side of each intake. It was a goodthing we did, as both bead blasting material and years of carbon buildup had made a new home under the plate. The bead blasting and plateremoval were followed up by a good cleaning in the solvent tank. Alittle touch of Chevy orange paint and our (heavy) cast-iron intakeswere ready for dyno action. We contemplated blasting the factory cast-iron exhaust manifolds, but they were left in as-delivered conditionsince they would be quickly replaced by long-tube headers duringtesting.




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