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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Replacing the factory single-snorkel filter assembly with an openelement version from Comp Cams improved the power output to 241 hp.

As usual, all of the engine dyno testing was performed at WestechPerformance ( SuperFlow 9010 engine dyno). Once assembled, the 350 testmotor was installed on the dyno and filled with a conventional 10W-30from Lucas Oil. After initial start up, we quickly adjusted the MSDdistributor (though the stock HEI worked fine as well) to achieve 36degrees of total timing at wide-open throttle. We relied on an InnovateLM-2 air/fuel meter to help tune the carburetors. Our break-in procedure(for the cam, lifters, rings and bearings) consisted of running themotor at varying loads (the Super Flow actually had a computerizedbreak-in procedure) for 25-30 minutes. Our standard volume Mellings oilpump was doing its job by providing a minimum oil pressure of 50 psi atany speed above 1,500 rpm. After the break in procedure, we ran ProjectChevys Gone Wild in stock trim (from the stock two-barrel air cleanerdown through the stock exhaust manifolds (through a dual exhaust).Equipped as such, the bone-stock Chevy 350 produced 229 hp at 4,600 rpmand 350 lb-ft of torque at just 2,900 rpm. Not exactly a high-rpmscreamer, but the two-barrel motor could sure be used for towing giventhe impressive low-speed torque production.

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The next step was to improve the exhaust side of the equation byinstalling a set of 1 5/8-inch Flow Tech headers. Given the relativelylow power output of the motor at this stage, the stock exhaust manifoldsdid not represent much of a restriction. Despite the low power output ofthe test motor, the headers improved the peak power numbers to 248 hpand 366 lb-ft of torque.

The 229hp small-block was certainly designed with low-speed torqueproduction in mind. Though torque production exceeded 350 lb-ft out to3,300 rpm, the torque curve fell off rapidly thereafter. A motor likethis would feel snappy at part throttle, giving the illusion ofperformance, but with only 229 hp, would certainly fail to deliver uponthose promises. On the plus side, the motor (with proper gearing) wouldlikely deliver decent fuel economy and years of trouble-free service.Our list of modifications started out small, the first being a simpleair cleaner test. I can remember swapping out the air cleaner on my veryfirst car (a '70 split-bumper Camaro RS) for a chrome (which isobviously faster) open-element performance filter. The sound difference(if not the actual performance) was certainly noticeable on mytwo-barrel small-block, but what would the dyno say about this one?Replacing the stock single-snorkel filter with an open element versionfrom Comp Cams resulted in a jump in power from 229 hp to 241 hp (seegraph 1). The new filter resulted in a drop in manifold vacuum (at WOT)of one full inch (from 5.5 inches down to 4.5 inches), a sure sign thatthe stock filter assembly was a restriction.

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Knowing that the two-barrel intake and carb were restricting thesmall-block, we installed a factory four-barrel intake and Q-Jet carb.

After the simple filter upgrade, we started to get a little moreadventurous, first with the exhaust system and then again with theinduction system. First off, we replaced the stock cast-iron exhaustmanifolds with Flow Tech long-tube headers. Breathing into the same dual('70-'81 Camaro system from Hooker) exhaust, the headers improved thepower output from 241 hp and 359 lb-ft of torque to 248 hp and 366 lb-ftof torque (see graph 2). Given the mild state of tune, we didn't reallyexpect too much from the headers at this point. Next up we replaced thecast-iron two-barrel carb and intake with a factory (the original forthe motor) four-barrel intake and Q-Jet carb. Cast-iron intakes, headsand exhaust manifolds should all be illegal, strictly from a weightstandpoint. Despite its heft and factory origins, the four-barrel Q-Jetinduction improved the power output from 248 hp and 366 lb-ft of torqueto 278 hp and 385 lb-ft of torque (see graph 3). Not just in peaknumbers, the four-barrel carb and intake improved the power outputsubstantially from 3,000 rpm to 5,000 rpm, with little to no trade offin low-speed torque (maybe 1-2 lb-ft at 2,300 rpm). So far, everythingwas going according to plan.

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The new induction system reduced the manifold vacuum under WOT byseveral inches and upped the power output to 278 hp and 385 lb-ft oftorque.

Having had our daily dosage of iron, off came the stock four-barrelQ-Jet intake and on went an (oh-so-light) aluminum 8004 intake fromWeaind. The new intake (using the same 750-cfm Q-Jet carb) resulted in ajump in peak power from 278 hp and 385 lb-ft of torque to 287 hp and 372lb-ft of torque (see graph 4). We found out that it is tough to beat thestock Q-Jet intake down low and that the power gains offered from 4,000rpm on up cost some torque production near 3300 rpm. Here is where thepower gains started to get serious. After the installation of the Weiand8004 intake, of came the stock 882 heads and auto-parts store specialfactory camshaft. These stock components were replaced by the set ofported (and big-valve) 882 castings from Power Heads along with a mild(and emissions legal) PE246 cam from Comp Cams. The dual-pattern PE246offered 0.429/0.438 lift split, a 203/212 duration split and a110-degree lobe separation angle. Basically one step up from a stockcam, the PE 246 combined with the ported 882 heads to produce animpressive power gain. The head and cam combo increased the power outputof the 350 test motor literally everywhere, from 2500 rpm all the way to5600 rpm (the new cam and heads allowed us to rev the motor higher). Thepeak numbers with the new hydraulic flat-tappet cam and ported heads nowstood at 340 hp and an even 400 lbs. ft. of torque (see graph 5).

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We'd install the Weiand 8004 aluminum intake just to get rid of theheavy cast-iron factory Q-Jet intake, but the icing on the cake was ajump in power from 278 hp to 287 hp.

We were plenty impressed by the current combination, since the motor wassporting the smallest cam in the Comp Cams catalog along with a $100after market intake and a set of ported stock heads. The motor idledalmost like a stocker while offering even better low-speed torque and aton more high-rpm power. Torque production from the 350 small-block nowexceeded 350 lbs. ft. from below 2500 rpm all the way to 5100 rpm. Thefinal modification for part one of Chevys Gone Wild was the installationof an Edelbrock Performer RPM Air Gap and 650 Might Demon carburetor.Though a dual-plane like the Weiand 8004, the Air Gap intake offeredgreater cross section for improved power production. Naturally we wereconcerned about a loss of low-speed power, since the previouscombination worked so well, but our fears were unfounded. Installationof the BG carb and Edelbrock intake not only upped the peak power outputfrom 340 hp and 400 lb-ft of torque to 364 hp and 422 lb-ft of torque(see graph 6), but did so without any trade of in low-speed torque (evenas low as 2,400 rpm). So far, we had managed to improve the peak powernumbers of the 350 small-block by nearly 200 hp (229 hp vs 422 hp) andnearly 75 lb-ft of torque (350 lb-ft vs 422 lb-ft). Check back with usnext month when we step up to not one but two different sets of aluminumheads, a couple of different cam profiles and even a single-planeintake.




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