Chevy’s Other W En­gine

She’s Real Great, My 348

Street Rodder - - Contents - By Ron Ceri­dono | Pho­tog­ra­phy by the Au­thor

She’s real great, my 348

We whole­heart­edly agreed with the Beach Boys back when they sang “She’s real fine, my 409,” but to­day we’re singing a slightly dif­fer­ent tune. With apolo­gies to the guys in the band, we’re singing “She’s real great, my 348.”

When we de­cided to build a W-mo­tor for an up­com­ing project, it didn’t take long to find that orig­i­nal 409s and en­gines based on re­pro­duc­tion blocks and com­po­nents are much too ex­pen­sive for our build bud­get. On the other hand, 348s are plen­ti­ful and much more af­ford­able, which means more of that bud­get can be al­lot­ted to per­for­mance parts.

Al­though it’s a com­mon be­lief that the 348/409 en­gines were called W-mo­tors due to the shape of their valve cov­ers, it was ac­tu­ally be­cause of an SAE paper writ­ten by Chevro­let en­gi­neers John T. Rausch, Howard H. Kehrl, and Don­ald H. McPher­son. Chevro­let needed a larger dis­place­ment en­gine for in­creas­ingly heavy cars, as well as light- and medium-duty trucks, so at least three new en­gines were be­ing de­vel­oped. They were given the code names: W, X, and Y. The X and Y en­gines were small-block based, the W used a new block and heads that al­lowed for more dis­place­ment. Ul­ti­mately the W de­sign was cho­sen for pro­duc­tion and the let­ter des­ig­na­tion stuck.

Like its small-block pre­de­ces­sors, the W en­gines use tubu­lar pushrods that de­liver oil to the stud-mounted,

stamped-steel rock­ers. But un­like the small-block that de­liv­ers oil from a gallery down through the cam bear­ings to the main bear­ings, the W-blocks have a gallery run­ning low in the left side of the block to feed the mains di­rectly (ad­di­tional pas­sages feed the lifters and cam bear­ings). But, what re­ally sets the W-se­ries apart from the small-block is the com­bus­tion cham­ber de­sign. Small-block heads have con­ven­tional com­bus­tion cham­bers with the block’s decks at 90 de­grees to the crankshaft cen­ter­line. The heads for the W en­gines are flat with no com­bus­tion cham­ber (some trucks and ma­rine heads have small cham­bers to lower com­pres­sion) and the decks of the block are at 74 de­grees to the crankshaft cen­ter­line. The re­sult is 16-de­gree wedge-shaped com­bus­tion cham­bers in the cylin­ders be­tween the top of the pis­ton and the heads. This de­sign cre­ates tur­bu­lence in the cham­ber (or cylin­der, if you will), and cou­pled with the lo­ca­tion of the spark plug, a fast-mov­ing flame front is cre­ated that helps pro­duce lots of low-end torque that is re­sis­tant to det­o­na­tion.

First ap­pear­ing in 1958, the 348 was avail­able through 1961 in cars and 1964 in trucks. It had a bore of 4.125 inches and a stroke of 3.25 inches and was of­fered in an as­sort­ment of horse­power rat­ings. The base en­gine was dubbed the Turbo-Thrust and was rated at 250 hp. The op­tional Su­per Turbo-Thrust with three two-bar­rel car­bu­re­tors was rated

at 280 hp. The Po­lice Spe­cial with a sin­gle four-bar­rel was rated at

315 hp. Very late in 1958 came the Spe­cial Turbo-Thrust with a sin­gle four-bar­rel rated at 305 horses with 11.0:1 com­pres­sion and 320 hp with 11.25:1 com­pres­sion. For 1959 and 1960, horse­power for the high-com­pres­sion en­gines rose to 320 for the Carter AFB-equipped four-bar­rel ver­sion, and 345 in the three-deuce edi­tion. In 1961, horse­power was bumped to 340 with a sin­gle four-bar­rel, and 350 with Tri-power (the high­est rat­ing the 348 would achieve). By then the 409 had eclipsed the 348 in horse­power; of course it wasn’t long be­fore the 396 would re­place them both.

When we be­gan shop­ping for a W en­gine for an up­com­ing project we found re­built 348s for roughly half the price of most 409s and re­build­able cores were about two-thirds less. Our 348 was a real bar­gain as it came to us for next to noth­ing, thanks to a good friend who wanted an LS rather than a vin­tage W. Ac­cord­ing to the orig­i­nal owner the en­gine is a '60 ver­sion of the 280 Su­per Turbo-Thrust and was orig­i­nally equipped with triple carbs. Un­for­tu­nately, the in­take man­i­fold and carbs had been swapped in fa­vor of a sin­gle Rochester four-bar­rel car­bu­re­tor and man­i­fold, but other than that the en­gine was in­tact and run­ning.

To han­dle build­ing our 348 we turned to John Beck of John Beck Rac­ing En­gines. A Bon­neville racer and record holder, mas­ter en­gine builder, and all-around good guy, Beck builds first-class en­gines for any ap­pli­ca­tion, from rac­ing on land or wa­ter to daily driv­ers. He has col­lab­o­rated with us on project en­gines from Flat­heads

to mon­ster stro­ker mo­tors and ev­ery­thing in be­tween. And he loves build­ing “stealth” en­gines that look like mild-man­nered stock­ers on the out­side but are killer stro­kers on the in­side.

The first step in re­ju­ve­nat­ing our en­gine was to tear it down and in­spect all the com­po­nents. Beck would treat the block to his usual pro­ce­dure of blueprint­ing all di­men­sions and bor­ing it 0.030-inch over­size. Sur­pris­ingly, the crankshaft was in re­mark­able con­di­tion and only re­quired pol­ish­ing of the jour­nals and bal­anc­ing to ac­com­mo­date the new pis­tons and rods. On that sub­ject, if these en­gines had a weak spot it was the rods. We opted for a set of Scat 6.385-inch

H-beam re­place­ments with 7/16 ARP cap screws (stock 348 rods are 6.135 inches long; 409 rods are 6.00). The longer rods al­lowed us to use Ross pis­tons from 409 guru Jack Gibbs with shorter com­pres­sion heights (the dis­tance from the top of the pis­ton to the wrist pin), which makes them lighter.

For top-end com­po­nents we turned to in­dus­try leader Edel­brock. We se­lected Power Pack­age Top End

Kit for 409s (PN 2039). It in­cludes Per­former RPM alu­minum heads, roller lifters and camshaft, tim­ing set, in­take man­i­fold, gas­kets, and fas­ten­ers. The camshaft in­cluded in the Power Pack­age has a du­ra­tion at 0.050-inch lift of 230 de­grees on the in­take and 234 on the ex­haust; lobe sep­a­ra­tion is 112 de­grees and lift at the valves is 0.616 inch on the in­takes and 0.628 on the ex­hausts. It’s those last specs that make this kit 409 spe­cific, as in most cases 348s won’t ac­com­mo­date a camshaft with that much lift. It’s al­ways

ad­vis­able on any en­gine to check valve clear­ances with a pis­ton at top dead cen­ter and the valves at max­i­mum lift, and an ab­so­lute ne­ces­sity when run­ning this big of a cam in a 348. In our case the ex­haust valve clear­ance notches in the block and the Ross pis­tons sug­gested by Gibbs pro­vided the clear­ance nec­es­sary. Edel­brock pushrods and alu­minum 1.7:1 full roller rock­ers com­plete the val­ve­train.

From the fac­tory our 348 had a rather small in­take and ex­haust valves that mea­sured 1.94/1.65 inches, re­spec­tively. The ports were small, and the rocker studs were pressed in place. Those short­com­ings, plus the ex­pense of re­fur­bish­ing them and open­ing up the ports, were just some of the rea­sons we elected to swap the cast-iron heads for the much-lighter T356 alu­minum ver­sions from Edel­brock (at 31-1/2 pounds they weigh roughly half of the orig­i­nal cast-iron heads).

While the Per­former RPM heads are sim­i­lar to the best Chevro­let of­fered on the 425-horse 409, Edel­brock took that ba­sic con­fig­u­ra­tion and im­proved upon them by re­design­ing the ports that work with valves mea­sur­ing

2.19 inches on the in­take and 1.72 on the ex­haust. To en­sure re­li­a­bil­ity and rocker arm sta­bil­ity dur­ing high-RPM op­er­a­tion, 7/16-inch screw-in studs (as op­posed to the pressed in and pinned orig­i­nals) are used. While all those fea­tures and the sub­stan­tial weight sav­ings are rea­son enough to go with these heads, their real strength are the out-of-the-box flow num­bers. Thanks to the 220cc in­take and 115cc ex­haust ports these heads will han­dle 273 cfm on the in­take and 216 on the ex­haust at 0.600-inch lift.

With our 348 in Beck’s ca­pa­ble hands, we fol­lowed along as the ma­chine work and ini­tial as­sem­bly took place. Next time we’ll fin­ish as­sem­bly then strap our W to the dyno for test­ing and tun­ing.

Clues to Iden­ti­fy­ing W En­gines Other than check­ing cast­ing num­bers on the rear of the block, an ob­vi­ous clue to iden­tify one W from another is the lo­ca­tion of the dip­stick—348s are on the left, 409s are on the right. Keep in mind pans in­ter­change so this may not be the most ac­cu­rate means of iden­ti­fi­ca­tion.

Another in­di­ca­tion is the shape of the crankshaft flange. Both en­gines use forged cranks, but the 348 has a round flange while the 409 is D shaped.

■ John Beck primes the oil sys­tem of our 348—and yes, we painted the Edel­brock alu­minum heads Chevro­let orange.1

■ Beck made sure our block was square by check­ing the main bore align­ment as other crit­i­cal mea­sure­ments are taken from its cen­ter­line. When cor­rec­tions are nec­es­sary a light hon­ing usu­ally does the trick.3

■ Chevy’s W en­gines are eas­ily iden­ti­fied by the scal­lops along the lower edge of the rocker cover seal­ing sur­face. Note the orig­i­nal stamped steel rocker arms.2

■ With the crankshaft cen­ter­line ver­i­fied the block’s decks are checked to en­sure they are par­al­lel with the main bear­ing bores.4

■ To make the decks par­al­lel, per­fectly flat, and equal dis­tances from the crankshaft, Beck took a small cut off each sur­face.5

■ Af­ter the block was bored it was honed for moly rings. Note the notch in the cylin­ders for ex­haust valve clear­ance and the angle of the head sur­face in re­la­tion to the fin­ished bore.7

■ Our block was bored 0.030-inch over­size. Thanks to so­phis­ti­cated equip­ment, when the cylin­ders are bored they can be “repo­si­tioned,” if nec­es­sary, to make them 90 de­grees to the crankshaft.6

■ W-blocks have two-bolt mains (most af­ter­mar­ket alu­minum blocks have four), so we added ARP studs for ad­di­tional bot­tom-end se­cu­rity.8

■ Our crankshaft was in re­mark­able con­di­tion, only re­quir­ing pol­ish­ing of the jour­nals and bal­anc­ing.9

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