Hot Rod - - Contents - HOTROD. COM/ Johnny-Hunk­ins

Over­head-valve pushrod en­gines are sup­posed to be dead. At least, that’s the procla­ma­tion all the ma­jor in-mar­ket car mag­a­zines made on the eve of the LS1’s de­but in 1996. The cam-in-block, two-valve-per-cylin­der V8 was an anachro­nism with one foot in the grave, soon to be re­placed by all man­ner of in­no­va­tion—in­ter­nal com­bus­tion and oth­er­wise. And while many of those rapidly de­vel­op­ing tech­nolo­gies have come to pass—di­rect in­jec­tion, diesel, hy­brid, elec­tric, and vari­able dis­place­ment to name a few—we still have ma­jor break­throughs in “knuckle-drag­ging” V8s every few years.

These ad­vances have of­ten been com­bined with pushrod V8s to raise the bar of me­chan­i­cal ef­fi­ciency—a term that’s as­so­ci­ated with fuel econ­omy, but is re­ally a proxy for horse­power. Try as its de­trac­tors might, the mighty pushrod V8 in the guise of the small-block Chevy has yet to be de­throned 22 years later. Just when we think we know ev­ery­thing there is to know about the me­chan­ics of in­ter­nal com­bus­tion, an­other tech­nol­ogy gives “two valves per cylin­der” a new lease on life.

So why have the smartest guys in the room pre­dicted the end of two-valve com­bus­tion en­gines for so long? The ge­n­e­sis of that an­swer is in a some­what ob­scure con­cept known as the ra­tio be­tween the valve cur­tain area and swept cylin­der vol­ume. His­tor­i­cally, a tra­di­tional pushrod en­gine hits an air­flow limit be­fore it hits the me­chan­i­cal limit of its ro­tat­ing assem­bly and val­ve­train; at some point, the pump­ing losses to draw air through a small open­ing can’t be over­come. To com­bat this, hot rod­ders use per­for­mance camshafts to in­crease valve lift and du­ra­tion, boost­ing the air­flow into the com­bus­tion cham­ber, but at a sig­nif­i­cant cost.

More event du­ra­tion causes a drop in dy­namic com­pres­sion ra­tio. The up­per limit for cylin­der pres­sure and thus horse­power is ul­ti­mately con­trolled by the amount of air and fuel trapped in the com­bus­tion cham­ber, so clos­ing the in­take valve later and later means less air and fuel trapped. Sure, you get back some of that with pres­sure wave tun­ing and scaveng­ing, but there are lim­its. Sooner or later, you pay the piper with poor idle, dirty emis­sions, a peaky power curve, and low vac­uum. For years, it was thought the panacea was adding more valves, and that’s ex­actly what Chevy did with the first it­er­a­tion of the LT5 in 1989 and what Ford did with the four-valve InTech Mod mo­tor a few years later. Dou­bling the in­take and ex­haust valve cur­tain area (the valve cir­cum­fer­ence times the valve lift) for the same dis­place­ment means hav­ing your cake and eat­ing it. It’s just harder to run out of flow be­fore the me­chan­i­cal lim­its of the en­gine are reached, which man­i­fests as more power at a higher en­gine speed (wit­ness Ford’s Voodoo V8 with 526 hp at 7,500 rpm from a mere 5.2L).

Dual-over­head-cam V8s proved more pow­er­ful, all things be­ing equal, but all things aren’t equal (namely, the com­plex­ity, cost, and ser­vice­abil­ity). Dur­ing the 2000s, other in­cre­men­tal im­prove­ments were be­ing made that took some of the wind out of the DOHC’s sail, pri­mar­ily the dizzy­ing progress of com­pu­ta­tional fluid dy­nam­ics. Break­throughs in CFD meant that the dis­charge co­ef­fi­cient of OHV in­take ports started go­ing way up, most no­tably with the rec­tan­gle-port LS3 and the Chrysler Apache Hemi heads—some­thing DOHC pro­po­nents never bar­gained for.

It’s in this mi­lieu that Ham­mer­head Per­for­mance En­gines owner Greg Brown found him­self in sev­eral years ago. Brown, who at the time worked for famed Ford en­gine guru Jon Kaase, well knew the ben­e­fits of Ford’s 385-series Boss 429 Hemi. Brown had a front-row seat to the devel­op­ment of Kaase’s in­spired Boss Nine cylin­der heads and lamented that the small-block Ford guys had been left be­hind. That pas­sion con­sumed him to the point that he struck off on his own to start Ham­mer­head.

His first job was to cre­ate the hemi-based cylin­der heads you see this month, tak­ing full ad­van­tage of the lat­est devel­op­ments in flow, mat­ing them to the in­her­ent ad­van­tages of a hemi com­bus­tion cham­ber. But wait, these are Ford Wind­sor cylin­der heads on an LS3-based en­gine. What gives?! The mind of the true en­gi­neer isn’t Ford-cen­tric or Chevy-cen­tric, it’s air­flow-cen­tric, and the ports Brown had de­vel­oped for his Wind­sor hemi had in­cred­i­ble flow. As luck would have it, the bore cen­ters for the Wind­sor and the LS3 were close enough that mi­nor tweaks to the ma­chin­ing of the bolt holes and pis­ton crowns would al­low fit­ment on an LS3. With just 416 ci and a laugh­ably small hy­draulic roller cam, Brown’s LS hemi puts down 636 hp at a loaf­ing 6,500 rpm and pulls enough vac­uum to suck Lake Michi­gan dry. It fits un­der a flat hood and runs on 91 oc­tane, too. Yeah, we’d say pushrod two-valve V8s are a long way from dead!

[ Hemi heads aren’t new, but the Ham­mer­head LS cylin­der head piles the new­est ad­vances in CFD on top of the Hemi’s al­ready sig­nif­i­cant air­flow ad­van­tages. The re­sult: air­flow of such a high quan­tity and qual­ity that it ob­vi­ates the need for a gi­ant...

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