How Does the 392 Hemi Whale Mo­tor Re­spond to Bolt-on Good­ies?

Hot Rod Deluxe - - Contents -

Mak­ing the most out of a 392 Hemi.

In a 1952 pre­sen­ta­tion to the So­ci­ety of Au­to­mo­tive Engi­neers ti­tled “New Hori­zons in En­gine De­sign,” Chrysler En­gine De­sign Chief James Zeder wrote, “The power of an en­gine should be based on physique, not on stim­u­lants.” Had Zeder been a sports coach ad­dress­ing a locker room full of ath­letes, his mes­sage would have been akin to urg­ing the guys to hit the gym in­stead of pump­ing steroids.

As we’ll see in this buildup of a Chrysler 392 Fire Power V8, there’s a lot of “physique” in the le­gendary whale mo­tor. But who ex­actly was Zeder ac­cus­ing of juic­ing with “stim­u­lants” in his pre­sen­ta­tion? That would have been Gen­eral Mo­tors’ ground­break­ing ’49 Caddy and Oldsmo­bile “Ket­ter­ing” V8s (named af­ter GM en­gine de­sign boss Charles Ket­ter­ing). No, GM wasn’t stash­ing hid­den ni­trous ox­ide sys­tems in early Olds Rocket 88s and Coupe Devilles; rather (in Zeder’s opin­ion), GM’S “Boss Kett’ was too re­liant on high com­pres­sion—and high­oc­tane gaso­line—to com­plete the pic­ture.

In 1921, GM’S fuel re­search lab, led by Charles Ket­ter­ing, dis­cov­ered tetraethyl lead (TEL). The pe­tro­leum in­dus­try adopted it, and the prob­lem of spark knock in car en­gines was greatly re­duced. The ad­di­tion of TEL to the na­tion’s fuel stocks al­lowed en­gine mak­ers to nudge com­pres­sion ra­tios up­ward from the Model T’s 3.98:1 into the 5s, 6s, and low 7s by 1940. The added com­pres­sion was good

for over­all ef­fi­ciency, not just peak power, as each drop of gas was bet­ter uti­lized.

So when GM con­jured its new, post­wwii OHV V8s, it banked on everesca­lat­ing com­pres­sion ra­tios and pub­licly pre­dicted the av­er­age pas­sen­ger car en­gine would be as high as 12.5:1 by 1960. This was to be made pos­si­ble by wartime ad­vances in fuel qual­ity, as the av­er­age oc­tane jumped from 65 to 80 points af­ter the war.

But Chrysler’s Zeder didn’t agree. He rea­soned that re­ly­ing on ex­ter­nal fac­tors like high-oc­tane gas (the “stim­u­lants”) would spell dis­as­ter if fuel short­ages ever ma­te­ri­al­ized and only low oc­tane was avail­able—which is what hap­pened in the early 1970s with OPEC.

Else­where in Zeder’s 1952 SAE pa­per he wrote, “In re­cent years, so much at­ten­tion has been paid to fu­els that it is nec­es­sary to re­mind our­selves pe­ri­od­i­cally that we work with a hot-air en­gine; and in order to get power out we must get air in…it is amaz­ing how of­ten the hot air finds its way into the ad­ver­tis­ing, and not into the en­gine.” Thus, in­stead of GM’S com­pres­sion/oc­tane-based strat­egy, Chrysler em­braced the hemi­spher­i­cal com­bus­tion cham­ber for its “oc­tane in­dif­fer­ence,” i.e. abil­ity to run on lousy gaso­line.

Be­tween July 1945 and De­cem­ber 1947, Chrysler built a group of ex­per­i­men­tal en­gines with many com­bus­tion cham­ber con­fig­u­ra­tions, com­pres­sion ra­tios, cylin­der counts, and crank­case lay­outs. One of these en­gines would be cho­sen for mass pro­duc­tion and play the key role of mo­ti­vat­ing Chrysler cars for the next decade. No pressure, right? Wedges, pen­troofs, Heron-style, and hemi­spher­i­cal

com­bus­tion cham­bers were all eval­u­ated, and through it all, the hemi-type proved its abil­ity to make solid power with­out the need for high-qual­ity fuel. “Physique” won out over “stim­u­lants.”

In Jan­uary 1948, the de­ci­sion was made to bring the 331ci Hemi to re­al­ity for the ’51 model year. It was a hum­ble start. With its sin­gle two-bar­rel car­bu­re­tor, sin­gle ex­haust sys­tem, and 7.5:1 com­pres­sion, the in­au­gu­ral ’51 Chrysler Fire Power de­liv­ered 180 hp at 4,000 rpm and 312 lb-ft at 2,000 rpm. But it was a full 20 hp ahead of Caddy’s top ’51 V8, which also uti­lized a 7.5:1 com­pres­sion ra­tio, dis­placed the same 331 cubes, and in­haled through a sin­gle two bar­rel, but had wedge-type com­bus­tion cham­bers.

From there, the Hemi grew from strength to strength and spawned smaller De­soto (1952) and Dodge (1953) sib­lings. By 1958, the Fire Power maxed out at 392 ci; and with a solid cam, dual Carter WCFBS, and 10:1 com­pres­sion aboard the mighty 300D, it de­liv­ered 380 hp at 5,200 rpm and 435 lb-ft at 3,600 rpm.

But as his­tory has shown, the oc­tane race never ma­te­ri­al­ized, and oc­tane sta­bi­lized at 90 to 104 points for the next two decades. To suit these con­di­tions, Detroit com­pres­sion ra­tios lan­guished in the 8.5 to 10.5:1 range, with sky-high numbers re­served for fac­tory Su­per Stock ap­pli­ca­tions. (Chrysler’s 413 Max Wedge tick­led the 13.5:1 mark in 1962.) None of this val­i­dated—or dis­cred­ited—ei­ther Ket­ter­ing or Zeder’s strat­egy.

Seventy years later, we now know that the mas­sive Hemi’s oc­tane in­dif­fer­ence was a largely un­ap­pre­ci­ated/un­nec­es­sary mar­ket­ing fea­ture. In­stead, its breath­ing po­ten­tial be­came the key sell­ing point. Un­for­tu­nately, per­for­mance po­ten­tial didn’t sell new cars, and the sub­stan­tial added cost associated with its dual rocker shafts and jewel-like rocker arms trig­gered ter­mi­na­tion af­ter the ’58 model year (though some ’59 Dodge trucks were Hemi equipped).

As the cheaper-to-pro­duce wedge-head 413 big-block took over as Chrysler’s prime mover in 1959, the early Hemi be­came the go-to en­gine for nitro drag rac­ers like Don “Big Daddy” Gar­l­its and grow­ing le­gions of rod­ders who sim­ply ap­pre­ci­ated its “physique.” With its broad shoul­dered look, there are few en­gines that gather a crowd when the hood goes up like a Hemi.

Let’s watch as Don­nie Wood and the crew at R.A.D. Auto Ma­chine ex­ploit the whale’s physique with some in­ter­est­ing in­take and ex­haust good­ies.

1. A 0.040-inch over­bore brings the cylin­ders to 4.040 inches. The first­gen­er­a­tion Hemi block lacks the crank­case skirt ex­ten­sions of the se­cond- (’64-’71) and third-gen­er­a­tion (2003-present) blocks. This rules out cross-bolted main caps, but with qual­ity ma­chine work and as­sem­bly, it’ll han­dle 600 hp.



2. Like the post-wwii Cadil­lac 331, Oldsmo­bile 303, Stude­baker 232, Ford Y-block, Buick nail­head, Pon­tiac 287, and Packard 320, the Fire Power’s tap­pet cham­ber is sealed by a baf­fled, stamped-steel cover. The CE57 stamp­ing on the right-hand end of the block iden­ti­fies this block as be­ing from the ’57 model year.

7 7. The nearly flat pis­tons with valve re­lief notches yield a pump-gas-com­pat­i­ble 9.5:1 com­pres­sion ra­tio, just half a point lower than the ’58 300D. With its 0.040 over­bore, this 392 now dis­places 398 ci. Rings are plasma-moly faced Speed Pro (PN 24122) gapped at 0.018/0.020 (top/ se­cond).


3. The 68-pound, forged-steel 392 crank’s out­put flange is drilled for eight fly­wheel fas­ten­ers, just like the later 426 Hemi. But ob­vi­ously, they’re not in­ter­change­able. Key swap meet give­aways are the Fire Power’s non-threaded flange holes and ab­sence of the raised fly­wheel/flex­plate regis­ter ring seen on 426 Hemi cranks.

5 5. The pen points to the pol­ish­ing work per­formed on the forged rod beams. For con­trast, the fac­tory-is­sue grainy sur­face tex­ture (right) can trig­ger stress cracks. Ear­lier 331 and 354 rods are shorter than 392 units, 6.625 inches ver­sus 6.951, and have smaller big ends, 2.250 inches ver­sus 2.6875. The 392 block’s 10.865-inch deck height is also taller than the 331/354 block’s 10.38/10.32-inch re­spec­tive spans. As such, 331/354 and 392 in­take man­i­folds do not in­ter­change with­out ef­fort.


6. Spi­ral locks se­cure the float­ing pins within the KB Silv-o-lite hy­per­eu­tec­tic pis­tons. The 392’s “small­ish” 103cc com­bus­tion cham­bers don’t re­quire mas­sive (and heavy) pis­ton domes to achieve com­pres­sion. By con­trast, se­cond-gen­er­a­tion 426 Hemis have 172cc com­bus­tion cham­bers and re­quire larger domes to achieve the same com­pres­sion ra­tio.


4. To set the thrust bear­ing, con­stant for­ward pressure is ap­plied to the crank while the 2.6875-inch-di­am­e­ter main caps are torqued to 90 lb-ft. Ear­lier 331 (’51-’54) and 354 (’55-’56) Hemi mainand rod-bear­ing di­am­e­ters are smaller at 2.500 inches.

12. Pop quiz: Which cylin­der head is heav­ier, a 331 Hemi or a Chevy 454? Sur­prise! At 64.4 pounds bare, the Hemi is 3.8 pounds lighter than the fabled Rat! The free-flow­ing square in­take (top) and ovoid ex­haust ports (bot­tom) com­ple­mented the hemi cham­bers and have won count­less races. Later 354 and 392 iron heads are also much lighter than Bow Tie good­ies. 12

15 15. Any Mopar 273, 318, 340, or 360 dis­trib­u­tor will fit the 392 block as long as a Hot Heads in­ter­me­di­ate shaft (PN 21930) and align­ment col­lar are used, as shown here in the lifter gal­ley.

13. A set of Hot Heads dual valvesprings (PN 40062) works with the stock re­tain­ers and locks to de­liver 135 pounds of pressure (closed) and 325 pounds at full lift. In­stalled height is 1.700 inches. P.c.-style seals con­trol valve stem lu­bri­ca­tion. 13

10 10. With the fresh ARP rod-cap fas­ten­ers torqued to 52 lb-ft, a stock 5-quart Chrysler cen­ter-sump oil pan and matched pickup tube work with the Hot Heads oil pump (PN 21920). Hot Heads of­fers a rear sump pan that’s ideal for most hot rod ap­pli­ca­tions (PN 21811). Higher ca­pac­ity oil­ing sys­tems are also avail­able from Hot Heads and Milodon, but the stock ar­range­ment is ad­e­quate for this 6,000-rpm street ma­chine.

14 14. R.A.D.’S Don­nie Wood care­fully guides the heads into po­si­tion atop the Best com­pos­ite head gas­kets (PN 585). Com­pressed, the gas­kets are 0.040 inch thick and help de­liver the 9.5:1 com­pres­sion ra­tio. First-gen Hemi heads are in­ter­change­able side to side as long as bolt-on caps seal the un­used wa­ter pas­sages at the fire­wall end of things.

8 8. Lack of the rare and ex­pen­sive ad­justable rocker arms used in Chrysler 300D and cer­tain ma­rine/in­dus­trial ap­pli­ca­tions forced us into a hy­draulic cam. For this street-and-strip build, we opted for an Isky Mega 280 with 0.485-inch lift, 280/280 de­grees ad­ver­tised du­ra­tion (232/232 @ 0.050-inch lift) on a 108-de­gree LSA. It’s hot­ter than the 300D cam’s 0.435/0.442inch lift and 276/276 de­grees of du­ra­tion. The hy­draulic lifters im­pose no penal­ties what­so­ever at this level of per­for­mance.


9. A nifty vintage finned alu­minum FGT multi-piece tim­ing cover con­tains the Cloyes True Roller tim­ing set (PN 9-1103). R.A.D. painted the en­gine black rather than the stain-prone sil­ver paint orig­i­nally used by Chrysler.


11. Though 392 heads won’t spoil the recipe, ear­lier 331 heads are said to have bet­ter port floors. Bear­ing cast­ing num­ber 1556157-1, the stock 331’s 1.81/1.5-inch valves and seats are up­sized to 2.00/1.75 inches, match­ing stock 392 di­men­sions. Metal was also re­moved from the throat area di­rectly be­hind the valve heads.

16 16. Proven sta­ble to more than 7,000 rpm (with suf­fi­cient valvesprings), the cast iron rocker-shaft stand hold-down bolts do dou­ble duty as head bolts. Though only four bolts pinch the head gas­ket atop each cylin­der, the ar­range­ment is bul­let­proof when nat­u­rally as­pi­rated. Su­per­charged ap­pli­ca­tions must em­ploy studs and other tricks to in­crease clamp­ing force.


17. For an ex­tra mea­sure of con­trol, Hot Heads 3⁄8-inch di­am­e­ter chrome-moly pushrods (PN 21086) with ad­justable ends con­nect the lifters to the rocker arms. R.A.D. set them at half a turn be­yond zero plunger lash.

19 19. Work­ing with the Hot Heads drive­shaft and align­ment col­lar de­scribed ear­lier, a box-stock Pertronix Flame-thrower bil­let alu­minum dis­trib­u­tor (PN D141700) fires the Au­to­lite No. 65 plugs at 32 de­grees BTDC. Though first- and se­cond-gen­er­a­tion Hemi spark plug tubes are not in­ter­change­able, the wires and rigid in­su­la­tors are. A set of 8mm Tay­lor wires (PN 75089) need only fi­nal trim­ming and ter­mi­nal crimp­ing for use.


18. R.A.D.’S Steve Ch­mura in­stalls the vintage Mickey Thomp­son finned, casta­lu­minum rocker cov­ers. At 6.100 inches, se­cond-gen­er­a­tion (426-style) Hemi spark plug tubes are 0.250 inch too long for use on the 331-392. Hot Heads of­fers re­place­ments for lost items.


20. The stock cast-iron 392 ther­mo­stat hous­ing (in hands) is too short when 331 heads are used on a 392 block. Hot Heads reme­dies the has­sle with a hose kit and adapter fit­tings (PN 21404). Though this dyno setup uses an elec­tric wa­ter pump, Hot Heads of­fers nu­mer­ous street- and strip-friendly al­ter­nates.


21. Hot Heads of­fers these adapter spac­ers (PN 20209) when us­ing shorter 331 heads on the tall-deck 392 block. Two sets of gas­kets are needed.

26 26. With the head­ers still in place, the old­school Weiand dual-quad in­take man­i­fold and tan­dem 500-cfm Edel­brock Per­former car­bu­re­tors (PN 1405) were in­stalled. The twin Edel­brocks work just fine right out of the box, though the bot­toms of the link­age arms in­ter­fere with the in­take bolts. A sim­ple trim solves the mat­ter.

25 25. Switch­ing from stock man­i­folds (in hand) to Hot Heads 17⁄8-inch block-hug­ger head­ers (PN 60010) un­leashed an ex­tra 23 hp and 25.6 lb-ft. Hot Heads also of­fers a full line of un­der-chas­sis and equal-length head­ers as well as re­pro­duc­tions of the “big mouth” iron man­i­folds used on Chrysler 300 let­ter cars.

23 23. For the sin­gle-carb test, R.A.D. used a 750-cfm Quick Fuel dou­ble-pumper (PN HR-750) to me­ter fuel and air.


22. To eval­u­ate the classic and the new, let’s com­pare a vintage 7263 Weiand dual-quad man­i­fold (left) with a mod­ern Hot Heads 50000 high-rise, sin­gle-four-bar­rel unit. With so much dis­tance be­tween the M/T rocker cov­ers, will the sin­gle car­bu­re­tor look naked com­pared to the dual-quad setup?

24. Ex­hal­ing through stock cen­ter-dump Chrysler New Yorker ex­haust man­i­folds, the Quick Fuel carb de­liv­ered 408 hp at 5,500 rpm and 463.6 lb-ft at 3,300 rpm. Box stock me­ter­ing is ideal.

27. The dual carbs de­liv­ered 436.5 hp at 5,700 rpm and 440.4 lb-ft at 4,400 rpm. Sure, the ex­tra 6.5 hp is nice, but los­ing 44.8 lb-ft of torque is a hard pill to swal­low.

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