BUILD­ING FOR BOOST

As­sem­bling an LS foun­da­tion to sup­port 1,000+ horse­power

Chevy High Performance - - Contents - TEXT & PHO­TOS: Barry Kluczyk

As­sem­bling an LS foun­da­tion to sup­port 1,000+ horse­power

With all the 1,000+ horse­power rat­ings per­me­at­ing the pages of mag­a­zines and web­sites, it’s easy to get com­pla­cent about achiev­ing those lofty num­bers. Af­ter all, they’re seem­ingly so com­mon that any­one with a sal­vage yard 5.3L, a cou­ple of Chi­nese tur­bos, and some clev­erly routed tub­ing is just a few de­grees of tim­ing away from the four-digit dyno club.

It ain’t that easy. It’s true that the air­flow ca­pa­bil­ity of the LS en­gine family en­ables out­put in street en­gines that wasn’t even dreamt of for old-school small­block rac­ing-en­gine builders, but get­ting there takes care­ful plan­ning and prep work. We’re talk­ing about the bot­tom end of the en­gine, as well as the clamp­ing ca­pa­bil­ity for the cylin­der heads, be­cause when the boost level heads to­ward 20 psi and be­yond, con­tain­ing that cylin­der pres­sure and en­sur­ing the high-rpm dura­bil­ity of the ro­tat­ing parts en­sures re­peata­bil­ity of that stel­lar dyno re­sult.

It was for those rea­sons that Aus­tralian per­for­mance spe­cial­ists Har­rop En­gi­neer­ing turned state­side and to ex­pe­ri­enced LS builder Brian Thom­son to helm the assem­bly of an en­gine topped with their lat­est 2.65-liter su­per­charger. Like the LT5 en­gine in the new Corvette ZR1, the su­per­charger uses the lat­est and larger Ea­ton TVS ro­tors to pump out more boost. Im­proved adi­a­batic ef­fi­ciency, as well as re­duced drive power re­quire­ments, helps ex­pand the power ca­pa­bil­i­ties from the com­pres­sor’s new ro­tors. On a 427-cu­bic-inch foun­da­tion and push­ing about 15 psi of boost, that should make for about 1,000 horses or so on E85.

“There may be a lot of 1,000-horse­power en­gines out there, but get­ting there takes as much at­ten­tion to de­tail in the assem­bly as it does in the amount of boost you can cram into it,” said Thom­son. “You have to be very dili­gent about mea­sur­ing all the clear­ances through­out the en­gine, be­cause at the lev­els of cylin­der pres­sure and tem­per­a­ture that come with 1,000 or more horse­power, there is no room for er­ror or ‘close enough’.”

An all-forged ro­tat­ing assem­bly goes without say­ing in a build like this and we’ve out­lined the de­tails in the ac­com­pa­ny­ing pho­tos. When it comes to the block, how­ever, Thom­son de­cided on Con­cept Per­for­mance’s LSR alu­minum block. We out­lined the block’s at­tributes in an ear­lier issue of Chevy High Per­for­mance, but this rep­re­sents the first build for Thom­son with the block, as well as our first en­gine-build story fea­tur­ing it. Like Chevro­let Per­for­mance’s iron LSX

block, it offers six bolts per cylin­der head clamp­ing, but in an alu­minum cast­ing that weighs only 113 pounds.

One thing the LSR block doesn’t of­fer, how­ever, is pro­vi­sions for oil-jet pis­ton cool­ing, giv­ing us the op­por­tu­nity to try out an­other new prod­uct: Get’M Garage’s Pis­ton Cool­ing Sys­tem, which al­lows the main web­bing of the block to be tapped for oil jets.

“At the power level we’re talk­ing about, the cylin­der tem­per­a­tures are ex­treme and the oil helps keep the pis­tons from lit­er­ally melt­ing,” said Thom­son. “It’s a must in a su­per­charged LS en­gine.”

Ad­di­tion­ally, Thom­son spends hours de­bur­ring the cylin­der block, smooth­ing out and knock­ing down cast­ing edges and other stress ris­ers to elim­i­nate po­ten­tial sources of cracks.

In part 2 of the story, we’ll fin­ish off the en­gine with a set of Chevro­let Per­for­mance LSX alu­minum cylin­der heads and the in­ter­cooled Har­rop su­per­charger sys­tem then push it into the dyno room to see just how eas­ily and re­li­ably 1,000+ horse­power is achiev­able on a well-prepped foun­da­tion. CHP

03 | The val­ley braces, how­ever, in­ter­fere with GM lifter val­ley plates, which in­cor­po­rate crank­case ven­ti­la­tion duct­work. On a strictly rac­ing en­gine, that duct­work could be elim­i­nated, but it should be re­tained on a street en­gine, so Thom­son trims the tops of the braces for clear­ance.

05 | Spun duc­tile iron cylin­der lin­ers of­fer a ten­sile strength of around 120 ksi ver­sus the ap­prox­i­mately 30 ksi ten­sile strength of the con­ven­tional gray cast iron used in most OE en­gines. Duc­tile iron is also rel­a­tively plas­tic, mean­ing it flexes more than com­par­a­tively brit­tle cast iron, which helps pre­vent crack­ing of the sleeves.

04 | One of the LSR’s unique fea­tures is dou­ble cross-bolts for main caps #2, #3 and #4. That makes them eight-bolt caps for greater crank­shaft lo­ca­tion ac­cu­racy and over­all strength. The main caps are from Pro-Gram En­gi­neer­ing and are made of sturdy SAE 1045 bil­let steel. With the dou­ble cross-bolt fea­ture on caps 2, 3, and 4, they of­fer 40 per­cent more main cap sur­face area than stock-type caps.

02 | A cross-braced lifter val­ley is an­other of the LSR’s rigid­ity-en­hanc­ing fea­tures. Each val­ley sec­tion has its own oil drain-back hole. The block cast­ing also fea­tures thicker front and rear val­ley walls than pro­duc­tion LS blocks.

01 | The LSR block cast­ing is made of 356-T6 heat-treated alu­minum and weighs a scant 113 pounds with the main caps. It’s de­signed to ac­cept all of Chevro­let’s pro­duc­tion and LSX cylin­der heads and other com­po­nents.

08 | A fea­ture that en­gine builder Brian Thom­son likes to in­clude on his en­gines, but isn’t in­cluded with the LSR block is pis­ton-cool­ing oil jets, which are used to douse the bot­tom of the pis­tons with en­gine oil. It’s a smart way to enhance over­all per­for­mance and dura­bil­ity. Thom­son typ­i­cally makes his own squirters, but for this project Get’M Garage’s new oil jet kit, which in­cludes the jets, as well as the fix­tures, drill bit, and req­ui­site tap to in­stall them.

12 | With the block prepped, at­ten­tion turns to the ro­tat­ing parts, start­ing with a Cal­lies DragonSlayer 4340 forged steel crank­shaft de­liv­er­ing a 4.000inch stroke. Thom­son or­dered it pre-bal­anced with a 1,850-gram bob weight, which elim­i­nated the need to ma­chine the crank and add mallory metal later. By the way, the crank is spe­cific for a GM fac­to­rystyle dry-sump oil­ing sys­tem, with a 1-inch-longer snout to ac­com­mo­date the oil pump.

13 | Thom­son tack-welds the steel re­luc­tor wheel to the crank­shaft. It’s a holdover habit from build­ing early LS en­gines that had sheet­metal 24-tooth wheels that tended to slip. Al­though he hasn’t had any real slip­page prob­lems with later-style 58-tooth wheels, it is nonethe­less an added mea­sure of in­sur­ance. The wheel is TIG-welded us­ing sil­i­con bronze weld­ing al­loy.

10 | Af­ter run­ning a tap through the holes, the jets are threaded into the block, with just a touch of blue Loc­tite thread sealer to se­cure them. Thread down un­til they’re just be­low the bear­ing sur­face of the main web. And while the jet looks like it’s go­ing straight into the main web, it’s an­gled sev­eral de­grees to­ward the cylin­der.

11 | Here’s the in­stalled oil jet, which has a 0.020-inch out­let. It will shoot en­gine oil at the bot­tom of the pis­ton to keep down its tem­per­a­ture. At the ex­treme cylin­der temps that come with su­per­charg­ing or tur­bocharg­ing, the pis­tons and rings can soften without an aid like this.

07 | The block was then com­pre­hen­sively de­burred to elim­i­nate sharp edges that could lead to cracks un­der ex­treme cylin­der pres­sure. Every de­tail counts when build­ing for 1,000 durable horse­power.

09 | In­stalling the oil jets starts with se­cur­ing the Get’M Garage fix­ture to each main web of the block and drilling down through the oil gal­leries un­til the drill bit breaks into the bot­tom of the cylin­ders.

06 | The block was de­liv­ered bored and honed with 4.125-inch bores, but Thom­son prefers to put his own hone pat­tern on the cylin­ders, so he took the lin­ers out to 4.130 inches.

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