'In the October '00 issue, CC built an Olds engine ("455 Buildup: New Life for an Olds Engine"). That was a fairly typical build for the day based on a 455 and sporting Edelbrock heads. The basic idea was to show the type of power one could expect when assembling what was essentially a stock short-block with the then-new aftermarket heads along with a dual-plane and a streetable hydraulic cam. It made 460 hp with the tame cam a dual-plane, and nearly 500 later with more cam and a single-plane. A nice package, but not exactly a revolutionary combination.
Then, while shooting last month's cover at Westside Performance in Santa Monica-an old-school speed shop that's been under our noses for the past three decades-we spotted a bright red Olds big-block in the shop that appeared to be our 455's twin with its Edelbrock heads and Performer intake. Proprietor Ted Toki informed us that this was actually a more unorthodox approach to Olds power, using a 425 short-block with aftermarket rods and custom pistons, along with the Edelbrock hardware we'd started with. Opportunists that we are, we figured we could con the Westside guys to haul the red Rocket to our usual testing facility for some flogging and tuning.
The StrategySo why not just use a 455 and go for the extra cubes? Ted has his reasons. Primarily, he favors the 425's shorter stroke and the resulting over-square bore/stroke relationship it yields. This is in contrast to the 455's under-square arrangement, where the stroke is actually larger than the bore. Ted feels that if the goal is to build horsepower, the bore should be large in relation to the stroke for optimum cylinder filling, particularly when using street-oriented out-of-the-box cylinder heads.
Another advantage of the 425 is its extra-long connecting rods-nearly 7 inches from the factory. Ted intended to use aftermarket rods but didn't want to have to resort to radically altered piston designs for this street engine just to accommodate a long rod. In the end they used 7.100-inch Scat H-beams spec'd for a big-block Chevy to replace the stock 6.998-inch Olds I-beams. This necessitated turning the rod journals on the stock crank-a factory-forged steel unit unique to 425s-from the Olds 2.50-inch to the BBC's 2.100-inch. Custom Ross flat-top pistons with BBC 0.990-inch pins make up the difference and utilize a modern 11/416-11/416-31/416-inch ring package for reduced drag without sacrificing seal. The resulting compression with the 77cc Edelbrock heads is 10.25:1; as a bonus, each piston/rod/pin assembly shaves nearly 250 grams over the stock stuff.
Ted cautioned that the only real flaw with the combo was the issue of actually finding a 425, but Westside customer Navid Vahedi scored a complete standard-bore '67 425 on eBay for a mere $300.
After machining, the 425 was assembled using ARP fasteners, out-of-the-box Edelbrock Olds heads, an Isky 280 Mega-Hydraulic cam (232/232 duration at 0.050, 0.517/0.517-inch lift, 108-degree lobe separation angle), and an Edelbrock Performer intake.
At The DynoWestside's Jeremy White brought the 425-turned-433 to Westech for the thrash along with an anxious Navid, there to witness the moment of truth when his first engine build would see fire. The Olds initially ran with an MSD Billet Plus electronic distributor and an Edelbrock 850-cfm Quadrajet carb, which Ted favors for street BOP engines. Navid also brought the 131/44-inch Hooker headers that would eventually be installed in his Cutlass, which fed a pair of 3-inch tubes mounting Flowmaster mufflers.
After the cam was sufficiently run in, Westech's Steve Brul took the 425 to 5,500 rpm several times as he and White figured the tune. Total timing seemed sweetest at 34 degrees, and once the air/fuel was dialed, the 425 made 444 hp at an even 5,000 rpm. The 516 lb-ft maximum torque reading seemed to be on the downslope of torque curve, but it's a safe bet that the peak happened just prior to 3,500 based on the 5,000-rpm horsepower peak. We wondered what a traditional-style square-bore carb would do, so the Q-Jet was swapped for a 750-cfm Speed Demon. After minor tuning, the 425 responded with 456 hp at 5,100 rpm and 526 lb-ft at 3,600.
The Edelbrock Performer manifold is a nice unit but a bit closer to stock than we'd like to see for this combination. A Performer RPM would have been perfect, since they almost always boost upper rpm power without sacrificing anything, but for some reason, Edelbrock doesn't make one for the big Olds. A Torker would be a good alternative; we ran one on our 455 and squeezed out another 20 hp, but we couldn't lay our hands on one in time for this session. Instead, we tried a one-inch carb spacer-one of Wilson's tapered-combo designs that uses a four-hole configuration topside that blends into an open plenum underneath. It was good for five additional horsepower and pound-feet of torque. Swapping for a traditional open spacer reduced these gains by about half.
Westech has a set of Hooker Super Comp headers in its arsenal that feature 2-inch primaries, so we figured they were worth a try. We swapped them on along with a pair of 311/42-inch straight-through Race Magnum mufflers, but power gains were a mere 2 hp, and torque barely nudged up by a similar amount. Apparently, this engine didn't need bigger headers.
Any Regrets?When it was over, the Westside crew was pretty stoked with their Olds. It did what it was supposed to, making a hearty horsepower number at an rpm level that didn't jeopardize the hardware, and it had a mega-fat torque curve. Even with the 108-degree lobe separation on the cam, the idle-vacuum readings at 850 rpm were in the range of 16.5 inches-plenty for a street machine. We wished we'd had another intake-there's almost definitely more power in there, but that'll have to wait. One area that will be addressed before the engine is run again is oil control, as our test revealed that the stock pan was allowing the crank to whip the oil into a froth, sapping power and compromising oil pressure in the upper rpm range. We'll revisit the 425 once it's installed in the Cutlass for evaluation and to watch Navid deal with his newfound traction deficiency.
425 OLDS BEST Q-JET BEST DEMON RPM LB-FT HP LB-FT HP 3,{{{300}}} 525 330 - - 3,400 523 339 3,500 517 344 540 360 3,{{{600}}} 516 354 538 369 3,700 514 362 538 379 3,800 511 370 538 390 3,{{{900}}} 509 378 534 397 4,000 508 387 531 {{{405}}} 4,{{{100}}} 506 395 527 412 4,{{{200}}} 503 403 525 420 4,300 500 410 521 427 4,400 497 417 515 432 4,500 494 424 510 437 4,600 487 427 {{{505}}} 443 4,700 482 432 499 447 4,800 477 436 495 453 4,900 472 441 491 459 5,000 466 444 489 466 5,100 454 442 480 467 5,200 446 442 471 467 5,300 434 438 462 467 5,400 424 436 450 463 5,500 415 435 442 463 THE RECIPE Description PN SOURCE PRICE Olds 425ci V-8 core N/A eBay ${{{300}}}.00 Ross pistons custom Westside $645.91 Akerly & Childs piston rings 10375-30 Westside $102.50 Scat H-beam rods (8 x $5.95) custom Westside ${{{600}}}.00 Clevite 77 rod bearings CB542P10 Summitracing.com $47.60 Clevite 77 main bearings MS804P10 Summitracing.com $51.95 Clevite 77 cam bearings SH1354S Summitracing.com $21.95 Fisher harmonic balancer custom Fisher Custom Balancers $375 Edelbrock aluminum cylinder heads 60159 Summitracing.com $1579 {{{M}}}/T valve covers (used) N/A eBay $60.00 Corteco head gaskets (composition) 21367CS Westside $60.08 Mr. Gasket intake gasket w/o bathtub 404 Summitracing,com $15.95 Corteco oil pan gasket 16314 Westside $7.93 Corteco timing cover gasket 14007 Westside $9.35 Head-bolt kit for Edelbrock heads 180-3600 Summitracing.com $69.95 Specialty valve-cover stud kit 2991 Westside $10.00 Specialty intake-bolt kit 2920 Westside $8.85 Specialty oil-pan stud kit 2620 Westside $12.00 Melling high-volume oil pump M22FHV Summitracing.com $45.95 Isky 280 Mega-Hydraulic cam 691281-10 Summitracing.com $123.69 Isky Olds hydraulic-lifter set 692-HY Summitracing.com ${{{100}}}.69 Cloyes double-roller timing set 9-1113 Westside $85.00 Harland Sharp roller rockers, 1.6:1 S5003 Summitracing.com $229.95 Smith Brothers pushrods custom Westside $125.00 Edelbrock Performer intake manifold 2151 Summitracing.com $239.95 Edelbrock Quadrajet carb 1910 Westside $641.71* Speed Demon 750 carb 1402010 Summitracing.com $439.00 MSD Pro-Billet distributor 8566 Summitracing.com $304.88 Aluminum water-pump pulley 8855 Westside $66.95 Aluminum crank pulley 8856 Westside $33.95 Machine work: Bore block N/A Performance Engine $120 Hone block N/A Performance Engine $52 Deck and square block N/A Performance Engine ${{{200}}} Custom cut crank N/A Performance Engine $200 Balance rotating assembly N/A Auto. Balancing Serv. $150 TOTAL (Including Demon Carb) $6,495.03 *Discontinued