Head-Flow DataRHS 220cc intake-runner Pro Action heads equipped with 2.02/ 1.60 valves were flowed at 28 inches of water by Sherman on his SuperFlow bench. In theory, the flow numbers indicate these heads should be able to support nearly 620 hp at 0.700 inch lift.
LIFT (INCHES) INTAKE (CFM) EXHAUST (CFM) 0.{{{100}}} 68.4 55.2 0.{{{200}}} 127.7 99.4 0.{{{300}}} 182.5 132.5 0.400 232.6 159.6 0.500 269.3 184.3 0.{{{600}}} 290.0 191.7 0.700 301.1 201.4Can you assemble a small-block Chevy, starting from scratch, that makes at least 500 hp and runs on pump gas, on a $5,000 target budget, without sacrificing durability? That's what we wanted to find out, so we tried. The objective is to prove that aftermarket parts technology availability combined with user-friendly parts pricing has advanced to the point that a streetable 500hp small-block engine is within range of the average hot rodder's engine-building budget. Time constraints due to the typical realities of running a monthly publication with fixed deadlines influenced the approach and some of the parts choices: For this reason, we decided to start with a preassembled, large-displacement short-block, then go big on the heads and cam. We also went to ace engine builder Joe Sherman, who has built more budget small-block engines that make serious power than just about anyone else around. Sherman handled the cam selection, major component assembly, and complete dyno test and tune-up.
If not constrained by sanctioning-body rules, there is no replacement for displacement. Nowadays, 383 stroker assemblies built using a 4.030-inch, 350-based block with a 3.75-inch-stroke crank cost the same to build as 350-based engines. On the other hand, the even larger 406ci packages, based as they are on rare 400 blocks or aftermarket blocks, cost at least $900 more. The 383s have therefore become the sweet spot in budget, performance, small-block Chevy engine building.
So, for the basis of this engine we selected a Coast High Performance (CHP) 383ci Street Fighter short-block assembly. Coast High has long been a player in Ford small-block stroker packages, but it has recently aggressively moved into the Chevrolet market as well. Although pricier than a built-from-scratch engine, CHP's short-block eliminated the need to locate and test a suitable core block that would clean up at 0.030-over and then wait for everything to be machined. Howard Cameron at A&A Midwest Enginequest, a leading nationwide core bank, told us, "Only 4 out of every 10 two-piece rear-main-seal blocks are usable these days."
CHP offers an entry-level 383ci Street Fighter SS short-block for around $2,000, but because it's forged, stock-replacement-type, four-eyebrow pistons have valve-clearance issues with the high-lift cam we'd be using, so we moved up to CHP's $2,300 383ci Street Fighter. The extra $300 gets you better rods and full-floating, flat-top, CNC-machined pistons that solve the valve-clearance issues.
Sherman estimated that to make the power on pump gas, the cylinder heads needed at least a 210cc intake runner. Most aftermarket heads with this size runner are cast from aluminum, raising their cost beyond the scope of our budget. Locked into an iron head due to the budget, we chose the RHS Pro Action (formerly Pro Topline) 220cc runner design with angled spark plugs. Fully assembled with 0.100-inch-longer-than-stock 2.02/1.60 valves, trick beehive springs, guideplates, and screw-in rocker studs (with 716-inch threads top and bottom), they go for a very reasonable $1,100. These heads flow great on the flow bench, accept production-style, 23-degree valve-angle valvetrains, and maintain the intake entrance and exhaust exit in the stock location. However, the intake-port opening is slightly larger than stock, so it requires a Fel-Pro PN 1206 intake gasket and correspondingly large-port aftermarket intake, such as Edelbrock's Super Victor.
Feeding the Super Victor is a Demon 850-cfm vacuum- secondary carb. The price is less than a Demon mechanical- secondary 850 and is no more expensive than its smaller 750 sibling. After installing a light-tension secondary spring and rejetting, it made the same power as Sherman's reference 850 double-pumper. And it was cheap, since Jeg's High Performance sells remanufactured 850 Demon vacuum-secondary carbs for about $370.
Normally, when you want serious power, you step up to a roller cam, which also eliminates the need to deal with the flat-tappet durability issues we've been encountering the past few years. But a roller and its associated valvetrain are way beyond our budget, costing upwards of $1,000. That left a mechanical flat tappet as the only viable choice. Oval trackers are about the only racers left regularly using solid flat tappets today, so Sherman and Comp Cams specialist Billy Godbold put their heads together to spec out a radical oval-track grind that they felt could do the job. With 0.050 duration numbers in the 260s and more than 0.600 inch theoretical lift with 1.6:1 rockers, it's pretty aggressive.
A mean cam like this requires special care and feeding to survive in today's world. Comp highly recommended we go with its optional Johnson-style lifters and have the cam nitrided, a special process that increases the cam's strength while making the lobe surface more slippery. Although nitriding adds about $125, the durability increase and peace of mind is worth the added price. "Anytime you get a flat tappet past 0.500 lift or 330 pounds [of spring pressure] over-the-nose, nitriding's the best thing you can do to improve the cam's wear characteristics," said Comp Cams' Godbold. To further fail-safe the flat tappet, Sherman slathered plenty of moly-lube on the cam lobes, filled the 6-quart CHP oil pan with Shell Rotella T diesel oil (unlike modern street-car oils, it still has a full complement of extreme pressure additives), and then dumped in some GM EOS (Engine Oil Supplement).
Most experts maintain that an engine of this caliber requires at least 134-inch primary-tube headers, but even the most affordable 134 tube configurations are about $70 more than 158-inch headers. So, we stuck with Summit 158 headers for the baseline test.
Thank God for Summit's low prices, both on its own branded items and on name-brand parts. Not only was Summit the price-source for the headers and many of the major name-brand parts used on this engine, it also had great prices on all those nickel-and-dime accessories--front cover, valve covers, fuel-pump block-off, water neck, distributor clamp, long pushrods, and other assorted small parts.
We also saved bucks by using generic foreign imports for the rocker arms, harmonic damper, and flexplate. Sherman's preferred supplier for these parts on low-buck builds is Performance Racing Warehouse, which sells nationwide through selected distributors, including Sherman himself. Generic parts, such as a remanufactured water pump and starter, were priced from standard auto parts stores like NAPA. We also saw some really friendly prices for GM items like a head-bolt set from a place called GM Parts Direct, which basically sells genuine GM stuff for 10 percent over dealer cost. Where a unique fastener wasn't really needed, we were also able to use generic SAE Grade 5 or 8 bolts and AN or SAE washers. Outfits like the Bolt Depot and Aircraft Spruce sell bolts and washers by the piece at very friendly prices.
Sealing the engine also can nickel-and-dime you to death--but good sealing is a prerequisite for reliability and longevity. Fel-Pro's heavy-duty line was our choice for all critical gaskets. Even though many of the new parts already came with the necessary gaskets, we found it was still cheaper overall to purchase a complete gasket kit plus the oversize intake gaskets than to price individual gaskets separately. This may not necessarily hold true if you purchase minor gaskets separately through a friendly auto parts store. Then of course there are additional sealant compounds and cements. Ka-ching, ka-ching: there goes $5,380.
Fully assembled, the engine's static compression ratio came in at 11.02:1. Yikes! Compression is good for making power if the engine doesn't get into detonation, but at first glance, this high a ratio seems excessive for an iron-headed engine on 91-octane. However, with the big-overlap cam, cranking compression was only 182-185 psi, well within Sherman's comfort zone. In his experience, anything less than 200 psi is permissible for running a small-block Chevy successfully on pump gas. And in fact, running 91-octane, the engine would make its best numbers with 36 degrees of total advance with no evidence of detonation using NGK UR6 plugs gapped at 0.039 inch.
For now it was time to pull the handle on the dyno. Did we make the right parts choices? Dialing in the engine showed the cam liked a tighter valve-lash setting than the recommended 0.016/0.018 figure. In fact, power kept improving as Sherman tightened the lash all the way down to 0.010/0.010, indicating the engine wants an even larger cam--Sherman estimates at least 5 degrees more at 0.050 inch tappet lift. Nevertheless, once the lash, best timing, and carburetor jetting were established, the assembly did exactly what it was supposed to, coming in at 502 hp at 6,400 rpm and 471 lb-ft of torque at 4,600.
Of course, there are extra-cost, power-adding options. In Sherman's experience, a 1-inch phenolic spacer is usually worth power on single-plane intakes like Edelbrock's Victor series. Summit sells a spacer with mounting hardware and gaskets that adds about $17 to the cost of this build. On this engine, it was worth 8 hp and 6 lb-ft.
All this was still with the 158-inch headers. Moving up to 134 headers and the spacer adds about 19 hp at the cost of 16 lb-ft of torque at the peaks for a new total of 529 hp and 461 lb-ft. However, with more area under the curve, on the street in its present form, the 158-inch combo would likely yield better overall performance and driveability, even though it gives away some on top. Assuming even the most inexpensive 134 headers, you're now looking at about a $5,480 outlay. But remember, that assumes you have nothing and includes everything needed to run this engine.
In baseline form without the optional stuff, the engine is around $380 over our target $5,000 goal. But that's with a preassembled short-block. Suppose you went out and found a good core, farmed out essential major machining operations, procured a CHP rotating assembly (crank, rods, pistons, rings, and bearings), and put everything together yourself. We priced the core at A&A Midwest Enginequest, who said the going rate for an increasingly rare 350, two-piece rear-main-seal core is about $300. A late, one-piece seal casting is easier to find and might be $100 cheaper. A&A doesn't sell directly to the general public, but you can contact the company for availability and then purchase the parts through your machine shop.
We priced basic machining costs at a local Southern California shop. The price to clean and mag the block, bore and hone without a torque plate, deck to square off the original deck, install cam bearings, and balance the assembly generally costs around $450. Fancy procedures like deck-plate honing, squaring using a BHJ fixture, or even align-honing aren't needed at this level to make the numbers, according to Sherman. Bearing this in mind, the basic build with small headers and no spacers would come in around $5,010. With the big headers and spacers, the total comes to just over $5,100. But any way you slice it, that's a heck of a lot of power for a very reasonable outlay.
Blueprint DataThese dimensions were verified by Joe Sherman on CHP's preassembled short-block and the RHS heads. All dimensions in linear inches, except as noted.
COMPRESSION RATIOBore x stroke: 4.030 x 3.75Block deck height: Milled to 9.019Piston deck height: 0.006 (below deck)Piston volume: -4cc valve reliefsHead gasket compressed volume: 9.1 ccCombustion-chamber volume: 64 ccStatic compression ratio: 11.02:1Cranking compression: 182-185 ps
CAMSHAFTManufacturer: Comp CamsType: Mechanical flat tappetGrind: CS 6255/6266 S106.0 (+4)Duration, 0.020 tappet lift: 286/297 degrees
Duration, 0.050 tappet lift: 260/268 degreesLobe displacement angle: 106 degreesIntake centerline: 102 degreesLobe lift: 0.376/0.387Rocker-arm ratio: 1.60:1Valve lift at zero lash: 0.602/0.619Valve lash (design): 0.016/0.018Valve lash (best performance): 0.010/0.010Valve lift at best running lash: 0.592/0.609
VALVESPRINGSManufacturer: Comp CamsValvespring PN: 26120Type: Single beehive with ovate wireRetainer PN (steel): 741Valvespring od: 1.095/1.445Valvespring id: 0.650/1.000Seat pressure: 155 lbs @ 1.880Open pressure: 377 lbs @ 1.28Spring rate: 354 lbs/inCoil-bind height: 1.230
DYNO RESULTS 158 HEADERS 158 HEADERS 134 HEADERS NO SPACER 1-INCH SPACER 1-INCH SPACER ENGINE SPEED TORQUE POWER TORQUE POWER TORQUE POWER (RPM) (LB-FT) (HP) (LB-FT) (HP) (LB-FT) (HP) 4,{{{600}}} 470.6 412.2 4,700 459.3 411.2 477.3 427.1 4,800 463.0 423.2 474.2 433.4 4,{{{900}}} 458.1 427.4 470.9 439.3 459.9 429.1 5,000 449.3 427.7 467.4 445.0 461.1 439.0 5,{{{100}}} 454.3 441.3 472.4 458.7 453.0 439.9 5,{{{200}}} 456.8 452.3 470.4 465.7 454.7 450.2 5,{{{300}}} 460.6 464.8 470.8 475.1 459.3 463.5 5,400 450.5 463.2 462.2 475.2 450.5 463.2 5,500 457.1 478.7 457.1 478.7 444.6 465.6 5,600 445.0 474.5 447.6 477.3 436.6 465.5 5,700 450.6 489.0 450.9 489.4 454.2 492.9 5,800 443.0 489.2 448.4 495.2 447.1 493.8 5,900 429.7 482.7 439.4 493.6 454.0 510.0 6,000 439.8 502.4 434.1 495.9 452.9 517.4 6,100 430.6 500.1 428.0 497.1 449.6 522.2 6,200 420.3 496.2 430.2 507.9 446.1 526.6 6,300 413.3 495.8 423.3 507.8 440.6 528.5 6,400 411.7 501.7 416.9 508.0 428.6 522.3 6,500 399.7 494.7 412.2 510.1 425.2 526.2 6,600 388.1 487.7 {{{405}}}.5 509.6 416.5 523.4 6,700 381.5 486.7 396.7 506.1 407.1 519.3 6,800 376.8 487.9 389.2 503.9 401.2 519.5 6,9O0 367.2 482.4 382.9 503.0 Avg. overall 432.4 469.7 440.3 482.7 442.1 490.9 Avg. 4,900-5,800 452.5 460.8 461.8 470.0 452.1 460.3 Avg. 4,900-6,800 430.8 477.2 439.7 487.0 442.1 490.9 Avg. 5,900-6,800 409.2 493.6 417.6 504.0 432.2 521.5