How To Build A Kick-Ass, Pump-Gas, NPAA 680HP Small-Block Chevy

Ccrp 1212 680Hp Pump Gas Npaa Small Block Chevy Engine No Power Adders 01

This is what a 680hp, pump-gas small-block looks like on the dyno. No nitrous, no blower, just excellent cylinder heads, a big cam, and lots of rpm.

This is what a 680hp, pump-gas small-block looks like on the dyno. No nitrous, no blower,

This is a story about a return from the dead. It begins when Car Craft family member Greg Smith’s 600hp, 434 small-block Chevy munched a mechanical lifter on the street one night. This was (notice the use of past tense) a really nice small-block with AFR 227cc heads, a big mechanical roller cam, and 10.5:1 compression. On Westech’s dyno, it had made 610 hp and had pushed Greg’s ’55 to low 11s. But that was before one fateful Friday night. “It began making a funny noise about halfway home from the cruise. I shoulda’ stopped,” Greg says, “but I didn’t.” By the time he arrived home, the dead lifter had puked all its little needle bearings into the engine, the bearings moving around like little mechanical piranha eating all sorts of sweet-meat metal parts. Greg disassembled the small-block and took it to Barrington Engines, where owner Don Barrington Sr. put on his CSI hat and pointed out all the carnage. Several pistons and cylinder walls were heavily scored, and the cam was lathed, but the rest of the engine was surprisingly unscathed. The fix would involve a new cam, lifters, and a set of pistons.

Sometimes, what appears to be a disaster is also an opportunity. While Greg was assembling parts to rebuild his existing horsepower package, AirFlow Research (AFR) announced a brand-new, big-port small-block Chevy head. Dubbed the 245 NPP (no pushrod pinch) head, this 23-degree casting rearranged the intake-port landscape to eliminate the pushrod “bump.” While this worked to push the flow numbers up to 350 cfm at 0.750-inch lift, there is a price for this added airflow. The heads require a dedicated shaft-rocker system from either Jesel or T&D, which significantly adds to the cost. Standard rocker arms will not work because of the need for a sizeable intake-rocker offset. AFR says you can either go with a 0.450-inch offset combined with a 0.180-inch offset lifter or 0.550-inch offset rockers and standard lifters. Greg elected the latter option. The 245NPP head is also a non-raised runner casting, which means it will accommodate any of the larger, 23-degree small-block intake manifolds. This is important, because it allowed Greg to add AFR’s new Titan single-plane composite intake manifold we first introduced back in the June ’11 issue (“Make 561 HP Using AFR’s Composite Intake and 195cc V2 Heads”). All that was left to do was figure out a cam—a gnarly, give-me-lift-or-give-me-death kinda camshaft.

This is what two of the original Mahle pistons looked like after the escaped lifter-needle bearings worked their evil. This required taking the 4.155-inch bore motor out to 4.165 to clean up the scratched cylinder walls.
This is what two of the original Mahle pistons looked like after the escaped lifter-needle
Don Barrington Sr. bored and torque-plate honed the World Products block to fit the new Mahle pistons. He also lightly trimmed the deck to make everything square.
Don Barrington Sr. bored and torque-plate honed the World Products block to fit the new Ma
The Mahle pistons also feature full-floating wristpins, requiring installation of the lock rings on both sides. Barrington uses a notched screwdriver to guide the round locks into place. We tried this trick, and it works very well.
The Mahle pistons also feature full-floating wristpins, requiring installation of the lock

So we called longtime Crane Cams pal and camshaft connoisseur Chase Knight for a recommendation. With a cylinder head that can take full advantage of 0.750-inch of valve lift, we knew we had to have something a little more aggressive than a basic catalog cam. Crane has a custom lobe book with dozens of lobe families, offering the engine builder the ability to create his own camshaft. Knight suggested the Crane 4381 lobe. Crane describes this lobe as a circle-track design that offers great durability, which is what we preferred over an overly aggressive drag-race lobe that would make great power but might eat valvesprings faster than a sugar-starved four-year-old devouring a Tootsie Roll. We conspired on a cam, and soon a very cool mechanical roller showed up on our shop doorstep.

By this time, we had also lined up a new set of Mahle 4.165-inch flat-top pistons, rings, and new wristpins. Following some superb machine work, Barrington assembled the short-block. We were able to reuse the original Eagle 4340 steel 4.00-inch stroke crank and Lunati Pro Mod I-beam 6.00-inch rods installed with new Clevite rod and main bearings set at 0.002-inch bearing clearance. With a near-zero deck, the compression came in at 11.4:1, which is still OK with pump gas because of the size of the camshaft. We then spent some time installing the T&D rocker-shaft system. Shaft rockers demand very accurate pushrod length because there is only about 0.050 inch of usable adjustment in the pushrod cup where lash is set. Often, a dual-pattern camshaft can have different base-circle diameters that directly affect pushrod length. After carefully following T&D’s instructions, we finalized our pushrod length, which we sent off to Trend Performance for a set of 3⁄8-inch, 0.135-inch-wall-thickness, tapered pushrods we knew would be necessary to minimize pushrod flex. A big reason for the large pushrods are the PAC springs on the AFR heads that produce over 700 pounds of load at full valve lift. We topped off the engine with one of AFR’s new composite Titan TXR single-plane intake manifolds that had shown great power potential when we first tested them a year ago. We also knew we’d need a bigger carburetor than Greg’s previous 950-cfm Holley, so the call went out for a serious upgrade to a Quick Fuel 1,000-cfm, 4150 style–carburetor. With the MSD distributor and copper alloy gear in place and a new Crane timing set, we were ready to make some noise.

It’s easy to spot a Crane mechanical roller cam by the distinctive copper color between the lobes. The lifters are Crane’s best Ultra Pro lifters that Greg will be checking more frequently to ensure reliability. These lifters should last longer since they feature pressure-fed lube to the rollers.
It’s easy to spot a Crane mechanical roller cam by the distinctive copper color between th
The big change to the small-block was AFR’s new 245 NPP 23-degree small-block cylinder head. While there are bigger small-block heads, these will accommodate any normal small-block intake.
The big change to the small-block was AFR’s new 245 NPP 23-degree small-block cylinder hea
The fully CNC-ported 345cc intake port looks almost jewel-like. Smaller 8mm valve stems help flow as well. Without the intrusion of the pushrod wall, it’s nearly a straight shot right to the back of the valve. Flow increases when it doesn’t have to move around corners.
The fully CNC-ported 345cc intake port looks almost jewel-like. Smaller 8mm valve stems he

Cam Specs
Original Roller	Duration at 0.020	Duration at 0.050	Valve Lift (inches)	Lobe Separation (degrees)
Intake	300	264	0.631	112
Exhaust	306	269	0.631
New Crane Roller
Intake	298	266	0.657 (0.746)*	112
Exhaust	296	264	0.630 (0.703)*

*Net valve lift with 1.75/1.70:1 rocker ratios and subtracting 0.020 valve lash

Test Day

Even with all these good parts and a careful assembly, Greg was a little nervous on test day. He knew we were gonna spin this baby past 7,000. We filled the Moroso oil pan with Joe Gibbs Driven 5w20 race oil and pre-lubed the engine. The break-in procedure went flawlessly, and after a quick tune and 34 degrees of lead, the first yank on the dyno produced a gratifying 665 hp at 7,100 rpm and 579 lb-ft of torque at 5,100 rpm. This produced an improvement of more than 50 hp from Greg’s previous combination. Beyond the peak horsepower, we also zoned in on the spread between peak torque and peak horsepower. Big-cam motors can be very peaky, but his combination was pleasingly wide, with a 2,000-rpm powerband between 5,100 and 7,100 rpm. But we were still in search of more power, and by the end of the day, we had tightened the exhaust lash and added a Wilson 2-inch-tall carb spacer that was worth a little more power.

Fitted to the classic heart-shaped 70cc combustion chamber is a pair of 2.125/1.60-inch valves. The valve spacing is the same as AFR’s next-smaller heads, so there was no problem with the position of the valves relative to off-the-shelf pistons.
Fitted to the classic heart-shaped 70cc combustion chamber is a pair of 2.125/1.60-inch va
With the exhaust-to-intake flow relationship solidly in the 70-percent-and-better range, the exhaust ports on the AFR245 heads are every bit as efficient as the intake side.
With the exhaust-to-intake flow relationship solidly in the 70-percent-and-better range, t
The AFR 245 heads do require a complete rocker-shaft assembly, so we called in help from T&D and created a 1.75:1 intake rocker combined with a 1.7:1 ratio on the exhaust side. Note the large intake-rocker offset. This is necessary to clear the relocated intake-port wall.
The AFR 245 heads do require a complete rocker-shaft assembly, so we called in help from T

Conclusions

While we were successful in making a thumpin’ 680 hp, we underachieved. When checking piston-to-valve clearance during pre-assembly, we discovered a somewhat tight exhaust piston-to-valve clearance. Erring on the conservative side, your humble author chose the next-shorter duration exhaust lobe rather than reducing lift with a 1.6:1 rocker ratio. AFR’s Tony Mamo wanted more exhaust duration than we used, but in the rush to order parts, we went with the shorter, 264-degree exhaust lobe. We managed to improve power by tightening the exhaust lash, which effectively increases the exhaust duration by a couple of degrees. This move, plus the Wilson 2-inch spacer, bumped the power up to a respectable 680 hp at 7,200. We’re not sure whether we would have been able to make 700 hp, but we are confident we could have been very close.

The shaft system also requires a very carefully selected pushrod length because the lash adjustment, located in the rocker-arm cup, has limited travel. We selected a 3⁄8-inch double-taper pushrod from Trend Performance because of its reputation for stiffness, which will help valvetrain stability at 7,000 rpm.
The shaft system also requires a very carefully selected pushrod length because the lash a
With all this lift, checking valve-to-piston clearance is a requirement. We did the Play- Doh method. As you can see, we have sufficient intake clearance of around 0.100 inch and also good radial clearance between the valve and the vertical wall of the piston’s valve-clearance pocket.
With all this lift, checking valve-to-piston clearance is a requirement. We did the Play-
The AFR 245 heads do require a complete rocker-shaft assembly, so we called in help from T&D and created a 1.75:1 intake rocker combined with a 1.7:1 ratio on the exhaust side. Note the large intake-rocker offset. This is necessary to clear the relocated intake-port wall.
The AFR 245 heads do require a complete rocker-shaft assembly, so we called in help from T

The 436ci is now back in the engine compartment of Greg’s black ’55 Chevy, and he fully intends to drive the car on the street. As to whether this is a true street engine comes down to how much hassle you’re willing to endure. This bruiser is no long-distance cruiser, and Greg has already decided that, at what would normally be an oil change interval of 3,000 miles for a daily driver, he will inspect the lifters for wear. The majority of lifter abuse comes from a combination of long idle periods and high valvespring pressure. With more timely inspections, Greg suspects his engine has a long future ahead of it. In terms of quarter-mile times, we simulated his combination at 10.50s at 128 mph using the ’55’s 3,660-pound weight with driver. The cam and cylinder head tuneup certainly delivered on the investment. With no loss of torque, this new package delivered a solid 70hp increase from the previous combination. And as a great little spiff, in our world, there are few more pleasing sounds than a 680hp small-block singing at 7,000 rpm.

Dyno Numbers

Ccrp 1212 680Hp Pump Gas Npaa Small Block Chevy Engine No Power Adders 14

We also combined AFR’s new Titan TXR composite intake with a Quick Fuel 4150 carb that flows 1,000 cfm and a Wilson 2-inch, tapered spacer to make our final 680hp number. End

We also combined AFR’s new Titan TXR composite intake with a Quick Fuel 4150 carb that flo

Test 1: This was the initial test of the engine. Header size is 13⁄4-inch primary pipe with an 18-inch-long, 3-inch collector extension. No mufflers were used.

Test 2: This was the final result of adding the Wilson 2-inch tapered spacer, a slight high-speed bleed adjustment, and tightening up the exhaust lash to 0.011 inch.

RPM	Test 1 TQ	Test 1 HP	Test 2 TQ	Test 2 HP	TQ Diff	HP Diff
4,500	573	491	579	496	+6	+5
4,700	572	512	576	515	+4	+3
4,900	576	537	579	540	+3	+3
5,100	579*	562	584*	567	+5	+5
5,300	578	583	584	589	+6	+6
5,500	571	598	577	604	+6	+6
5,700	567	616	572	621	+5	+5
5,900	563	633	572	621	+9	+12
6,100	555	644	562	653	+7	+9
6,300	543	651	551	661	+8	+10
6,500	529	655	538	666	+9	+11
6,700	516	659	525	670	+9	+11
6,900	504	662	514	676	+10	+14
7,100	492	665*	502	679	+10	+14
7,200	---	---	496	680*	---	---

Parts List
Description	PN	Source	Price
AFR 245 NPP head	1137	AFR	$2,524.00
AFR Titan TXR intake	4801	Summit Racing	581.03
AFR valve covers	6705	Summit Racing	163.95
T&D rocker shaft	20047	T&D Machine	1,087.40
Trend pushrods, 3⁄8-inch	T78251353	Trend Perf.	$245.92
Crane mech roller	11R001859	Crane	400.00
Crane roller lifters	11570-16	Summit Racing	705.60
Crane timing set	11975	Summit Racing	101.20
Crane distributor gear	11979	Summit Racing	42.80
Mahle pistons	SBC550165F05	Summit Racing	651.57
Clevite rod bearings	CB663HN	Summit Racing	71.60
Clevite main bearings	MS1038HX -0.001	Summit Racing	89.95
Durabond cam bearings	CH8 HP	Summit Racing	21.88
Melling oil pump	M55	Summit Racing	28.95
Fel-Pro head gasket, MLS	1144	Summit Racing	81.95
Fel-Pro 1-piece pan gasket	1880	Summit Racing	40.95
Wilson 2-inch carb spacer	004150	Summit Racing	196.95
Quick Fuel carb, 1,000-cfm	RQ-1050-AN	Summit Racing	931.00
Autolite race plugs	AR-3910	Summit Racing	28.00
Joe Gibbs Racing oil	AP-1 (5w20)	Summit Racing	99.75 (5 qts)
Machine Work
Hot tank	N/A	Barrington	60.00
Install cam bearings	N/A	Barrington	40.00
Bore and torque-plate hone	N/A	Barrington	290.00
Surface block	N/A	Barrington	190.00