Chevy Small Block Dyno Tests - Old School Meets New

The basis for our Gen I challenger...        read full caption The basis for our Gen I challenger was a well-seasoned 400 small-block core, which Coast High Performance clearanced for a 4340 forged-steel crank working 6-inch rods through a 3.750-inch stroke--a combination Coast High calls its 406ci Pro Mod short-block.

You've noted that our 400...        read full caption You've noted that our 400 uses two-bolt mains. Our engine builder, Jun Nakawatase, pointed out that four-bolt-main 400s are actually weaker than their two-bolt brethren, since the extra bolt runs through the thinnest part of the cap and the block casting. We used ARP main studs for maximum strength.

The reciprocating assembly...        read full caption The reciprocating assembly contained in the 406ci Pro Mod short-block consists of Probe SRS forged pistons with full-floating pins and Lightweight 4340 forged steel connecting rods. Using 6-inch rods maximized our power potential by optimizing our rod-to-stroke ratio.

Coast High Performance 406ci Stroker
In short, I felt like the man who takes a knife to a gun fight. But as it turned out, what I needed for this fight was a big 'stick--a really big 'stick. In fact, "Get the biggest dual-pattern cam you can find," was the first marching orders given to me by Coast High Performance's Shawn Mendenhall. Since this Torrance, California-based outfit specializes in building high-horsepower stroker small-blocks, I listened.

Given that the basic architecture of our starting point was created more than 50 years ago, it would be easy to label this contest "space-age versus stone-age." And there's no denying that GM has created an amazing new line of engines. On the other hand, it turns out that spacemen and cavemen have a lot in common when it comes to what's under the hood. Both engines are overhead-valve, pushrod powerplants, which means they're both air pumps. Get the mixture in, burn it, get it out. It ain't rocket science, for a Gen I engine or a whiz-bang Gen IV.Therein lay our dilemma. The Gen III/IV engines certainly have improved lower ends, but where they really shine is in breathing ability. How would we match up? The rules of this showdown required that all parts be off-the-shelf...so we reached for the top shelf, going with Dart's fully CNC-ported Pro 1 227 heads. These 23-degree aluminum heads are serious breathers, moving 309 cfm at 0.700 inch lift. Dart calls them "professional-quality competition cylinder heads." Using a 400 block as our basis gave us needed displacement and room for the mondo heads to breathe. So there you have our formula: Big bore, big stroke with 6-inch rods, big cam, big heads, and lots of compression and timing make lots of power.

We did just that, and by the numbers we matched the 402ci LS2, and did it on 91-octane to boot. What's striking, however, is how far we had to go to do it. Race heads, a port-matched intake manifold, and one big hairy cam--and that's just for starters. We might go so far as to call this thing a street motor, but someone might ask, "What street?" and we'd be stuck for an answer. It would certainly be one that's driven without power brakes, since that serious 'stick doesn't provide much in the way of vacuum (6.5-7 inches). And as for idle quality...well, let's not discuss idle quality.

All in all, the component parts of the 402 are rather tame by comparison. Yet the total costs were close to equal. Essentially, we had to build a hydraulic-roller race motor to match the new kid on the block, and that we did. At this point in time, old versus new, it really comes down to what you want with your 583 hp. In human terms, one is a svelte gent, a real James Bond, simply charming until he whips out the newest of Q's gadgets and obliterates your ass. The other is a crude brute, swinging wildly from the trees like a Neanderthal until he jumps down and starts beating you over the head with a leg bone from a brontosaurus. And there's the question of the hour, friends. Spaceman or caveman? Personally, I like 'em both.

583 hp, 533 lb-ft, and 91-octane-friendly--but not the tamest of beasts.

400 blocks are getting hard to find, but aftermarket versions are getting cheaper.

Edelbrock PN 2900 is a CNC port-matched Victor Jr. intake. Nice touch.

Dart Pro 1 227 CNC heads provide excellent flow numbers; Dart cast-aluminum valve covers top them off in style.

Comp Cams 2-piece Billet Aluminum Timing Cover allows for precise cam endplay settings.

Milodon Pro Competition Stepped Sump oil pan uses a crank scraper to free up a few extra ponies.

Hedman 13/4-inch long-tube headers with 18-inch extensions take out the junk.

To achieve the compression...        read full caption To achieve the compression we were looking for, the block was decked 0.0020 inch and flat-top pistons were used to create a zero piston deck height. We came in a smidgen above the limit at 11.1:1. Nakawatase used a bit of racer savvy to maximize the potential of our 406, deburring the sharp edges on the pistons to help minimize hot spots, and thereby detonation. Did it work? Given that our optimum total timing was 39 degrees, we'd say it didn't hurt.	To achieve the compression...        read full caption To achieve the compression we were looking for, the block was decked 0.0020 inch and flat-top pistons were used to create a zero piston deck height. We came in a smidgen above the limit at 11.1:1. Nakawatase used a bit of racer savvy to maximize the potential of our 406, deburring the sharp edges on the pistons to help minimize hot spots, and thereby detonation. Did it work? Given that our optimum total timing was 39 degrees, we'd say it didn't hurt.	We knew we'd have to move...        read full caption We knew we'd have to move massive quantities of air to match up with our Gen IV opponent, so we reached right for Dart's top shelf, choosing a set of Pro I 227 CNC cylinder heads. These gorilla lungs are cast of 355-T6 aluminum alloy and run 2.08/1.60-inch intake/exhaust valves. The valves are controlled by 1.550-inch springs, which are held in place by 10-degree titanium retainers.
The intake ports of the Pro...        read full caption The intake ports of the Pro I CNC heads are thoroughly massaged, measuring 227cc and moving 302 cfm at 0.600 inch lift. Our stout cam, when combined with 1.6:1 rockers, works 0.600/0.619 inch lift and 248/254 degrees duration at 0.050--an ideal match for these heavy-breathing heads.	Of course, our primary motivation...        read full caption Of course, our primary motivation for choosing the Pro 1 CNC heads is the fact that they're fully ported. The port volume on the worked-over exhaust side comes in at 85 cc, which is a full 10 cc over the regular Pro 1 head. This side flows 220 cfm at 0.600 inch lift, which combined with our cam to move burnt gases out quickly and efficiently.	Unsure of what the future...        read full caption Unsure of what the future would hold for our 406 creation, Coast High went ahead and drilled the steam passages in our heads. This is definitely a "measure twice, drill once" type of task.
Speaking again of fully ported,...        read full caption Speaking again of fully ported, the Pro 1 227 CNC heads also feature a thoroughly worked-over and bowl-blended combustion chamber. Once the machines have had their way with the castings, the chambers each measure 66 cc--not the more commonly seen 64 cc. It makes a difference when calculating compression ratio.	The extensive Fel-Pro gasket...        read full caption The extensive Fel-Pro gasket kit we used included top-grade MLS (multilayered steel) head gaskets. Compressed thickness measures 0.041 inch. The gasket edges don't reach all the way to the intake valley, so a little bit of sealant is needed (arrow).	After consulting with ARP,...        read full caption After consulting with ARP, we used 12-point Pro Series head bolts. These fasteners are rated at 200,000 psi, the same as ARP's head studs, giving us better-than-average strength, to say the least. As is standard we used ARP's moly lube on the bolt heads and thread sealant on the appropriate area, which passes though the coolant passages.
Continuing our quest for as...        read full caption Continuing our quest for as much valvetrain stability as possible, Coast High installed a set of its prototype shaft-mount 1.6:1 offset rocker arms atop our Pro 1 heads. (They'll be in regular production by the time you're reading this.)	Given the pushrod angles our...        read full caption Given the pushrod angles our heavily ported heads created, we upgraded to Comp Cams Magnum one-piece pushrods. Nakawatase tightened each rod 3/4-turn past zero lash.	We outfitted the front end...        read full caption We outfitted the front end of our stroker crank with a Rattler torsional vibration absorber. Also note our one-piece oil gasket. Our block required a piece with a thick front seal (PN 1880), marking it as a '75-and-later small-block timing cover. Note that it also provides clearance for our stroker crank setup.
In the name of achieving every...        read full caption In the name of achieving every last pony possible, we took note that the Dart Pro 1 227 CNC heads are gasket matched to Fel-Pro 1206 intake gaskets...	...and so is the port-matched...        read full caption ...and so is the port-matched version of Edelbrock's ubiquitous Victor Jr. manifold. This CNC gasket-matched intake is an off-the-shelf part, so we went for it. When it comes to intake flow, every little bit counts, right?	All that remained was for...        read full caption All that remained was for Nakawatase to bolt the Victor Jr. into place, then take a moment to admire his handiwork before loading this contestant into the truck and heading off to the dyno. If you look closely, you'll note that Nakawatase fitted our ARP intake bolts with larger-than-normal washers, a step he always takes with slotted intake manifold bolt holes.
On the scene at Westech, Steve...        read full caption On the scene at Westech, Steve Brulee quickly set up our MSD Pro-Billet distributor. Brelee installed the largest advance stop bushing, limiting centrifugal advance to 18 degrees. He also installed one silver and one blue advance spring, ensuring all our timing would be in by approximately 2,800 rpm.	All that work led us to this...        read full caption All that work led us to this point, on the dyno in our 406's best fighting trim--and this thing is a fighter. We achieved max power with a 76/83 jet combo in the 750-cfm Mighty Demon mixer both engines used; in other words, our powerplant needed the four jet sizes Brulee removed for the Gen IV runs. It looks cool, sounds nasty, and makes as much power as its 402ci opponent, which gave us just about everything we could want.