Chevy Small Block Dyno Tests - Old School Meets New

406ci Traditional Mouse Vs. Late-Model 402ci LS2

Step By Step

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 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 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.

0701ch_23_z Chevy_small_block_dyno_tests 4/41

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.

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