Small Block VS Big Block - A Game of Rat And Mouse

Big-Block Vs. Small-Block: The $6,500 Build-Off

Bob Mehlhoff May 9, 2007 0 Comment(s)
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The build-off always starts off as a friendly staffer competition, but as the builds get closer to being complete, it boggles me how my cell phone will start ringing completely off the hook. What's he planning? How far is he into the build? Have you heard any dyno numbers yet? And believe me, the questions go on and on. It's not to say that this is a terrible thing; it's actually nice to have two guys who are being gung ho and making an attempt for bragging rights-at least until the next friendly shootout.

This month, we wanted to see how a small-block would fare against a big-block with a strict $6,500 budget. Right off the bat, everyone involved was saying that the big-block would trounce all over its little brother. However, it's all relative and really depends on the type of performance you're expecting and the chassis you plan to mate it to. Personally, I'm more of a big-block kind of guy so that should tell you who I was cheering for. Still, I have to admit that the small-block did a great job of letting all of us know it wouldn't go down without a fight.

If you want my personal opinion, both builds were created by thinking outside the box and presented incredible packages that can easily be replicated. That's right, we didn't stumble across a lucky bottom-end score through the classifieds, nor did we just happen to have a set of ported heads lying around to make budget. What you see is what you get, and should you want to follow suit, we've listed every single part number along with its cost.

You've seen what we did-and are about to see the final dyno numbers, so let me leave you with the following question: Given the same opportunity, what would you have done different? What combination would you have built? E-mail your thoughts and build specs to me at chevyhi@primedia.com. -Henry D

John's Engine
JMS Racing Engines 505ci Big-Block
Let's face facts, friends: $6,500 isn't a lot of dough with which to build a big-block, not to mention something with some decent performance numbers. Actually, I was looking for better than decent. A big-block has big advantages, but I'd have been nuts to dismiss my Mouse motor opponent. And so the crux of the issue quickly arose: Where would our money be best spent?

The first question, posed by Mike Johnson of JMS Racing Engines, our talent for this shindig, was this: What kind of motor do you want? A dyno queen was immediately ruled out. I wanted a big number, but not at the expense of real-world performance. I laid it out baldly. "I'd like 600 hp-or close to it-but I'd also like just as much torque and a Kansas-flat torque band, thank you." That's not asking too much, is it?

That settled, the big question, as kicked around by Mike and yours truly for a day or two, was pretty straightforward. Should we keep a stock stroke and try to score some good heads, or should we stroke the thing and cheap out on the heads? We chose Plan B. We'd add a quarter-inch stroke to our 454 base to create a grunt-happy 496, and Mike would port a set of 049 heads for us to use. Or so we thought.

Further digging turned up a set of new GM rectangular-port heads, fully assembled and with a spring upgrade from Aerohead Racing for $1,115. Visions of those big, fat 325cc intake ports dancing in my head, I called Mike to describe my find. His response? "Hell yes, let's do it." Just like that, we got to go with both Plan A and Plan B. This battle would be fought with a big stroke and lots of airflow.

We pretty much knew we'd be using a two-bolt main core, which Mike assures us is more than adequate for this power level, assuming main studs are used. Ditto the cast crank. Forged is great, but a properly prepped cast crank can handle much more than we're throwing at it. On the other hand, another change came when we decided to rescue a 454 core that was already 0.060 over, which would create a 505ci big-block. If a big bore is good, a bigger bore is better, right?

In essence, one thing remained, and that was to spec out a camshaft with Isky Racing Cams. This thing was destined to be a solid flat-tappet cam motor from day one, oil additive issues be damned. Given my powerband desires, Mike huddled with the brains at Isky and cooked up a 'stick...which produced exactly the power characteristics I wanted.

In the final analysis, creating a setup that works is what this project was about. What we did, in short, was maximize our combo within the budget constraints. Cam, heads, bore, stroke, compression ratio; everything was right. "We wanted a long torque band that kicks in right away," said Isky's Nolan Jamora. Yes we did, and that's what we got. "It's pretty impressive," chimed in Mike Johnson. "We did our homework, and that's all that matters."

Well, not quite all; we thumped the small-block, in case you haven't noticed. With 83 more cubic inches, a 4.250-inch stroke, and heads that outflow just about any small-block head, are you surprised?

505ci Big-Block- Dyno Details

Headers 211/48 Hedman long-tube headers with 18-inch extensions
Fuel 91-octane unleaded
CARBURETOR Mighty Demon 850 carburetor
Jets 80/91

BOB's engine
Larry's Track Pro 422ci Small-Block
Building a small-block on a $6,500 diet to make big-block power means you'd better come to the party with a decent amount of displacement. With this lofty goal, I penciled out a plan to gain 422 ci from a production 400 small-block with a Scat 3.875-inch-stroke crank, Scat 6.00-inch rods, and off-the-shelf Ross forged pistons. Through the help of Jim Escamilla of Larry's Performance, we uncovered a useable 400 small-block core. This block was a 3951509 two-bolt item, originally installed in a '79 Chevy delivery truck, and it only required general machine work and a 0.040-inch bore job to be squared-to-the-world and ready for assembly. If a modest budget and shrinking calendar were not the limiting factors, I would have opted for even more cubic inches.

The central goal for this competition was to make as much big-end power as possible and run it on high-test (91-octane) pump gas. This meant it would not be a well-mannered street-performance motor with a big, broad power curve. Instead this would largely be a single-purpose powerhouse, a welcome breaking away from decorous convention.

With these parameters drawn, I selected a series of performance parts designed to make lots of power above 4,500 rpm. I considered several cylinder heads for the test that would flow a large amount of air, were easily obtainable, and came at a budget price. Next I wanted a cam with off-the-map lift numbers and lots of duration. On the intake manifold side, the engine needed to draw hordes of air and fuel quickly into the engine. Because the price of carburetion wasn't part of the $6,500 budget, I decided to mount a pair of 750-cfm double-pumper four-barrels to a tunnel-ram intake manifold. Again, this engine's single purpose was to make as much upper-rpm power as possible. On a street- or weekend-performance car, this engine would be a hassle to drive, sort of like using a racehorse to pull a cart.

By the time I had the engine completed and ran a tally, the numbers fell just dollars below our $6,500 cap. Had there been a little more time, I would have liked to spend some time on a flow bench improving the cylinder head's flow capabilities, and with the big cam it would have been possible to run more compression in this engine on the dyno. As with any engine build, though, you walk away with a to-do list for next time. What's especially noteworthy with this 422 is that after we finished the dyno pulls, the little powerhouse outperformed its competition with 1.36 hp per cubic inch. All in all, I think I would have traded that triumph for the higher horsepower mark.

Small-Block Dyno Details

Headers 171/48 Headman headers
Fuel 91-octane unleaded
CARBURETOR Dual 750-cfm Holley carburetors
Jets Test 1: 71/80 Test 2: 72/77

422ci Build sheet
Specifications not listed are the same as stock. Except as noted, all dimensions are in inches or fractions thereof. All prices sourced through Larry's Performance and Summit Racing.

Included machine work and assembly, SCAT forged 3.875 crank, King silicon bearings, Scat 6-inch rods, Ross Forged pistons and rings, complete gasket set, two-row roller timing chain, and ARP main bolts.

Sources

Comp Cams
Memphis, TN 38118
800-999-0853
http://www.compcams.com
Summit Racing
Akron, OH
800-230-3030
SummitRacing.com
Westech Performance
Mira Loma, CA 91752
951-685-4767
www.westechperformance.com
JMS Racing Engines
El Monte, CA
626-579-4567
http://www.jmsracing.com
Ross Pistons
El Segundo, CA 90245
310-536-0100
www.rosspistons.com
KB Performance Pistons
Carson City, NV
800-648-7970
http://www.uempistons.com/
Isky Racing Cams
Gardena, CA 90248
323-770-0930
www.iskycams.com
RPM International
Cerritos, CA 90703
562-926-9188
http://www.racingpartsmaximum.com
High Velocity Heads
865-573-9151
www.HighVelocityHeads.com
Scat Enterprises
310/370-5501
scatenterprises.com
Milodon
Simi Valley, CA 93065
805-577-5950
www.milodon.net

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