From the early dial-up days of the Internet, I remember a website titled something like, “HolyChurchOfTheSmallBlockChevy.com.” Can’t find it on Google now, but if any of disciples are still around, they must be mourning knee-deep in sackcloth and ashes following our story on the 600-cubic-inch engine from CFE that sports an industry first 4.6-inch bore spacing for a small-block footprint. 

Here’s the engine causing the commotion. CFE Racing Products developed a billet block with 4.6-inch bore centers and matching cylinder head based on its SBX profile. Depending on deck height, the engine has the potential to exceed 600-plus cubic inches but still fit in nearly the same space as a small-block Chevy. And it looks like a Chevy small-block.

Reaction to the announcement quickly generated a wide range of comments on enthusiast forums:

  • When does it go from being a “small/big” block to just a being a block? — YellowBullet
  • Call it what it is: a big-block. — SmallBlockPosse
  • Since it no longer has 4.400-inch bore spacing, 9-inch deck, 23-degree heads, etc, etc. I’m not sure what part of this engine design is actually “SBC?” Seems like there are more differences than similarities. — Speedtalk
  • Why not just make it a 6.000-inch bore space, 14.000-inch deck height , and call it a small-block? — YellowBullet
  • As far as I’m concerned, a true “small-block” is the original 265 – 350ci configuration. — Engine Tuning & Drag Racing, LinkedIn
  • It’s definitely a bad-ass piece, but just because it has small-block based heads doesn’t make it a small-block. Small-headed big-block, maybe? — YellowBullet
  • Thats not a small-block, but it is creative? — Need2Speed
  • If you own it, it’s a small-block. If your competing against it, it’s not a small-block. — YellowBullet
  • A small-block will always be determined by the outside dimensions of the block. The only limitations of the block will always be not building the engine beyond its ability to survive long term use at extreme horsepower and torque levels. — Engine Tuning & Drag Racing, LinkedIn
  • BLOCKZILLA!!!!!!!!!!!! — YellowBullet

The original 1955 small-block Chevy.

In my mind, if you’re going to be a true believer in small-block performance, you have accept both evolution and intelligent design as a means to zoom zoom. It doesn’t happen by faith alone. The new block continues the evolutionary steps that started when the 1955 265ci small-block grew to 283ci two years later and was fitted with mechanical fuel injection. If tradition was that important, all small-block Chevys and their aftermarket replacements would still have 2.30-inch main journals, ram-horn exhaust manifolds and 2-piece rear main seals to go along with the obligatory and apprently sacred 4.400-inch bore centers.

A Chevy-based foundation with 4.600-inch bore centers is simply next logical step after NASCAR approved the Chevy R07 engine with its 4.500-inch bore centers. GM already had a 4.500-inch bore-center block in the late ‘90s for Pro Stock Truck drag racing, and there was no theological revolt. But NASCAR’s  approval was like the pontiff himself gave the church’s blessings to a new generation of Chevy engines. Here was validation from the highest spiritual order in the American motorsports universe. CFE is simply preaching and preparing the for the third coming of outrageous horsepower.

They (GM companies) were competing against each other more so than Ford and Chrysler. — Richard Maskin, Dart

So, how did such a stubborn denomination like NASCAR — which had always spread the gospel of stock blocks — become a non-believer and actually bless new technology? It came during the baptism of Toyota into the brotherhood.

During the ‘60s, it was open warfare among Ford, Chevy and Chrysler NASCAR engine developers who gave us such great icons like the Boss 429, 426 Hemi and 427 Mystery Motor or Porcupine. In the early ‘70s, NASCAR called a truce and said all engines had to be 358 cubic inches and based on manufacturers current small-block platforms. Ford went with the Windsor line (4.380-inch bore center), Dodge/Plymouth used its LA series (4.461-inch bore center) and Chevy was still building off its venerable Gen 1 architecture (4.400-inch bore center).

Engine development gone mad

The former Olds Rocket Block is now marketed as the Dart Iron Eagle block.

In the ‘80s, the manufacturers worked mostly to get new cylinder heads approved. Other GM marques — Buick, Oldsmobile and Pontiac — joined the fray, as well.

“They (GM companies) were competing against each other more so than Ford and Chrysler,” remembers Richard Maskin, head of Dart Machinery. “We built a Buick head but it wasn’t allowed by NASCAR. It was later used in ARCA and Comp Eliminator. Wherever they let it run, it was successful.”

GM then mandated a little organization and split up the racing disciplines among its divisions. One of the moves was to give Oldsmobile priority in drag racing (which explains why Pro Stock body styles were so boring in that era), so Olds approached Maskin to build a drag racing block that would accept the popular aftermarket gear designed for the GM Corporate small-block platform — which was basically the Gen I Chevy.

I fudged the block. — Sonny Leonard, SAR

The result was the famed Rocket block, which offered wider pan rails, a raised cam location, optional main sizes and optional deck heights. All those modifications were geared to allowing longer stroke cranks and cylinder bores up to 4.187 inches. Big-block displacements were then possible in a small-block. (The Rocket block is now marketed by Dart under the Iron Eagle brand.)

In 1994, Sonny Leonard made the most of that potential when he built the first — and possibly only — 500ci small block based on a block with 4.400-inch bore centers. Using a tall-deck Rocket block, he stuffed in 4.250-inch pistons and a 4.437-inch crank for a total 504ci displacement. So, how did Leonard exceed the recommended max bore?

The Chevy R07 engine and cylinder block

“I fudged the block,” says Leonard, explaining that he stretched the bore centers to 4.450 inch by offset boring the cylinders. “I used a symmetrical-port GM head. We had to move the bolt holes around and also the valve guides, and get special head gaskets. Lot of welding and epoxy. It was a for a grudge racer. Made over 1,000 horsepower.”

GM followed the same mentality when it released the medium- and short-deck BowTie blocks that came with very small bores and no head-bolt or lifter holes. In other words, there was a lot of iron you could machine for 4.400- or 4.500-inch bore centers, depending on your needs or the rules. The block was used briefly in Pro Stock Truck in the late ‘90s and is still around in Comp Eliminator. But as it developed the Gen III & IV LS engines, as well as the Gen V LT platform — all with traditional 4.400-inch bore centers —  GM never got truly serious about 4.500-inch bore centers until NASCAR allowed all the teams clean-sheet engine designs for the new millennium. And that concession came when Toyota wanted to join the party.

Getting back into NASCAR

When Dodge returned to NASCAR in the Craftsman Truck Series in the late ‘90s, teams used parts leftover from the ‘70s, including R1/W2; but Chrysler soon developed the R3/W8 components — again, all based on the LA platform’s 4.461-inch bore center and also a cam location higher than Ford or Chevy, which by then was running the SB2 head but still on a conventional block. When Dodge wanted to run Cup cars in 2001, a clean-sheet, race-only block was approved. It had 4.461-inch bore centers, but also an open-deck design, and this block led to the R5P7 engine, which was used in our dyno story with AEM.

Toyota’s clean-sheet engine developed for NASCAR racing.

About the same time, Toyota was petitioning to enter NASCAR by starting out in the truck series. Since it had no pushrod V8 upon which to base a race engine, Toyota was given freedom to clean-sheet an engine based on what was already in the garages. Toyota Racing Development (TRD) purchased Ford, Chevy and Dodge race engines and took more than 8,000 measurements. TRD engineers then pushed the dimensions as far as they could negotiate with NASCAR. For example, they asked for 4.550-inch bore centers but were allowed 4.500-inch. Toyota also went with eight cam bearings, front-mounted distributor and 20 head bolts. In the end, Toyota obsoleted all the other engines, so NASCAR allowed clean-sheet designs from the other three. Chevy responded with the R07, Dodge came out with the closed-deck R6P8 and Ford followed with the FR9. All have 4.500-inch bore centers but NASCAR still mandates a 4.185-inch maximum bore to keep cylinder head development and valve sizes in check. However, the wider bore centers allow intricate cooling passages, and cooler engines mean less tape on the front grille.

The Dodge R6P8, left, and the Ford FR9.

Unlike the new CFE 4.600-inch block, Chevy’s R07 block bears no visual resemblance to the traditional Chevy small-block. However, GM has no reservations calling the engine a small-block — a reference sadly not bestowed by GM officials on the LT5 that came in ZR1 Corvette and had 4.4-inch bore centers but was designed by Lotus and built by Mercury Marine.

The aftermarket now offers numerous Chevy-based aluminum and iron blocks with 4.5-inch bore spacing — apparently with no haters sounding off. About the only limiting factors in more acceptance are the rules makers and costs. The next step is simply a 4.600-inch bore-center block, such as the one developed by CFE. Whether that’s really a logical step will have to be determined by how engine builders utilize the components. No doubt there are numerous performance dynamics such as friction, side loading, piston speed and more that will have to be addressed — and the bore-stroke ratios to reach 600ci in a 4.600 block may prove to be completely inefficient. But let the engine builders determine the fate of a 4.600 block, not the traditionalists.