last issue, we began an in-depth look at Chevy’s big block bow tie blocks – this one was a tall deck job. As we pointed out in that segment, there are lots of options out there today when it comes to racing and general high performance cylinder blocks. What we’re doing here is to show you what the blocks offer. Down the road, we’ll look at other cylinder blocks. Meanwhile, check out part two of our Chevy Performance bow tie block series:
One thing you should be aware of with any block, no matter who manufactured it, is that the oil galleries are drilled. We’ve seen some off-make blocks where the galleries weren’t finished, and in one case, where a piece of drill tooling was broken off in the cylinder block. Bow Tie blocks are all inspected to ensure that oil holes are properly drilled. Further to this, CNC-machined bow tie blocks are also leak tested prior to shipment. It’s simply good insurance and well worth the price of admission.
Another consideration with cylinder blocks is the actual deck height. This is the distance between the crankshaft or main bearing bore centerline and the top of the block. The standard small block Chevy deck height dimension is 9.025-inches. The standard big block dimension is 9.800-inches. Truck blocks (big block) measure 10.200-inches in deck height, and so do bow tie blocks destined for large displacement applications (such as this one). Chevy Performance also offers small blocks in a “tall” version (aluminum) at 9.525-inches and two short versions in iron – 8.700-inches and 8.325-inches. DRCE (“Drag Race Competition Engine”) big blocks come in several different varieties that measure anywhere from 9.525-inches to 9.250-inches. They can be machined down to 9.00-inches total deck height.
Something seldom considered is the actual fuel pump boss. Late model production-based big blocks did not have provisions for a mechanical fuel pump. Neither do DRCE cylinder blocks. Early productions blocks (production and bow tie) have a pump boss. Similarly, late model Chevy Performance Parts bow tie cylinder blocks come equipped with a fuel pump boss. When inspecting non-bow tie blocks with bosses, check to ensure that the pushrod hole is actually drilled! We’ve seen off-brand blocks where the hole is either missing or not completely bored.
See the angle of the main cap bolt? It’s splayed 16-degrees. All three-center caps have this feature. Splayed caps provide more clamping power, and as a result, prove stronger than conventional straight bolt cap assemblies. This bow tie block is equipped with nodular iron caps. They’re good for at least 800 HP before becoming stressed. Past that point, you should consider a cylinder block with billet steel caps (Chevy uses 8620 steel for maximum effort bowtie race blocks and 4140 steel in DRCE blocks).
Something else that differs between bow tie big blocks and more pedestrian production line counterparts are the additional head bolt bosses (actually, four per bank, eight total). Certain Chevy and aftermarket cylinder heads are engineered with the extra head bolt holes, or in certain cases, the heads can be modified to accept additional bolt holes. The result is (rather obviously) more cylinder head clamping force. This really isn’t a dilemma for low compression, naturally aspirated engine combination, but if a bunch of nitrous oxide is added, or the engine is supercharged in some form or if the compression ratio is in the stratosphere (or a combination of nitrous and high compression), then the additional head bolts prove to be a big bonus.
Compared to a conventional big block cylinder case, the bow tie examples have much more “meat” surrounding the respective lifter bores. This serves several purposes: You can safely sleeve lifer bores with this setup (necessary with keyway roller lifters or to repair worn lifter bores) or you can install oversize lifters (all Chevys use a rather small 0.840-inch or so diameter lifter). Further to this, bow tie blocks are machined in the valley in any area that is adjacent to the lifter. This is particularly important when it comes to clearance for roller lifter assemblies (hydraulic or solid). Because of this, engine builders don’t have to concern themselves over roller lifter tie bar clearance and other issues when assembling the block.