Chevy Engine Block - Cutweight Horsepower

Swapping a Cast-Iron Block for an Aluminum One on a Chevy Small-Block V-8

Mark Stielow Sep 1, 2006 0 Comment(s)

The Bow-Tie block can be ordered with many different features, since this is the block required for use in all GM-bodied NASCAR vehicles. A customer can order one from any GM dealer, but you'll probably want to find the closest GM Performance Parts Authorized Center (go to www.gmgoodwrench.com) to get some guidance from the pros. Stielow likes to work with GM Performance Parts dealer Scoggin-Dickey Chevrolet, in Lubbock, Texas.

All Bow-Tie blocks come with some high-end features, like screw-in coolant plugs (shown, left) and billet rear cam covers with inset O-rings (shown, right), priority main oiling systems (practically a must for real performance engines) and more.

More important to the enthusiast is that Bow-Tie blocks are available in either cast-iron or aluminum, set up for dry- or wet-sump oiling systems, and with various main bearing diameters (the NASCAR Cup boys have experimented with small journal sizes to reduce frictional losses). There are also a few different deck heights, and the option of purchasing a rough bored block so your local machine shop finish bores and hones. Why are there so many variations? Because there are so many ideas on how to build the "ideal" performance small-block V-8.

In general, some classes, like Nextel Cup, have rules that require a cast-iron engine block-so the racers want cast-iron as the block material. Again, Nextel Cup allows the expensive and complex dry-sump oiling systems, so the racers want a block that is already designed, cast, and machined to take full advantage of the dry-sump system-and the Bow-Tie block is set up for that. The different bearing diameters and deck heights are requested by these same engine builders, as the rules don't specify exactly what they need to be-so the racers are always experimenting with different setups in the quest for more power, durability, and...well, any advantage they can find.

Notes from test: Fuel rail pressure was set at 60 psi, engine coolant temperature averaged 173 degrees F, oil pressure averaged 61 psi and oil temperature averaged 178 degrees F during dyno run

RPMTrq (lb-ft)Power (hp)A/F Ratio (left side)Maniold Vacuum
300039022313.470.2
310039923613.380.2
320040824913.440.2
330041626113.490.27
340042327413.590.27
350042628413.410.3
360042228913.040.3
370041829512.870.3
380042030412.850.3
390042031213.040.33
400042332212.080.4
410042933513.080.4
420043434713.070.4
430043935913.10.49
440044537213.140.5
450045138613.220.5
460045940213.240.59
470046641713.250.65
480047243213.190.69
490047544413.070.7
500048145812.940.7
5100488474130.7
520049048512.980.79
530049550013.030.85
5400BF51413.020.89
550049952413.040.9
560049953213.030.9
570049653913.010.99
580049657412.851
590049355412.841.09
600049056012.831.1
610048456212.811.18
620048056612.831.2
630047557012.681.2
640047257512.591.3
6500467BF12.471.3

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