Words And Photos: Richard Holdener

Cylinder heads are an integral part of any performance equation and the best thing about a set of great cylinder heads is the better the combination, the more power they are worth. The Brodix BB-3 Xtra 332 heads tested on our 496 are a perfect example, as they offered huge gains but in reality, this test only scratched the surface of what they were capable of. Before we could start swapping heads, we needed a test motor and a good one at that. Not satisfied that a 454 would suffice (who builds a 454 any more), we stepped up to the next logical stroker displacement. The 496 BBC was the result of combining a .060-inch overbore with a 4.25-inch stroker crank.

Not wanting to skimp on quality, we contacted the stroker experts at Scat Enterprises for a solid rotating assembly. Scat supplied a BBC combination that featured a 4340 forged steel crank and matching set of 6.385-inch, I-beam rods. Our late-model, big block required use of a crankshaft design specifically for a Gen 6 block. The Scat crank and rods were combined with a set of forged slugs from JE. Offered as part of their SRP line up, the JE Pistons featured 18-cc domes to produce a static compression ratio of 10.0:1 with a typical BBC combustion chamber measuring 120cc. This test motor was built not to maximize power production but to simulate a hot street/strip combo.

The Scat/JE stroker assembly was installed into Gen VI block after balancing and machining was completed by L&R Automotive. Also part of the package was a set of Total Seal rings to ensure proper sealing. Looking to take full advantage of the available airflow offered by the Brodix heads, we installed a healthy but not wild solid roller profile from COMP Cams. Designed as a blower grind, the 300BR-14 offered .652 lift, a 255/262 duration split and 114-degree LSA. Naturally the roller cam required roller lifters, but the Gen 6 block required use of a set of .300-tall solid roller lifters.

COMP Cams also supplied a double roller timing chain, but since the cam and timing chain were designed for the early Gen 4 block, we eliminated the factory (Gen 6) cam retaining plate. Instead, the cam was retained using a conventional cam button. The cam swap also necessitated the use of a custom front timing cover (pt#217) from COMP Cams. The new cover provided adequate room for the thicker, double-roller chain (factory Gen 6 covers must be run with a single-roller chain). Since oiling on big blocks can be problematic, we installed a complete Milodon oiling system including a street/strip pan, pick up, windage tray and HV oil pump. Topping off the test mule was an Edelbrock Victor Jr. 454-R intake, a Holley 950 HP carb and SFI-approved, neutral damper from Procomp Electronics.

This test involved running the stock GM heads then replacing them with the BBX-3 332s from Brodix. Before heading to the dyno, we took the liberty of comparing the two sets of heads on the flow bench. Though flow numbers are only an indicator of the power potential, it is always nice to correlate the airflow data with the changes in power. Tested on the flow bench, the stock, iron, GM rec-port heads (088 casting numbers) were hoisted up on the flow bench. Iron heads should be abolished and replaced by aluminum heads just on principle.

Tested on the flow bench with a 4.310 bore, the stock iron heads checked in with peak intake flow numbers of 335 cfm. That’s hardly impressive considering a port volume of 316cc. The exhaust flow was even less impressive, peaking at just 201 cfm though the 121-cc exhaust port. By contrast, CNC porting unleashed plenty of flow from the 335-cc Brodix heads. Intake flow checked in at an amazing 409 cfm while the exhaust port flowed 296 cfm. That represented flow gains of 74 cfm (intake) and 95 cfm (exhaust) over the factory heads. The Brodix heads had enough airflow to support well over 800 horsepower on the right application, but our mild test motor (like most street/strip combos) was going to get nowhere near those numbers, so just how much power could we expect from the new heads on our 496? Only one way to find out.

After the airflow bench sessions, we headed straight to the dyno with our new test motor. Equipped with the stock GM iron heads, the 496 was given multiple break-in cycles before putting the hammer down. The 496 was perfectly repeatable and most might not complain about having a BBC that produced 631 hp and 578 lb-ft of torque, until they saw what the stroker combination did once we installed the Brodix 332 heads.  Still, torque production with the stock heads exceeded 560 lb-ft from 3,200 rpm to 6,000 rpm, ensuring plenty of thrust on tap for almost any street car.

Happy as we were with the stock heads, the situation improved dramatically once we installed the Brodix heads. In addition to a huge weight savings (iron BBC heads should be abolished), the Brodix heads increased the power output from 631 hp and 578 lb-ft to 704 hp and 624 lb-ft of torque. Not just more peak power, the Brodix heads swap increased torque production through the entire rev range, from 3,500 rpm through 6,500 rpm. Having more power is good, but having more power everywhere is even better. Credit big flow gains without resorting to dramatic changes in port volume for all that Xtra power.

Just the Facts:

Stock GM Rec-Port (088 casting)/Brodix BB-3 Xtra 332
In. Valve-2.19/2.30
Ex. Valve-1.88/1.88
In. Port Vol-316cc/335cc
Ex. Port-121cc/133cc
Combustion Chamber Vol-123cc/115cc
Peak Power- 630 hp @ 6,600 rpm/704 hp @ 6,400 rpm
Peak Torque- 577 lb-ft @ 5,300 rpm/624 lb-ft @ 5,300 rpm

Stock GM Rec Port (088 casting) vs Brodix BB3-Xtra 332
Flow Data: CFM @ 28-ins

Upgrading your big block is always fun, especially when you manage to add more power. Upgrading the factory heads on this 496 test motor netted not just impressive peak power gains, but huge chunks of power through the entire rev range. A portion of the credit goes to the change in compression resulting from the difference in chamber volume (115cc vs 123cc), but don’t count out increasing intake flow by 74 cfm and exhaust flow by a whopping 96 cfm! Making this all the more impressive was the fact that these flow gains came with an increase in port volume of less than 20cc. On the right application, these Brodix head were capable of supporting well over 800 horsepower.

Sources

Brodix
brodix.com

COMP Cams
compcams.com

Edelbrock
edelbrock.com

Holley/Hooker
holley.com

JE Pistons
jepistons.com

L&R Automotive
lnrengine.com

MSD
msdignition.com

Total Seal
totalseal.com