Brodix Heads – Part II

Brodix

Last issue we examined the intake side of Brodix’s latest BR 7 series of cylinder heads (designed to fit Chevy’s LS-series engines).  From the intake perspective, the BR7’s are over the top when it comes to air flow capabilities – so much so that they pretty much eclipse all original Chevrolet big block production line castings.  The reality is, they’re better than many very, very good aftermarket big block heads too.

When it came to the heads, something was nagging away.  And that something was the exhaust port.  Now, for an older hot rodders, it’s not hard to forget Ford’s first 351 Cleveland and Boss 302 motors. Way back when (in the late sixties and early seventies), it was no secret that the intake port was pretty much awesome, at least for the time.  The exhaust port on those things, on the other hand wasn’t exactly great.  The intake/exhaust ratios were way off too.  Here’s a look at the flow numbers of a 4 barrel 351 Cleveland head (2.19-inch intake; 1.71-inch exhaust):

 

Ford 4V Cleveland

 

Valve Lift (inch):                   .200    .300    .400    .500    .600    .650

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Intake Flow:                          131    188    220    256    269    279

Exhaust Flow:                         88     129    146    159     165    166

 

The racer’s solution to the under-performing exhaust port was straightforward and to the point:  The exhaust side of the head was machined right off and a plate was screwed onto the head, effectively raising the exhaust port.  It was something you could get away with on a drag race only engine, but certainly not something you could live with on the street. So is the Brodix BR head in that league?

We’ll find out in a minute, but using the same parameters for comparison as we did in the first article, let’s examine the flow data on various known Chevy heads (flow data in cubic feet per minute (CFM) using a baseline figure of 28-inches of water for comparison purposes):

 

Chevy Small Block 492 w/1.60-inch exhaust valve

 

Valve Lift (inch):                   .200    .300    .400    .500    .600    .700

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Exhaust Flow:                      107     125    137    141    141    141

 

Chevy Big Block 290 with 1.72-inch exhaust valve

 

Valve Lift (inch):                   .200    .300    .400    .500    .600    .700

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Exhaust Flow:                      90       118    138    160    174    184

 

Chevy Big Block 291 with 1.72-inch exhaust valve

 

Valve Lift (inch):                   .200    .300    .400    .500    .600    .700

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Exhaust Flow:                      112     139    163    180    194    197

 

Chevy Big Block 990 with 1.88-inch exhaust valve

 

Valve Lift (inch):                   .200    .300    .400    .500    .600    .700

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Exhaust Flow:                      106     140      162    181    204    207

 

So far so good, but how much air does the Brodix BR 7-series cylinder heads move?  Here’s a look at figures we collected (again, in CFM using 28-inches of water as the benchmark):

 

BR 7 with 1.614-inch exhaust

 

Valve Lift (inch):                   .200    .300    .400    .500    .600    .650

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Exhaust Flow:                      113     158     188    208    216    221

 

STS BR 7 with 1.614-inch exhaust

 

Valve Lift (inch):                   .200    .300    .400    .500    .600    .650

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Exhaust Flow:                      116     169     208    224    233     235

 

STS BR 273 with 1.614-inch exhaust

 

Valve Lift (inch):                   .200    .300    .400    .500    .600    .650

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Exhaust Flow:                      116     169     208    224    233     235

 

As you can see, the exhaust flow on the heads pretty much knocks it right out of the park, but how do they compare to the benchmark CNC ported big block head we discussed in the first segment of this series?  Here are the exhaust flow numbers for the Brodix STS RR BB-2 Plus heads (remember, these are the super cool direct replacement heads we mentioned in the past article):

 

STS RR BB-2 Plus with 1.88-inch exhaust valve

Valve Lift (inch):                   .200    .300    .400    .500    .600    .700

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Intake Flow:                          126    164    201    228    251    267

 

As you can see, the rat motor outflows the BR 7 heads from roughly 0.400-inch lift and up, but keep in mind the valve is considerably larger on the big block (1.88-inch versus 1.614-inches). From a flow perspective, it’s pretty tough to beat the new head.  And in this case (big flow from relatively small port volumes), that will translate directly into real world performance. There’s a wee bit more to the equation (combustion chambers, deck bolt patterns and top end hardware).  We’ll examine some of those items in the next issue.  Meanwhile check out the accompanying photos.  There’s a lot to think about.

Brodix

Brodix
Here’s the exhaust port on Brodix’ BR 7 series head. The port is fully CNC-machined, and it’s used on both the STS BR 7 along with the big brother STS BR 273.

Brodix

Brodix
Exhaust ports on the BR 7 series cylinder heads are engineered for use with conventional Chevy LS7 components. That means headers (or manifolds) designed for those combinations are a direct fit. Also, note the streamlined guide (with a bronze insert) shown here.
Brodix
Compare these. On the left is the “benchmark” Brodix STS RR BB-2 Plus big block head with the STS BR 7 on the right. The rat motor head eventually outflows the little BR 7, but not before the valve lift hits 0.500-inch.
Brodix
All Brodix BR 7 heads incoroporate a 1.614-inch diameter exhaust valve. The stems are 8-mm in diameter and they’re 5.230-inches long.
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