It seems I have been asked these questions a lot recently. I will try to help answer these questions with some data. I recently did some flow testing on some stock cast iron heads that were both stock, as cast, and ported, a set of Brodix BB-2Xtra CNC that had also been hand ported and some AFR 357 CNC heads. This is by no means a scientific experiment. However, I did try my hardest to keep all of the variables the same. These test were done on the same flow bench with the same fixture, using the same operator.
The first thing I was trying to see is how much my port work helped. Next, how much better are the aftermarket heads then a set of stock cast iron heads. Finally, were the CNC heads maxed out or was there more to be found with porting.

Disclaimer!!!
This is not a scientific test. These numbers will be on the low side as compared to published numbers. I was looking more for a comparison then all out max flow. Several factors will cause my numbers to be low.....I used a 4.5" bore fixture instead of a 4.600" that most manufaturers use. That larger bore fixture will help flow by unshrouding the valves. Next, I did not use a pipe on the heads. I never have used one in the past, so I wasn't going to start now since I would have no way to compare to previous tests. The pipe will not only increase flow, but it will also represent more realistic conditions since there will be a pipe on the heads on the engine. These two factors alone could account for 30 -40 cfm or more. Again, I am not looking to see what the max flow is as much as I am looking to compare the heads and see if porting will help.
Here are the numbers:

Stock GM cast iron head (188 casting)

Exhaust stock ported

.200 117.3 117.3
.300 149.8 150.6
.400 174.4 180.0
.500 183.9 191.8
.600 187.0 197.0
.650 187.0 197.0

Intake stock ported gain
.200 149.0 150.1 .9
.300 197.0 203.8 6.8
.400 232.6 246.4 13.8
.500 258.1 277.8 19.7
.600 279.6 303.5 23.9
.650 287.0 311.4 24.4

This was not a full port job. I only did the chambers and the bowls, since they were the worst. I did not touch the runners at all. So with a little more work these heads can really be improved. The bowl area was really bad. The seats did not match up with the head at all, so there was a large step left in the head when it was cut for seats. This is where I did most of the work ( along with the area around the valve guides)

Now for the aftermarket heads. First up are the Brodix heads. They are the BB-2Xtra 355 CNC . I flowed one of the heads right out of the box and one that I did some port work to. I didn't really do a bunch of aggressive cutting. I spent more time on polishing and cleaning it up. Now you may say why do you have to do any work to a CNC head. Well, you don't have to but the numbers show that they can certainly be improved upon. It really depends on what you are looking for in terms of hp if it is nesseccary. I haven't done any work to the AFR heads yet. I'm not sure if I will. They really look nice and I was expecting them to really outflow the Brodix heads. They did in the lower lift, but not in the upper lift ranges.

Brodix BB-2Xtra 355CNC:

Intake: stock ported gain
.200 148 148 0
.300 220 224 4
.400 282 292 10
.500 323 335 13
.600 354 370 16
.700 375 394 19
.750 383 403 20

Exhaust: stock ported gain
.200 128 128 0
.300 165 168 3
.400 227 231 4
.500 255 257 2
.600 271 277 6
.700 281 286 5
.750 285 289 4

AFR 357 CNC:
Intake exhaust
.200 159.0 141.1
.300 235.2 190.2
.400 289.2 237.8
.500 326.1 248.8
.600 355.1 252.0
.700 378.6 254.2

Like I said, I haven't done any port work to the AFR's yet. When I do, I will post those flow numbers. Again, these numbers are going to be low compared to the published numbers for the reasons listed above. I hope this may help someone make a decision as to which route to go. Thanks for looking.
Eddie

Superb, thank you.


UD

nice read, thanks for sharing. the alum heads really made a big gain over the iron heads.

My pleasure guys. While it does show that the aluminum heads seriously outflow the stock cast iron, keep in mind that the aluminum heads have much larger runners. Not only that, but they are completely cnc ported, where even the port work that I did on the cast iron heads did not include porting the runners. Those two things are huge advantages for the alum. heads.
I also wanted to show that the cast iron heads can be helped a bunch with some porting. This is a viable option for guys that don't want to spend the cash on alum. heads or want to keep cast iron heads for corrosion properties.
Eddie

I know as of late you have been using the brodix heads just wondering if you have tried the new dart pro 2 on any thing ? And your thoughts on the coated marine heads dart offers . And for what it is worth I think it's great that you take the time to share with me and the rest of the members the information that you do . Jeff

Eddie I'm pretty sure Jim Valako told me that he had the same findings with AFR's exhaust flow at higher lifts.

good short blocks make them live good heads make horspower

You need to see what Jim is working on right now. I think there might be a New bolt on aluminum head in the mix. Designed specifically for the marine industry. Can you say 400cfm (same test method as Eddie) at approximately 325cc. The port velocity is great.

love my afr 325's woke my 500 efis right up!

I love valakos (im honestly not sure its "his" ) bore notching idea. For all I know all saavy high end guys do it.

You lose a few CC's of chamber pressure and pick it up and then some in flow...

Not really sure of all the implications but Valakos a sharp cat.

Again thanks Mr. Young.

Uncle Dave