I am a little disappointed with the dart heads I just bought. they say the heads will just bolt right on. well they are wrong. first you need longer head bolts on the exhaust, mine were shipped with the wrong valves and dart had to send out new ones. The rocker stud holes were not tapped far enough the studs would not tighten. the slag on the castings is poor, you can see where they cleaned some spots with a dremel and left others. the port match was pis poor I spent acoulpe days matching the ports. I had to grind my stock valve covers for they would not tighten down, all the holes in the front and rear of heads are smaller than stock so all new bolts had to be bought. I just hope to hell they work better then they look.

Great information in this thread. I am upgrading to a larger displacement 588 or 598 with long rods and will be using CMI etops with std. tails. I am thinking that the 325 AFR's may be big enough, I don't think the CNC 315 will be in the buget. The target RPM is 5500 or so and I am not after some 800hp number I would rather have killer torque from 2500 to 5500 and good valvetrain longevity.
What do you think? Thanks, Chris

One thing you can do is call RMBuilder/Bob Madara of Marine Kinetics and ask him what he thinks. He can help you with the correct head size selection and cam application for the amount of cubes you have and the RPM range you want to run it in. You'd be doing yourself a favor. Have fun with your project.

ARAOENGINEERING.COM 32 valves check them out!!!!!!

Do they make any big block stuff?

Here are some flow #'s on JimV ported Dart 308 Iron Eagles. These flow #'s was done at an another shop, so you can be confident in Jim's skills and results. Lot's of benefits on the cast iron vs. aluminum in marine; the numbers that are killer. We were looking for the best results we could get in the intake port in 320 cc range. This head was used as a test mule; we then picked the best ports and Jim made us two sets.
Over 800 hp NA on dyno (780+ w/ CMI Sport Tubes) with only 503 ci. Great low and torque!

ARAO makes BB chevy, SM chevy and lots of other stuff, these heads are incrediable 4 valves per cylinder, the valves, since there are two, don't have to open as much, can use less spring pressure, less cam etc, if I ever get a spare $20,000 I'll buy them.

two as in intake and exhaust, for a total of 4 per cylinder.

I have the CNC Machined AFR's on my 540's .

There were a couple of guys interested in the AFR 315 CNC heads that I am using on my 540's. We finally flow tested them this week on a Superflow SF600 flowbench.

Here are the results and comparisons to what AFR claims @ 28" H20. The heads are "out of the box" with no additional porting or epoxy.

We tested with an out of the box Manley Severe duty intake valve, and then with a backcut inconel Del West Intake valve of the same diameter which I am using.

..........AFR CLAIMS.......MANLEY SEVERE........B/C Del West
.200........169.0..................169.28......... .............177.45
.300........249.0..................248.64......... .............261.45
.400........312.0..................306.36......... .............327.60
.500........353.0..................352.98......... .............363.59
.600........380.0..................375.18......... .............391.40
.700........387.0..................390.72......... .............394.74
.800..........N/A....................391.12......................3 94.91

I would say that AFR's claims are pretty accurate. The discrepancy's are around 1% which can be accounted for by atmospheric conditions and variations between flowbenches.

With the right combination, these heads could support 750-775 hp in an NA application

The basic combo is: Dart Big M block, 9.0:1 static compression, 4.500" bore x 4.25" stroke, 9.800" deck, Crane 741 hydraulic roller cam, Crane roller lifters, AFR 315 CNC heads with backcut Del West stainless intake valve, Del West inconel exhaust valves, Isky (PSI) "Tool Room" springs, Crower stainless rockers, JE forged pistons, Crower 4340 billet 6.386 rods, Crower semi-lightweight 4340NT crank, Victor Jr intake, Holley marine 850cfm 4150 carbs, MSD Pro-Billet Distributor

Cigrocket, I remember another guy who had a 35 Cig in the Chicago area a few years back who used some 315 AFR CNC ported heads with copper beriliam (spelling?) seats and had much better results with the Del West valves than any other valve. At least that was what he was reporting with the flow bench tests he had. What kind of flow numbers did you see on the exhaust side....and what brand/type of exhaust valve? Thanks