Holy monsters!

"The new Big M is our biggest big-block heads. With huge 410cc as-cast intake runners that flow 430cfm, the Big M meets the airflow requirements of large displacement motors."

Specs...

Material: High–density 355–T6 aluminum
Valve Angle: Intake—24° (rolled two degrees)
Exhaust—15° (rolled two degrees)
Intake Ports: 410cc
Combustion Chambers: 119cc as cast; can be milled to 105cc minimum
Intake Valves: 2.350", +.350" long
Exhaust Valves: 1.925", +.100" long
Guide Spacing: Exhaust moved .045" from bore centerline to accommodate larger valves
Rocker Stud Location: Relocated for revised valve angles; longer exhaust stud required (must use stud girdle designed for Dart heads)
Spark Plugs: Gasketed 3/4" reach plugs
Valve Springs: 1.625"

Whats new over the previous Big M?

Hello, Guys,
This is a great head, but not exactly what you need for most of our applications. Too big kills performance!!! If you are considering these heads, talk to Canfield or someone knowledgable on the subject BEFORE you send any money. These are for really big airflow applications such as race only. If you are turning less than 6,000rpm on even a blown 600cid engine, these are too big.

Yes, Talk to Canfield. I have two sets of the 310 runners and love them. Do yourself a favor and save some money, talk to CANFIELD.

If any one is interested I will be dynoing some Big M heads against some 325's on a 565ci motor in a couple of weeks.

would you tell us the specs on you 565 dyno . have you made wedges for thes heads. and are the flow nubers close being true

I run a set of fully ported and polished 360's on my 632. These heads make great power all the way to 7,000. Although I prop to turn 6200. I'm sure there is some power loss in the 6,000 range (~10hp) but @ 7500+ it would probably be 75+hp. Put a set of Sonnys Pontiac heads on and you'd see 125+hp up top. Blown1500 is right the Big M is overkill unless its pure race.

MTM

I will post the dyno numbers when I get them. I am a small port guy myself. I ran the Big M heads with a blower on my 555 with great results. I didn't dyno but the boat went over 100 on the GPS (1992 27 fountain). I removed the blower and went with a tunnel ram efi, bumped the compression and increased the bore to 4.600. With the big M heads and TR the boat is at 91 mph so I think the heads are working OK. Both motors ran a hydraulic roller camshaft.

My Big M heads flow 420 cfm @ .700 lift. With drag race set up Im sure they will flow the advertised 430.

The 325's flow 400 cfm @ .700. Both head's exhaust ports are flowing over 300 @.700

The dyno test will show the difference of the port volumes and what 20 cfm is worth. I do have one set of wedges for the big M heads.

Blown 1500/jdnca 1
I would have thought they would be overkill as well (I broke my own rule) but the boat speed is not that bad.

At 90% throttle position and up there is no increase in rpm/speed. I suspect the smaller heads will increase to 100% throttle position with no speed increase but I still gots to know.

Can you imagine these on some 700ci N/A motors?

Very old 20+ year old thread
I once knew of a boat that had a pair of BBC Super Tall Deck (11.625" deck height), 705cid, TBS 14-71 super chargers, with intercoolers built by Sterling in Detroit that supposedly made 1350hp @ about 6000rpm or so and it had Dart "Big M" heads on it.

Apparently Sterling seemed to think they were adequate enough for a supercharged engine of 705cid to make enough power @6000rpm for a marine hi-perf application, at least in this reference.

But engine tech has certainly come a long way since then especially with all the new CNC head designs.