I'm looking at pair of cylinder heads, that have mercury cast into the head, and casting # 900-843425
cant seem to find out any information
they are aluminium, rectangle port look to be conventional 24 degree heads
can someone point us in right direction?

cheers
Brett

Must be 525/600/700 heads. Only ones I know of with “mercury” cast into them.

does anyone know what cc, port cfm, they are any good, compared to dart, edelbrock 320 cfm + heads?
cheers

If they are the Mercury 525efi head I think its a 315. Dart sells direct replacement heads for the 525,600,700 mercury engines. "Mercury Racing 525 replacement style heads. Three intake runner sizes offer potential for increased levels of performance.

We’ve retooled Dart’s PRO1 BBC castings to produce a true bolt on upgrade for the Mercury Racing 525 engine. The PRO1 24° 525 MMR is available with 310cc, 325cc or 345cc intake runners and has the correct exhaust bolt pattern for the factory manifolds. A grey chromate surface treatment inhibits salt corrosion for marine usage"

Is there anyway to identify which port size the heads are, markings.
I had read that edelbrock made the castings for mercury
actually not sure what motor these came off.
do the heads flow the following relative to 454/502 ci and blower size
525 sc = 310 cfm
600 sc = 325 cfm
700 sc = 345 cfm
Brett

Keep in mind that the exhaust bolts locations on the Mercury heads are not the same as standard BBC heads.

Griff
is it the bolt pattern is slightly different for few bolts, or the complete bolt pattern is different
I just purchased pair for US$300,they will be shipped within a week
may need work

figured I would lose 70lbs in weight off the engine with alum heads, on closed water cooling on 502 or 560ci
was hoping to run the imco powerflow plus exhaust

Not really up to speed on the mercury engines, as been playing with MKIV and Gen VI engines
Im assuming the heads fit conventional BBC intake manifold
Brett

Exhaust bolt pattern is different on the mercury heads. You will need to drill and tap the heads on a few holes to use standard exhaust pattern

thanks for the information
is there anyway to identify the differences in the heads between 525sc, 600sc and 700sc ?
is there a part # stamped into the head ?

The 525 is EFI but not SC when discussing the goofy bolt pattern, if I recall top 4 line up and the bottom 4 dont, the 600 - 700 have blowers, Ill see if I have a part # for the 525 EFI Mercury head