Does anyone know the CFM on the Heads for the Mercury 500 EFI? Thanks in advance for any insight

Call Bob Madera he will know http://www.marinekineticsonline.com/contact.html

.200=149/117
.300=197/150
.400=233/174
.500=258/184
.600=280/187
.700=287/187

ERRONEOUS NUMBERS. THROW THESE OUT THE WINDOW. REFER TO CALLING MERCURY RACING TECH LINE, OR MARINE KINETICS TO SEE WHAT A STOCK 500EFI HEAD FLOWED ON THEIR FLOW BENCH BEFORE PROCEEDING


Everyones flow numbers will be different. Those numbers were tested on a 4.500 bore, no pipe on the exhaust. Gives you an idea. Going to a Dart, AFR, Brodix, RHS, Trick Flow, etc, is a sure way to see power increases. Those old Merc Iron heads, were pretty poor stock, compared to a modern Hi performance aftermarket head.

When comparing flow numbers, keep in mind the bore size the heads were flowed on, whether or not the exhaust had a pipe on it, etc. Also, was it an actual out of the box head, or did it have a trick valve job for magazine promotion, etc .

Have fun! As Mild stated earlier, compare and contrast how they were flowed.
http://users.erols.com/srweiss/tablehdc.htm

those numbers suck,just like gm rec port heads do.

when strippoker had his heads flowed,they were in the 300's for intake and 200's for exhaust.not sure wer you got those numbers,just saying.
plus,I guess at rebuild time,you should get a trick valve job like all the after market heads get .

Question, say you are at refresh time and decide on a set of aftermarket heads, do most raise the exhaust port changing your exhaust pipe location? Meaning same headers but new tails?

most do raise the exhaust port.but sometimes,trimming the hole a little bigger gets the pipe thru.its a matter of trying after committed to new heads.

I made them up.

BB Chevy heads have two different intake ports and the "good" port is always the advertised port. The "bad" port can be 20+ cfm below the "good" port through mid lift numbers. Just a valve job on those heads can be worth 20 cfm so comparing these flow numbers with another set of the same heads is pointless. A pipe on the exhaust will also make a big difference on the flow bench.