I think you need to ask about the flow again...usually stated as *** cfm @ *** lift...
like 250 cfm at .500 lift...on the intake side...
260cfm x 2 =520hp, maybe thats what he's being told...which are easy number to be had with these heads.
quality of flow vs. quantity is far more important to efficiency ( performance ) and big flow numbers are not always the prize at the end of the puzzle.
This statement is too general and does not apply to heads he's asking about.
Have you ever measured the port volume of a J or X head? Do you have a flow bench and can/have you measured the fps at flow?
The factory castings are small volume wise, the air speed is insane, so much that it's hard to keep them from going turbulent. There is no velocity issue, especially when ported and flowing big numbers.
These are not large port race heads, you need to start over and disregard anything you've been told.
With that cam , a 2.02 valve and good valve job , coupled with a gasket match and pocket porting would really wake it up.
Gasket matching hardly does a thing, if even anything t all....waste of time in my opinion.
GOOD VALVE JOB & BOWL WORK is what will make a difference you can see and feel at the track and on the street.
You'll want to keep runner velocity as high as possible , so a max'ed out port job is not the answer unless you plan on spinning the motor pretty hard.
The factory j/x heads have way more velocity than any after market offerings, they are 155-160cc's.......... What are RHS[179cc!] or EQ's???
If driveability and manners are important , you would look for other flow characteristics and enhance them.........low and mid lift flow for example.
Which is where ported factory heads flow big, low and mid lift.
I have some now that go 77-80cfm @.100 lift and touch 200cfm at .300 lift 249 @.400.....w/2.02
It it were a truck or heavy car , I'd look at keeping the small intake valve and maximizing torque via increased intake charge velocity.
You will almost certainly lose some bottom end by going with the big port job and valve.
The port controls the velocity, not the valve.
Again...if he was to go by your thinking, he'd run 318 heads.
The port volume starts out so small that even after porting they are still on the small side 'volume wise' and carry tons of air speed.
Make the parts you have work together and you will be a lot happier........a small cam doesn't need a big carb or monster flow numbers.
Forget that a motor is nothing but an air pump for a minute........O.K. , don't forget.......but think of it as a team.
make the parts play together as a unit instead of expecting one to do everything. I have seen crazy stuff from small valve / small carb combinations that took very little porting and cash.
355 Chev with a small hydraulic cam and 650 carb that a friend of mine did made 425 h.p. on pump premium and over 600 with spray ........nothing exotic about it in the least , but everything worked well together.
It idled and drove like Grand Ma's Biscayne. 
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This is not a short rod pos chevy, and combos are combo's...
Do you know what the port volume is of a sbc iron head?
In a nut shell, just based on valve size, yes, you'll loose torque, but not a lot. Likewise, the same for the HP level upstairs in the RPM band. You'll gain some, but it'll be small.
Its a 360 cid, he's not gonna lose any torque....he's going to gain torque with air flow and increased velocity.
Hi there i was just wondering if someone could help me out here...
i have a 360 LA engine with these specs .. 9:8.1 comp. standard style cast heads with minor match porting to the edelbrock rpm manifold, it has 1.94 inch inlet with 1.60 exhaust, open chamber heads 62cc..i am running the 280 h comp cam. and a 650 d/p hp street carb.. goes quite well, but was wondering if i put a set of heavily ported j heads with 2.02 inlet and 1.60 exhaust valves on this bottom end would i loose torque with the 280 h combo? i also have a 750 mighty demon laying around at home too...cheers Daniel
Daniel, Get the flow sheet for the heads in question and post it here.
If I were you and the numbers are better than stock and better than the current heads you're running, i would bolt them on in a heartbeat.
