... flow (cfm) is making power... and blench flow tests show about 5-10 cfm difference, im trying to find the link again right now, but they are not "much larger" they just have a different port

 

I've flowed several sets of 4V heads on a flow bench myself. The 03/04 castings flow ~15-18 cfm more on the exhaust port than earlier tumble port heads. They are much more efficient than you think.

 

are they not the same size valves?

 

and have you tested a B head w/o the imrc plates - otherwise stock, that was the comparision im trying to remeber

 

They both share the same stock valve size (ie. 30mm).

It's the port design that makes it much more efficient.

I have not played with any B heads, as they really have no use to me.

 

well the 03 cobra heads are about 3 times the cost of 99 cobra heads what if got them ported and polished?

 

They aren't quite 3x the cost, if you look around you can get a set of 03/04 casting for ~$700/pr.

Even after porting, the 03/04's are far superior. However, C heads are no slouch and will make more than enough power for most people. My set of ported C's flowed 300/230 after port work, and high port velocity.

 

Im still going to say that if your going to boost it, dont get hung up on this too much.. any of these setups has the potential to make more power then youll want, just depends on how much boost you intend to run. Im not going to argue, obviously slow has the correct flow numbers here, but I will say that in my personal experience I have not seen too much of a difference between ported b/c/03 cobra heads as far as how much power those cars will able to produce, maybe just a lbs of boost difference + or -

 

Any of the 4V heads mentioned will make great power, no doubt. Like I said, none of them are slouches and will make more power than most people need.

However, tumbleport (ie. C and 03/04 castings) make more midrange power, which is something most modular engine owners like to have more of.

Flow does not always mean the same thing, as port shape, port velocity and mixture motion are all contributors to making a power band. Having too large of an intake port volume (like B heads) makes for a dog in low-mid RPM's.

C heads are rather cheap these days, and I suggest them as the starting point for almost any setup. If you have teh cash, the 03/04 heads with a wet port divider are also a much better upgrade, but will cost slightly more.

 

what are B/C heads?