its kind of like "light duty" and "heavy duty" in trucks, or more accuratly i guess 1/2 ton and 3/4 ton. There is no "standard" to being a heavy duty or 3/4 ton truck. its just that company's "better" truck.

same thing with heads

stage I is usually thier light touch up
stage II is full porting, chambers - everything
stage III us usually aftermarket castings

Then again, a company can call their all out port work stage III and aftermarket castings stage IV just to sound cooler.


And I agree with phil (suprise!), the mroe i read about it- the less worth flow numbers seem to have, Maybe in the ideal/theoretical engine where valves open at TDC and BDC, where air has no mass, combustion chamber shape didnt matter, eveerything is static, not dynamic and everything is "perfect" it would make sense. "my heads can get 280 cubic feet of air in while yours get 250 cubic feet of air in so I win

 

i have seen ported lt4's dip into the high 290's low 300's at around 600 lift.. pretty damn insane imho...

its not just about flow though... TFS TW heads generally dont flow crazy numbers.. but they make damn good power.. quality is more important that quanity-to an extent

 

My JPR ported LT1 heads flow 271 cfm @ .550". I have less invested in port work, and the 2.0"-1.56" Manley valves than a set of LT4 heads would've cost me.

Frank

 

Impala heads were iron, ours are alum... I know Lloyd Elliot and Combo are coming up with nice numbers on stock lt1's too these days.

 

Here is a webpage with the best LT1 head flow numbers I have found.

LT1 head flow data website

bob

 

Nice site! wow!! Dominion 32 valve heads are monsters they just keep flowing right up to .600

 

There's a lot to be said about part lift numbers.

I know a guy that had his heads down by Agostino. 280/200 cfm

He has a cc306.

I have an XE 230/236 and my heads flow 265/185 cfm at the same lift.

I run 3 tenths faster and make more power on the dyno than him. All other mods are basically identical.

Its not all about peak cfm numbers.

 

How true. Peak cfm numbers sound great when you are bench racing, but the problem is the valve is only open at that point of peak flow momentarily. It's more important how well they flow up to that point. IMHO