Anyone know of what these puppies flow. My heads are flowing around 260cfm and im seeing if i need a bigger intake or how much am i restricting the heads

 

Depends on the cam and carb you are using, but I really doubt it would hold you back. I know a few guys with really top notch heads and big cams using that manifold, and changing up to a single plane did nothing but kill off some low speed drivebility. Thats a very good manifold.

 

Ive heard polishing the intake manifold (inside obviously) does almost nothing. But various HP softwares, like the one from crane cams that helps you select a cam, says i can gain a ridiculous amount of power with their XE284 cam. Like 60hp gain or something.

 

 

thought it might be a relevant question since were talking about flow.

You mentioned that his intake is probably the best he can have, but i was curious if it makes a difference if you polish it.... (not port matching) but just making the cast surface smooth.....

 

it's usually a bad thing. You want the rough surface to keep the fuel in suspension. Also think of the divots on a golf ball right?

Anyway, that was a smidge off topic.
How would you flow test a manifold eh?
at what lift value? You see how this is a silly question? Your heads flow 260cfm at what, .600" lift? PER RUNNER ! Then your carb flows what, 750cfm, at what, 1.5" vacuum?

Now how are you going to measure your manifold? Exactly why you don't see any published numbers It's just kinda a "well bob did this, and joe did that, so you should be fine".... Unfortunate, but true.

 

With port EFI (ie. TPI, LT1, etc) polishing the ports is fine, but not a good idea with a carbureted or other 'wet intake' system, because you need the turbulence that the rough surface creates to keep the air/fuel mixture atomized properly... if its too smooth, the airflow is too smooth, and the fuel will just kinda "fall" out of the intake charge. This is why no one reputable reccomends polishing intake ports on your heads after porting, yet they do on the exhaust side - with exhaust, theres nothing to keep in suspension, so the smoother and faster it comes out, the better.

As for flow-testing an intake manifold - Sonix is right. What parameters do you set up? Its not like flowing a cylinder head, where you have variables that you can control (ie. valves, valve lift) - an intake port is just a big open hole from top to bottom, with no controlled variables, so under what conditions could you measure flow that would be meaningful? Until the industry sets a standard, any intake flow numbers would be almost meaningless, unless you used them as before/after when porting an intake.

It'd be sorta like way back when, when all the cam manufacturers measured their cams at different starting points - some at .004" lift, some at .006" lift, some at .050" lift... meaning that if 3 different manufacturers had a camshaft measured at 270* duration, you would have 3 VERY different cams, making the measurements basically useless.

Sicne then, they set an industry standard of measuring at .050" lift, so now you can compare different manufacturers cams fairly against each other, since they are now all measured the same way.

The same thing was done with cylinder heads, when people started wanting numbers to go along with the port work they had done, and when aftermarket cylinder heads became more popular.

Untill the same sort of thing is set up for intake manifolds as well, any numbers you'd have would be meaningless.