Gregory

iTrader: (4)

So, if the FAST 90 and L76 intakes flow about 300cfm, what is the advantage to getting heads that flow 340+ cfm? I can see where there may be some slowed flow when the intake valve is closed, but other than that, what good are high-flowing heads?

Thanks!

mrdragster1970

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More air you can add more fuel = more HP

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tee-boy

iTrader: (8)

I also say if you have high quality heads, you cam run smaller cam and get the same results as a bigger cam and low quality heads. Better heads will allow your cam (whatever it is) to perform to it's potential.

RicoL

I think what he's saying is:

If your intake can only flow 300CFM, there's no point to getting heads that flow 340, because they'll only flow 300, due to the intake.

In theory, I'd agree with that, but in practice, we've seen gains from getting heads that flow better than your intake does. I guess it's got something to do with if you're pushing the limits of the head's flow or not. I.E., a head that flows 340 will flow 300 easier than a head that flows 300 max.

Am I completely wrong?

1989GTA

Right. It is a cumalative effect. Say the intake manifold is 300cfm. One pair of heads flow 300cfm and the other 340 cfm as stated. With the 300cfm heads mated to the 330 cfm intake manifold lets say that the total flow is 270cfm. With the 340cfm heads mated to the manifold the total flow may be 280cfm. Just another way to look at it.

XtrmLS1spd

iTrader: (6)

Great topic Gregory! We all know that the FAST flows at 300cfm. Now, put that on two set of heads. One that flows 315 at .600 and the other flows 340 at .600. Guess what? the head that flows 340 wins every time. Why? Well, 9/10 times the head that would flow 340cfm has a much better mid-point numbers, which is where you make your money. True, you may not be able to take full advantage of your top end power, but your mid-range would more than make up for it.

Built LT1

iTrader: (3)

I see what you're saying, but if the only advantage is in the mid range, then the intake is still a restriction, which makes the thread starter's question valid as to why one would not want to mate an appropriately matched intake.

Big-DEN

Sometime total flow goes down with the bigger head.

However for the point we are making, is often the 340 head will flow more at each lift point below .500" than the 300 head.

So the cam is more effective at each lift.

However if the system flows LESS with the bigger head, you'll make less power.

Thats how it really works.

1320FEVER

iTrader: (9)

The way it was explained to me is its like a "resistor in series" effect if you will. Each item in the intake stream can knock the flow down some. If you have a weak link (which is often the intake) it will knock the flow down more than a better intake would, but the system flow will not be limited to the intake, just hindered. Hope that makes some sense.

RednGold86Z

A big point that some of you are trying to say, but in lay terms: The cam is only open to peak for a small % of the time during an intake stroke. All the rest of the time, it's (the cam is) making the head flow less than the peak 340cfm. Flow under the curve of the cam is bigger with the better heads. In other words, the flow gets up to near the 300 cfm sooner, and stays there longer, during the intake stroke.

Also, yes, the head loss at peak flow is more with worse ports. A large tube with a little bit smaller choke point placed anywhere will flow more than a tube that's equal diameter as the smaller choke point, assuming it's not actually choked (see first paragraph).

ss53mech

Also I would add one additional point, you would be able to get the most out of those heads with an intake valve timing to match the flow rate vice the intake. You could get up with a cam guru, which I am not and he would be able to match you a cam to get the most out of your heads with the intake combo.

Gregory

iTrader: (4)

Thanks for the interesting feedback. I was looking for someone with a fluid dynamics background to leave some insight. It's an important question for me as the cost between sets of heads with 40 cfm difference in flow can be thousands of dollars.

gametech

iTrader: (1)

Remember that ANY flow #'s are derived at a specific pressure drop. 340cfm heads will flow the same as 300cfm heads at a lesser pressure differential. Therefore, they "could" flow more despite what intake they are bolted to, up to the rated pressure drop. However, all else being equal, "which it never is" the heads with higher flow will have larger runners which decrease flow velocity. Port flow velocity can have a HUGE effect on low and midrange torque. Simply put, those $'s spent on marginal flow increases on the top end may well hurt overall performance if the rest of the induction isn't up to task. On the other hand, if the rest of the parts are capable, the $/HP ratio may become favorable again.

Harold Sutton

If the heads aren't maxed out you can always have the intake worked on to increase the total flow.

3.4camaro

iTrader: (1)

Cant wait to see what happens when I put my trick flow heads on with my LS1 intake

Then put on a FAST and gain 800 hp. LOL.