bigSS

Do good flow numbers equal a good head? For example, my cam is in the .600 lift range (G5X2), are flow numbers at .600 lift the most important numbers for me to look at, or do the lower lift numbers matter just as much? Since I have a large split cam (232/240), will the exhuast flow numbers not matter as much, since I have alot of exhaust duration? Also, what are you opinions on keeping the stock valves, or getting larger (or lighter) valves? At what point is it worth it for larger valves?

BTW, my car will probably stay stock cubes forever, with a power adder added later on. Not sure how that affects my question/your answer.

jlsnsw

You definitely want a set of heads that will flow well at all ranges. If you can look at a flow sheet, just make sure that the heads are not very "peaky". Also, in your case, with a .600 lift cam and a large duration, I would definitely step up to larger valves, even if you are staying with stock displacement.
Just my .02

Paul F

iTrader: (2)

Good flow number are an important part of a good head but they don't totally tell the whole story. We have had very good flowing heads that we were excited to put on a car and then were later disappointed with the dyno numbers and track time compared to "lower" flowing heads. Just don't put a lot of faith in "flow numbers only". Good consistant dyno numbers and track time are really what makes a good head shine.

Tin Indian

I am no head expert, but what Paul said is really true. Although head flow numbers are VERY important as an indicator of a good set of heads, Flow Velocity is also important. So, just high flow numbers don't tell the whole tale.

Ron,

Crazyquik

You shouldn't overlook mid-lift flow just because you've got nearly .600" lift.

The reasoning is your cam is going to reach its peak lift once every cycle, yet it will go through its mid range twice. Of course your cam profile will reveal how long the valves are going to be open at each point.

J.

BurnOut

iTrader: (1)

Good flow numbers != good heads.

Something that is often overlooked regarding cylinder heads is port velocity; the problem here is that it is very difficult to quantify. Really, the only thing that you can realistically look at (as a consumer) is the port flow vs. port volume. While not entirely accurate, it can be reasoned that for a given flow rate, the smaller port will flow at a higher velocity than the larger port.

The unfortunate thing about port velocity being so difficult to quantify is that it, more than port flow volume, will determine when/where in the RPM range the heads really start to make power. This is because on a naturally aspirated motor, getting the cylinder as full as possible is the challenge; and a high-velocity port will result in a sort of "ramming" effect, resulting in a more complete cylinder fill.

While flow numbers are important, they are only half the story (it could even be argued that it is the less important half) of what makes a good head.

bigSS

Paul, Crazyquick - Both of you guys make good points, thanks. What are your opinions on valves?

BurnOut

iTrader: (1)

On valves, you have to be careful not to increase valve size to the point where the cylinder wall will end up shrouding a considerable portion of the open area. Of course, the same considerations have to be made regarding port velocity, since the valve is part of the port that the cylinder "sees".

Paul F

iTrader: (2)

What he said.

bigSS

So is that a yes or a no?