Porting4power

What is the most you have seen a stock valve size 241 and 243 casting flow? Stock port as well as ported.

Old SStroker

With your screen name Porting4Power, why do you ask? Haven't you measured them?

Do you think max flow is a good criteria for judging a head's ability to make power?

Perhaps I don't understand why you asked.


Jon

SOM WS9

Are you looking for complete numbers or just peak numbers? I would be more concerned with the low and mid-lift flow numbers than peak numbers. Your valves don't spend too much time at max lift so the peak numbers really don't say too much for a head's potential to make power.

Old SStroker

Oops! Not necessarily, Pilgrim.

Jon

gametech

iTrader: (1)

I'm not sure I understand the "oops". Mid lift flow numbers are EXTREMELY important. The only argument I see is what may be considered "low", "mid", and "high" flow. This would all be cam dependant. Of course this would be much better explained/understood in graph form as opposed to text arguments.

Asmodeus

mid and low lift numbers are good, and so is peak... and so is port volume/velocity. It's a combination of everything.

Old SStroker

The "oops" meant that not everyone agrees with your statement. Some who do not agree make lots of power. I thought this might generate some discussion.

I suppose you could split the valve lift into thirds for discussion of "low", "mid" and "high" lift flow.

What happens in a operating engine is quite far removed from what happens on a steady-state flowbench test.

Jon

Stang's Bane

iTrader: (22)

I would say that they spend more time in the top 10% of lift than any other 10% area.(Other than closed)

Look at the lobe on a cam

SOM WS9

I guess I should rephrase. It's really not safe to say flow in any one area is more important than another, and I feel that people often ignore the low and mid lift numbers in favor of peak numbers. I see people that buy which ever head has the best peak numbers, and end up with an engine that doesn't make the power it's expected because the intake ports are lazy in the low and mid-lift ranges.

Old SStroker

No offense, but you might want to rethink how an engine moves air during the entire valve event. Things change a lot during the valves' lifts.

I agree that folks buy the peak numbers, especially if they are not too knowledgeable. I disagree with your analysis of what constitutes good port flow and why some heads don't perform, especially in higher power engines.

It is fairly easy to detrmine if a head makes torque and power by running the engine, but it is much more difficult to explain why the port "worked"...or did not work. If we pick the wrong explanation, and try to correct the port to jibe with our analysis, we may not get the improvements we expect. Tom Ankeny was correct.

Jon

SOM WS9

No offense taken. We're all here to learn.

Can you give us a better explanation of how you determine whether or not a port will work well for a given engine combination? I'm always looking to learn.

Old SStroker

There is no simple answer to your question. I suggest you study the basic fundamentals of how engines move air. Unfortunately these basics are fairly complex in practice, as are many things in nature. The sticky Books 101 has some good reference material.

It seems to me that many people in the "engine building" business either don't understand how engines "move wind", or simply ignore it and try to get engines to do what they, the builder wants them to do, rather than what the engine itself wants to do.

There is a reason we call her Mother Nature and not Father Nature.


Jon

pddye

iTrader: (14)

So back to the original posters question which I am also wondering about which heads flow better stock and ported? I have a set of 243's on my ls1 right now and I also have a set of 241's sitting on the shelf I was given. Anyone have any real world experience?

Bad Blue WS6

iTrader: (41)

ported 241's will flow better than ported 243's when ported correctly, up to .400, after that its the 243's for the win.

Bad Blue WS6

iTrader: (41)

Bingo.

Old SStroker

Nice avatar!

Jon

Stang's Bane

iTrader: (22)

This ******* I know built it

Schwanke Engines

iTrader: (1)

Airflow of a cylinder head is still relavent to the hp potential. Now, in saying that, there are a lot of people that think that airflow is everything. If you are talking about an all out drag engine that lives life in a very small operating RPM range, then yes, peak numbers are where it is going to make the most sense.

I believe for the rest of the world, it is all about having the correct flow for your camshaft. Don't make the port so big that you loose the velocity, but don't make it to small and sacrifice flow.

You have to look at airflow from a changing displacement aspect. If you graph piston velocity vs. angle, you will see that the peak velocity occurs roughly 70-80 deg. before and after TDC. So, this means that the greatest change in displacement is happening around there.

So, in order to take advantage of that it is best to have your peak flow numbers just before peak velocity, gives the air time to catch up.

But, again, this is dependant on RPM. Sorry, I think I am rambling on here, but chime in with input.

Cascazilla

I would never change a head to fit a camshaft for an engine. I would do it the other way around.

As for the average flow versus peak flow, on LS6 headed small displacement engines with .590 lift the engines really only respond to increses in flow over .400 lift, and especially .500-.600 for the largest increase in power. Having lots of low lift hurts power substantially on the bottom end and has a small benefit of helping to carry power a little better after peak. Average power suffers when you use "Internet Logic" to port heads.

Most of the time, on an LS6 head, if you do something to increase the .500-.600 flow it will hurt the low numbers if you are doing it with the valve job.

Making peak flow just before peak velocity sounds like it makes sense. I used to actually think that too. It is easy to believe because it's logical in a basic sense. In reality, it absolutely won't work and can't be made to happen anyways.

Cascazilla

Stock valve size 243 321cfm on a 3.900 bore 221cc port. Stock 243 port 282cfm(valve job only)