Greg Good

I think a good question to ask a head porter would be "How much do the heads flow over stock"? That should eliminate some of the discrepancy between the way benches read. A bench that reads high will start off with a higher than normal stock cfm number and that will be the tip-off.

Flow benches differ. Always have, always will. Some of it is the machine, some of it's the operator.

Here in Houston there are quite a few flowbenches, and a lot of us flow back and forth regularly. Oddly enough, the highest reading bench that I know of is a Superflow 1020, and the lowest reading one is a manual Superflow 600. There is 30 cfm between those two benches. My bench is right in the middle of them.

I try to keep on top of how my bench compares to others around town. I finished a set of LS6 heads a couple of weeks ago. I wanted to give the customer some independent flow numbers. I flowed one of the ports on my bench, a manual Superflow 600, then took it immediately over to SAM and troubled Casey to flow it on the schools Superflow 600 with FlowCom. That same port flowed about 5 cfm less than on my bench. That's pretty close as far as I'm concerned. My bench has always been repeateable, has never given me questionable flow numbers, and I have no intention of replacing it any time soon. I know, it's old and archaic, but a new 1020 is not going to make me a better head porter.

I think it's up to each head porter to know how his bench reads, whether it's a little higher than others, or a little low.

Hysteria

It may be a little of topic but how much do you charge to flow heads?

Greg Good

I usually charge 25-30 bucks. That's enough to cover the time on the bench and a little time answering questions.

Hysteria

PM me your number.

GC99TA

iTrader: (30)

Yeah, I can see your point, but consider this: You are correct that the head of the vavles make up about 80% of the area of the ceiling (for lack of a better term) of the chamber, but consider a chamber's shape. The area at the bottom (at the deck surface) of the chamber is much larger. Therefore removing .030 at that portion of the chamber removes more total area than if you could remove it from the top portion of the chamber. Now granted, when you sink the valves, you do gain back some of the total area you just got rid of, but I'm not so sure it's as much as one would think because of two things. One thing is that the larger diameter of a 2.02 vavle head will take up more area in the chamber than the stock 2.00 and the fact that aftermarket vavle heads are generally thicker than our stock intake vavles. I would think this extra valve head material would cause the valve head to protrude slightly more into the chamber, taking back some of the area lost. So, would you gain as much compression when milling and sinking the vavles as you would have if you hadn't sunk the valves? No, it's impossible. But, would you have gained atleast enough compression to make it worthwhile? I think so, but I very well could be wrong. I'm just expressing some of my ideas and I'm by no means an expert on this. I just find it all very interesting. The only reason I believe this is true is because my heads were milled .030 and my valves were sunk the same amount. My chambers CC'd ~ 62cc. Has anyone else milled an 853 head .030 with 2.02 intakes and (stock exhaust)1.55 unsunk valves? What was the CC value on you chambers? I would be curious to know.

jrp

iTrader: (16)

stock 241 heads are flowing ~230 on the intake @ .600.

jrp

iTrader: (16)

another thing to take note of is the CFM that is flown through both intakes. you'll be hard pressed to find most vendors giving you what there heads flow through any intake. besides jay and a few from brian there are none. what would you rather have, a head that flows 310 w/ a inlet plate but only 265 through an intake or one that flows 297 w/ a inlet plate but 280 through an intake.

checking and specing your **** not only allows you to see what you are actually working with but it also eliminates another avenue of potential low numbers. not implying that everyone with low numbers has bad heads but how many times have you seen posts with people upset they barely gained anything with there new cam and stg 2 heads that flow "300+" cfm.

also something to look at is the port variation. in the above example you can see its quite substantial especially with the intakes strapped on. knowing what all 4 ports flow you can get an average that will give you a better picture of the heads over a flow sheet thats just been flown on one port.

Greg Good

The intake port needs to flow as much as possible with a radiused orifice.

How much an intake manifold drops a head is an indication of how good or bad the manifold is, not the head.

If you have a really good flowing head and the intake drops it a bunch, you need a new intake.

CHRISPY

One thing though I wouldnt label the advent of CNC machining as a "Problem" as you have stated:

Problem two: The proliferation of low cost CNC heads makes it economically difficult for the shops doing hand porting to be able to devote the man hours necessary to a set of heads that they may need while still remaining profitable.


If they (hand porters) dont adapt and buy a CNC machine it is THEIR problem NOT the consumer.

The hand porter should design the port and then have it digitized for CNC. They can then hand finish or do whatever they want to it afterwards.

The introduction of CNC ported heads is a WONDERFUL thing for us as consumers. Precision, repeatability and mass production.

TVWilkes

I couldn't agree more.

J-Rod

True to some extent, but you have core shift on stock heads. In many cases you can have a CNC program, and once you have your port dialed in, if the port has moved around, you may not end up touching the port in certain places. Once you open up the program to take into account core shift you may pick up 10-15CC in the runner size to ensure you hit it thoroughly.


When you do them by hand, you can control where you hit the port.

Another important part of CNC work that often gets overlooked is tool path. You can take the same port and digitize it, and adjust the tool path and totally ruin the way the port works.

I agree that CNC is a way to obtain repeatability. I like CNC, don't get me wrong. My point about CNC is that when you have a CNC head that flows about 95% of what a good hand ported head flows at half the price, its sometimes hard to justify that extra expense. Hence for the hand porter they must either loose customer base, or cut cost. To cut cost you have to do less work on the head or drop your per/hr rate. In most cases you end up doing both. When you cut corners, quality can suffer, its just a fact.

So, you are right back to what I was talking about. If they spent more time, then you get the number, if they have to shave a bit of time off, well, the heads are good, but maybe they are down 10 or 15CFM over what you'd expect.

TD's z

mostly low to mid lift loss but i have seen that to cause a port to stall
that may be atributed to buy it having less of a short turn after the sinking

FASTONE

A stock vortec sb head will flow 225 cfm so a ls1 is only 5 better?A stock ls1 flows about 250!!At .500 at .550 and.600!!

FASTONE

A local porter that ports all kinds of heads said its no problem to get 300 cfm with the stock 2.0 valve on a superflo 600 flowbench,as he's done it before !!!As mentioned flowbenches can vary a lot!!

FASTONE

GC99TA,when you cc a head the fluid goes in the chamber itself not on the flat part or deck of the head,so this area has nothing to do with chamber volume.I f you mill a head this flat stays in the same place on top of the head gasket,you gain no compression.Only volume in the chamber will change the cr. on the head itself!!

CHRISPY

AFAIK alot of the newer CNC machines now can account for core shift. They are accurate within 10000s of an inch even with core shift present. I'll try to remember where/from who I heard that.

Also a CNC is FAR more precise than a hand port period. There is no comparision really.

Especially within different ports/chambers within the same head. I have seen top hand ported heads with quite a bit of variance between ports on the same head.

If the port is designed properly and digitized properly it'll be Ultra accurate. The amount of work need to be done by hand GREATLY reduced and with a good hand finish it'll be super repeatable and consistent flow wise.

Hysteria

David Vizard has a book out that has cylinder head mods and comparisons and the amount of flow on the vortec(96-99 sbc truck) head ported was about that, 239 or so, and the stock numbers were about 30 below that. I am not certain on this because I do not have the book here. I have seen reported flow numbers of LS1 heads flowing 250 but more so around 230-239. I believe the later.

Ed Curtis

The old flow numbers game huh...

Well...

People who buy cylinder heads based solely on advertised flow figures are like some people on a diet...

Instead of using the same scale to see what the results of the diet really are, they search high and low for a scale that reads the number that they want to weigh. Then "that's" the real figure...

Flow benches are TOOLS to be used to make something better...

Forget all the "advertised" numbers. Ask for the DELTA between the starting point and the finish point. There's the real key to how good the port work is...

What if someone shows up with a 310 cfm @ .600" head on XYZ's bench... Nice number... But what was the "base" number on XYZ's bench before the porting? There inlies the head's true potential over it's stock configuration...

Enough... this thread should get good so I'm making some popcorn and standing by..



Ed

GC99TA

iTrader: (30)

I think you may have misunderstood what I said. I was only refering to the portion of the chamber that is closest to the deck of the head, not the deck itself. In other words, if you flip a cylinder head upside-down and are looking at the chambers, the uppermost portion of the chamber (closest to the deck of the head) has a larger area per a given of depth (we'll say .030 for this example) than the portion of the chamber that is further from the deck of the head. This is because the chamber walls aren't perpendicular to the deck surface. They angle outward a bit, from the ceiling of the chamber, toward the deck, causing there to be a larger open area closest to the deck.

Sport Side

iTrader: (6)

J-rod,

Where should we be at now in terms of the discussion process? Still focussing in on flow numbers?

Its plain and simple to see that alot of the flow number wars are unrealistic. I think Ed's post is good. A way we can detect flow number BS.

good thread