TAQuickness

iTrader: (28)

Need some help to determin if a head upgrade is worth the cost. I don't want this to turn into a pissing match so I'm not going to name any head vendors.

In a nut shell, I have a spread sheet with the flow numbers from my current heads, and the flow numbers from 3 different heads I'm trying to decide upon. The spread sheet takes into account the flow at various lift points and calculates a total flow number. In all cases, the exhuast flow differences are marginal, so my focus is on intake flow.

Head 1 show's an increase in flow of 0.6%

Head 2 show's an increase in flow of 7%

Head 3 show's an increase in flow of 8%

Question 1: How do you relate an intake flow increase to power at the wheels? I know there are a lot of variables that can effect this, but all things being equal, does a flow increase of 1% = xRWHP?

Question 2: Knowing that intake manifolds are a restriction, would the increased flow percentages be as dramatic with the manifold in place? Example: If the inake manifold is only capable of flowing 200cfm then the heads would be restriced to 200cfm max flow because of the manifold.

TAQuickness

iTrader: (28)

could use some help with this one... anyone? anyone?

TAQuickness

iTrader: (28)

OK - as my searching for these answers continues, about all I can dig up is that intake manifolds do impose a restriction. Nothing yet as to how they would effect over all air flow and nothing at all on x% increase in flow = x HP...

TAQuickness

iTrader: (28)

to the top - where are all the head experts on this one?

Jason 98 TA

iTrader: (4)

The main problem your going to have is finding honest flow #'s. The best way to compare several different heads is on the same flow bench, & that's hard to do

What cylinder head are you currently running?

Ben R

An engine running at 100% volumetric effeciency will make 2.04 HP per CFM. Or so says Harold Bettis.

TAQuickness

iTrader: (28)

No kidding... If I had the budget, I would pick up a set of the 3 I'm considering and have them flowed on the same bench. Based on the comparisons of my heads vs the advertised numbers of the other 3, I'm thinking there's not much to be gained by the swap (not a good hp/$ ratio for my budget).

Would preffer not to say in this thread as to avoid any possible pissing matches.

TAQuickness

iTrader: (28)

good info... will definately help.

pardon my ignorance, but who is Mr. Bettis? Not a name I'm familiar with.

danf1000

iTrader: (2)

had a wonderful response typed, but the computer failed on it's end, but here's a quick summary:

flow is a function of not choke points (unless sonic flow) but the summation of resistances of different components (intake, maf, tb, intake, head) therefore a 10% intake head flow increase might be worth half that in overall flow (you can easily see by the summation thing that if you had low resistance or hight flow intake, maf, tb, and intake, this ratio might be different) and then half again in power increase (let's not forget the exhaust part of the equation, add another 2.5% for the accompanying exhaust flow that would certainly be part of any head upgrade)

that would be 20 hp for a 400 hp engine. add a camshaft to that and the vitally critical cylindrically shaped flow area between the head and valve is increased again, increasing the gain.

this is not a empirically found ratio, just a guess. and each engine design is again going to have it's own increase of flow/power for a corresponding head increase...

TAQuickness

iTrader: (28)

so, for simple comparision, if the intake tract is only capable of flowing 200cfm, then a head capable of 300cfm will be limited to 200cfm because of the intake tract - is my thinking clear?

danf1000

iTrader: (2)

no, again, flow is a function of the summation of all the resistances, not indicative of a choke point.

in conventional flow path calculations, pressure loss is found for each individual component (for a given inlet pressure). say that there is a differential pressure of 14.7 (complete vacuum in the combustion chamber). then there is a pressure loss of .5 psi for the maf and tb, 1 psi for the intake and 2 psi for the head. then you could say that the resistances are limiting the flow to a total pressure differental of 11.7 psi, a loss of 4 psi.

i think they call these losses "head loss"

Patrick G

iTrader: (14)

In simple layman's terms, bolting up better flowing cylinder heads will make you more power, even with a restrictive intake manifold and TB/MAF/Lid. Let's say you have a set of heads that make average flow (.300-.600") of 265 cfm (@28" H2O). Let's say those heads make you 425 rwhp. You're also running an LS6 intake and 75mm TB that only flow 245 cfm. Does that mean your heads will only flow 245 cfm? No is the answer because even with the restriction, the draw of the motor will overcome much of the choke of the intake. Now you decide you want to add some better heads...ones that flow an average of 285 cfm. In a perfect world, you would make a little over 40 more hp for the extra 20 cfm gain, but we don't live in a perfect world.

Remember, we have a 245 cfm intake. The good news is the intake will not choke the 285 cfm heads down to 245 cfm, but somewhere in between. In this example, the better heads may still be worth an additional 20 hp.

Now let's say you add a ported FAST 90mm intake on those 285 (avg. flow) heads. Because you eliminated more of the restriction in front of the heads, you might pick up that extra 20 hp. Even in NASCAR restrictor plate classes, racers went faster every time they added better flowing cylinder heads...even though the restrictor plates severely choked the flow.

Ben R

Harold Bettis is the Vice President of Super Flow.

TAQuickness

iTrader: (28)

Thanks for the info guys. I've been mulling over my research and yet a few more questions come to mind.

Aside from flow, what other factors will determin a HP gain or loss?

I would imagine the combustion chamber design has an effect, but I don't know how to compare combustion chambers. Does a CC with CNC marks produce more power as opposed to a CC that has been polished? What other characteristics in a CC are desirable?

When head vendors change the valve angle, is this done to increase head flow, or does the valve angle have a direct effect on HP (other than increased flow)?

Beast96Z

iTrader: (21)

Changing valve angle could be somewhat related to advancing or retarding your camshaft. Diffrent heads react diffrently, but for comparisons sake, we'll say 45* is a optimum range of flow across the board. If you changed that valve angle to 50*, then in most instances, that head would lose in the low to mid range, but pick up quite a bit up top. Vice versa for 40*. Most companies would use a 45* angle unless the combo looked as if it would benifit from something else.