Comparing heads - Need Some Help
Comparing heads - Need Some Help 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.
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.
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...
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?
What cylinder head are you currently running?
__________________
Jason
Co-Owner, Texas Speed & Performance, Ltd.
2005 Twin Turbo C6
404cid Stroker, 67mm Twins
994rwhp/902lb ft @ 22 psi (mustang dyno) www.Texas-Speed.com
Jason
Co-Owner, Texas Speed & Performance, Ltd.
2005 Twin Turbo C6
404cid Stroker, 67mm Twins
994rwhp/902lb ft @ 22 psi (mustang dyno) www.Texas-Speed.com
Originally Posted by Jason 98 TA
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
Originally Posted by Jason 98 TA
What cylinder head are you currently running?
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Originally Posted by Benji
An engine running at 100% volumetric effeciency will make 2.04 HP per CFM. Or so says Harold Bettis.
pardon my ignorance, but who is Mr. Bettis? Not a name I'm familiar with.
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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...
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...
Originally Posted by danf1000
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...
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...
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"
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"
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.
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.
__________________
2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2022 Cadillac Escalade 6.2L A10 S&B CAI, Corsa catback.
2023 Corvette 3LT Z51 soon to be modified.
Custom LSX tuning in person or via email press here.
2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2022 Cadillac Escalade 6.2L A10 S&B CAI, Corsa catback.
2023 Corvette 3LT Z51 soon to be modified.
Custom LSX tuning in person or via email press here.
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Originally Posted by TAQuickness
good info... will definately help.
pardon my ignorance, but who is Mr. Bettis? Not a name I'm familiar with.
pardon my ignorance, but who is Mr. Bettis? Not a name I'm familiar with.
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)?
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)?
Originally Posted by TAQuickness
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)?
