head to head

[gtxrt]

if you have a cylinder head that flows say 200 cfm at 500 lift and another head that flows 250 cfm at 500 lift how much would you gain in HP and TQ. not changing anything else, same Carb, intake, exhaust manifolds and same 500 lift cam say with 224-224 duration @.050. and keeping the rpms at max 5500 rpms.

 

[GTX JOHN]

I would need a lot more information, as there
are a number of variables in the engine to consider.

 

[DanielSlocum]

1 cfm of airflow can support up to aprox 2 HP .

 

[Doorkicker]

At the most basic level... knowing there are other things to consider... more air allows more fuel, and the more air/fuel permitted creates more HP. At the end of the day, that's it.

 

[gtxrt]

1 cfm of airflow can support up to aprox 2 HP .

so 200 cfm can support 400 HP. if the engine is making 375 HP now so there is no gain going to 250 cfm.

 

[gtxrt]

I would need a lot more information, as there
are a number of variables in the engine to consider.

what variables are there ?

 

[gtxrt]

guys went to high flow aluminum heads from stock and lost power most likely from a loss of compression but who knows what else caused the loss of power.

 

[Doorkicker]

guys went to high flow aluminum heads from stock and lost power most likely from a loss of compression but who knows what else caused the loss of power.

just out of curiosity, are you suggesting alum reduces cr?

 

[gtxrt]

just out of curiosity, are you suggesting alum reduces cr?

not sure what cc heads they were running plus they say if you have 9.5 compression with iron heads then with alum heads you need 3/4 to a full point more static compression so 10.25-10.5 to equal 9.5.

 

[PRHeads]

One thing I’ve learned when trying to improve the performance of mild-ish combos that are using restrictive induction and exhaust is that a lot of the “conventional wisdom” hot rod techniques/parts don’t always pan out.

As an example, prior to the circle track crate motor craze, one of the local series that had some pretty restrictive rules for one of the classes.
Had to use factory 2bbl iron intake, non-hp ex manifolds, under .500” lift, and stock heads(SBC) that came with 1.72” intake valves, 8.5cr max.
I flow tested piles of different castings and played with valve jobs.
There was a pretty big spread in runner volume and the bigger heads had a minor, but predictable flow advantage.
There was a particular casting number that was one of smaller runner volume choices, that didn’t look very special on the flow bench, but those heads always made more power than the higher flowing larger runner options.

I have no doubt that with headers and a better intake manifold, the better flowing heads would have been able to surpass the smaller/lesser flowing castings.

My takeaway on those engines was that the smaller runner heads had higher port velocity on the running engine…….which was better than a higher flow bench number from a larger head.
It’s all about finding the right combination.

 

[Budnicks]

not sure what cc heads they were running plus they say if you have 9.5 compression with iron heads then with alum heads you need 3/4 to a full point more static compression so 10.25-10.5 to equal 9.5.

Wrong, flat out wrong
it was proven on Engine masters, I suggest you actually check
do some real research, not speculations, or fodder & not spread fallacies like that
that's a wives-tale/false & complete fallacy/internet BS

don't get sucked into that crap

if anything the aluminum heads reduce hot spots, that create detonation
which aides in making power,
& it's more of a difference in a bigger combustion chamber size,
'if any loss of power at all', that even doubtable for the most part
there is so much better technology in alum. casting & cfm flow rates today
even a low compression alum. head combo can make gobbs of power,
with a better port design, than cast iron heads, yeah there are some decent iron heads too
but the material doesn't make it have more power, it the port & combustion chambers
cfm flow that make more power, more than material
(it was never a thing it's wrong, completely & utterly false)
most aluminum heads can be had in a smaller or bigger combustion chamber volume
enhancing compression ratios/or decreasing them...

It has nothing to do with materials, it's about flow
& heat is mostly an enemy to performance, across the board
(cast iron holds heat, hence detonation/dieseling issues)
you don't need more compression with alum. heads,
vs cast iron that an old lie wives-tale/BS
but it will create or dissipate the heat much faster, with alum.

 

[33 IMP]

if you have a cylinder head that flows say 200 cfm at 500 lift and another head that flows 250 cfm at 500 lift how much would you gain in HP and TQ. not changing anything else, same Carb, intake, exhaust manifolds and same 500 lift cam say with 224-224 duration @.050. and keeping the rpms at max 5500 rpms.

Going by conventional wisdom, 2hp/1cfm, so POTENTIALLY 100hp.
The chances of that happening with NO changes otherwise, are nil!
EM did a test of heads on a mild 440. 906s which flow just a bit over 200cfm, verses a 440 source stealth, at around 250. The stealth were roughly 20 hp better, rpm 20 more better, and tf 20 better still.
No changes, AT ALL, to an engine that's not overtasking the existing head?
I'd expect 15-20 hp. More cam, more carb, better intake to work with the better heads, would COMPLETELY skew those results.

 

[gtxrt]

Wrong, flat out wrong
it was proven on Engine masters, I suggest you actually check
do some real research, not speculations, or fodder & not spread fallacies like that
that's a wives-tale/false & complete fallacy/internet BS

don't get sucked into that crap

if anything the aluminum heads reduce hot spots, that create detonation
which aides in making power,
& it's more of a difference in a bigger combustion chamber size,
'if any loss of power at all', that even doubtable for the most part
there is so much better technology in alum. casting & cfm flow rates today
even a low compression alum. head combo can make gobbs of power,
with a better port design, than cast iron heads, yeah there are some decent iron heads too
but the material doesn't make it have more power, it the port & combustion chambers
cfm flow that make more power, more than material
(it was never a thing it's wrong, completely & utterly false)
most aluminum heads can be had in a smaller or bigger combustion chamber volume
enhancing compression ratios/or decreasing them...

It has nothing to do with materials, it's about flow
& heat is mostly an enemy to performance, across the board
(cast iron holds heat, hence detonation/dieseling issues)
you don't need more compression with alum. heads,
vs cast iron that an old lie wives-tale/BS
but it will create or dissipate the heat much faster, with alum.

no need to be a jerk about it. I didn't spread anything except which has been said and printed hundreds of times. it was a fact he said he went slower after the alum heads. if he went from 79 cc iron heads to 88 cc alum heads he most likely went slower. alum heads were out years before engine masters did their tests did you know that was a fact before engine masters did their show ? did everybody watch that episode ?

 

[Budnicks]

edited;
Yep I knew it before watching that episode,
I've raced at a high level for 45 years, had many & built many engines
& 26 racecars before I hung it up...
had a t a min. 3 times that in street cars street/strip cars...
Facts is, heat is a enemy for the most part to performance,
especially where it effects fuel & it's combustion
so is bad port design & cfm flow, an engine is just a huge air pump
what goes in, must come out freely, it doesn't know it has iron or alum (esp. heads)
unless it's more reciprocating weight, or unsprung weight
which is also a determent to performance..

All equal same water temp. etc.
they'd make the same power, (alum. more likely without detonation)
if the combustion chamber
the port configuration, timing, valve size, valve weight
spring open/close rate & it's weight on the seet,
or the cc's of the port & how it's designed or cfm flow is close
on a dyno;
it won't mater as much
but in a car;
any car, it will make a difference
front has less weight, better weight transfer, better breaking
better shock/suspension operation
the front end is lighter, 35#-75#s lighter, just with alum. heads,
especially with a BB
& the less (negative, heat/hot spots) unwanted heat in the combustion chamber
**** that causes detonation, alum transfer from the piston, to plug or lifting rings
& added BTUs does not necessarily make power,
& it often can cause detonation & dieseling also, can ruin the engine...

Both/all are serious issues in an I-C-E combo...
It's well known & Performance 101

Just the facts & actual reality
it's not, me not telling the truth & spreading BS, or internet speculations
just because some 18 y/o post from some forum member said so

do your research

 

[33 IMP]

....in other words, putting stealth heads on a 2bbl 361 with manifolds and single exhaust will probably get squat.
Replacing stock 906s on a 12 to 1 512 with a stout cam, with stealth/rpm MIGHT just get 75-100 hp.

 

[gtxrt]

I'd expect 15-20 hp.

so 15-20 HP there plus if changing to alum heads and adding another 3/4 point of compression you could add even more hp plus more compression will help bottom end torque

 

[gtxrt]

for me in a street car I will stick with iron heads.

 

[GTX JOHN]

what variables are there ?

All the Specifications on engine.

Not limited to but including Displacement/Compression/
Carb/Intake/Camshafts.

 

[PRHeads]

When the RPM heads first arrived on the scene, I tested a ported set(basic mild full port)against some pretty nicely ported factory iron heads.
This was prior to it being done by any magazines.

Iron head combo was 11.0cr, RPM 11.5cr.
Iron heads used 2.18” intake valve, 2.14” for the RPM.

600-ish hp 448……. 300cfm RPMs vs 280cfm iron……. About 20-25hp difference.

 

[33 IMP]

When the RPM heads first arrived on the scene, I tested a ported set(basic mild full port)against some pretty nicely ported factory iron heads.
This was prior to it being done by any magazines.

Iron head combo was 11.0cr, RPM 11.5cr.
Iron heads used 2.18” intake valve, 2.14” for the RPM.

600-ish hp 448……. 300cfm RPMs vs 280cfm iron……. About 20-25hp difference.

That must have been a really nice set of iron heads. I'm assuming 915s.