Slightly strange head flow question.

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Rat Patrol

Rat Patrol

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Here's the question.:

The build includes - Cam .540 lift, M1 intake, 392 cui stroker, 800cfm carb

With ported 589s (2.02 valve) that flow [email protected] the engine makes 420 HP

With OOTB RHS heads that flow 255 @ .550 it might make around 435 HP?

With "hyperported" Eddies that flow 300 @ .600.............would it make any more HP ?

............or is there a point that the heads won't show any improvement?

In other words...is there an "ideal" port peak flow # and how is this calculated?

(Assume the intake is gasket matched etc and best valves etc.)
 
With the Eddys being aluminum you can bump up the compression which will give you more power plus better cooling
 
there is a point when the flow wont make a diff. that point is when the ve (volumetric efficiency) is 100% or close depending on your combo of parts. some engine will be even higher then 100%. rare for most street engines. as far as the flow numbers for your engine and what it can handle is a guess at best because its related to the parts your using and what rpm you are achieving your hp numbers. my opinion your engine could easily see a increase from 300 cfm head flow. question is now how much increase. that's the million dollar question.
 
The Wall has it right. With the later heads you have the POTENIAL to make more HP but without changing some things you could actually loose some HP. Without optimizing your cam specs, compression, fuel (basically your VE) you could loose power with too much air flow
 
Rat Patrol said:
Here's the question.:

The build includes - Cam .540 lift, M1 intake, 392 cui stroker, 800cfm carb

With ported 589s (2.02 valve) that flow [email protected] the engine makes 420 HP

With OOTB RHS heads that flow 255 @ .550 it might make around 435 HP?

With "hyperported" Eddies that flow 300 @ .600.............would it make any more HP ?

............or is there a point that the heads won't show any improvement?

In other words...is there an "ideal" port peak flow # and how is this calculated?

(Assume the intake is gasket matched etc and best valves etc.)
Click to expand...

There are more important things than flow. The RHS head has a much better chamber, much better ex. port and flows more air. It will make at least 20HP more than a nicely ported OEM head.

The edelbrocks fully ported will make more power on that engine, but it won't be alot. Mainly because the build is so mild, it won't help a ton. I would say maybe another 20-25HP over the RHS unless your using the small valve in the RHS then you'll see a larger gain.

Flow is dependant on many things like piston speed (rpm and stroke), bore size, intake, headers, carb, and so on. So if any of those things kink the rest of the build, the good flowing head won't shine.

Brian
 
Cheers guys...

Brian - I understand where you're coming from on different chamber characteristics etc.

Assume like to like on everything but port flow #s......

I guess I'm trying to get a handle on "how much port flow is too much"...assuming the heads and valve train are compatable with the engine stroke and compression etc.

Am I right in understanding what other posters are saying?

- That ideal port flow is not an exact science, and can't be predicted exactly for each engine?

EG - That 320cfm might be worse for the 392 than 270 cfm?
 
The cam has .540 lift with 1.5 rockers? If it's a 59* SB you won't see that lift at the valve unless you run 1.6 rockers because of bad pushrod/lifter angles.

300 cfm at .600 lift doesn't mean much if you only poking the valve .500-.540. and realizing/accessing flow numbers around .500 at best.
 
I agree with Brian on this, but I don't think there will be that much better boost with the same cam with the RPMs over the RHS. Because the RHS is a farily small but fast port, it works well with low lifts. The RPMs at "full boogie" are a slower port at lower lifts. You would have to cam to match them. No port can do any good without the valve being open to the point where the port works. This is why good porting does not simply make a lot of flow at high lifts, but improvements from the seat to max lift. But if a port flows good at.500 and great at.600, you'll never be able to reach "great" with a .520 lift cam.
 
OK - gotcha on the lift ratio and the relationship between valve lift and runner size.

Maybe if we compare identical style heads - say Edies - but one set is ported to flow 300 @ .600 and the other 270 @ .600 -

What sort of difference in HP could be expected with the cam under discussion....Any improvement at all?
 
Rat Patrol said:
OK - gotcha on the lift ratio and the relationship between valve lift and runner size.

Maybe if we compare identical style heads - say Edies - but one set is ported to flow 300 @ .600 and the other 270 @ .600 -

What sort of difference in HP could be expected with the cam under discussion....Any improvement at all?
Click to expand...

I like the wall's answer since I know what he's talking about on a technical level. *There are formulas for this and he uses them.*

it's about the VE, or in lamens terms -parts combo lol


and really, if you are lifting the valve .540, what ever the heads flow at that lift or just below say .030 u are gonna get/access if you're lucky enough to have the rest of the parts and mods done to achieve a better VE, and yes csa will effect hp/rpm....let alone air speed differences/port distribution...yadda yadda.....
You can say it's about parts and compression, lift, the moon and the stars, but really it ALL comes down to VE.


And again....if you not living at that lift.....those numbers mean dk.

The other thing is this......rhs heads are restricted to a shape that fits into a stock casting still using the push rod pinch, the closed chamber is great and does make some horse power.....but keep it real, the j head ported can go the same int numbers as an rhs head and it helps to have someone who's works with oem heads port them in the 1st place...
btw When I pick up an rhs head it feels like Im picking 1 1/2 oem heads lol, they have sooo much extra meat in them, good heads though.
 
RP,

When you review ported heads, it's more important for you to take the "averaged" flow numbers when you evaluate them. The reason:

You engine will not be performing at "only" .500 or .600 lift. Your engine must make significant power (and torque) "across" the powerband, and that's why averaging is more important.

You must factor in the converter "flash point" to ensure a good launch, and the numbers, post launch are critical to get you to your desired shift point and finish line RPM.

Again, IMHO, you should avoid using "peak" values as they do nothing to define your performance "curve". The best "averaged" numbers will result in the best "overall" performance. Remember, you need to make good torque (high port velocity) to launch the car, and enough horsepower to push you down the track for your class (or desired ET).

Once you've averaged your flow numbers, you be able to determine if the cam you're running will produce the results you desire. I hope this helps.

Southernman
 
(Sorry if I repeated something here....)

The port size also has alot to do with power and the given size of an engine. In example, a set of RPM heads on a 318 (Or smaller engine) would be a very large head. You can make great power from a 318 with ported 302 heads. These ported 302 heads may only flow 230 cfm, give or take a few cfm on ethier side. (Ported by who? is the question. Reguardless)
If you put a 360 head on top, you may make more power, but it will be in the top end of the scale.

Velocity!

One of the reasons is port velocity. If the air is moving slowly through the port, the fuel is not atomizing well which creates a poor burn of the fuel. 2, even though the port is larger and will flow more air, the smaller engine can not take advantage of this possible potentail until the rpm's go up to get some velocity going in the big port.

Velocity is key. There is a point that there can be to much velocity, but at what point I do not know. This point also changes with engine size and the head port size, valve size, cam being used, etc......

A large port window will contribute to a lazy sluggish feel on the street at a low RPM. While tihs RPM area is ignored by a drag racer since there making use of a high stall converter and gear toluanch at, a street - street/strip machine will probably not want to do this (Very) high stall and rear gear.

Now if you can get a small port window, like a 302 head on a 318 to flow 300 cfm without createing problems, then performance should go up. (Even more so if low lift doesn't change, but theres allways a trade off.)


This example I gave above also translates to any engine. For a street engine, a certain port size is recomended. Then, for a street strip engine, the size will go up. etc... This size will be determines bythe whole package. And I mean everything. Car weight, intended performance level, cam and rpm's intended wth the build. I mean everything.

This is a key factor that is missed alot. Alot of builds here on the board are decent, but not a well thought out sci. project.

There are some good minds answering this question here today.

Ooo, soorrry, I should say everybody here today. I noticed after I worte it, everyone has great answers and have a great understanding how crap works.
 
one point i want to make. ported 589 heads cant get to big to cause a velocity issue on 392 inch motors. rhs heads cant get to big to cause velocity problems on 392 inches. even if the cam timing is set up for only 5000 rpms if you increase the flow in the lift that you are using you will gain some power. 300cfm will make a increase in your engine.
 
yep.


I'll add to this...if you swap 360 heads onto a 318 outright.....the loss of torque might have something to do with the 4-6cc bigger chamber that just knocked around 7-10 psi out of the dynamic and killing the 'response'....in other words....mill the head to the same cc you had with the previous..

Response is not necessarily as important as overall torque, you can stick a 600 cfm carb where a 750 carb sat and feel more bottom end off the line or that nano second of tipping the throttle....but when 3-4000 rpm comes round it's falling flat cause you just knocked the balls off of it 'killed the peak torque'

More airflow within the same used lift range 'when it comes to oem sb iron port volumes' will always make more peak hp/tq, the ports are just simply not that big.

another thing about big ports vs small cid, since people talk ''combo''...is if the car has a lack of bottom end but pulls the top....put some gears in it already..lol...theres ur combo.
 
Ok thanks all-

So to summarise -

If I understand correctly - if the cam can't take advantage of the peak flow of the head, there's little likelyhood of seeing any improvement, and it may go backwards due to a drop in velocity.

I also undertand the point about "averaging" the flow rate across the lift in order to determine the likely HP improvements -


BUT - is there a simple formula or theory that will give an idea of the target peak Head flow for a certain cam/combo?

I suppose I could have saved a lot of this by asking "How does a builder/head porter know when the head flows enough for the combo?"

1Wild mentioned formulas - do they apply to this issue?
 
ok im going to give this a shot. i feal the anweser to your question is short and simple. lets say you have a pair of w2's that you hust sent out to a reputable shop and had the ported and flowed. Lets say the shop proves the heads to peak flow 300cfm at .600 lift. now considering the WHOLE rest of the car is set up and dialed in and taking into acount valvetrain geometry and lash, youd want the cam to open the valves slightly more than that .600 lift peak flow. so lets say you can get .625int at the valve there you go. your reaching the full power potential of the heads. just my 2 cents
 
And that deoends on the cam style and even spec 'g stock/stock class lift limited'... how much above the peak you would need to go.

A flat tappet cam only see's that peak flow for a blink, it's the time/flow during the open/close cycle that you see more of.-think under the curve.

Lifting the valve over the peak flow also makes up for lag time of inertia driven intake charge.

roller has more open time at peak lift.

and part of the of idea is 'lag time', that is also closely related to intake/ram tunning...that is where the tail end catches up or inertia from the low pressure signal/pulse and how long/much it translates-Think big flying by you while standing on side of the road and the tail wind/gust that comes after ...

placing the mid ramp where/@ peak/desired flow is how you realize the potential in that area....but if the heads fall off a ton much past that...you need to be concerned with how much time you have the valve held open where it's backing up-also refer to the fact that intake manifolds usually slow the air down/limit total flow which is the same in a way

so thats the idea in my screwy way of stating it...since Im 8 beers into this
 
Rat Patrol said:
Ok thanks all-

So to summarise -

If I understand correctly - if the cam can't take advantage of the peak flow of the head, there's little likelyhood of seeing any improvement, and it may go backwards due to a drop in velocity.

I also undertand the point about "averaging" the flow rate across the lift in order to determine the likely HP improvements -


BUT - is there a simple formula or theory that will give an idea of the target peak Head flow for a certain cam/combo?

I suppose I could have saved a lot of this by asking "How does a builder/head porter know when the head flows enough for the combo?"

1Wild mentioned formulas - do they apply to this issue?
Click to expand...

In the head depot...You have to flow the head/intake/carb together and work the intake and head to flow X number with carb venturi size being used required for desired hp goal.

i cant remember right now.... but something like 11% is what a 1000cfm eats from the the total flow 'intake w/head', Ill dig into my notes..you could maybe come close by adding another 2% loss per 100 cfm decrease, maybe.

The rest is dialing the valve events per stroke/rod length and compression to max the octane being used....but basically working around the intake/exhaust system at the same time OR being very versatile with changes...

You can build around a lot of things, heads an intake...bt there so many factors....simple one like if you cant fit the size header u need in your car...

Whats this for?
Maybe some heads that flow huge in the low .1-.500 lift is what you should be after with that .540 lift cam u mention, and the rpm band is what?
Maybe the dual plane intake 'good to 7k' is the ticket 'ported of corse'...


hmmm....There was one guy who states in a video that he never had a head perform well that fell off or went turbulent like one that didnt, and he claimed even lifting the valve under the backing up, cam wise.

roll that around.
 
Maybe this will help

XS282S Cam - .520/.540 lift @ .50, 244/252 @ .50 duration, recommended 2500-6500 rpm

If I have access to two two pairs of identical Edelbrocks (springs valves etc)

- one set flows 260cfm at .550, the other 290cfm at .650,

For arguments sake, lets say both display "healthy" low-mid lift figures also.

Which should I use and why?

Assume the cam, M1 SP, 800cfm carb and everyting else will not be changed.
 
Rat Patrol said:
Maybe this will help

XS282S Cam - .520/.540 lift @ .50, 244/252 @ .50 duration, recommended 2500-6500 rpm

If I have access to two two pairs of identical Edelbrocks (springs valves etc)

- one set flows 260cfm at .550, the other 290cfm at .650,

For arguments sake, lets say both display "healthy" low-mid lift figures also.

Which should I use and why?

Assume the cam, M1 SP, 800cfm carb and everyting else will not be changed.
Click to expand...

on the dyno....the head that flows more from .0001 to what ever the actual valve lifts will make more power, given all is the same otherwise.
If they both flow the same throughout but one go's to a higher lift to make it's peak....the one thing I can say about that is port distribution/csa,..hmmm glug glug.. not gonna side track yet...

But the 1st line answers you're question.
The why is obvious.
you arent opening the valve to .650 lift or even close.

heads flows x amount peak at .600, cam lifts only to .540, then figure geometry losses and intake tract losses, mainly you arent lifting the valve to the .600 peak.....you are only gonna get .500'ish flow, if you open the valve to .600....then you'd see that flow...
 
Thanks 1wild - Now I get it - I can see now how peak flow well above valve lift won't mean anything to the engine.

So in my combo - I need to keep a close eye on the flow values upt to .550, but above that is irrelevant...yes?

Thanks to all - I suspect my question was a little more "basic" than some of the clued in guys on here expected. :)
 
1W&CG stated it preety good for "8 beers into it."

Heres a peice of good news. No matter what your head flow is, great combo cam be put togther without getting nutz on the cam specs.

A basic view;

Build the engine to compliment the cars intended performance.

A race car will look for every bit of lift and then some. (As mentioned before) More lift than the head flow, excesive converter and gear.

A street strip car will look to mimic the race car, but with a little less comp. ratio for pump gas, a litle less cam and converter. Total cam lift at or near max head flow.

A high performance street machine will look for things like a milder cam that doesn't take advantage of the heads flow ability's 100%. Maybe some where in the 85% plus area.
Total cam lift would be close but yet still a bit far away from peak flow. The head may not be fully ported ethier.

High performance street will not care so much. An example of pocket ported head, the lift may even be as short of peak head flow abilty by .030 lift.

CFM & HP gain talk again;


You have it right... as it goes in the real world. Only because the head, in order to gain more flow cfm, at least to the level of 300 cfm for the small block will require a bigger port window. The way around this is to raise the port, as seen on some race(y) heads.

The only other way around this I can think of is to charge the engine.
(AKA Super Charger/Turbo)

Now combined with the above, what is your intended target? At some point, getting more cfm will mean a getting the other parts to work with it better. Building an engine, lets say other wise stock minus the cam and heads but with a big cam and fully ported heads will create a combo of miss matched parts and poor performance. Simply adding a converter and gear may not be the best way to go about it and make matters worse.
 
Rat Patrol said:
So in my combo - I need to keep a close eye on the flow values upt to .550, but above that is irrelevant...yes?
Click to expand...

This is the only thing you need to concern yourself with if comparing the same two heds and ports. You also need to do the empirical measuring to get lift at the valve, and then take some more lift off for the short duration it sees at max lift.
 
rumblefish360 said:
1W&CG stated it preety good for "8 beers into it."

Heres a peice of good news. No matter what your head flow is, great combo cam be put togther without getting nutz on the cam specs.

A basic view;

Build the engine to compliment the cars intended performance.

A race car will look for every bit of lift and then some. (As mentioned before) More lift than the head flow, excesive converter and gear.

A street strip car will look to mimic the race car, but with a little less comp. ratio for pump gas, a litle less cam and converter. Total cam lift at or near max head flow.

A high performance street machine will look for things like a milder cam that doesn't take advantage of the heads flow ability's 100%. Maybe some where in the 85% plus area.
Total cam lift would be close but yet still a bit far away from peak flow. The head may not be fully ported ethier.

High performance street will not care so much. An example of pocket ported head, the lift may even be as short of peak head flow abilty by .030 lift.

CFM & HP gain talk again;


time to have fun... race car dosnt look for anything.only the racer does and hopes he did enough.example stockers in nhra are stuck with a lot of numbers we dont like as racers but 71 demons in stock class run 11.98 et pretty fast.and in racing there are winners and losers some with the right stuff and some without.

a street strip car doesnt mimic anything my version of street strip is different then yours. i tend to go more to the edge probably

a high performance street machine doesn't look for anything, i do as a builder.example a 589 head and rhs head isn't as big as a w2 head but the factory put them on the little red express proto type trucks and ran stock 340 cam holley 600 stock comp 360 and ran 13s in the quarter and smoke the comp.

point is this my w2 s out of the box flow 265 at .450 lift if that what the factory was working with i now there smarter then you and me its good enough for me

hang on im opening beer 9 ha ha got you beat 1 wild
Click to expand...
 
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