Is there a limit to head flow

[Ed-vancedEngines]

I am not sure what the intent is, with this meaning that is in this thread.

"You can get bad advice from SpeedTalk or good advice" and then he mentioned comments here by Big Joe and by Mr Harold, in a manner like he is calling thier words bad advice.

I hope my words here in this post straightens some of that up. I do not appreciate any of our dedicated loyal professionals to be talked against. Big Joe has likely built more engines and been written about than almost anyone in racing. UD Harold has probably designed and ground by now thousands of camshafts which many are still selling through big cam companies.

I now consider Big Joe Sherman one of my friends of Internet, Phone, and in knowing many of the same people. I have admired Big Joe or as I call him Mr Joe, for many many years, and still do. Yet I am not always in complete agreement with him. No biggee. No one agrees with anyone all the time. I hope. I consider Mr Joe or to you all Big Joe to be a valuable asset to SpeedTalk and we are blessed he is here with us.

Mr. Harold Brookshire, is one of the old time, all time Camshaft Greats. He is respected by most people in the camshaft industry. I also consider him a friend and at times, a professional business associate. MY first contact with Mr Harold was through Tim Allen who I used to buy all my Lunati through, and I wanted custom designed and ground cams, not off the shelf stuff always. He turned me on the Mr Harold and he did several cams for me that I liked very well while he was with Lunati. Mr Harold is one of the few men who has even now camshaft designs in catalogs in at least 3 and possibly 4 different big cam companies that are still selling cams he designed years ago. He knows the Cam business. Like Mr Joe, I also consider Mr Harold Brookshire to be a valuable asset to SpeedTalk and am happy he took my offer to come join with us here.


Quote: from Big Joe Sherman

You have to be carefull, If the engine does not have high compressiobn ( 14 or 15 to one )the big lobe centers wont work.Pro stock engines have very high compression, ( 16 and higher) that is the reason it will work for them. On a low compression street type motor, wide lobe centers will give away lots of overall power .

JOE SHERMAN RACING ENGINES

Joe is mostly correct in this suggestion when it comes to racing engines. Joe is talking about peak power and average power. He is not talking about low end torque and spreading out the torque curve so someone can pull a stump outta the ground. He is talking racing. Plus the customer is talking about a little nitrous too. I am guessing that is where the customer is getting the idea of 112 LSA. Ooops. Original Poster, not customer. My bad.

No where yet in that thread is the original poster talking about this being a street car. I will say though that the 10.00- 1 compression is not the best ticket for anything performance related. You can still make one run with low compression as much as it is capable of though.

=========================================

Now to the member talking about the guy whom you admire at Comp Cams, I am guessing you may have misunderstood him. If not he is wrong, I don't care who he is or how high up in his company he is.


Quote: from 540 Rat

Actually it was Billy Godbold of Comp Cams fame, who originally turned me on to the idea of choosing duration and overlap, then letting the LSA fall where it may. I fully agreed with him, and have since used and recommended that thinking myself. So, in the end, I guess maybe you are disagreeing with another Cam expert who knows a thing or two about cams also

Perhaps Big Joe or Mr Harold knows Mr Godbold and can ask him to join with the rest of us idiots here on SpeedTalk? I can not imagine a person with his position making an error in statement like that.

Here is the way I see some of what is in this discussion;
To begin with, A rough cam core from the heat treating but not finish ground is not a bar with round lobes to have as a starting place. There are lobes cast into the cam with defined LSA possibilities within parameters of the grind and how deep it goes into the heat treated surface. So to select the right core to grind, you need by then to have a pretty close idea of the LSA.

LSA is not just an accidental happening becuase of duration and overlap. Duration and overlap mean squat to what LSA the cam ends up with. The amount of LSA is derived from the Intake and the Exhaust Centers, that is where the exhuast lobe is at maximum right on the toe and where the intake is at maximum centered right on the toe. Or nose or you prefer. LSA is the position in a circle of degrees separating the lobes or as it is called Lobe Separation Angle. Any lobe design with any lobe profile can be moved to almost any LSA while the cam is in desigining. You can achieve the same LSA with many different cam designs and many different opening and closing positions but the relationship between max intake lift and max exhaust must stay the same for the LSA to stay the same.

Please bear in mind, I am talking about hypotheticals that can be ground on a cam. not what can make the most power. I am talking about what is physically possible. There is no way to let the LSA simply fall where it wants to be, becuase it is only a byproduct of the grind design. It is not. It is only a byproduct of Angles of separation between max intake and max exhaust lift.

Now the grind or overall lobe profile with durations, ramps intensities with LSA does determine the amount in degrees of overlap. Keeping all lobes the same but separating them further will decrease the degrees of overlap, all things equal. Likewise shortening or bringing the lobe separation angles of intake and exhaust closer together, all things equal, will increase the degrees of overlap.

Decreasing overlap with wider LSA will give a smoother idle, increased manifold vacuum, better drivability with a sacrifice of peak power and average power but will hve a lower but more broad torque curve, so it is preferred by the OEM for street driven vehicles. It is also many times preferreed by engine builders like myself when building daily street drivers in heavy cars or trucks. That way I can build in a lot of duration with strong lobe profile but have manageable street manners, in higher compression street driven vehicles. I do this quite a lot with hydraulic roller cam engines. We are talking drivability, not whatever it takes to get maximum performance when we do this though. Actually when Harold was at Lunati we together cooked up a few of these off the wall street hydraulics for my customers.

Back to the person asking his original question;
Why 10.00-1 compression in this kind of engine? Your compression is holding you back from being able to more effectively use a cam that would do you better. With 10.00-1 compression statis and the overlap a big racing cam will have your actual running compression or what is called dynamic compression will be very low.

=============================================

Quote: from 1320 racer & from Bad95GTs

Would you post a couple of examples of the whole threads you have received bad advice here from?

Quote from Bad95GTs

There is good and bad advice here on Speedtalk.
For one saying 114 lobe separation will not work with 11 to 1 compression.
This has nothing to do with anything.
Valve opening and closing events are what is important.
Lobe separation is an end result.
No one who knows anything picks the lobe separation first and then designs the cam around that number?

Please read all of the above.

Quote:
Is there a limit to head flow??


I guess literally there is.
You would not want a pro stock head a 2.0 liter engine.
Most heads on a typical engine are no where near big enough resulting in an inefficient cam design.

The original poster asked the question wrong for what he wanted to know. He got not bad advise. [Ed]

Part of your statement is bad advice though.

Quote:
Is there a limit to head flow??

Most heads on a typical engine are no where near big enough resulting in an inefficient cam design.

Quite incorrect. Why? Becuase I says so. lol.
Fact is in most amateur racing engines the cylinder head runners and measured on the bench CFM are too large for what the overall engine needs and the vehicle needs for the application.

Not for sure at all what you are meaning about insufficient cam designs. The reason many engines have a cam design that is not well matched to their combination is becuase they shop in a book to pick out their camshaft from existing designs, not really fully understanding just what the numbers they see can represent and usually foloowing the advice of a buddy or a cam advisor who will design you the perfect cam for your needs in 5 minutes or a little longer.

We here at SpeedTalk pride ourselves in being a vehicle of good information for our many members and guests. However who is to say just what is good advice and what is bad advice? Shall I be the judge of which advice posted is bad or good solely based on my opinions? I think not. To put is a different way here. For example if I were to ever publicly post exact details of how I set up cylinder heads for serious high rpm high horsepowered applications, the majority of readers, members, and even other engine builders would see my words as bad advice, becuase it goes against what is accepted and is widely done by most everyone. Yet it works great for me. Another example; I very good friend of mine and a good engine builder and I have butted heads for years about building and design techniques for a nitrous engine. In his words and in the opinions of many, I am doing it all wrong. Recently that person told me I had been right and he now was doing what I been telling him to do and it works better with more power. When he was not accepting the info I told him, to him it was bad advice. Now he is on the band wagon and doing it similar to me. So just maby at times what we think is bad advice just may not be. We allow a mix-mash of differening ideas and opions here so the reader can read and see more what can better fit their needs. At least we try.

Ed

[n2xlr8n]

I think more than a few members would do well to lurk, snoop, and read the threads on this forum before making comments about someone's expertise in a given area. I'm amazed at the patience exhibited by those senior members, most were going "fast" when I was a sperm cell.

I've noticed more and more lately folks questioning solid advice they are given (imo), even based on what little relevant info given by the original poster. If you disagree, either be respectful, or keep your trap shut and try to learn something.

Remember, fast is relative. Back in 1990, I used to think my 10.40 street car was fast...until I moved to Md and got wasted by a Chevelle Wagon.

Steve

[Bad95Gts]

This forum as all forums are very largely opinion driven.
Not everyone can get the same results form similar combos.
Just because one person may not be able too achieve a performance level does not mean that someone else can not.

A comment like the one based on LSA very well can lead to confusion for someone reading that post.
It alludes to the fact that the LSA is why the engine is down on power and simply changing the LSA will fix the problem?
I have no doubt Joe knows how to make it run and make it run well.
I was not suggesting that Joe was wrong just that the in the posts context it was bad advice.

Which leads to this

I enjoy this board and if someone like BIGJOE1 says 114 loses power on low compression high hp drag race engines, more than likely when I have one to build I'll avoid that thought unless I totally have reason to back myself.

[Ed-vancedEngines]

Bad95GTs,
Very good explanation and you do make sense with what you mean.

I am sure that I too mess up but I do try mostly to consider that many people will read the thread not just the original poster. So I do at times go off the deep end in explaing things which the original poster did not ask but to my way of thinking are related to the discussion even if barely. I am trying to supply info that could possibly be helping many who for whatever reason never ask but are still reading the threads to see what is said or to try to learn from them.

You can get a good idea of what I mean if you look at any thread and look at the total responses vs the total hits on the thread. Many are looking and reading but a few are asking. We do all try to help those whom are asking but embelishing so others may see more along the same subject area.

Seldom at SpeedTalk will we edit or remove a post but we will if it is so wrong of info as to cause possible trouble if the advice were to be followed. If it will cause harm we will remove that kind of advice or suggestion.

Most any time here if anyone including me, posts information in error, we do have good members whom will correct me and say I am wrong. I do not want wrong information on SpeedTalk. Don the owner definetly doesn't want wrong info on his board. Information or advice that differes from the way I do things or is done by the mainstream though just may not be bad advice but good advice that is unknown to the maasses.

Bad95GTs,
Thanks for explaining and you are correct.

Ed

[Bad95Gts]

Thanks Ed.

I would like to contribute more things as well, but some of my thinking is rather unconventional and I only like positive things to come from what I post.

At one time Speedtalk was the premier board for Experts only.
The board now sees more and more people of Intermediate and beginner skill level and quite often posts are confusing.

Most heads on a typical engine are no where near big enough resulting in an inefficient cam design.

Take this post.
I left out too much information to make it a worth while post.
It is Bad advice as well for the average person who reads it.

On a side note I really learn alot from Ed's posts.
They are well thought out and thorough.


Thanks Guys

[Procision-Auto]

At one time Speedtalk was the premier board for Experts only.
The board now sees more and more people of Intermediate and beginner skill level and quite often posts are confusing.

We do our best to keep advanced topics in the Advanced Tech forum
where the pros can disucss their needs.

It's always nice to see the big guns come over to Engine Tech to help
with routine projects, and less intense topics.

[randy331]

Is there ever a time when a gain in peak airflow, but at a lower cfm per SQ in, will result in a power gain

This I take it is a lowering of the velocity in the port yet resulting in more power?

That's not what I was getting at. I didn't mean changing the port to flow the same, but at a slower velocity. What I mean't was, when does gaining flow, but at less cfm per sq in of area, lose power, and when does it gain power.
This seems to me to be VE related. Take a stock head sbc, any gain in air flow gains power, as the engines become more developed, the port speed, cfm per sq in of csa, all seem to become more important.
I'm guessing as the VE of an engine increases, and cylinder filling after BDC is the only way to further improve VE, the speed, cfm per sq in of csa, velocity profile etc, all become as, or more important than total cfm.

Randy

[maxracesoftware]

That's not what I was getting at. I didn't mean changing the port to flow the same, but at a slower velocity. What I mean't was, when does gaining flow, but at less cfm per sq in of area, lose power, and when does it gain power.
This seems to me to be VE related. Take a stock head sbc, any gain in air flow gains power, as the engines become more developed, the port speed, cfm per sq in of csa, all seem to become more important.
I'm guessing as the VE of an engine increases, and cylinder filling after BDC is the only way to further improve VE, the speed, cfm per sq in of csa, velocity profile etc, all become as, or more important than total cfm.

Randy

when does gaining flow, but at less cfm per sq in of area, lose power, and when does it gain power.

As an example,
CFM per SqInch of Valve Area,
like a recent Thread about #781 BBC Heads,
i gain HP every time i go from 2.190 to 2.250 or especially 2.300 valves
even though the 2.190 valve might be at 79.64 CFM/Inch (300 CFM)
-VS- 2.300 at 77.0 CFM/Inch (320 CFM)

Same results in a bunch of different Head types,
like a series of tests with Vortec cast-iron SBC #906 castings
going in steps from stock OD to 2.020 then to 2.055 then to 2.080
the CFM per SqInch of Valve Area numbers will be declining but
the overall CFM will gain and so will HP.


Like in Comp or ProStock, you should always strive for the highest
CFM/SqInch as this becomes more important in these applications,
but there are many instances where gains in overall CFM Flow
gain more HP at a slight decrease in CFM/Sq Inch when trying out
a larger valve.

to further improve VE, the speed, cfm per sq in of csa, velocity profile etc, all become as, or more important than total cfm.

Velocity FPS + Velocity Profile thru the Port, along with
overall Port Shape and correct CSA for the application,
are very important, as important as Total CFM

Too fast or too slow FPS hurts Torque and HP and RPM potential
regardless of FlowBench CFM Numbers.

The FlowBench tells you Flow CFM Numbers
and the FlowBench can also tell you many other things
while you are Flow Testing if you know what
to look for or how to measure it..like using a Pitot Probe
to measure Velocity Profile thru the Port.
Theres so much more a FlowBench can tell you
than just Flow CFM Numbers.

On the overall maximum Flow an Engine can use at any RPM,
in other words, "Flow Saturation" at a particular RPM,
you can use PipeMax's Piston CFM Demand Column's numbers
to see whats the maximum CFM an Engine will ever want or use
at a given RPM.

If your Heads Flow more than the Piston CFM Demand,
it will never use all of that Flow,
instead you will need to find a way to move Peak HP RPM higher
in an attempt to use all your Cylinder Head Flows.

[randy331]

As an example,
CFM per SqInch of Valve Area,
like a recent Thread about #781 BBC Heads,
i gain HP every time i go from 2.190 to 2.250 or especially 2.300 valves
even though the 2.190 valve might be at 79.64 CFM/Inch (300 CFM)
-VS- 2.300 at 77.0 CFM/Inch (320 CFM)

Same results in a bunch of different Head types,
like a series of tests with Vortec cast-iron SBC #906 castings
going in steps from stock OD to 2.020 then to 2.055 then to 2.080
the CFM per SqInch of Valve Area numbers will be declining but
the overall CFM will gain and so will HP.

That's the kind of answer I was looking for.
Larry, on the examples above, how much if any did it raise the rpm for maximum TQ, and HP?
If you were trying to gain HP, without raising the rpm of the engine, would you try to increase the cfm per sq in, in the port, or gain cfm with the larger valve like above, then lower rpm with a smaller cam?

Thanks Randy

[jeffmckc]

Randy You put it much better than I did, and that was the answer I was looking for too

maxracesoftware


On the overall maximum Flow an Engine can use at any RPM,
in other words, "Flow Saturation" at a particular RPM,
you can use PipeMax's Piston CFM Demand Column's numbers
to see whats the maximum CFM an Engine will ever want or use
at a given RPM.

If your Heads Flow more than the Piston CFM Demand,
it will never use all of that Flow,
instead you will need to find a way to move Peak HP RPM higher
in an attempt to use all your Cylinder Head Flows.




It seems I need to get that pipemax program back out, I know it does more than I understand.

I talked with Ed on the Phone and told him I did not have a good wording for my post, but Randy has worded it well. Thanks to him for putting it in the correct terms

[Bad95Gts]

When you lower the cfm per sq/inch you are lowering the velocity.
I guess i did not use the correct terminology?

Velocity FPS + Velocity Profile thru the Port, along with
overall Port Shape and correct CSA for the application,
are very important, as important as Total CFM

I adhere to this as well.
This is why I brought up velocity.
To me the cfm is an end result.

[maxracesoftware]

When you lower the cfm per sq/inch you are lowering the velocity.
I guess i did not use the correct terminology?

Velocity FPS + Velocity Profile thru the Port, along with
overall Port Shape and correct CSA for the application,
are very important, as important as Total CFM

I adhere to this as well.
This is why I brought up velocity.
To me the cfm is an end result.

You need to be very careful to differentiate
between Theoretical Calculated Velocity
and measured Velocity.

Even the measured Velocity with a tool such as a Pitot Probe
will be different from live Engine running conditions.

the Pitot will be more accurate than the theoretical calculated FPS.

long ago i posted Dyno and DragStrip ET results from
NHRA SS/IA Class SBC with 2 different #041x castings and
1 #462 casting.

the 2 #041x castings had identical Flow CFM Numbers
on Intake and Exhaust sides, same Port Volumes at around 165CC's
same Chamber volumes, same Flow Coefficients,
same Curtain Area Coefficents, etc.
and same "Theoretical FPS" based upon Port Volume + Port Length

The only major differences between these same #041x castings
were the internal Port shape and actual Pitot Probe FPS readings.

on the Dyno 1 pair of #041x Heads were approx +105 HP more
at 7500 RPM

So all the various Flow Coefficients didn't tell the entire Story
and neither were they controlling.

i can re-Post the Dyno results if you want ?
____________________________________________


More examples of "Flow Saturation"

a theoretical BBC at 500 cubic inches

around 5930 RPM a 500cid will be Flow Saturated at 361.3 CFM
or maybe up to 381.3 CFM as my FlowBench is conservative

at 5930 RPM point of Peak HP, suppose you had a 2.000" OD intake
valve that was at 115 CFM/SqInch..this equals 361.3 CFM

you then put another Cylinder Head on the Engine that has a
2.500" OD Intake valve at 115 CFM/SqInch which is 564.5 CFM
but at 5930 RPM all a 500cid Engine can effectively pump and use
thru Inertia + Wave Tuning is around 361.3 CFM.

Both the 2.000 and 2.500 OD Intake Flow same 115 CFM/SqInch
or for FPS , its just a easy matter of 2.4 times 115 to get FPS

115 CFM/SqInch times 2.4 = 276 FPS potential

So both pairs of Heads with the 2.000 and the 2.500
have the same 276 FPS Velocity and CFM/SqInch
yet at 5930 RPM the 2.500 Valve Head w/564.5 CFM will be too much Flow
and not cause enough Cylinder depression soon enough
and low enough...to create the necessary ram effect
at the intake valve closing point.

2.000"OD at 115 CFM/In = 361.3 CFM and 276 FPS velocity
361.3 CFM times .257 times 8 Cylinders= 742.8 HP typical potential

2.500"OD at 115 CFM/In = 564.5 CFM and 276 FPS velocity
564.5 CFM times .257 times 8 Cylinders= 1160.6 HP typical potential

1160.6 HP - 742.8 HP = 417.8 diff

if you have a Cylinder Head with a 2.500 OD Valve flowing 564.5 CFM
you need to find a way to cause Peak HP to occur at
9260 RPM or higher to take maximum adavantage of Flow CFM

500cid @ 9260 RPM is about Flow Saturated around 564.5 CFM
(or about 584.5 CFM depending on how conservative/liberal
your Bench is)


You couldn;t expect to successfully utilize a 564.5 CFM flowing Head
on a 500cid at only 5930 RPM..it would be definetly Flow Saturated
no matter what you did in terms of Tuned Lengths + CSA's

Vice/Versa same with 2.000"OD and 361.3 CFM trying to operate
at 9260 RPM successfully on a 500 cid.

Most of all the Professional Type relatively high RPM Engines
will close the Intake Valve @.050" in a relatively narrow event window
of between 60 to 80 degrees ABDC,
so this means to be highly succesful, the "Start" of the major cylinder
depression that causes the Ram Effect also has around a
20 degree critical span...too soon or too late a start,
and the timing of the ram effect and tuned wave is not as beneficial
at the Intake Valve closing point.

Too great a depression = equals greater pumping losses
too little not enough velocity and ram effect , VE% suffers.

(Speaking in terms of Naturally Aspirated, as Blowers/Turbos are a different density/VE% aspect )

[randy331]

You need to be very careful to differentiate
between Theoretical Calculated Velocity
and measured Velocity.

Even the measured Velocity with a tool such as a Pitot Probe
will be different from live Engine running conditions.

the Pitot will be more accurate than the theoretical calculated FPS

So the closer calculated average port velocities are, to actual measured velocitiy,(pitot probe) at any given point in the port the better?

Randy

[RL]

Another post by Larry might explain a little more

Quote (stevenford @ Jan. 25 2008,16:42)
I tried to work out a VE by looking at cyl head and piston demand table but I seem to have too much flow, my head flows 290cfm but he table says I need 282cfm for 135VE

I don't think this engine could have that much VE, 4cyl Toyota

Quote Maxrace
The Piston CFM Demand Column
is all the Engine's ever going to want at that RPM.

if your Heads flow more than Piston CFM Column,
you need to operate the Engine at a much higher
RPM Range to take full advantage of Flow CFM.

i would never set VE% higher than 125.0% when
beginning to design an Engine.

i've just recently changed VE% recommendations in
PipeMax a few weeks ago due to more Data gathered from
Users...like a sort of National Average.

1st Section
Instead of 115.0% VE for ProEngine,
i'd start off with 110.0% and work upwards

2nd Section
Instead of 104% VE ...i'd start off at 100.0VE% first.

And i left the 3rd section as it was at 95.0% VE

----------------------------------------


Just about all the Record setting Engines i've seen or built
or Ported Heads for...will come very close to using what the
Heads FlowTest on a FlowBench, allowing for Flow CFM losses
from Carb + Manifold attached .

But when there's a bad combination or other factors like
Choke Areas or Tuned Length problems,
then PipeMax will calculate it only takes for example
300 CFM to create the HP you've made on the Dyno,
yet your Heads flow 320 or 340 CFM or so.

All the great Engine Combos i've seen that had no
outstanding problems will come very close
to making correct HP for Head Flow CFM.

Theres a few exceptions like a completely all aluminum
engine with Block and Heads.
The combination of aluminum Block + aluminum Heads
"Trend" towards making much less HP per CFM.


Alum Heads on a cast-iron block make much more HP

cast-iron heads on cast iron Blocks a little more

cast-iron heads + cast iron blocks running without
any water inside, for very short DragStrip tests
have made the most HP for Flow CFM i've seen,
as well as very high Piston Speeds will make more
HP per CFM of Flow .

If there are no severe Choke areas,
very high piston speeds will make more HP per CFM,
although they will not make the greatest HP per CID Ratio.


A NHRA ProStock 500cid will make
outstanding HP per CID and a great Flow to HP Ratio
but
a 632cid or larger similar Engine with higher Piston Speeds
and more Stroke,and a worse Rod Ratio
will make more HP per CFM of Flow
and worse HP/CID Ratio.
The Vac-Pump will cancel out the short rod ratio.

The 1st tip-off there's something wrong in your
Engine Combination is if you are not using most
of what your Cylinder Heads Flow.

[jeffmckc]

This is now answering what I thought I had ask, very good information and lots to think about.