I am beginning to think that the question asked was not what was intended.

RACE ON!!![/QUOTE]

...I think he's still trying to figure out how much power he "left on the table"... and I'm starting to think he's trying to dazzle us with fancy footwork.

 

...I think he's still trying to figure out how much power he "left on the table"... and I'm starting to think he's trying to dazzle us with fancy footwork.


[/QUOTE]

I am not trying to dazzle anyone. I asked a question and got responses the veer off into other realms.

 

Gotcha. I tired to keep it as non specific as possible to try to get a handle WHY everyone is so wrapped up about CFM. I was intentionally non specific.

I understand your position is 4%. That the correlation is liner.

So on a 450HP CHP motor, you're getting about 20HP.

Do I have that correct? Is it really that simple?

Right, hence covers both dimishing returns and greater returns on the bottom end.
I may not have asked it right, see above.

 

Your only at 24.26 posts per day. I bet 23 of those are about cylinder heads and flow etc......

I had to when you mentioned the 421.


Your motor is an airpump. Is it making sense now finally?

 

...I think he's still trying to figure out how much power he "left on the table"... and I'm starting to think he's trying to dazzle us with fancy footwork.


[/QUOTE]On the former, possibly. On the latter, not capable.




What does, "That the correlation is liner." mean? The 4% is the simple answer to the question as asked, but not as being answered by most. Others are reading into your question and answering more than you wrote into it. The more I read your responses, the less I think you know about what you are asking.



As stated in the original question, yes. But even the way you phrase, "Is it really that simple?" makes me think that the "IT" in that question is different in your mind now, than as expressed in the question back in post #1.

You don't understand the basics of the subject of your own questions. Therefore the answers aren't making sense to you. And that is one reason why the answers are all over the place. The answers can't make a lot of sense if the questions don't. Your follow up questions reveal your lack of understanding. You need some basics in fluid dynamics before you can even fully grasp the questions, let alone the answers. You lost your cool when I made that suggestion in a different thread on a related subject, and I apologize, but it doesn't appear you've learned much in the interim.

RACE ON!!!

 

That would be almost as irritating as someone that had 6,632 (3.80 posts per day) hounding everyone that posted any sort of a modification, including an after market air cleaner element, what his flywheel horse power and torque numbers were, his rear wheel horse power and torque numbers, and his 1/4 mile ET and mph. We all have our crosses to bear, right, ricky ticky?

RACE ON!!!

 

this might be of to interest you:
http://www.epi-eng.com/ET-VolEff.htm

 

 

now THAT is just flat-out beautiful

 

On the former, possibly. On the latter, not capable.[/quote]

don't care.


"IT" means if you have 4% more air, you have 4% more power. If I knew everything, I'd be...oh never mind.

I probably have to go back and re read WTF was said.

Same it, see above. Increase flow by X means more power Y. What is the relationship. That is what I'm trying to understand.
I understand it, and frankly when I am stuck behind the desk I tend to multitask while I post. That's a new way of saying not really paying attention. I am ALWAYS learning.

 

Most of those posts are in PRC. You should stick your head in there, we'd have a ball.

See, at least I'm trying to learn something here, I simply don't take a magazine article and shoot my mouth off like I'm some kind of expert. I try to learn by reading, posting, reading some more, and googling. When I post something I like to have a clue either through personal experience or detailed research. That includes technical documentation. I simply don't lap up the popular opinion and spout it like gospel having no idea why. So when some internet ball swinger asks me to back it up, I can. See where I'm going with this... Your contributions to the thread has been evidence of my point.

 

Hey CFI, others, I realize I'm probably frustrating you, however like I said above, your responses probably deserve more attention than I give them while at work. I apologize for that. I will go back and read the entire thread again, the intelligent responses anyway...

 

Thanks, will do.

 

The problem here, other than the interjections from some, is that the question you asked is/was not real defined the way some of us read it.

Furthermore, its not a perfect world/scenerio to say that you will gain or loss X amount with the CFM change you mentioned. However a rule of thumb is 2hp for every CFM - this seems to be widely used, but again its NOT perfect nor always true.

As I pointed out you may be able to get more power with less actual CFM if the velocity is right/better for your particular application.

Here you go istraight from Reher-Morrison Racing and it mentions many of the things I alluded to in my responses: Its GOOD READING!

===

Our era is often referred to as the Information Age, but not all of the available information is necessarily useful. I am beginning to think that flow benches should be labeled with a government warning: "Caution! Excessive reliance on flow numbers may be harmful to your engine!"

I'm kidding, of course. Used wisely, a flow bench can be a useful tool in engine development, just like a timing light or a dynamometer. Unfortunately, some racers believe that a flow bench is the ultimate answer machine. When the subject is cylinder heads, the four words I dread to hear are, "What do they flow?" Novice racers and magazine writers share a fixation about airflow. The mistaken belief that "more is better" is often the false assumption that produces an underperforming engine.

I learned this lesson myself when my partners Buddy Morrison and Lee Shepherd built our first flow bench in the mid-'70s. It was a great contraption that could just about suck the windows out of our rented shop on Arkansas Lane. While this homebuilt test bench boosted our racing program, it certainly didn't make us engine experts overnight - even though we initially thought we had found the key to the vault of knowledge.

We had been racing 287-cubic-inch small-blocks in various Modified and Comp classes before we decided to make the move to Pro Stock with a 331ci engine. (Students of Pro Stock history will recall that the '70s was the era of weight breaks for various engine and chassis combinations.) We were determined to be "scientific" in our approach, and reasoned that a 15 percent increase in engine displacement demanded a 15 percent increase in airflow. We dutifully enlarged the ports, increased the valve diameters, and hit our airflow targets. We set off to conquer the world of Pro Stock - but our pride and joy was a dog.
After struggling to even qualify in our initial outings, we pulled an old pair of Modified heads off the shelf. Lee worked on the ports for an afternoon, we bolted them on our Pro Stock short-block, and we qualified fifth at Englishtown in our next race.

If you went strictly by the flow numbers, those heads would hardly enough air to satisfy a respectable big-inch bracket racing engine - and yet they were magic on the race track. That was when I realized that cfm isn't everything. It's a lesson that I have seen repeated countless times in the last 25 years.

A flow bench measures air movement in a very rudimentary way - steady-state flow at a constant depression (vacuum). Obviously the conditions that exist inside a running engine are quite different. The flow bench can't simulate the effects of the pistons going up and down, the reversion pulses as the valves open and close, the sonic waves that resonate inside the runners, the inertia of the fuel droplets, and all of the other phenomena that influence engine performance in the real world. When you flow test a cylinder head, you are simply measuring how far you can move the liquid in a manometer.

The bigger you make a port, the more it flows. That's hardly shocking news. Bolt a sewer pipe onto a flow bench and it will generate terrific flow numbers. So should we use ports as big as sewer pipes on our race cars? The flow bench says we should - the time slip says something completely different.

If airflow were everything, we would all use the longest duration camshafts we could find - after all, more duration means more flow. In fact we know that there is a finite limit to how long the valves can be open before performance
suffers. That is because the valve events have to be in harmony with the rest of the engine.

The same principle applies to cylinder heads. Simple airflow capacity should never be the first consideration in evaluating cylinder heads. Characteristics that are far more important include air speed, port cross section, port volume and shape, and the relationship between the size of the throat and the valve seat. If these attributes are wrong, you can work forever on the flow bench and not overcome the fundamental flaws.

Here is a do-it-yourself example: Turn on a garden hose and the water will dribble out a couple of feet. Now put a nozzle on the hose and the water will spray across your backyard. The water pressure and volume haven't changed, but the velocity has increased dramatically. Now think about the air and fuel going into your engine's cylinders. Which would you prefer: slow and lazy or fast and responsive?

An engineer will tell you that an engine requires a prescribed amount of air and fuel to produce "X" horsepower. In a perfect world, that may be true - but we race with imperfect engines. The shape and cross-sectional area of the runners are absolutely critical to performance. For example, I have two sets of Pro Stock cylinder heads that produce nearly identical flow numbers, yet one pair produces nearly 150 more horsepower at 9,200 rpm than the other. The flow bench can't tell the difference between them, but the engine certainly can.

There are software programs that claim to be able to predict an engine's performance based on airflow numbers. Unfortunately, a critical shortcoming of many of these programs is that they are based on inaccurate information or false assumptions. A computer is an excellent calculator, but it is not an experienced engine builder. The software doesn't know whether a port's short-turn radius is shaped properly, whether the flow is turbulent at critical valve lifts, or whether the flame speed is fast enough. Racers have a tendency to believe that computers are infallible, so they accept the software's solutions as gospel, when in fact they may be badly flawed.

Textbooks would lead you to believe that an exhaust to intake flow ratio of 80 percent is ideal - yet a typical Pro Stock head has exhaust ports that flow less than 60 percent of the intake runners. You can improve the exhaust flow
tremendously with about 40 minutes of work with a hand grinder - but the supposed improvements will just about kill the engine's on-track performance. I know because I've been there.

We have also learned that low-lift flow (meaning anything below .400-inch valve lift in a Pro Stock engine with a .900-inch lift camshaft) is relatively unimportant. Think about the valve events in a racing engine: From the point when the valve first moves off its seat until it reaches mid-lift, the piston is either going the wrong way (that is, it is rising in the cylinder) or it's parked near TDC. The piston doesn't begin to move away from the combustion chamber with enough velocity to lower the pressure in the cylinder until the valve is nearly halfway open. Consequently it is high-lift flow that really matters in a drag racing engine.

The shape of the combustion chamber also has a significant impact on performance. A conventional chamber with deep reliefs around the valve seats and a relatively flat valve seat angle can produce terrific flow at .200 to .300-inch valve lift. Today a state-of-the-art chamber typically has 55-degree valve seats and steep walls that guide the air/fuel mixture into the cylinder to enhance high-lift flow.

This doesn't mean that every racer needs state-of-the-art Pro Stock cylinder heads - along with the high maintenance they require. The heads have to match the application. Conventional combustion chambers and 45-degree valve seats are just fine for a dependable, low-maintenance racing engine that will run a full season between overhauls.

The classic Hemi combustion chamber is capable of producing impressive flow figures, but it's not going to make impressive power. Engine technology in all forms of motorsports is converging around smaller, high-efficiency combustion chamber designs. You can see the result in lower brake specific fuel consumption (BSFC) numbers, which indicate improved engine efficiency. Twenty years ago, a racing engine with a .48 BSFC was considered very good; today's competition engines produce BSFC numbers in the neighborhood of .35. This means that a given quantity of fuel is being atomized and burned more effectively to produce more power. A cylinder head's combustion efficiency can't be measured on a flow bench, yet it has a huge impact on performance.

I am not against flow benches; in fact, we use computerized flow benches daily at Reher-Morrison Racing Engines. What I am against is over reliance on flow numbers as the primary measurement of a cylinder head's performance. A flow bench is a valuable tool that can help a racer fine tune a combination - but it is not the ultimate authority.

=======
As I said, there are MANY factors that must be considered before you can answer even the "simple" question you asked.

These are the questions that increase EVERYONE's IQ - there is nobody that should be bashing you or giving you a hard time for asking such an interesting question that brings about good conversation.

 

That was a FANTASTIC article and seems to validate my beliefs. (which is only important to me) In choosing parts, all and any, I spoke to many engine builders and engineers who provided a lot of opinions. Based on their input, I made choices. Hearing all the noise about flow flow flow I wanted to have a sanity check to ensure the choices I made were the choices I should have made.

The article articulates what I was trying to say over and over and over, just not quite as eloquently.

So although there may be a 2HP per CFM "assumption" given other factors, even a higher CFM head could reduce performance. A smaller flowing head with a good overall design will outperform a higher flow head. That seems consistent with the information I got from CFI-EFI and a number of engine builders. There are elements of design that are simply more important than flow. The 2HP per CFM is best case if I understand right.

I had more than one engine builder tell me they were making "crazy power" (quote from one of them) with Brodix Race Rites. Then I look at guys like ol'RJ right here on Corvette forum who used AFR then went to Dart and made a whole bunch more power, with lower flow numbers, and I wanted to understand WHY....

Seems to me the conclusion of the article, if I can Cliff Note it, is that only a real know nothing amature hack would use flow as a single benchmark of performance. Anyone with 1/2 a brain that does this for a living knows there's more to it.

Since there seems to be a lot of confusion, and very little in the way of answers, I thought I'd throw this out there. Sorry if it drove people nuts, however, I think it was important. Just look at the views vs. posts numbers on this thread and you know people are interested. There is nothing wrong with trying to educate a population on the choices they make, hell, I'd even say on a forum like this it is our responsibility to do it. If this thread inspired just one person to hop on the internet and learn a little more and assisted in helping them making informed decisions about their build, the thread was a success. Too many people do the work and end up unhappy with the results.

 

I could probably buy into your last post except, unlike some, i've read the 8 pages of "AFR 195-180" here on page 2, and the 7 page rant on the other Forum, about the ones on here. Now I wonder when you ask a question, if you're really seeking an answer, or just "pokeing the cat" as you said.

 

I don't pretend to know everything. I am trying to understand to verify that the time and effort I put into my original research verifies my conclusions.

This thread has done that.

On the up side, every day, every minute is an opportunity to learn something. I don't care if it's a cab driver or doctor, there's always something to learn from people. Forums such as these exist for exactly that reason, and I'm glad they do. The only issue is that when people take what they hear on the interweb as gospel, and try to spread that gospel, is a dis service to the online community. I wanted to know once and for all if I were full of crap. I think that's a fairly honorable position, don't you. Better than having concepts and ideas based on nothing and promoting them to other poor slobs, wouldn't you say. Other than verifying my previous research, I have no interest in outcome other than truth, weather it supports my position or not. I guess that's what makes me different.

I have gotten a number of PMs thanking me for starting this thread, a lot of people wanted to know. I am glad I did even if it annoys you.