Head flow for 98”

[Johnwesley]

        The topic of conversation is is there a flow velocity place that is needed to perform well and after that number not really much difference? for example if a head with 1.9 intake flows 250@28 and another has a 2.0 and flows 300@28 on a little 98" would the extra 50cfm make anymore power? Just for details, say you have a 98" with  T-man 625 is the extra flow helping as long as the Tb and exhaust isn't the bottle neck?  If I am missing a critical piece of the puzzle point it out. Of course I could be all wet as normal.

[Johnwesley]

Could it be that if a head flows more air then you could get by with a smaller cam? Since the head could allow more air in to the cylinder you wouldn't need to keep the valve open as long to make power?

[Don D]

A working IC engine does not operate at 28" wc. You need enough airflow to support the pumps demand. The heads influence is only one of the factors between the air inlet and the tip of the tailpipe end.

[Hillside Motorcycle]

        The topic of conversation is is there a flow velocity place that is needed to perform well and after that number not really much difference? for example if a head with 1.9 intake flows 250@28 and another has a 2.0 and flows 300@28 on a little 98" would the extra 50cfm make anymore power? Just for details, say you have a 98" with  T-man 625 is the extra flow helping as long as the Tb and exhaust isn't the bottle neck?  If I am missing a critical piece of the puzzle point it out. Of course I could be all wet as normal.

50 cubic feet per minute is a large increase, and the average from .100" to say .650" is probably huge.
Yes, there will be increases.

[Don D]

I remember learning how to read when I was a kid. Car and driver and hot rod were where I spent my grass mowing money. They made all sorts of statements like "..a bunch of power.." and such. As I got older I learned they were just advertising for their vendors.

The larger you open the barn door on the heads the more the flow on the flow bench will increase. Demand provides the decision where to stop so that velocity still remains reasonable. Intended rpm, volumetric efficiency,  and cubic inches figure heavily into the equation. Bottom line a "bunch" more airflow may = a soggy mess hard to tune and low on performance the average street rider can feel. Torque curve, the shape and aggregate production of torque where we ride is important.

[RTMike]

  And Don don't forget the 3/4 and full race cams everyone talked about then.

[Brew61]

And Don don't forget the 3/4 and full race cams everyone talked about then.

Wow 3/4 race cam  Have not heard that in a very long time!

Bruce

[Don D]

Hard lessons learned, the general kinetics 304deg cam in a stock 2 brl 265 v8 in a 55 Chevy wagon. What a dog. I dont know what  race that was but I couldn't wait to put the stock cam back in

[rigidthumper]

Buddy put a Woods 999 cam in a 103 with SE MVA heads "cuz they was the best".
Whatta 

[Coff 06]

Pulled the same stupid thing.Put a 340/600 cam in a stock 71 454 with 8.5/1 compression and a tunnel ram with 2/4s.It would finally run if you had enough hiway      Coff 06

[rking1550]

I remember the first small block Chevy I built.  Did the same thing way back then I do with a Harley motor. Added a lot of compression bored & 12.5 pistons. Don't remember the cam,  but it ran well on airplane fuel. Lol
Guess I learned at a early age motors / cams respond to compression. Lol

[Coff 06]

After my stupidity I built a 12.5/1 1k HP 468" out of that 454.Live and learn  :emoGroan. Coff 06

[dsvracer]

there is a formula on how much air a motor can use. if you want to find out how much air a motor uses the formula is
rpm X  (ci on one cylinder) divided by 2000 equals amount of air needed for a 95" motor to make power to 6,000 rpm.
example:  6000 x 47.5 divided by 2000= 142.5 cfm.  if you wanted power up to 6500 then use the same formula. i guess the simple answer to your question is yes more air will make more power but it will be at the top of the power curve, if you want to rev the motor that high.

[Admiral Akbar]

there is a formula on how much air a motor can use. if you want to find out how much air a motor uses the formula is
rpm X  (ci on one cylinder) divided by 2000 equals amount of air needed for a 95" motor to make power to 6,000 rpm.
example:  6000 x 47.5 divided by 2000= 142.5 cfm.  if you wanted power up to 6500 then use the same formula. i guess the simple answer to your question is yes more air will make more power but it will be at the top of the power curve, if you want to rev the motor that high.

I think you need a pressure for the flow. Looks like 10"h2o.

[Don D]

√ of 28 ÷ 10 = conversion from 10" to 28" wc. Use 1.4hp / CFM and you will be ballpark.

[Hillside Motorcycle]

28" used here on our 600 SuperFlow.
10" on the SuperFLow 120....can't have too many flow benches....

[Johnwesley]

there is a formula on how much air a motor can use. if you want to find out how much air a motor uses the formula is
rpm X  (ci on one cylinder) divided by 2000 equals amount of air needed for a 95" motor to make power to 6,000 rpm.
example:  6000 x 47.5 divided by 2000= 142.5 cfm.  if you wanted power up to 6500 then use the same formula. i guess the simple answer to your question is yes more air will make more power but it will be at the top of the power curve, if you want to rev the motor that high.

so you are saying that if a head is already flowing 150cfm @ 10" then flowing any more is of no real advantage on a 95" with peak Hp at 5500. Its just flow that will never be realized since the motor cannot process any more air.

[Don D]

Somewhere in this discussion is a head porter that did the original heads, basics. Also I guess that there is another that is selling an "upgrade"
They would have to be the one to prove the worth. A 2" valve and a port proportional to that which makes a real 300 cfm @ 28" is big for a 98" motor unless you have 6500 rpm in your sights often. If I was looking to run that cam I would be using a 1.95" intake or if a sacrifice of 2 or 3 horsepower was acceptable a 1.9 intake and those still flow 280 and the 1.95 flow 295.

[Hillside Motorcycle]

Well, when one does it for a living everyday, for over 30 plus years, one see's things, others do not.

[dsvracer]

so you are saying that if a head is already flowing 150cfm @ 10" then flowing any more is of no real advantage on a 95" with peak Hp at 5500. Its just flow that will never be realized since the motor cannot process any more air.

that is what i am saying.

not sure what the point don is trying to make, sounds like jibberish.
scott,  please tell us about the things you and no one else can see.  what !!!!!!!!!

[Don D]

Simple, velocity matters.
Cross section matters
Open the barn door too far and the flow bench loves it and rewards with big flow numbers but that is no guarantee of a build that actually will function well or tune easily.

[joes124]

...and don't overlook the "RV" cam 

[Johnwesley]

Somewhere in this discussion is a head porter that did the original heads, basics. Also I guess that there is another that is selling an "upgrade"
They would have to be the one to prove the worth. A 2" valve and a port proportional to that which makes a real 300 cfm @ 28" is big for a 98" motor unless you have 6500 rpm in your sights often. If I was looking to run that cam I would be using a 1.95" intake or if a sacrifice of 2 or 3 horsepower was acceptable a 1.9 intake and those still flow 280 and the 1.95 flow 295.

In honesty I have been listening to a build/ porter talk about his philosophy on head flow cams and and the like. He seems extreme on all accounts to me, but then I really don't know anything. So I wanted to hear some people's thoughts that do this thing for a living. Don you have heads that flow different numbers for different builds and most offer different levels, based on needs. Yet others say build the head the "best" you can, flowing as much as possible with the proper velocity. Then let the cam make power in the range you want. Yet another says the more air, with proper velocity, you can flow the smaller duration cam you need to run to make power. With all this talk from experts comes the question of Head flow how much can a smaller engine really take advantage of. I used 95" since it's a smaller motor and close to what I have. 95"-98" would be the range. For me personally I have a buddy I ride with a lot and have easily walked off from him, but he got a new bike and we are really neck to neck now, but once more stuff comes up for the bike that will all change. If there is much of an advantage to more flow and caming to match the head, then I may pursue that to keep my advantage. 

[1workinman]

Could it be that if a head flows more air then you could get by with a smaller cam? Since the head could allow more air in to the cylinder you wouldn't need to keep the valve open as long to make power?

Not 100 percent certain but I heard that a really good set of heads can make a cam carry out further. Of course its the total package  .

[kd]

Could it be that if a head flows more air then you could get by with a smaller cam? Since the head could allow more air in to the cylinder you wouldn't need to keep the valve open as long to make power?

Not 100 percent certain but I heard that a really good set of heads can make a cam carry out further. Of course its the total package  .

But that would be at sacrifice to the left side and lower end torque.  It's torque that gets the load moving.  Here's a reasonable explanation of the relationship between Torque and horsepower and how they work together. I know it's about cages but the relationship is the same.

https://www.autogravity.com/autogravitas/cars/horsepower-vs-torque-getting-speed#important

[doctorevil]

Over the years i have been guilty sacrificing the left side. not as quick but damn those bikes were fast

[TorQuePimp]

Simple, velocity matters.
Cross section matters
Open the barn door too far and the flow bench loves it and rewards with big flow numbers but that is no guarantee of a build that actually will function well or tune easily.

Velocity is the key......airflow/raw numbers don't mean much

[No Cents]

  what will wet flowing tell you that an air flow bench doesn't?

[Admiral Akbar]

Could it be that if a head flows more air then you could get by with a smaller cam? Since the head could allow more air in to the cylinder you wouldn't need to keep the valve open as long to make power?

Not 100 percent certain but I heard that a really good set of heads can make a cam carry out further. Of course its the total package  .

But that would be at sacrifice to the left side and lower end torque.  It's torque that gets the load moving.  Here's a reasonable explanation of the relationship between Torque and horsepower and how they work together. I know it's about cages but the relationship is the same.

https://www.autogravity.com/autogravitas/cars/horsepower-vs-torque-getting-speed#important

Got to love that stuff for the folklore,  not for any reality.   

"Horsepower is torque measured over time and distance."  shows that the writer really don't understand or he is a really crappy writer.
 

[TorQuePimp]

  what will wet flowing tell you that an air flow bench doesn't?

Wet flow is a development tool

Used in developing the entire induction system

The port is basically painted white and a purple/ blue fluid is drawn or blown thru

Areas that are stained need enlarged or reshaped or both

Staining in the chamber also indicates different issues

There aren't many around and even fewer people who really know how to use one

Matt Chalmers took a TC head down to mondello when they were still in business and what a Harley head should be and what most are, are very different things

[No Cents]

  you are correct John...I just wondered if anyone else knew what a wet flow bench would show you vs an air flow bench. I've read a few articles about Joe Mondello and all his testing he did with one. Joe was a man with vision. He found like you stated...when you add a dyed fluid into the mix, representing what the air and fuel mixture is actually doing...you end up with a totally different view than what an air flow bench shows you. It changed the whole ball game in what we think we knew. The ability to actually be able to see what is happening inside the intake and head ports is data that is useful to help make improvements in the needed areas. If you go into the top Nascar engine building shops...you will find a wet flow bench being used for testing and future design changes.

[dirt1954]

Joe started a head porting school in Pasa Robles, Ca. in the late 90's. His favorite was Olds 442 stuff-dabbled in HD. Later moved his shop to somewhere on the east coast-lost track of him. He had a good head for flow, and started some of the cutting edge technology. Glad to see some (Ray) still remember. I have not heard anything about Short Block Charlie, somewhere in Arizona I believe-another guy with good ideas-not given much credit.

[SP33DY]

Short Block Charlie posts some good info on You Tube. Search for charlie lawlor

[Hossamania]

He pops in here occasionally.