why is everyone so hung up up on "CFM"?? - Honda-Tech

miller · 11-19-2006, 10:38 PM

Well recently i have had an over abundance of customers who have a very very basic knowledge of the workings of an i.c.e. Yet they are all hung up on this "CFM" thing when it comes to heads.

There seems to be this big myth here on the internet that cfm will automatically give you xxxx amount of power and im tired of hearing about it. I have personally tested engines on several occasions where i will have head (a) and head (b) and head (a) will flow xx amount more cfm then head (b). Yet head (b) kicks the shit out of head (a) on the dyno and on the track.

What im trying to get at is there is alot more that goes into designing and porting a head then just getting the biggest port or the most cfm out of it. I very very rarely hear anybody discuss the other things going on like velocity, port volume, port shape and what about the ports cross section? I dont know if i have ever seen anybody discuss the effects of the tulip on the valve and what the cause and effect of that would be? What about the proportionate relationship between the
size of the throat and the valve seat?

Im sorry for my rant im just sick of people thinking that the flowbench is the end all be all of what a head is.

Combustion Contraption · 11-19-2006, 10:45 PM

Tulip'ed valves usually flow well on heads where the throat isnt so 'vertical'.

As far as velocity goes, its tougher for the average joe to understand/quantify the importance. I look at CFM like some people look at dyno #'s. Everyone just wants that big peak #.

As far as your comment on seat/throat relationship, ive always felt throat size dictated mid range power.

b19coupe · 11-19-2006, 10:51 PM

The flowbench is not the be all and end all, but it can often show the potential of a head. I had two heads-one done by x and another done by y. Head x flowed 300 cfm @ 0.500" and head y flowed 280 cfm @ 0.500". Head x made 12 more HP after just bolting it on in place of head y.

miller · 11-19-2006, 10:56 PM

but see this is the big misconseption that people have, they think bigger numbers in turn are going to always equal a greater result.

i understand where you are coming from with you dyno analogy but even if you have good flow numbers across the board that dosent mean your gonna make the power.

why not just make the damn port as big as you can and stick the biggest valve in it all the time and call it a day. i mean it ill probably flow great on the bench but not do shit on the dyno or track.

im sorry im tried and cranky, i had one of those "know it all" customers arguing with me tonight about something he read online, lol

Combustion Contraption · 11-19-2006, 10:57 PM

Quote:

Originally Posted by b19coupe

The flowbench is not the be all and end all, but it can often show the potential of a head. I had two heads-one done by x and another done by y. Head x flowed 300 cfm @ 0.500" and head y flowed 280 cfm @ 0.500". Head x made 12 more HP after just bolting it on in place of head y.

damn you and your empirical evidance.

Unfortunately i can label the variables x and y but choose not to.

miller · 11-19-2006, 11:01 PM

but like i said before i have seen the opposite effects on several occasions, when trying different approaches.

b19coupe · 11-20-2006, 07:48 AM

Quote:

Originally Posted by miller

I had one of those "know it all" customers arguing with me tonight about something he read online, lol

Those are the kind of customers that it is better to pass on. You can never make them happy, and the experience dealing with them makes you want to tear your hair out. I understand where you are coming from, but flow numbers are all most lay people have to go on.

miller · 11-20-2006, 08:01 AM

Quote:

Originally Posted by b19coupe

Those are the kind of customers that it is better to pass on. You can never make them happy, and the experience dealing with them makes you want to tear your hair out. I understand where you are coming from, but flow numbers are all most lay people have to go on.

lol, that is 99% of the sport compact community.

vtecvoodoo · 11-20-2006, 09:04 AM

CFM is the new buzzword replacing spring rates. Everybody needs to know spring rates these days even though nobody knows how to apply them at all

MAX_CFM · 11-20-2006, 09:13 AM

IF done " right" more CFM = more power

The Destroyer · 11-20-2006, 09:14 AM

Instead of ranting about the customer can you inform the know nothings what these are and how they affect power?

Velocity:
Port volume:
Port shape:
Port cross section:

miller · 11-20-2006, 09:36 AM

Quote:

Originally Posted by MAX_CFM

IF done " right" more CFM = more power

see that is the issue, doing it "right".

brad, how many heads have you seen ported wrong and just flat out ****ed up? i have seen more bad ported heads the i could have ever wished to.

SIred91 · 11-20-2006, 09:46 AM

Finally, some people talking about some tech issues that are truly left up to myth as far as the average street ricer tuner goes. What about the quench sizes in relation to the amount of flow the head provides? Big valves, ported, polished blah blah, but at the atomization of the mixture, can the amount that the head lets in be overkill unless boosted? ie....too much fuel and or air regardless of tune will just be wasted? I dont know, its just a question, these are things I'm trying to learn.
I could be just another dumbass when it comes down to the physics.

Master of the Universe · 11-20-2006, 09:56 AM

Same reason why everybody want's 200whp from their 1.5L. They are consumers of a number.

But more flow = more peak hp potential. That is for sure.

JerseySiPOS · 11-20-2006, 10:36 AM

Quote:

Originally Posted by Don Lackey

Same reason why everybody want's 200whp from their 1.5L. They are consumers of a number.

But more flow = more peak hp potential. That is for sure.

So the engine in it's original form and original flow characteristics, can technically make the most cylinder pressure in a given rpm range? So would you aim to make more cylinder pressure at a higher engine speed, or is that asking for too much, rather just trying to keep the torque curve as flat and long as possible, compared to the original design? Trying to put it into words the best i can...

Combustion Contraption · 11-20-2006, 10:37 AM

Quote:

Originally Posted by Don Lackey

Same reason why everybody want's 200whp from their 1.5L. They are consumers of a number.

But more flow = more peak hp potential. That is for sure.

DonF · 11-20-2006, 11:11 AM

There are some posts on here about that, but most ignore them. There are 3 races the flow bench race, the BHP race, and the race track race. Only one matters.

Master of the Universe · 11-20-2006, 11:15 AM

Quote:

Originally Posted by JerseySiPOS

So the engine in it's original form and original flow characteristics, can technically make the most cylinder pressure in a given rpm range? So would you aim to make more cylinder pressure at a higher engine speed, or is that asking for too much, rather just trying to keep the torque curve as flat and long as possible, compared to the original design? Trying to put it into words the best i can...

I am not really aiming at anything other than that is my answer to the posted question, "why is everyone so hung up up on "CFM"?? ". It's more psychology than engine building.

If you want to go fast you build the engine to have the highest average hp over the rpm range that the motor sees during the gear changes. But if building the highest average HP on a 1.8L involves only making 199.8whp peak you'll be out of the business of selling to the general public.

Master of the Universe · 11-20-2006, 11:19 AM

Quote:

Originally Posted by DonF

There are some posts on here about that, but most ignore them. There are 3 races the flow bench race, the BHP race, and the race track race. Only one matters.

The BHP race

. Who really cares if you can't win at the track. At least you have a big dyno sheet.

ImportechPerformance · 11-20-2006, 11:40 AM

miller · 11-20-2006, 12:29 PM

Quote:

Originally Posted by Don Lackey

Same reason why everybody want's 200whp from their 1.5L. They are consumers of a number.

But more flow = more peak hp potential. That is for sure.

yes it will have the potential to make more power if everything else is right. of course more cfm will = more power if it is done the right way.

I have seen alot of heads of late that flow these great numbers but dont do shit on the dyno or track. Like i stated earlier people live and dye by the flow numbers as if it is the bible. They just dont understand that there is alot more that goes into designing a port then just the overall flow numbers.

miller · 11-20-2006, 12:31 PM

Quote:

Originally Posted by Don Lackey

The BHP race

. Who really cares if you can't win at the track. At least you have a big dyno sheet.

exactly how most people look at things

Suzukii · 11-20-2006, 12:42 PM

There are some engine simulation software available that can predict within a few hp of the eventual output. CFM is integral part of the equation. But like everyone says its peak numbers. For race use, its the effective RPMs that helps to win the race not just the peak number.

Anyone here uses Ricardo wave?

11-19-2006, 10:38 PM	#1
miller H-T Sponsor Join Date: Dec 2001 Location: long island, ny, united states Posts: 10,673	why is everyone so hung up up on "CFM"?? Well recently i have had an over abundance of customers who have a very very basic knowledge of the workings of an i.c.e. Yet they are all hung up on this "CFM" thing when it comes to heads. There seems to be this big myth here on the internet that cfm will automatically give you xxxx amount of power and im tired of hearing about it. I have personally tested engines on several occasions where i will have head (a) and head (b) and head (a) will flow xx amount more cfm then head (b). Yet head (b) kicks the shit out of head (a) on the dyno and on the track. What im trying to get at is there is alot more that goes into designing and porting a head then just getting the biggest port or the most cfm out of it. I very very rarely hear anybody discuss the other things going on like velocity, port volume, port shape and what about the ports cross section? I dont know if i have ever seen anybody discuss the effects of the tulip on the valve and what the cause and effect of that would be? What about the proportionate relationship between the size of the throat and the valve seat? Im sorry for my rant im just sick of people thinking that the flowbench is the end all be all of what a head is. __________________ www.NRGtechracing.com my car isnt fast enough to put the times in my signature......

11-19-2006, 10:45 PM	#2
Combustion Contraption Senior Member Join Date: Jan 2003 Location: So Cal Posts: 8,534	Tulip'ed valves usually flow well on heads where the throat isnt so 'vertical'. As far as velocity goes, its tougher for the average joe to understand/quantify the importance. I look at CFM like some people look at dyno #'s. Everyone just wants that big peak #. As far as your comment on seat/throat relationship, ive always felt throat size dictated mid range power. __________________ EARL LASKEY, YOU WILL BE MISSED CCCylinderheads.com Check out the INDUCTION SPECIAL Matco Doublebay Toolbox FOR SALE Click Here!

11-19-2006, 10:51 PM	#3
b19coupe Senior Member Join Date: Mar 2002 Location: Southern, California, U.S.A. Posts: 9,299	Re: why is everyone so hung up up on "CFM"?? (miller) The flowbench is not the be all and end all, but it can often show the potential of a head. I had two heads-one done by x and another done by y. Head x flowed 300 cfm @ 0.500" and head y flowed 280 cfm @ 0.500". Head x made 12 more HP after just bolting it on in place of head y. __________________ C.A.T.

11-19-2006, 10:56 PM	#4
miller H-T Sponsor Join Date: Dec 2001 Location: long island, ny, united states Posts: 10,673	Re: (Combustion Contraption) but see this is the big misconseption that people have, they think bigger numbers in turn are going to always equal a greater result. i understand where you are coming from with you dyno analogy but even if you have good flow numbers across the board that dosent mean your gonna make the power. why not just make the damn port as big as you can and stick the biggest valve in it all the time and call it a day. i mean it ill probably flow great on the bench but not do shit on the dyno or track. im sorry im tried and cranky, i had one of those "know it all" customers arguing with me tonight about something he read online, lol __________________ www.NRGtechracing.com my car isnt fast enough to put the times in my signature......

11-19-2006, 11:01 PM	#6
miller H-T Sponsor Join Date: Dec 2001 Location: long island, ny, united states Posts: 10,673	Re: why is everyone so hung up up on "CFM"?? (b19coupe) but like i said before i have seen the opposite effects on several occasions, when trying different approaches. __________________ www.NRGtechracing.com my car isnt fast enough to put the times in my signature......

11-20-2006, 09:04 AM	#9
vtecvoodoo Senior Member Join Date: Sep 2001 Location: SoCal Redneck Posts: 23,696	Re: (miller) CFM is the new buzzword replacing spring rates. Everybody needs to know spring rates these days even though nobody knows how to apply them at all __________________ fs: New Ground Control Coilovers w/ custom rates-$315 shipped!!! fs: New Ground Control Top Hats for $125 shipped!!!! Eibach Springs-Horsepower for the turns

11-20-2006, 09:13 AM	#10
MAX_CFM Senior Member Join Date: Jan 2003 Location: Charlotte, NC, USA Posts: 1,004	Re: (miller) IF done " right" more CFM = more power __________________ NEED TO CONTACT ME rlzengineering@yahoo.com

11-20-2006, 09:14 AM	#11
The Destroyer Senior Member Join Date: Nov 2002 Location: Comb as a Balm Posts: 7,084	Re: (vtecvoodoo) Instead of ranting about the customer can you inform the know nothings what these are and how they affect power? Velocity: Port volume: Port shape: Port cross section:

11-20-2006, 09:46 AM	#13
SIred91 Rainman Join Date: Mar 2006 Location: Kills, Utah Posts: 6,238	Re: (miller) Finally, some people talking about some tech issues that are truly left up to myth as far as the average street ricer tuner goes. What about the quench sizes in relation to the amount of flow the head provides? Big valves, ported, polished blah blah, but at the atomization of the mixture, can the amount that the head lets in be overkill unless boosted? ie....too much fuel and or air regardless of tune will just be wasted? I dont know, its just a question, these are things I'm trying to learn. I could be just another dumbass when it comes down to the physics. __________________ I'll have the tuna.

11-20-2006, 09:56 AM	#14
Master of the Universe Join Date: Mar 2002 Posts: 6,493	Re: (SIred91) Same reason why everybody want's 200whp from their 1.5L. They are consumers of a number. But more flow = more peak hp potential. That is for sure. __________________ Semi-Retired as of April 25, 2007. Don't bother to PM me. I am tired of internet fools. Contact via RM Dealer or e-mail.

11-20-2006, 11:11 AM	#17
DonF Senior Member Join Date: May 2002 Location: Atl. Beach, fl, duval Posts: 4,701	Re: why is everyone so hung up up on "CFM"?? (miller) There are some posts on here about that, but most ignore them. There are 3 races the flow bench race, the BHP race, and the race track race. Only one matters.

11-20-2006, 11:40 AM	#20
ImportechPerformance Senior Member Join Date: Oct 2001 Location: Aka 3l Redskoolingbus Posts: 3,187	Re: why is everyone so hung up up on "CFM"?? (Don Lackey) __________________ ImporTech Performance <FONT COLOR="blue">Vist our new Ebay store!</FONT> http://stores.ebay.com/Importech-Performance

11-20-2006, 12:42 PM	#23
Suzukii Senior Member Join Date: Sep 2005 Posts: 150	Re: why is everyone so hung up up on "CFM"?? (miller) There are some engine simulation software available that can predict within a few hp of the eventual output. CFM is integral part of the equation. But like everyone says its peak numbers. For race use, its the effective RPMs that helps to win the race not just the peak number. Anyone here uses Ricardo wave?