Ok for each cfm of flow on a V8 it = 2 HP and on a V6 it is 1.5 . with all that there are engines that have great flow but the HP is not that great why ? it is due to you must have a intake ,cam and exhaust system that are tuned to the heads max HP .
stock heads N/A
3800 heads flow like 191 stock that = a max HP 295
3.4 Tdc flow 270 i think that = 417 HP max
3.9 i think flow 230 that = 355
4.3 vortec 211 = 326 HP
now if I am wrong on the flow numbers pleas correct me and i used this calculator for HP figures
http://www.speedwaybids.com...cs/powerfromcfm.html remeber that is there max HP potentail some engine like the 3.4tdc would be running about 9000 rpm to get that HP so you need good parts to take that rpm.

I prefer to think of potential power in terms of airmass instead of CFM - in either case you need to take into account temperature and air pressure.

At STP (70*F and 14.696 lb/sq in), 1 CFM contains approximately 0.074887 pounds of air, so ~13.35 CFM are required to obtain 1 pound of air, which would produce 9-10 HP. A more realistic number for a push rod gasoline engine might be .75 hp per CFM. I don't believe that a V8 has any particular advantage in producing power per unit of airflow over a V6. It might be better to consider different engine's power potential in terms of Brake Specific Fuel Consumption (BSFC) which is a measure of how efficiently an engine converts the energy contained in the fuel to mechanical energy. Airflow determines how much fuel you have to add. Combustion chamber design, compression ratio, valve timing, etc. affect how well the fuel's energy is extracted to perform useful work, instead of just excess heat.

There are a lot of variables that affect the potential power of an engine, most of which impact Volumetric Efficiency, but others have more impact on how the air/fuel mixture burns. You've identified important issues that affect airflow, I'll throw out a few more for discussion:

Compression ratio
Combustion chamber design (impact on turbulence, burn rate, valve shrouding)
Intake runner length, cross sectional area, and taper
Intake plenum size and shape
Valve size

Cheers

All comes down to a little thing called %VE.

edit: wow... my post is a little underwhelming, eh?

[This message has been edited by carbon (edited 10-30-2009).]

yes every thing you say is true i was just giving a basic idea of what cfm mean for HP. i see to many that think that one engine is not good due to low stock HP numbers when in fact it isnt even close to its potential HP. yes VE is where it is at thats why better flowing heads on an engine make higher VE with out having fuel drop out of suspension so a good port will also have high velocity. Oh a you need good combustion chamber swirl. with all that most factory heads are pretty decent on swirl and port velocity

[This message has been edited by engine man (edited 10-30-2009).]

That's what turbos and superchargers are for. If you don't want to do either of those, the it's simply efficiency of what does come in. As Smokey Yunick so famously said, all things being equal, there is no substitute for cubic inches. And if you can't get more air in there, squueze the hell out of what you can.

Did you guys notice the gent making 400+ HP out of his turbo 2.8L had removed the shark fin from the intake runner? I have a spare set of heads that I am seriously considering removing that fin to see if it makes a difference. I do realize GM says it makes for more air velocity but I'm still not convinced it would be better for a turbo engine.

even with turbos and superchargers more flow from the heads mean more power . Boost presure is kinda tricky you can have 2 identical engines except one has better flowing heads with the same boost but they wont make the same power.

quote Originally posted by engine man: Ok for each cfm of flow on a V8 it = 2 HP and on a V6 it is 1.5 .

Ignoring absolute numbers for the moment, what makes you think that the number of cylinders in an engine affects the HP produced per CFM of airflow? Can you explain how?

[This message has been edited by Marvin McInnis (edited 10-30-2009).]

well why i was saying that is 6 is 3/4 of 8

[This message has been edited by engine man (edited 10-30-2009).]

quote Originally posted by Hudini: Did you guys notice the gent making 400+ HP out of his turbo 2.8L had removed the shark fin from the intake runner? I have a spare set of heads that I am seriously considering removing that fin to see if it makes a difference. I do realize GM says it makes for more air velocity but I'm still not convinced it would be better for a turbo engine.

yes, but Turbo vs NA is a little different in what works with airflow.
with N/A, the air is being pulled into the cyl
with boost, the air is being pushed
it makes perfect sense to me that with boost, removing the shark fin is a great idea.
the shark fin exists in order to make a larger "pull" area around the valve, by using the 2 sides, instead of the 1 front for the "pull" area.

quote Originally posted by engine man: if you take a V8 with say 211 cfm it could make 435 HP and if you take a V6 with the same flow it shows 326 HP or 3/4 the HP [emphasis added]

Can you cite an authoritative source for any of that?

Think about it. You're claiming that a 12-cylinder 3 liter engine will produce twice the power of a 6-cylinder 3 liter engine, assuming that both engines are otherwise tuned identically. If all it takes to make power from a fixed airflow is more cylinders, why aren't we all driving 36-cylinder 500 cc cars instead of 6-cylinder 3 liter cars?

If you actually mean "CFM per cylinder" then you need to say so, but your original post would still be wrong. In that case you're mixing CFM per cylinder and HP per engine.

[This message has been edited by Marvin McInnis (edited 10-30-2009).]

yes i see what you are saying but the 12 cylinder has more flow due to more ports flowing 200 cfm than a 6 flowing 200 cfm per port . the 500 cc 36 cylinder would have way to many rpm

[This message has been edited by engine man (edited 10-30-2009).]

Wrong. 200 cfm is just that, it's not 201 or 199. I don't care how many inlets you use.

well they flow heads by each port not total cfm so you take that and put it in the formula if a 350 chevy flowed a total of 200 cfm for a total of all it cylinder it wouldnt make any power. i realy need to find the math

You are confusing CFM per cylinder with total CFM of an engine.

A 3.0L V-6 displaces the same volume as a 3.0L V-12. If the displacement of the engine stays the same, The total CFM intake is the same regardless of the number of cylinders.

The difference is each cylinder in the V-6 will flow twice as much air as each cylinder in the V-12.

Head flow rates are per head (not per cylinder) at a given lift. I've never seen head flow rates per cylinder.

So using a 2.8L engine at 6000 rpm it will require 290 cfm (If VE is at 100%) or 43.8 cfm per cylinder if it's a V-6. If it is a 2.8L 4-cyl it would flow 72.5 cfm per cylinder and a V-8 would flow 36.2 cfm. Regardless of the number of cylinders, The total engine flow at 6000 rpm would be a max of 290 cfm. It is a simple calculation of displacement vs. RPM. Number of cylinders has no effect.

quote Ok for each cfm of flow on a V8 it = 2 HP and on a V6 it is 1.5 .

You should have stated "for each cfm of flow per cylinder is = to 2hp. " *
Assuming that the V-8 engine has 1 cfm of flow per cylinder, It would then mean that 2hp per cylinder X 8 Cylinders = 16 hp
Now assume the same per cylinder flow rate for the V-6 It would be 2 hp per cylinder X 6 cylinders = 12 hp.

Which is why you keep thinking a V-6 has 3/4 the power of a V-8.

* = As for 1 cfm of cylinder flow = 2 hp, I don't think that is very accurate.

Per cylinder CFM, Head flow CFM, and total engine CFM are 3 distinctly different figures.

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

Happiness isn't around the corner...
Happiness IS the corner.
ZZ4 Powered !!

[This message has been edited by Oreif (edited 10-30-2009).]

yes i am saying if each port on the head flows 270 cfm then it will make more power than if each intake port on the head flows 200 cfm. I dont care what size engine it is if you have a 8 cylinder and each intake port flows 200 cfm then it will make more power than if you have 6 cylinder with each intake port flowing 200 cfm. the cylinder size in relation to the port size will determin the rpm.

Oh ya this is POTETIAL horsepower meaning that everything has to be 100% to get the max flow out of each cylinder intake port

quote Originally posted by Oreif: You are confusing CFM per cylinder with total CFM of an engine.

EXACTLY

Once we get everyone on the same page, the argument should vanish.

[This message has been edited by Blacktree (edited 10-30-2009).]

You don't know the potential horsepower of an engine based on CFM...

With the *exact* same air/fuel charge, torque can vary. Compression ratio & rod/stroke ratio will affect the torque.

It is quite possible that the cylinder head with the max CFM might not make as much HP as one that flows less CFM. It's the CFM under the lift curve that one needs to look at. Already been stated but, the more air/fuel you get into the cylinder the more power you make.

Port Velocity is not something to take lightly, I sell ALOT of velocity probes to Professional Cylinder Head shops in various racing venues

Don't look at CFM alone, it's a "sales tool" . . .

I plan on actually testing a complete intake tract from a 2.8L on my flowbench this Winter, this will also include some wetflow testing of a head. I keep reading here about the stock parts not flowing enough but never see any actual numbers?

In the end though it all depends on what you are after in your engine, stop light to stop light, 1/4 mile, just out for a fun afternoon drive on a backroad . . . if you can't crank up the RPM's to take advantage of the high lift cfm's and big ole ports what do end up having?

Just my view.

One more thing, CFM numbers without a test pressure are just that . . . numbers, you have no way of comparing apples to apples. Converted pressures also don't tell the real story. CFM numbers are also subjective from flowbench to flowbench even from the same Big Blue Flowbench manufacturer, I've seen a few "happy flowbenches".

quote Originally posted by engine man: yes VE is where it is at thats why better flowing heads on an engine make higher VE with out having fuel drop out of suspension so a good port will also have high velocity. Oh a you need good combustion chamber swirl. with all that most factory heads are pretty decent on swirl and port velocity

good thing folks dont read every thing you post

I flow about 730cfm on my turbo 3800's. Equals out to about 480-520hp.

oh, my heads flow about 190cfm, and I run 14psi of boost.

[This message has been edited by darkhorizon (edited 10-30-2009).]

yes that is about right you are runnig at about 2 atmosphere so that would push it to about duble the HP. but you must take into acount expansion of the heated air is less dense.

[This message has been edited by engine man (edited 10-30-2009).]

don;t include forced induction. that is a whole 'nother ball of wax.
in a n/a engine, ve is the holy grail. Heads make the power. ask any professional racer. you have to flow the air to supply the oxygen to burn the fuel. the whole argument of hp/cu or hp/cylinders is absolutely wrong. 2hp/ci is not hard on any motor.
you have to do more than a simple head flow to determine the power.(not that head flow is unimportant, it is extrememly important, but great flowing heads without intake and exhaust and proper combustion is useless). the shape of the combustion chamber, the compression ratio, etc etc etc are what determine the power output of the motor, and more to reality the power BAND of the motor.
It is the whole system of the motor, not just the cfm that provide the power.

tjm4fun you are right it is a whole package to make HP and i under stand that . lets take the 3.4 TDC it heads flow enough to make 415 HP but to do it it has to run 10,000 + rpm now can it do that with stock cam, intake,rods ,crank,valve,springs ,block and oiling system i dont think so but it would make a nice bang .btw forced induction is not a whole other ball game lets look at an extream top fuel drag cars now those heads can flow a whole sh*t load of fuel and air thats how they make 8000 HP not buy sticking some stock size port head on and running high boost. what is boost it is pressure how do you get pressure you must have a resistance so lower the flow the higher the resistance or in this case easer to get boost pressure

[This message has been edited by engine man (edited 10-30-2009).]

Oreif I looked at what you are saying and you are looking at how many cfm the engine has at a given rpm to determin the carb size . I am just looking at the port cfm and saying on that that one port one cylinder has the potential to make x amount of power and then that times how ever many cylinders you have

quote Originally posted by tjm4fun: don;t include forced induction. that is a whole 'nother ball of wax. in a n/a engine, ve is the holy grail. Heads make the power. ask any professional racer. you have to flow the air to supply the oxygen to burn the fuel. the whole argument of hp/cu or hp/cylinders is absolutely wrong. 2hp/ci is not hard on any motor. you have to do more than a simple head flow to determine the power.(not that head flow is unimportant, it is extrememly important, but great flowing heads without intake and exhaust and proper combustion is useless). the shape of the combustion chamber, the compression ratio, etc etc etc are what determine the power output of the motor, and more to reality the power BAND of the motor. It is the whole system of the motor, not just the cfm that provide the power.

You are simply speaking of combustion chamber efficiency, and you are correct. Japanese motorcycles are the perfect example of efficiency and power, retaining reliabilty. Figure the HP per cubic inch of a Hayabusa or Mad Max. It's a science apparently not well understood by some.

quote Originally posted by engine man: Oreif I looked at what you are saying and you are looking at how many cfm the engine has at a given rpm to determin the carb size . I am just looking at the port cfm and saying on that that one port one cylinder has the potential to make x amount of power and then that times how ever many cylinders you have

Yes, I understand that, But your "math" is more like "fuzzy logic". A cylinder has X amount of volume. CFM is determined by the volume times the rpm. (while this is the basic formula for determining carb size, It's also used for throttle body size and injector flow rates. It is the basic flow of the engine regardless if it's carb'd or EFI) So a 3.0L engine regardless of the number of cylinders is only going to flow a specific amount of air at a given rpm. It really doesn't matter if the heads can flow 500 cfm per port if the engine can only flow 300 cfm at 6000 rpm.

Yes if the head flows less CFM than the engine can use, you will have less horsepower. But the opposite is also the same. If the heads flow way too much for the engine, Your flow velocity into the cylinder decreases and you lose power with a normally aspirated engine.

quote Originally posted by engine man: yes i am saying if each port on the head flows 270 cfm then it will make more power than if each intake port on the head flows 200 cfm. I dont care what size engine it is if you have a 8 cylinder and each intake port flows 200 cfm then it will make more power than if you have 6 cylinder with each intake port flowing 200 cfm. the cylinder size in relation to the port size will determin the rpm.

No cylinder size and port size do NOT determine rpm. Actually the port size and cylinder size over a given RPM determine flow rates. They all have to work together. What you keep doing is backwards. Taking a flow rate and a given port size then coming up with an RPM and power is very inaccurate and misleading. (This is what the second website you posted does.) While maximizing flow rates creates the most power, you need to match things accordingly.

By your logic If I port a 2.5L Duke head to 500cfm the engine will make 700 hp at 23,700 rpm. Problem is at anything below 4000 rpm it will be a dog. There isn't enough velocity thru the intake to have any vacuum. So the fuel will not mix with the air properly and thus power will be extremely low. "Potential" power from "Theoretical" flow means nothing. You cannot "build" an engine to fit your theory if you keep trying to use flow rates that are not physically attainable on a given engine.

[This message has been edited by Oreif (edited 10-31-2009).]

Just last week I finished reading a book on intake and exhaust system design that a couple of British automotive engineers wrote (now that I have a TIG, I'm looking at building my own stainless intake and turbo headers for the 3.1). The book certainly provides an appreciation for the need to properly match the intake, exhaust system and cam timing to obtain maximum VE in the desired RPM range.

The book doesn't cover Helmholtz tuning, but does have comprehensive discussion of wave tuning in both the intake and exhaust systems. The primary goal is to have an exhaust system that provides a negative pulse to the exhaust valve just before it closes to ensure complete cylinder scavenging and ensure that a new charge is not diluted with residual exhaust gas (oh look, every engine has built in EGR when scavenging is incomplete).

On the intake side, the goal is exactly the opposite, you want to have both sufficient momentum in the intake charge to continue filling the cylinder after BDC, but before the intake valve closes, and a positive pressure wave hitting the intake port just before it closes to ensure the cylinder continues to fill.

At other than the designed RPM, the benefits of wave tuning are reduced or non-existent, but there is a range around the designed RPM where benefits are still obtained, so it's important that valves open and close at the correct time to take advantage of the pressure waves - that's why you have to match the cam to the rest of the system. With properly designed systems, VE in excess of 100% is attainable.

Cam design is not something I know much about. Fortunately, DYNO2003 has a feature to optimize valve timing based on the head flow, compression ratio, intake and exhaust systems (unfortunately this is limited to pre-defined intake and exhaust systems). It turns out that the Crane 2030 with 1.6 rockers is a good choice for a turbo application, the system could only improve area under the torque curve by 1%. Changes were increasing LSA by 3 degrees, increasing exhaust duration by 10* and decreasing intake duration by 7*. Valve overlap decreased by 4*.

I'm looking for software that allows more flexibility in defining engine parameters, anyone know if Dynomotion allows you to define your own intake and exhaust parameters rather than using pre-defined values?

Cheers

[This message has been edited by TiredGXP (edited 10-31-2009).]

Give this program a look:

http://www.maxracesoftware.com/pipemax36xp2.htm

I know lots of cylinderhead shops that use this program in conjunction with their head development work.

Some day, I'd like to come back and re-read this when I can understand it. Is there a good website or Engines for Dummies book that is easy to read and understand?

Jonathan

Alot of top engine builders around. use this forum and talk engines.
I read it everyday. Beware might hurt some feeling to a few.
Hard core truth about engines.


http://speedtalk.com/forum/viewforum.php?f=15

I dont believe in using magic formulas to figure anything with an engine. Ive had 2 identical engines, everything was the same (identical duh) and one put out over 50 hp more than the other. What hocus pocus would produce that ? They were both Lincoln 460 ci, 4 bbl, both brand new at same time with sequencial VIN nmbs. That was just one case. Using a formula is just an educated guess ...almost as bad as how ricers use sales ads for their aftermarket stuff to boast power increases.

[This message has been edited by rogergarrison (edited 10-31-2009).]