08:45:06pm, Friday, May 17, 2024
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SF Head Flow???
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Does anyone know what kind of CFM's the top Super Farm heads are flowing?
thanks in advance |
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Re: SF Head Flow???
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flow bench
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as much as they can get thru a stock intake and exhaust 
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Re: SF Head Flow???
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SFpuller
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Mine is flowing 400+. |
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Re: SF Head Flow???
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Registered: 08/02/2008 Posts: 236 |
How much if you only flow one valve at a time and plug the injector hole? |
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Re: SF Head Flow???
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flow geuru
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It better flow 400 or u just as well stay home |
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Re: SF Head Flow???
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Registered: 08/02/2008 Posts: 236 |
I love how guys claim their ported stock farm tractor heads flow comparable or more air than high performance automotive big block heads that are designed for airflow. Seems like there's a awful lot of manometer's that need replaced. For example, Trick flow's race version of the A460 head uses a 2.350 intake valve flows 423 cfm at .800 valve lift. measure your valves and lift. You do the math. |
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Re: SF Head Flow???
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Registered: 03/31/2008 Posts: 762 |
Agreed. I suspect some of these guys are measuring with no valve installed. I don't see the point in that... |
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Re: SF Head Flow???
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What is it ?
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What is the formula with tha valves and lift ? New one to me. |
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Re: SF Head Flow???
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ih head
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well on the bench on an ih head 293 on intake with stock valve and 280 on exhaust (slighly larger valve than stock) still 466 bore. Have seen heads flowing 300+ but never 400 i guess if its a dry head maybe. |
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Re: SF Head Flow???
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true head
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a stock head flows 290 -280 get real dude maybe 190 200 |
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Re: SF Head Flow???
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ih head
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Man you are exactly right on the stock heads, I ment after porting. |
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Re: SF Head Flow???
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big numbers dont mean big HP
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Big flow numbers doesnt mean big HP.Air flow still has to go in and out of a 3x3 charger.Big cubes doesnt mean big HP either.I know that a good 466 with 3x3 charger can run better than some 640's.Dont twist what I just said.I didnt say that it can beat em all. |
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Re: SF Head Flow???
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Registered: 03/31/2008 Posts: 762 |
What valve lift for the 293 & 280? |
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Re: SF Head Flow???
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for real engine engineer
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Using IH as an example:
On my SF300 bench, the best 'wet' head intake flow is 340cfm at 28" H2O and 'dry' head 385cfm or so. This is at .28 L/D ratio........625 lift and a 2.25" valve. This is flowing on a 4.75" bore fixture with the valve at that lift. My ports don't flow much more without the valve. The key to comparing heads is cfm per square inch of net valve area and L/D ratio. Kind of like comparing BMEP's for engine performance. Head flow on a Super farm is tricky. You would think more is better, but when you compare the volumetric efficiency of the intake system to the turbo compressor map it will make you think differently. For max power you want max cylinder filling which is max air mass flow at the correct cam timing, and that is what the upper right of a turbo compressor map desires. So a super high flowing intake may not give enough pressure ratio for the given turbo to put out the mass flow needed. A lower flowing head will raise the pressure ratio for the same mass flow. In my experience, the system needs to operate in sync no matter what the head flows. If you have the highest flowing head, but wrong cam timing and wrong injection advance, the guy with a lower flowing head and the latter tuned correctly will beat you. The only way to get all of it matched is on the dyno frankly. Generally speaking, a 2% drop in torque away from MBT timing, is about 7 degrees of injection advance (retarded from BTDC). 2% on a 1000HP Super Farm is 20 HP which could mean that extra 6 inches you can't feel from the seat. |
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Re: SF Head Flow???
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for real engine engineer
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typo on last line: should say 'retarded from TDC' instead of BTDC. |
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Re: SF Head Flow???
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in your opinion what would perform better then, a head that flowed better and less camshaft timing or a lower flowing head and longer camshaft timing? |
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Re: SF Head Flow???
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Registered: 03/31/2008 Posts: 762 |
Ok, so you're saying that using this map for an example compressor map it's maximum flow is at a pressure ratio of about 3.25 and that above or below that it will not flow as much? I always figured that it was just above the tested RPM's and/or at effencies lower than they mapped. Isn't there also a 60% and even 50% island that falls somewhere? At a higher RPM the 70 & 72% islands should close shouldn't they?
If I take your argument a step further... If an engine is matched perfectly - head, cam, & turbo - & you increase the bore without changing anything else I think your theory says the HP will go down... |
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Re: SF Head Flow???
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for real engine engineer
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Generically speaking, yes the HP may drop. If you think about it, changing the bore and nothing else, changes the cylinder size. So the air handling system up to that point is still the same. There is some benefit to reduced shrouding on the intake valve with the larger bore, but not significant. In order to draw in the same air, the engine speed must go down proportionally, so by the math, the power may go down, unless the torque goes up. And it may also go down because the cam timing is not in the sweet spot anymore. It's easy to play keyboard puller, but the dyno is the true test here.
Also, turbos generally do not operate too far off of published maps. If you look at dyno data from a super farm and back calculate the mass flow based on the boost, it is still on the edges of the map. A healthy super farm turbo is 120 lb/min I would say. |
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Re: SF Head Flow???
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Anonymous User
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I took his theory to mean that effeciency would go down. Not necessarily that HP would go down.
Maybe I can learn something here but it looks like this to me. 600 cid X 2 hp per cid theoritical X 75% effeciency = 900 hp. 640 cid X 2 hp per cid theoritical X 72% effeciency = 921 hp. The larger motor made more power but you might say that last 40 ci is only making a half hp per ci. Maybe I am way off base but this is an interesting thread. |
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Re: SF Head Flow???
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Color Man
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I agree this is an very interesting thread. I have some questions for "The Real Engineer": By the way I agree with what you are saying more than any other cylinder head thread that I have seen.
Questions: - Speaking within the 3" inlet relm of things, how much less should an exhaust port flow than an intake port on the same head? Does the bias make any difference? How does the bias percentage effect the cam grind or does it? How much stock do you put into a flow bench that operates with vacuum, when on a turbocharged engine the ports are pressurized? Where is a good match of both CFM vs airspeed / velocity (within the head) - in other words, at what point has the port became too big where CFM might still increase but HP / torque goes down due to a drop in velocity? I know it's not easy, but please do your best to describe yourself in terms that a I can interpret. No engineering degree - lots of knowledge however on the strength of #9 wire. I agree, the only way to match things completely is on a dyno. Thanks. |
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Re: SF Head Flow???
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Anonymous User
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While you are waiting on an answer, here is something to think about. On a N/A big block with 2 1150's on a sheet metal manifold at WOT maybe the ports are at 5 inch Hg. (guessing). At peak piston speed the chamber might see 25 inchs Hg. So are the ports pressureized? Yes, in comparison to the chamber. Then if you consider the velocity created by this pressure differential you have to take into account port size. Huge ports/valves means low velocity. Proper sized ports develope a perfect velocity that builds kenetic energy that will overcome the pressure being built in the cylinder due to a rising piston. That is where a late closing intake valve allows you to use the stored energy in the flowing column of air to over fill a cylinder with more volume than it naturally displaces. So IMHO a well designed N/A induction system will make a well designed boosted engine. Maybe add 10% volume for the amount of space taken up by the alcohol compared to gasoline.
My question would be this, (and I believe the answer is YES). If a properly designed N/A motor can make 110 % volumetric effeciency then wouldn't this same engine at 3 Bar or (14.7 X 3) be running at 330 % VE? not accounting for heat induction from compressing the intake charge. What I am asking is, wouldn't the stored energy in a moving column of air remain constant or increase exponentially with pressure (actually mass). If you consider the runners to be at a vacuum, and an engine developes 110 % plus VE (like nascar) then the port at valve closing has to go above atmospheric pressure. So in my perfect world theory, two identical tractors running the exact same 60 lbs boost, the over sized port engine would see 57 lbs boost in the cylinder and the perfect ports would see 63. anyway, its something to think about untill someone bashes you for thinking. |
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Re: SF Head Flow???
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real engineer
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See if this answers your questions:
Questions: - Speaking within the 3" inlet relm of things, how much less should an exhaust port flow than an intake port on the same head? I don't have a direct math relationship here that will work every time, but there is more than just exhaust flow. Getting the exhaust out of the cylinder is a balance between valve head size, bulk port flow, cam timing, and exhaust back pressure. For example if your head has a high flowing exhaust port with good sized valve (say 80-85% of the intake valve head), you can open the exhaust valve later (closer to BDC) and still have the same cylinder pressure at BDC. The blow down is very good with the high flowing port. The opposite is true for a smaller valve and lower flowing port, you need to crack the valve off earlier. A real example I have is a drag car with twin turbos I worked on a while back. Small block Chevy at 428 cubes, with 2.18 intake valves and 1.60 exhaust valves. Intake flowed 385cfm on my bench, exhaust 245 cfm which is very good based on the valve size but not up to Nascar or NHRA pro stock flows yet. The car on the chassis dyno with twin 88mm turbos made 2300 HP at 8800RPM on gas with those 'puny' exhaust ports! The exhaust to intake valve ratio was a measly 74%. Will this ratio work on a Super Farm? Probably not. The cam timing of the drag car was very exotic, meaning the exhaust had to crack off very early due to the duration needed on the cam lobe to keep the valvetrain from getting polio. But that small E/I ratio and the large duration cam lobe worked out to the right blowdown at BDC and still kept the turbos spooled. A 640 cube SF at 3500RPM doesn't need the exhaust duration for the valvetrain dynamics, so by the math it has to crack the exhaust valve off closer to BDC, and therefore needs a better flowing exhaust for good blowdown. Remember these are general rules, so if someone out there has a SF with this ratio and 1200HP, God bless them. The moral of the story is spend your money on the intake as the exhaust is less sensitive. Even a top fuel dragster has a E/I ratio of 78% or so, and they make 8000HP. Does the bias make any difference? How does the bias percentage effect the cam grind or does it? I don't put a lot of stock into intake vs. exhaust bias really, but the cam grind makes a big difference. Reference above. The general trend for turbos is large lobe centers (drag car cam above I designed at 118 LSA installed at 116). How much stock do you put into a flow bench that operates with vacuum, when on a turbocharged engine the ports are pressurized? I put a lot of stock in 'vacuum' yet. Remember the air we breath is pressurized at 14.7 PSI. A turbo increases that pressure obviously. Maybe I'm too lazy to build fixtures for my bench and blow through the intakes, but I have enough flow data that shows the conventional method of flowing still works okay. Where is a good match of both CFM vs airspeed / velocity (within the head) - in other words, at what point has the port became too big where CFM might still increase but HP / torque goes down due to a drop in velocity? A good velocity target is 300 feet/sec at max valve lift at the smallest section of the port, typically this is the throat which is within a 1/4" of the valve head. Anything under 250 feet/sec is a dog of a port. The velocity is measured with a pitot tube, or calculated based on the flow and area of the port. Velocity in feet/sec = (2.4) X (CFM at 28") / (Area inches squared). Anything over 350 is bad too. |
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Re: SF Head Flow???
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Color Man
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Crutch, Thanks for your thoughts. All of this is very though provoking to me and helps a bunch. Real engineer - same goes for you. You guys are obviously better versed at this stuff than I will probably ever be, but I can pick up on a lot from the info you have given. The bottom line is every engine / combination is different. I knew that before, but sometimes it is helpful to have a baseline or baselines of some sort to start from. Thanks for your insite. |
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Re: SF Head Flow???
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Anonymous User
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350 FPS @ 28" ,is very similar to 700 FPS in live running Engine
about .627 Mach just about double your Pitot Probe reading @ 28" to simulate live running conditions |
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Re: SF Head Flow???
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real engineer
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Use BMEP as a constant instead of HP/CID. You can google BMEP and see if you can understand, but basically BMEP is a specific torque and is used to compare engine to engine no matter how large or how fast they spin.
An example of how the power can go down: --605 cube IH SF 4 5/8 bore X 6 stroke = 1150HP at 3200RPM, 1887 ft-lbs at peak HP (this calculates to 32.0 bar BMEP, healthy BMEP for a SF) --up the bore to 4.75 which is 638 cubes = 1100HP at 2900RPM, 1992 ft-lbs at peak HP (same BMEP of 32.0 bar!!) So just upping the cylinder size, assuming a constant BMEP, loses 50HP and 300RPM, but gains 100ft-lbs at peak HP. The disclaimer here: if the 605 cube engine was not optimized (head flow, cam timing, etc.), then the BMEP may not be at its potential, so it is conceivable that upping the cylinder size could raise BMEP and raise power. Back to the example, if the cam could be optimized for the new cylinder size, one could maybe grow the BMEP and probably get that 50HP back again. 638 cubes at 1150HP is 33.5bar BMEP. There other ways to raise BMEP too: --increase the flow of air into the cylinder, which is why finding that right turbo is precious in a restricted turbo class, and why intercoolers make more power. --lowering the engine friction, and this includes lowering parasitic power loss such as water pumps, too high oil pressure (takes power to run an oil pump), etc., also includes engine oil temperature (heating the oil before every run is a good thing) |
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Re: SF Head Flow???
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are there any formulas for specing a camshaft to a cylinder head and cylinder size? |
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Re: SF Head Flow???
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Color Man
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So we have talked a lot about 600 plus C.I. super farm engines which is good info. How would what we have discussed apply to a 410 C.I. Light limited engine with a 3" inlet? |
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