| Author | Message | ||
     3boyz |
Can someone tell me what stock XB9 heads flow. | ||
| Alex |
You wonīt get an answer to this question as there are too many details missing (like test pressure, valve lift, with or without manifold/injection system, and so on). Even if You gave me all details it wouldnīt make too much sense to give You the numbers I measure as they are only valid for my flow bench with all test set up conditions that I use. But Iīm sure You are more interested in flow comparison between different heads rather than in absolute numbers (like: does an XB head flow higher numbers than a Thunderstorm head at high lift....). So if You specify Your question I will try to give an answer. Best regards Alex | ||
| 3boyz |
I am torn between using a set of ported T-storm heads with 1.94 valves that flow 140 @10" or a set of stock XB's. This is for a bar hopper with a semi hot 79" with R.S. 585 cams. I have some flow numbers for XB's using stock valves with a port "clean up" and the number was an impressive 152cfm @ 10". I was guessing stock to be around 140. If these number were close I could use the XB's and have a marketable set of T-storms set up for high lift cams. Which brings me to another question, how large of a cam lift will the stock XB springs support? Thanx, Rob | ||
| Alex |
Hey Rob, now this is where the problems start. It is very difficult to compare flow numbers between different manufacturers (thatīs why I dontīt make flow numbers public because they almost say nothing to anybody else). First of all You should find out at what valve lift theses numbers have been taken. A 140CFM@10" at .400 lift is pretty different from 140CFM@10" at .550" lift. Even better You take Your set of heads to somebody with a flow bench and try to get a set of XB heads to do a direct flow comparison (or maybe to somebody who had flowed some stock sets of XB heads before on his bench). Remember: low and mid lift numbers are as important as high lift numbers (most of the time even more important). Your numbers are a practical example of how people get confused with flow numbers. For me both numbers seem pretty strange. On the one hand You can get above 150CFM@10 at high lifts with a XB head with stock valves but it takes more than a simple port clean up. On the other hand 140@10 at high lifts with a TS Head with 1.94" valves would be pretty bad. Iīd expect above 160CFM at least from a professionally ported head. So unfortunately Iīm not too much of a help with this. Regarding the valve springs in XB heads: they can take pretty much lift (.585 is not a problem) but one will need to check several clearances (like top valve collar to stem seal) and valve pressure is limited. If You reduce installed spring height to increase pressure max. lift capacity is reduced. From measurements I would say You can get away with 140 lbs. seat pressure with a .585" lift capacity. For radical cams this might be not enough at high rpm. So again I would advice to talk to somebody with a spring tester and some measuring tools. Best regards Alex | ||
| Rocketman |
Alex, many years ago there was a vibrant discussion here about my Dick O'Brien flowed heads. I recall being told my heads flowed 161CFM@12 (but that's another story). My question is, after reading your above post, how does one quantify this statement..... A 140CFM@10" at .400 lift is pretty different from 140CFM@10" at .550" lift. Wh with the flow if different lifts still flow the same amount of air? TIA Rocket | ||
| Alex |
Ok Rocket, this will be a longer answer. Try to think of a flow bench in terms of dynos. We all know that one single bike can produce 20 different hp numbers on 20 different dynos (sometimes even 10 dynos will be enough to get 20 different results :-)). Now why is this so? Because the dynos are not all calibrated to a single "master horsepower" bike, because there are differences in the way they measure, because there are differences in the way the dyno guys work and so on. With flow benches it is pretty similar. They are not all calibrated to the same "master flow piece" and much more important every tuner has his own way to measure. There is no standardized test set up. Some measure with the manifold and a short velocity stack in place, some put modelling clay around the intake port opening to form an entrance radius, some measure through the complete intake system including air filter. Quite similar with the exhaust setup. So my numbers are only valid for me. I measure my heads always with the same set up so I can compare them to each other. I donīt really know if these numbers are "true" when checked against numbers measured on the most precise flow bench on earth (wherever this one may be) but I donīt really care. I know what heads flow on my bench and can compare them to any other head that I measure on my bench. So I live kind of in my own measuring universe. As long as my heads flow specific numbers and show good results on the street or track my little universe is ok. Thatīs why I donīt give numbers to others. Now there is another similarity between flow benches and dynos: most of the time people stray around with maximum numbers like 100rwhp or 150 CFM. Sounds good? Well, depends. Actually it depends on the curves that include the maximum numbers. For example: there is somebody claiming to have 150 hp on the wheel. What he didnīt tell You is that his power curve is almost flat at 30 hp between 3500 and 6000 rpm where it jumps up to 150 hp at 7000 rpm (pretty unusual but I know You got the point). Would You think this is a nice bike to ride? Not really (ok, I know there are some freaks out there who would love it :-)). So actually the shape of a power or torque curve is what makes it a happy engine or a pure dyno shoot out bike. The same with flow numbers. Looking at the maximum numbers doesnīt really tell too much. Low and mid lift numbers are pretty important. Furthermore additional information is necessary when looking at the numbers. Especially valve and seat ring size. Big numbers with big valves are not always the best. Sometimes they are. So what Iīm trying to say is that with only maximum flow numbers You can not judge if a set of heads is good or bad. There is much more behind. Now with having all this said we take a look at Your question: if we take both heads to my bench it will tell us that one head flows 140CFM at 10" test pressure with the intake valve .400" open while the other flows 140CFM at the same test pressure but with the valve .550" open. The 140 CFMs are the same (remember 140 Alexīs universe CFM) because right at the moment when measuring there is a flow of volume of 140 Cubic Feet per Minute through the intake. Still that doesnīt mean that both heads flow the same. Yes they flow the same 140 CFM. One head at .400" lift the other one at .550". But when we talk of head flow we need to look at the complete flow curve instead of one single point within the curve. We donīt know what head number 1 will do when we open the valve to the same .550" of head number 2. Maybe it flows 150CFM at .550". I think You know what I mean. 140CFM are 140CFM but they are nothing without test pressure, valve lift, valve size, complete flow curve and so on. Best regards Alex | ||
| Jimidan |
Good explanation Alex. Jimidan | ||
| Alex |
Thank You. | ||
| Rocketman |
Yeah Alex, I understand everything you say except the last part. For me your explanation works your way around. That is as you say We donīt know what head number 1 will do when we open the valve to the same .550" of head number 2. Maybe it flows 150CFM at .550". But head number 1 in your scenario only lifts to .400 yet it flows the same as head number 2 with .550 lift. All other things being equal, except the lift between both heads, which I believe was what your original comment implied, why would they flow the same? Not only that, but what if the .550 lift could only lift to .400, would it still flow 140CFM, or less? That is what I want you to explain, because for me, I just can't see how both equal heads with different lift could ever flow the same. One must flow more than the other, all things being equal, and that would be the .550 lift head. Rocket | ||
| Alex |
Ok Rocket, problem discovered. My scenario was based on 3boyzīs question. He had to choose between two different set of heads: head set 1: T-Storm ported, 1.94" intake valve head set 2: XB port cleaned, stock intake valve He gave the following numbers: head set 1 140CFM@10" and head set 2 152@10" without any valve lift information. On the first hand one would say head set 2 is better. But this might be a mistake as theses information are not comparable as too many details are missing. The flow numbers could look like this: head set 1 lift/flow @ 10" test pressure .100"/45CFM - .200"/95CFM - .300"/125CFM -.400"/140CFM - .500"/158CFM - .550"/165CFM - .650"/172CFM head set 2 .100"/32CFM - .200"/78CFM - .300"/105CFM - .400"/125CFM - .500"/148CFM - .550"/152CFM - .650"/153CFM By only picking out the numbers in bolt letters it would be a pretty wrong picture of the truth. Thatīs what I was trying to say. If we take Your assumption that we have two identical headswith one being said to flow 140CFM at .400" valve lift and the other being said to flow 140CFM as well yet at .550" valve lift it may look strange but still it is possible: The flow numbers could look like this (for both heads): .100"/25CFM - .200"/75CFM - .300"/112CFM - .400"/140CFM - .500"/140CFM - .550"/140CFM The ports maximum flow capacity would be reached at .400" lift and would stay constant at higher valve lifts. It wouldnīt be a lie to state one head flowing 140CFM at .400" valve lift and the other flowing 140CFM at .550" lift. But again picking out only one number from the flow curve is pretty misleading and pretty senseless. In this case we would not say that the .550 head flows more as the other head will do the same if You open the valve to .550" . Things get even more complicated when we take cams into account. But this is a different story. To sum it up single flow numbers are pretty useless. Rocket, Your questions show how easy it is to disturb people with some numbers and how misleading numbers can be. But You are on the right track: You start to ask questions. Best regards Alex | ||
| Rocketman |
Thanks Alex. Your scenario makes sense now. I assumed you were not talking about the two heads of 3boyz's, but two identicals with different lift. I wasn't paying attention, but doing so raised a good point eh LOL. I got the max flow scenario. That part at least, was easy. Everything else I'm sure, is just as you describe. Nice to have an expert spend the time explaining it. What a shame you weren't around when we had that ripping yarn about my Dick O'Brien flow numbers. I might have won that one back then  Thanks. Rocket | ||
| Alex |
Youīre welcome. Is there something about Your OīBrien numbers in the archives (maybe a link)? Alex | ||
| Xldevil |
Hey Alex. Let's assume someone's using the same cams,which head is more likely capable to be ported for the best streetable flow?XB or TS? Ralph (Message edited by xldevil on May 06, 2006) | ||
| Alex |
Your M-TeK heads are just perfect  Alex | ||
| Xldevil |
A big Yes After more than 10K kilometers,I can say,I'm more than satisfied with my M-Tek ported heads. Once again:Thank you Alex;but You know: Das Bessere ist des guten Tod!  So, I'm already planning a little performance upgrade for next winter , including Axtell/Naillin 1250cc,Hurricane pistons 10,5:1 and 585 cams. Do you think my wonderful M-Tek heads will still fit the needs of this combo? Or would you recommend some modifications? Ralph (Message edited by xldevil on May 06, 2006) | ||
| Rocketman |
Alex, the argument in 2000 was whether my heads flowed at 10" or 12". I always assumed 10", but we'll never know. With N9 cams, .555 lift, I worked out my max flow to 168cfm back then. Here are the numbers as emailed to me from Greg O'Neil on behalf of Dick O'Brien. Valve Lift............Flow 200 = c.f.m. 78 300 = c.f.m. 126.4 400 = c.f.m. 144.4 500 = c.f.m. 164 600 = c.f.m. 171 EX. 78% Rocket | ||
| Jkhawaii |
why are motorcycle heads flowed at 10 and 12 while automotive heads at 28? | ||
| The_old_poop |
RE: "why are motorcycle heads flowed at 10 and 12 while automotive heads at 28?" They aren't! The capacity of the flow bench has a lot to do with the test pressure used for a given set of heads. If you are flowing a set of hemi blown alcohol heads it is fairly common to use test pressures as low as 5" water, especially since these heads are capable of 200-220 cfm at 5". For what it is worth, flow data is directly proportional to the square root of the test pressure. Knowing this, you can convert data obtained at a given test pressure as follows: Calculated Flow Number@desired pressure = Orig. Flow Number / SQRT of original test pressure * SQRT of desired pressure. For example 200 cfm at 5" translates to 473 cfm at 28". | ||
| Steveshakeshaft |
And...... Flow is only half the story. I can flow your head to pass any amount of air you like, easily. I'll just make the ports huge. But then on the bike, flowing the CFM that the engine needs, the velocity will be low due to the huge cross sectional area of such a big port. Charge Velocity is very important in attaining maximum volumetric efficiency of an IC engine. The higher the charge velocity, the higher the volumetric efficiency is likely to be. So, in an ideal head, we need high flow AND high velocity. And that is hard to get! | ||
| Alex |
Ralph, the heads will work ok for Your set up when talking of flow. Still they can not handle a .585" lift with the stock springs. If You like there are some mods that can be done to squeeze out some more ponies. Talk to somebody who knows. If You canīt find anybody You can still call me Best regards Alex | ||
| Panic |
For what it is worth, flow data is directly proportional to the square root of the test pressure. Knowing this, you can convert data obtained at a given test pressure as follows: Calculated Flow Number@desired pressure = Orig. Flow Number / SQRT of original test pressure * SQRT of desired pressure. For example 200 cfm at 5" translates to 473 cfm at 28". Doesn't work. Not only will the result of the conversion hardly ever be the same as the actul test done at higher vacuum, but 2 heads that test the same at 10" will be different at 28". Reason for using 10": bench is too small to pull 28" vacuum. This is as "scientific" as using a drinking straw and a small child to pull .002" vacuum, and converting by formula. Reason NOT to use 10": doesn't respond to small changes that would be detectible on a dyno or by ET/MPH. You can remove 1/8" in some places before a 10" pull will show a change. Reason not to use 50": a hair stuck in the port will change the result - too nervous, changes that will NOT affect actual power show up on output. Quoting Smokey: '28" is the closest match between test results and actual changes in power'. | ||
| Pammy |
"Charge Velocity is very important in attaining maximum volumetric efficiency of an IC engine. The higher the charge velocity, the higher the volumetric efficiency is likely to be." Right on. We measure that as well. And, of course, don't forget swirl and tumble... | ||
| Xldevil |
@Alex. As you should know,you are me first(and only) address!  Sincerly,Ralph | ||
| The_old_poop |
Panic, If I am not misunderstanding your post, you feel that all test pressures other than 28" are worthless. On this I will agree to disagree. I merely stated a fact, that the flow rate is directly proportional to the square root of the test pressure. I also provided a "quickie" formula to approximate the lookup table Superflow included with all of their their flow benches. The particular bench I have had at my disposal off and on for nearly 20 years, is a model 600 and is capable of testing some big ports at 28". Apparently Superflow felt it was a valid conversion or they wouldn't have supplied it at all. In support of this position I would like to quote from: "Design Refinement of Induction and Exhaust Systems Using Steady State Flow Bench Techniques" by G. F. Leydorf, Jr., R. G. Minty, and M. Fingeroot (a SAE paper, numbered 720214) "EFFECT OF COLLECTOR PRESSURE - At outset of airflow work, we chose a collector tank pressure of 2 in Hg (27.2 in H2O) as representative of values to be expected during actual engine operation." [They had the same opinion at the outset as Smokey Y.] They continue: "We know of others who have used pressure ranging from 10 in H2O to 5 in Hg. To test whether tank pressure influenced the resulting flow coefficient, we selected an intake port notable for a drop in airflow at high lift, which might have been due to flow separation from the port surfaces. This port was flow tested using tank pressures of 6, 12, 18, and 27.2 in H2O. Flow coefficient was then calculated as described in the Appendix." "Flow coefficient is an index of how effectively the tank pressure is converted to velocity, and should be independent of tank pressure if flow remains turbulent and no flow separations or anomalies appear." "The resulting flow coefficient, for 0.05 in increments of valve lift to 0.50 in, exhibited a maximum spread of 2.6%, with most values within 1%. This spread includes the effects of manometer reading accuracy." "We conclude that, with our calculation methods which correct the orifice coefficient for the effect of Reynolds number, flow coefficient is insensitive to tank pressure over the range of 6-27 in H2O." As you can see, their data no longer supported their initial apprehensions or Smokey's. Like Steveshakeshaft, Wes and Pammy, I am very much a devotee of high port velocity. The only opinion I will share on flow testing is that raw CFM figures are only good for bragging at local bench racing sessions and tell very little about how a port will perform in practice. Port flow coefficients will give you a much more useful data set. Scott | ||
| Alex |
Now that we saw that flow numbers are a complicated topic we can see that there are even different opinions on measurement and data evaluation which makes the whole thing even more complicated. Time for me to go back to my own little measuring universe with my own evaluation philosophy. Good bye. Ralph, if You like contact me via mail and I will make You some suggestions of further tuning of Your engine. Over and out. Alex | ||
| Rocketman |
Well Alex, I posted my numbers for your perusal, yet it seems you are running off without comment now others have entered the thread. If I am to understand what Scott is saying, there is a suggestion that 'numbers' do make sense, providing of course, we all work from the same text book, in a manner of speaking. But I'm somewhat confused because you seem to have your "own little measuring universe with my (your) own evaluation philosophy". So what am I to believe when I look at my numbers for example? Nothing, because they are meaningless without more information, or, I can regard 10" or 12" of test pressure were used, and somehow using a specific formula, come to the conclusion that Dick O'Brien did a good flow job on my heads or not? Rocket | ||
| Alex |
Rocket, I just wanted to avoid discussions with the "pros" about port size, velocity, flow numbers or flow data conversion. I have my own experiences with head porting. Some of them go along with what "the big names" say to be true some of them are pretty different. So my head designs follow my philosophy and my numbers are measured with set ups that I feel to be ok for me. Now some words to Your numbers: again there is a little misunderstanding. Actually I just wanted to read about the discussion around Your numbers to see what others said instead of reading Your numbers. Unfortunately it is as You say: the numbers are pretty meaningless. It makes quite a bit of difference if they were taken at 10" or 12" of test pressure. Furthermore we donīt know anything about valve sizes, manifold size or test set up (or even engine size, cams or riding style). The only way for me to judge the quality of Your heads is to measure them on my flow bench with my test set up. If You like to know send them to me and I will do it for You. Best regards Alex (Message edited by Alex on May 09, 2006) | ||
| Pammy |
"raw CFM figures are only good for bragging at local bench racing sessions and tell very little about how a port will perform in practice. Port flow coefficients will give you a much more useful data set." So true. Horsepower in an engine is dependent on the displaced pumping volume over the rpm range being looked at. The flow availability to the cylinder, in and out, is dependent on cylinder pumping volume or flow, cross sectional area of the port, velocity of the port and cam events. So, you must understand, everything is relative and the flow bench and subsequently the numbers therefrom are all tools one uses to acheive a specific goal, whatever that may be. | ||
| Pammy |
Our flow bench will flow up to 100". Typically it is not necessary to do so. On testing throttle bodies and the like higher depressions are sometimes useful. One day I will have to post a chart from one of our heads. It shows velocity and flow at different points within the ports. We create a port velocity graph and try to leave nothing on the table when developing a set of heads. Mapping the ports is so important for maximum performance. But head porting is not a finite science or "art". New developments are being made on a regular basis around here. | ||
| Rocketman |
You guys and one blond bombshell really know your stuff it seems. So I have a really stupid question based around the flow bench being a tool for black ops. It would seem to me entirely possible that someone with a bit of wisdom in such head matters could port a head without the use of a flow bench and gain fantastic results over and over again. Am I right in thinking so, or has the black art moved on so much, technology needs to be in place to keep ahead of the game? Thanks for the offer Alex, but last time they went to the States, the wrong ones were returned, and eventually, when the right heads were returned to me flowed, they cost a fortune in shipping alone lol! Rocket |
