Flow starting and stopping is very relevant, and yes...a flow bench doesn't represent all of the conditions in a running engine. Like any other tool, it is up to the user to fully understand how to fully apply their knowledge. Guys like David Vizard and Harold Bettes incorporated flow benches as a part of their repertoire. That tool is largely the reason people can bolt things together with any predictability.
Well, DAH. X flow characteristics = will have the potential to run like = Y. After doing the flow test and then the final engine run test either on a dyno or at the track, tracking the same types of heads will allow the porter to hone in his skill using the reference of a flow bench to be able to predict how and engine will perform. o No: When we're talking about pistons moving with FPS(feet per second) and the number is well over 1,000 FPS vs a machine with a vacuum motor suctioning(creating a pressure drop, however you want to look at it) through the head's port is 2 VERY different things with 2 VERY different time frames that air is moving in and that's why I call a flow bench a reference tool. Just sayin, just because the flow may be measurable of stopping on a flow bench doesn't actually mean it has enough time to stop in a running engine, fluctuate maybe, stop, no. Derek
X-mas shopping now you say? The next good sale won't be until a day after Christmas! :eek2: ou: Ok then I'll shoot for the January thaw when(if) that happens. :TU: Derek
Well duh! That's why there are very accurate formulas based on what we see on the bench that assists in the planning of engine builds! I'm assuming the entire world knows that flow benches don't accurately duplicate every running condition, therefore under that assumption I conclude that your description is an attempt to diminish what professionals use to execute builds or develop products as mere observational tools. I might be wrong though.
Someone else mentioned how 'flow would stop' and there would be 'reversion', I was simply pointing out that there just isn't enough time for any of that nonsense to happen in a running engine the way that person was trying to explain things. Must of been from an over active imagination from imagining in slow motion air entering an engine with how it goes through a flow bench? Wasn't trying to discount or diminish the value of what flow testing can bring to the table, was just saying(which you seem to agree) that how air flows on a flow bench will be totally different than how it will flow into an engine. Derek
These overactive imaginations coupled with some math skills and a driven desire to want more and prove it are what led to the formulas, programs, and anything modern we've accomplished since the beginning of the piston engine. It's what put planes into the air. If you think about it, we didn't start off with wet-flow benches @ 100" depression and slowly hone in perfection of technology over a century. Very crude benches can offer the imaginative and intelligent crafter as well as the professional engineer far more insight than suspected. I'm not sure which statements you are being critical of and due to my not wanting to re-read the thread... I'm somewhat blindly defending a supposed position, but I'll go on a limb and say that anything I've read from Mart or SteveM and 66gsconv rings with 100% truth. Not being critical of you Derek, but I guarantee that even if you were to put together and spend some time with a wooden bench powered by a couple of shop vacs and read the Harold Bettes book along with a couple others, it would completely change your entire approach to engine building. With your attention to detail, willingness to put the time into executing things correctly, and being that you are your own shop without employees (overhead, SGA costs), you would have a serious advantage over anyone local with a Superflow or similar bench.
In general the flow numbers can be a useful measurement to show a gain over a baseline as long as the porting does not kill the velocity, distribution, and atomization... Of course this is the simplified summary but the fact is that people use flow numbers to quantify the head performance potential and then engine dyno is the most repeatable measurement of the actual engine performance... Of course some track data (MPH) to back up the dyno numbers. Just too many variables to use the track MPH as the main measurement for engine power... So flow testing and engine dyno data are the two measurements we are used to hearing about and I don't see that changing any time soon. We just need to understand that there is so much more in play and not just head flow numbers....
I think it's been stated over and over that CFM #'s are as wide as a barn door when trying to pinpoint the cross hairs of power potential. The flow bench CAN show velocity and with your measured CSA #'s derive a more accurate starting point than using CFM with a sim program, which can be backed up with a dyno predictably. They do teach this stuff in college textbooks. The same formulas used by engineers of days gone by are still entirely valid, as well as used with the computer sims. Useful stuff is abound with the internet at your fingertips. The shell game being played by less than honest or protective marketers is that they are intentionally showing you ONLY so much. (Not referring to anyone here, of course). If you don't have the velocity and CSA data, some programs assume the valve itself is the CSA...*and if it really is*- in the assembled engine, then they get much more accurate (not with respect that VJ's and valve OD/throat relationships can drastically alter flow amounts). [My point being that any skilled head guy with a flow bench and some basic engineering formulas can put your engine on point with desired goals. It is more predictable than the dyno's themselves.]
Blindly is right, nothing to do with anything those guys wrote. You are being a you know what stirrer for even insinuating that! I do this for a hobby/side job, I have zero need to own my very own flow bench. I'm the custom machining/build guy that I can at times trade that service for port work, or off the shelf aftermarket CNC or unported heads are utilized, or I may guide the person the engine is being built for how to do a basic port job that will equalize all the ports to slightly better than they flowed before. I'm the guy that did the custom machining to move the valve locations on the sbb 350 heads so 2.02" intakes will fit with 1.60" exhaust valves, all the while making sure the shrouding stays at a minimum. They were moved closer to the centerline of the bore and at the same time away from each other so those sizes would fit with each other. Otherwise 1.94" and 1.550" would be the max sizes that would fit, might even of been the 1.500" ex. valve?(its been a while) I do the rod narrowing so the nascar take out rods will fit in a sbb or the 5.4L rods will fit on a 455...etc.. I machine the block to convert it to splayed 4 bolt main caps and machine the caps so all they need is align honed instead of align bored and then honed. You know, the machining that most others don't have a clue how to do. I have even machined a sbb 350 girdle with a manual Bridgeport. Just a few of the custom machining tasks I do. With my regular job, no heat in the garage in the winter and no AC yet in the summer and the mentioned above doesn't leave me much time to mess with a flow bench.(I wouldn't want it in my house either) Maybe if in I hit the lottery I'll get one. Derek
Just the simple fact that we have a period where both valve are sealed off means that flow in or out of the motor fully stops and starts when it has the to do so rpm wise, or flow rate wise ,as the motor comes up in rpm the flow will still slow down to a large degree when compared to whatever peak velocity it may achieve.
I think I get what Derek is saying. Air flows into the engine at a fairly high rate, and the train ain't a stoppin'. For the most part, it goes past the venturi one way. The valves are opening doors and slamming shut. The compressible train crashes into the closed door and bounces around the intake. There's some second and third wave reflection coinciding the runners to the cylinder in an rpm range, offering some ramming assistance. There's also an intense pull from the header tube at overlap to help pull the mix into the cylinder, as much as 9x more intense than intake ramming. All of this wondrous imagination can be closely approximated by formulas that originate from nearly a century ago.
That "wondrous imagination" needs to NOT imagine how air flows on a flow bench flowing the same way as it does in a running engine is what my point is. On a flow bench typically the intake manifold isn't even bolted on the head and all the other things going on as you pointed out either. Derek
I'm better at humor attempts than writing explanations on induction tech. (that one failed, on both accounts) It isn't up to 100 years of science to prove a concept to anyone. It's up to you to accept it. I am not intending any disrespect. I had to read a few of Vizard's old books to understand things better. "Be the ball", lol. You can see a lot more on a bench than one might think. For example...you can momentarily lay something across a port to block it and it will easily pull 100"+, and hopefully you can release it before it sucks all the fluid out of the manometers. Even though there wouldn't be a pressure differential across both sides of your calibrated orifice, the port still sees it. I'm not suggesting any validity or procedures to that, just that everyone who plays with a bench plays with smoke or misted fluids. One also has to keep in mind that the depression below the valve changes throughout it's cycle in the running engine. The cycle begins with an already exhausting cylinder, either subject to reversion or scavenging depending on rpm range, so with a huge cam and being run at a low rpm range...there isn't much pressure differential. Obviously that changes at high rpm when the piston is at peak speed (rod at 90* angle, appx 72* atdc), then the port reaches critical velocities, thus arriving to peak torque and eventually peak hp, just before the port is sonically choked off. Vizard has been a proponent of the use of floating depression (even if low pressure) due to the engine's range of depression. It's still a better tool than not having one. The usefulness depends far more on the user than the machine. [My comment on buying/building a bench and reading a book or two was for better understanding, so that it would incite constructive conversation...I might have misinterpreted acknowledged validity of such testing and confused that with a person without a flowbench arguing with many people who do, and the supporting education and history behind it] As far as 'most of the time a head is being flowed without the intake'...that's exactly where your $$ takes you. If you kindly pay them (or me) by the hour, even if it involves making fixturing or other apparatii to support said intake, along with paying for intake flow testing separately, then at that point your wishes will come true. Most of the time you are looking for an intake that flows 10-15% more than the head on all runners and more importantly...doesn't change the direction of the flow patterns or characteristics at the manifold interface. The reason you don't see more testing like this is (once again)...........$$. If there's a dramatic difference in the flow path due to said manifold, it's expensive to change. Other than change intakes, what are you going to do about it? Also...it's been proven that even if the manifold presents a restriction that an increase in port flow still shows up as a power increase. Truthfully, you might be better off paying a retainer to a divorce attorney than for all-inclusive intake testing, as that's exactly where you are headed with such ventures... (No honey, we NEEED this , lol)
Here's what you don't get; You're trying to debate me on the premise that you think that I'm am discounting the usefulness of a flow bench which is TOTALLY false. Its a great reference tool that has repeatable results with the what you say the 100 years of math that can convert those flow bench numbers into how they would act on an engine. Again, a flow bench is a great reference tool. To say that someone can be a better engine builder if they play with a flow bench is ridiculous, and a back handed insult to boot! How is playing with a flow bench going to help anyone measure tolerances better or use a stretch gauge, or how to torque a bolt better? A flow bench has zero to do with the quality of a build.(period) Of coarse flow numbers are good to know for the design of the build which are 2 different things, and which I do use for choosing the compression ratio and cam. My whole point was simply that air doesn't flow the same as on a flow bench.(period) Which you seem to agree with but are still insisting on debating me, WTH? As well as it would seem, insisting that I am discounting the usefulness of a flow bench, which I am NOT. If you still don't get it please stop trying to debate me on something we already agree on! :beers2: Derek
Not debating, restating things for the benefit of the readers of the forum. I did interject a qualifier something to the effect of, "I may be mistaken", which was because I didn't have time to carefully re-read this. Thanks for the clarification of how you interpret engine building skills to include machining and tolerancing. I have a similar background as well. We were apparently splitting hairs over whether or not induction systems were being included in that definition, no big deal. In no way was I implying inferiority of said skills. I was stating that during certain periods of the engine's rotation air does flow like a flow bench, and that there are ways of getting things closer to running conditions beyond that. Some guys test to much higher pressures than 28". Some test wet. I'm also stating that even with unlimited budget and resources, it isn't needed to go that much further with flow testing capability equipment. Goals can be met already. I'm being persistent about this because I read so much misinformation about the subject repeated by people who don't use the equipment in general. I thought my qualifier released the pressures of singling anyone out.
Now that that's out of the way, let's talk about the effects of how air flow stops and starts and its effects on induction flow (vacuum, reversion, pressurized turbulence before the valve, etc.), and how this affects or compares to translating what one might see on a flow bench vs what's actually happening inside the engine in terms of FPS and the importance of velocities surrounding these. Add in valve timing events and how the cam's design influences this, not just in lift and duration, but event separation (including LSA, ICL/ECL and duration intensities (between .050 and .006, as an example) to show how important partial valve opening events really are, which influence scavenging and engine torque). Consider also the differences between single and dual plane induction, as well as header size and lengths, exhaust efficiency, etc., and this is just the air flow aspect of an engine. It soon becomes evident as to why engineering and science is important to building engines as is using the tools and parts created by (engineers and science). This is nothing new, it's been talked about before here not too long ago (by me and others), and now is a great opportunity to perhaps go into a bit more depth as to why, some of which has already been addressed in this thread.
