Homemade Flow Bench Part 1, How to Calculate CFM
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- เผยแพร่เมื่อ 25 ธ.ค. 2020
- This video goes into great detail on how to calculate CFM of Dry Airflow in a Pipe using two different methods. This information is critical to those who wish to build their own flow bench for cylinder head development in pursuit of maximum horsepower in their application.
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This is great, because I want to build a David Vizard style flowbench. He has a calibration plate design in his porting book.
I also have a video on how to build a flow bench.
Good explanation. Thank You. Currently building an orifice style flow bench. Have limited knowledge about the measurement side of it until now. I'm an operator at a 20MW research reactor in Sydney (OPAL). I'll bet the training you received is way more thorough than what we get here. Lol.
I am really glad you liked it and found it helpful! I will help as much as I can if you have questions. I think the research reactor stuff is awesome!
Thank you Tristan. As a instrument technician for 40 + years you are doing no more good than anyone on TH-cam explaining differential pressure measurement. I watch Favid Vizard on TH-cam and am going to flow test an old set of heads for a small Chevy engine. Just subscribed Sir. Keep up the good work.
I am sorry I did not do a good job of explaining it, I really did try to break it down simple for people who are new. Any suggestions?
@@tristan_white I think Ken meant Doing More Good and the "no" was a typo. Case in point, it's "David Vizard" not Favid... lol. You did an excellent job of describing your material, probably the best / most detailed video on youtube on the topic.
@@dfabeagle718 thank you, I will be doing more like this next year. I am in Nuclear Plant Assistant Unit Operator school right now, so my free time is nonexistent.
Thanks Tristan good info. Cheers from the U.K. 🇬🇧👍👌
Good deal!
@@tristan_white as long as we are out of the eussr😉👌
im honestly... glad i subscribed... u rock.. thank you for breaking this down im watching it now.. thanks agian i hope u had a merry christmas and a chance to see the chriatmas star.
I did, and thank you! I hope you find the video worth your time. Merry Christmas to you!
@@tristan_white hey is the comments spammed? on ur new video? like not hating but kinda weird how 3 suspect chicas r all about the flow bench?... when like me and 2 other guys comments but thank you for ur new video
@@jonathanschrader7881 yeah, not sure what that was all about. I removed the comments from the new video. Hope you liked the two videos so far. I will be doing more. The more interest I get the more I will do. If something I say doesnt make since just let me know. I am trying to make it all as simple as possible to understand.
Thanks for this . would there be or is there a flow bench that operates with lower power demand as a 60Amp supply and 6 fans is a real issue to me. I have 15 to 20 max. I appreciate it is a CFM and Inches water. requirement most probably.
Unfortunately if you want an apples to apples comparison with the industry you must be able to hold a steady state 28" H20 at all lift values. Depending on how well the port flows will determine the volumn of air it will take to maintain that pressure. However, if all you want to know is if you are making improvements then just make the bench as powerful as you can and just look for a larger pressure delta.
Absolutely true. Must air density +temperature +humidity and air direction vortex vs straight flow
Compensation is key
@@tristan_white disagree. Fire injector right before or at max air velocity will keep fuel atomized and suspended . Direct injection is 100% in cylinder rail injection only 85 to 90 % makes it into cylinder need for maximum velocity suspension. Direct injection minimizes variables
@@MrBlackbutang disagree with what?
@@tristan_white thought you were talking compensating manually?
@@MrBlackbutang no I agree with you was what I meant.
Is there any documented reference you can point me to for the formula on calculating the CFM using an orifice? Before I found this video I could not for the life of me find or figure out how to do this calculation. I finally decided to try TH-cam and here I am. But I would like some insight as to where the formula you're showing came from, if at all possible? It makes perfect sense when I used the factory orifce specs to this equation. I'm glad I found this video, everything is explained very clearly!
It is a simplified version of Bernoulli's equation. The square root of the differential pressure is directly proportional to flow rate. Watch my video later in the series for how to calibrate your bench. Once you know what flow you have using the pitot tube equation given a specific pressure drop across the orifice you can input it into the orifice equation. The square root of the dP is a percentage of a known flow at a fixed pressure drop. Does that help?
@@tristan_white Ya I'm definitely understanding it better, much appreciated in taking the time to write back!
@@Teddy8709 Anytime.
I built a U tube manometer I want to measure at 28 inches of water column. Do I fill the tube to 14 inches on both sides to equal 28inches in total or do I fill the tube to 28 inches on each side?
A 14" total displacement on each side would be 28".
Thanks for the prompt response.
@@VGHCX no problem, glad to help.
I learned a lot from this video. Just one question, do you feel with flowing a head meant for a turboed setup, does it make a differnce if you blow the air through the intake port or suck it through the intake port?
Using a power adder such as a turbo or supercharger changes nothing about how you develop an intake port. Keep in mind that a flow bench measures volume flow not mass flow. An intake port that flows 300cfm naturally aspirated will still flow 300cfm under boost. The difference is the mass of the air. A power adder generates an artificial atmosphere inside the intake manifold. For example, under perfect conditions we have 14.7 psia of atmospheric pressure available for the engine, so if you run 15psi of boost that means the engine sees ~30psia. This means you have twice as much oxygen available to facilitate the burning of twice the amount of fuel. More air does not make more power burning more fuel makes more power, but to burn more fuel you need a greater amount of oxygen. A power adder does not force air around the valve, all it does is increase the density of the air. To put it a different way, 1 cfm of air is made up of ~21% oxygen at atmospheric pressure, 300 cfm of air is also ~21% oxygen at atmospheric pressure. When we run 10 psig of boost we just increased this number by 68% so now we have ~35% oxygen available to burn more fuel and make more power. Make since? Build an engine to make power where you want the rpm band for your application to be, then boost will literally just shift the entire curve up. The power curve itself won't change, just move up on the y-axis.
@@tristan_white I understand what you are saying but I was just wondering if blowing through or sucking the air through while on the flow bench would make any difference. This will be on a 6cyl tractor that runs about 70 psi boost
@@TheJohndeere466 no, it makes no difference at all as long as the airflow is traveling the way it would in the engine. All the head sees is the differential pressure. When you suck through (what basically every bench does for intake port testing) the bench generates an atmosphere that is at a lower pressure the atmospheric. Air always passes from high pressure to low pressure.
@@tristan_white Oh thanks. I am designing a recast head for this tractor and I was going to have a guy flow it but he said on boosted engines, he always blows the air through on his flow bench. Not sure how he does that.
@@tristan_white I am working on designing a head for this tractor. We almost won the points championship this year and we won more pulls than anybody. The guy that did win the points was caught running illegal fuel but they checked it before he ran and allowed him to change fuel before he pulled. They didnt check fuel everytime so im sure he ran some of pulls with hot fuel.
So we are close. My plan is to design a head that flows real similar to the head we have but with the smallest port I can get away with. Our head also has siamese ports where 2 ports are combined until they get back in the head. I want to seperate the ports in the head and the intake to allow longer ports. This head was opened up a little and we did gain a little on top but we lost some torque. So we would like to get both. I am casting just one cylinder versions of the head and experimenting with the ports. I will eventually get the head flowed by a professional but I would like to try building a flow bench that I could tinker. with. I really dont care if it tells me how many cfm it flows. I just want to know if what I am doing is making it better or worse.
I was thinking of using a leaf blower and blowing air into the intake port and measuring the pressure right before the intake port with a well manometer mounted on slight angle from horizontal to allow for measuring very slight pressure changes. I figure more pressure equals less flow and less pressure equals more through the head. What are your thoughts.
I have build a flow bench using testo 510 but my differential pressure is only 0.2400 psi average with 3 vacuum pumps. What can be wrong . My orifice is a PTS 350 cfm @9" with a 2.933" hole.
What are you trying to flow test, and what is the test pressure set at? Whatever your flowing is at 57cfm if the calibration is correct for the orifice. What are you expecting for flow or dP?
@@tristan_white I’m actually now setting up the bench. The plan is to flow some 4 valve cylinder heads from some imports. Is there suppose to be a Great Depression before and after the orifice plate where the testo lines connect? I have great suction at the end of the 6” pipe but little suction where the testo lines connect
@@tristan_white what is the correct position to have those probes for the testo. Could I have them in a “dead” zone ? With no pumps on my DP reading is 0.0060. Then when I turn on the 3 pumps it goes to around .2500 with the 4” hole at the end of the pipe fully open and no cylinder head bolted to it
@stuntr1 make sure you zero out your testo. If the bench is off there should be zero dP. Also, make sure you have the testo just looking at dP in inches of water (inH2O). The pressure taps should be just like I have them in the video, as close as humanly possible to the orifice plate on both sides. You want them away from airflow or you will have the venturi effect and it will mess up your readings. Once all of this is verified do it again. If you get the same reading let me know.
@@tristan_white how do I zero out the testo?
Where do I get a calibrated orifice?
I purchased mine from performance trends for pure convenience, however if you have a shop close by that can stamp you out a 3" sharp edge orifice than it would probably be cheaper. You can calibrate your bench on your own. If you need help with that let me know.
@@tristan_white Thanks buddy. Once I create a successful analog system. I will go digital. I am well versed in microcontroller and application real time programming.
The inverse relationship is likes squeezing a hose
Since flow is not linear trying to measure 29%or less flow is hard to determine. When building an engine for boost you run a lower compression ratio to compensate for the boosted pressure. .
Radius of 6" is not .5 ft it is .25 ft.
Yes, I realized I wrote it down wrong when reviewing the video, if you watch the section where I explain it I had a pop up text that shows the correction.