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Volumetric Efficiency
- Thread starter dlehman
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GregLocock
Automotive
As Shaun implies, you need to measure it at full throttle.
You could measure the incoming air flow rate using an orifice plate with a U tube manometer across it, although calibrating it would be a pain.
Cheers
Greg Locock
You could measure the incoming air flow rate using an orifice plate with a U tube manometer across it, although calibrating it would be a pain.
Cheers
Greg Locock
Another example: I have seen customers buy a pair of heads from me that are drastically better on the flow bench compared to the ones they are giving up. Once they put them on the motor, they sometimes are pretty disapointed. Why? sure they have great low and mid lift flow, and better high lift flow than their old heads. The problem is when they finally ask me to go hunting for the problem based on info they give me,I always ask them what the cam is. 9 out of ten of them are extatic, but once in a while someone will buy a cam elsewhere because they won't pay the price. Upon answering my cam question, I find that it is almost always some really STUPID cam. You can't bolt a 550+HP set of heads onto a 350 Chevrolet and put a Hydraulic/Hydraulic Roller cam in the motor and expect your new investment in heads to come anywhere near the power numbers you were promised. AIR FLOW RESEARCH will send customers my way who are origionally upset with them, and then be made to understand that it is their rediciously stupid and miss-applied cam. They get the right cam and their 13 or 14 second 1/4 mile street car now runs in the mid 11's or low 12's.
I can't begin to stress that the CAMSHAFT is the great airflow controller in the engine and stated another way, is the great Governor of Volumetric efficiency!
Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)
I can't begin to stress that the CAMSHAFT is the great airflow controller in the engine and stated another way, is the great Governor of Volumetric efficiency!
Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)
- Thread starter
- #6
This is kind of the direction that I am going in too. I have a specific motor that I am trying to fit a cam to, but I don't have access to an engine dyno or other high tech measuring equipment. Are there methods to compute the theoretical air flows through the engine to figure the peak performance envelope of the engine? I know I could just pick up the phone and call a cam manufacturer, but I am an engineer at heart and would rather tinker and play with the numbers than take the easy road.
I like the idea of the orifice plate and manometer, but one thing that ShaunT says seems as though it would hold very true: the camshaft is the great airflow controller. So would measuring the airflow with one cam lead me to any conclusions about how a different cam would effect airflow through the same engine? It seems to me that I would have to measure a number of cams with slightly varying profiles to begin drawing any conclusions of that nature. This would unfortunately be a very cost prohibitive experiment.
What about simulation software? Is there anything out there for around $200 or less that would get me in the ballpark? Any other ideas? Someone must have done these type of calculations before. Does anyone know any equations that would apply?
I like the idea of the orifice plate and manometer, but one thing that ShaunT says seems as though it would hold very true: the camshaft is the great airflow controller. So would measuring the airflow with one cam lead me to any conclusions about how a different cam would effect airflow through the same engine? It seems to me that I would have to measure a number of cams with slightly varying profiles to begin drawing any conclusions of that nature. This would unfortunately be a very cost prohibitive experiment.
What about simulation software? Is there anything out there for around $200 or less that would get me in the ballpark? Any other ideas? Someone must have done these type of calculations before. Does anyone know any equations that would apply?
Not only do different cam profiles change things, but a Lobe Seperation Angle change of 4* will dramatically change things even with the same cam profile/family. I appreciate your desire to be the Detective/Engineer through research.
I also can tell you through mountains of experience that you won't find hardly anyone in the cam business that can tell you something and then explain it. It is hilarious to me when a cam guy answers a customers questions by saying: I don't know, let's see what the book say's. The other thing you will find is they will tell give you answers largely in part from middle-man or third party reports/feed-back. My Personal standard practice is: be nice to anyone who converses with me about cams/engines, even if I know that he is picking my brain with no intention of buying. I swear to myself that if I am nice, no matter what, he will come back. It has not EVER failed me yet. They always call me more screwed up then before saying: after trying everything everyone said, you are the only guy who has told me any thing that works and everything you said about what these other cams would do was right on, now how much for a cam, and can you re-grind these ones over here that didn't work out?
I get this all of the time. When you take an 11second 1/4 mile car and change cams and shave a full second off, or an 8 second ride and shave off 2-10th's without any other changes, it tends to make people smile really big. Especially when the car stands straight up. It also wins them and all their buddies for life if you treat them good.
So, play on, I'll be here to help any way possible.
Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)
I also can tell you through mountains of experience that you won't find hardly anyone in the cam business that can tell you something and then explain it. It is hilarious to me when a cam guy answers a customers questions by saying: I don't know, let's see what the book say's. The other thing you will find is they will tell give you answers largely in part from middle-man or third party reports/feed-back. My Personal standard practice is: be nice to anyone who converses with me about cams/engines, even if I know that he is picking my brain with no intention of buying. I swear to myself that if I am nice, no matter what, he will come back. It has not EVER failed me yet. They always call me more screwed up then before saying: after trying everything everyone said, you are the only guy who has told me any thing that works and everything you said about what these other cams would do was right on, now how much for a cam, and can you re-grind these ones over here that didn't work out?
I get this all of the time. When you take an 11second 1/4 mile car and change cams and shave a full second off, or an 8 second ride and shave off 2-10th's without any other changes, it tends to make people smile really big. Especially when the car stands straight up. It also wins them and all their buddies for life if you treat them good.
So, play on, I'll be here to help any way possible.
Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)
- Thread starter
- #9
It makes it sound like cam design is all art and no science.
Alternatively, cams can be designed through a combination of testing and analysis tools:
1) Flow bench testing is used to come up with flow vs lift characteristics for the ports + valves
2) A performance simulation model of the engine is constructed, using software such as WAVE, which incorporates the flow information gathered through testing
3) The engine performance simulation is used to calculate valve lift profiles that will give the desired engine performance throughout the running range (fuel efficiency, power output, etc)
3) A kinematic valvetrain analysis tool, such as CAMSPRING, is used to generate candidate lift profiles that approximate the desired lift profile while providing suitable contact stresses, oil entrainment, oil film generation, etc.
4) A dynamic valvetrain analysis tool, such as VALDYN, is used to study the valvetrain dynamic performance with the candidate lift profile, and identify potential problems with separation ("float"
, seating velocity, spring surge, etc.
5) 3 & 4 are repeated iteratively until satisfactory results are achieved
6) Cam cutting ordinates for the final profile are generated, and test cams are manufactured...
The WAVE analysis by itself can tell you (with amazing precision) how changes to the lift profiles will affect engine breathing, power output, efficiency, etc. The later steps are used to make sure that your preferred cam profile will actually last as long as you need it to, and that you won't pump up your lifters, float your valves, break your springs, etc.
Alternatively, cams can be designed through a combination of testing and analysis tools:
1) Flow bench testing is used to come up with flow vs lift characteristics for the ports + valves
2) A performance simulation model of the engine is constructed, using software such as WAVE, which incorporates the flow information gathered through testing
3) The engine performance simulation is used to calculate valve lift profiles that will give the desired engine performance throughout the running range (fuel efficiency, power output, etc)
3) A kinematic valvetrain analysis tool, such as CAMSPRING, is used to generate candidate lift profiles that approximate the desired lift profile while providing suitable contact stresses, oil entrainment, oil film generation, etc.
4) A dynamic valvetrain analysis tool, such as VALDYN, is used to study the valvetrain dynamic performance with the candidate lift profile, and identify potential problems with separation ("float"
, seating velocity, spring surge, etc.5) 3 & 4 are repeated iteratively until satisfactory results are achieved
6) Cam cutting ordinates for the final profile are generated, and test cams are manufactured...
The WAVE analysis by itself can tell you (with amazing precision) how changes to the lift profiles will affect engine breathing, power output, efficiency, etc. The later steps are used to make sure that your preferred cam profile will actually last as long as you need it to, and that you won't pump up your lifters, float your valves, break your springs, etc.
- Thread starter
- #12
Now we are getting somewhere. First of all, Shaun, I live in Goshen, Indiana (north-central Indiana; near South Bend).
Could you possibly direct me to some information about the programs mentioned? I am assuming that Wave is some type of computational fluid dynamics program and the other two, Camspring & Valdyn, are some type of specialized engine simulation tools(?). If you know of any associated websites, I would appreciate any links you can supply.
I don't know much about flowbenches. If I am correct, in its most basic form, it could simply be a manometer and orifice plate, as suggested by someone else, a high-volume vacuum source, some method of measuring valve lift, and a pair of pressure guages to measure absolute pressure on each side of the head. Am I on the right track here?
Forgive my ignorance of such matters, but I am more involved with electrical design than mechanical. However,I am trying very hard to learn everything I can. Thank you all for your assistance.
Could you possibly direct me to some information about the programs mentioned? I am assuming that Wave is some type of computational fluid dynamics program and the other two, Camspring & Valdyn, are some type of specialized engine simulation tools(?). If you know of any associated websites, I would appreciate any links you can supply.
I don't know much about flowbenches. If I am correct, in its most basic form, it could simply be a manometer and orifice plate, as suggested by someone else, a high-volume vacuum source, some method of measuring valve lift, and a pair of pressure guages to measure absolute pressure on each side of the head. Am I on the right track here?
Forgive my ignorance of such matters, but I am more involved with electrical design than mechanical. However,I am trying very hard to learn everything I can. Thank you all for your assistance.
If you know of any associated websites, I would appreciate any links you can supply.
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