This is not the reason why mid lift numbers are important at all. They could get hit 12 times for all I care... the fact is, on an agressive cam, the amount of time spent under 200 lift is very small compared to the time spent over it. The steeper the lobes, the less mid lift matters. This is a pet peeve of mine that has carried over from the days of flat tappet cams and non-agressive lobes.
i understand what you are saying,but mid lift flow on a pro stock motor is something like .400-.450,as compared to .275 for my TR220,or around .300 for a more aggressive grind.kind of an apples to oranges comparison.and you have to look at the valve events for a street motor compared to a pro stock or drag race only motor.so yes,mid lift numbers are important for a majority us,it all depends upon the lobe profile and valve events of your cam.
Great info....Looking at the list I have presented, what cylinder heads would you say subscribe the most to some of the principles discussed?? There is a guy on this board who has been trying to preach something very similar to the comments David Reher made....
Duh, can anyone post some flow numbers of the new GM LS7 427 head? I here the new heads use a different 12 degree intake valve seat to work better with the new port design. Never mind
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My point wasnt to necessarily say that they are insignificant, because they are not. They do affect performance, but not as much now as they used to and it is NOT because they get hit twice. That is a myth I hear WAY too much, and I am trying to dispell the rumor.
Quote:
Originally Posted by 66deuce
i understand what you are saying,but mid lift flow on a pro stock motor is something like .400-.450,as compared to .275 for my TR220,or around .300 for a more aggressive grind.kind of an apples to oranges comparison.and you have to look at the valve events for a street motor compared to a pro stock or drag race only motor.so yes,mid lift numbers are important for a majority us,it all depends upon the lobe profile and valve events of your cam.
Honestly, I dont have years and years of experience, but I do know more than your average Joe on this board. I am a student in Aerospace engineering and have taken more fluid dynamics/mechanics classes than most people on here, so I think I have some credibility to speak on cylinder head flow. If you dont believe me, why dont you read this article by David Reher (a professional engine builder).
Well Ive run 3 sets of heads and 6 differnet cams (not all my personal cars, but I did install them), but thats beside the point. I know enough to know what I do and dont know. If you wanna call me out, go for it... Im not trying to insult anyones intelligence or badmouth any business in particular. If you want to have an intelligent conversation about the importance of midlift and how they affect performance, then lets by all means.
I dont think my lack of experience automatically makes me any less knowledgable. I have friends who do this for a living who dont know about this stuff as much as I do...
Quote:
Originally Posted by 2c5s
Seems like the article backs up the AFR head to me. Just curious, how many cyl. heads have you ported, flowed and run on an engine to compare?
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question...all of these cylinder heads are larger then 225 cc. I understand they are mostly stage 3 and therefore intended for bigger cubes but with the added flow of the 225, would it not also be a good choice for a 346. I have heard this head was designed for larger cubes.
Thanks,
mr. on the fence.
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Before anyone starts letting their "knowledge" dick length become more important than their judgement, I want to share a few interesting numbers from a typical constant acceleration intake lobe profile, 236 deg. at .050, .603 peak lift with 1.7s.
Total duration spent between .01 and .10 valve lift: ~54 degrees
Total duration spent between .10 and .20 valve lift: ~32 degrees
Total duration spent between .20 and .30 valve lift: ~30 degrees
Total duration spent between .30 and .40 valve lift: ~32 degrees
Total duration spent between .40 and .50 valve lift: ~40 degrees
Total duration spent between .50 and .603 valve lift: ~97 degrees
Valve Lift during 90 degrees of peak piston velocity (downwards, obviously):.40 -> peak -> .582
Now... this does oversimplify (in some ways, grossly) the dynamics of valve timing, and very few lobes these days are exactly constant-acceleration.
But it certainly illustrated how important .40 and above flow numbers are in comparison to the .20 to .30 flow numbers. Obviously a head that goes turbulent at .55" of valve lift could really mess up cylinder filling during peak piston velocity. MANY after-market LS1 porting jobs go turbulant at .550 and above.
So... don't ignore the fellow that doesn't have 20 years of cylinder head porting experience... he was (IMHO) speaking in the right direction.
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With a port having a poppet valve in the way of flow, low or mid lift port velocity I would think must be very important to cylinder filling.
The air flowing in must have some amount of momentum but still the valve does close and interupt the momentum of flow to each cylinder every cycle.
So my way of thinking is that with a properly designed port/valve combination the low/mid lift compliments the high lift flow in a running engine.
It would be interesting to see a breakdown of how many degress a valve actually spends at each lift point. I wonder if Tony has done this for the 224 228 cam AFR recommends for their 205 head.
It must be a lot different from that simple example above since even the opening and closing rates are much different.
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It must be a lot different from that simple example above since even the opening and closing rates are much different.
Outside of the off seat aggression and somewhat gently letting it back onto the seat, the only thing cam manufacturers have done beyond a constant acceleration curve is to figure out how to use the variable spring pressure to open the valve *faster* than in my example. My example above *overstates* the importance of mid-lift numbers.
__________________ -Chris N. Miles Raymond: "No, if anyone orders Merlot, I'm leaving. I am NOT drinking any fu^&*%g Merlot!"
All the Reher-Morrison boys have some good things to say.
"Without question, the most common mistake in racing is to buy parts impulsively without having a clear vision of where you want to end up. The result is often a pile of mismatched pieces that will never work together properly." - David Reher
But it certainly illustrated how important .40 and above flow numbers are in comparison to the .20 to .30 flow numbers. Obviously a head that goes turbulent at .55" of valve lift could really mess up cylinder filling during peak piston velocity. MANY after-market LS1 porting jobs go turbulant at .550 and above.
So... don't ignore the fellow that doesn't have 20 years of cylinder head porting experience... he was (IMHO) speaking in the right direction.
i agree.i'll admit my thinking on this has been changed somewhat after reading this thread,and looking at the VEs of a few cams.lets keep this discussion going.
Total duration spent between .01 and .10 valve lift: ~54 degrees
Total duration spent between .10 and .20 valve lift: ~32 degrees
Total duration spent between .20 and .30 valve lift: ~30 degrees
Total duration spent between .30 and .40 valve lift: ~32 degrees
Total duration spent between .40 and .50 valve lift: ~40 degrees
Total duration spent between .50 and .603 valve lift: ~97 degrees
But it certainly illustrated how important .40 and above flow numbers are in comparison to the .20 to .30 flow numbers. Obviously a head that goes turbulent at .55" of valve lift could really mess up cylinder filling during peak piston velocity. MANY after-market LS1 porting jobs go turbulant at .550 and above.
Good info....
I will be plotting the actual crank degrees on the 383 project currently in the works (with a 234' XER intake lobe) when it comes time to degree the cam, check P to V, etc.
I have some things I would like to add but I'm buried right now. I will probably amend this post later.
Also, I updated the list to reflect an additional four cylinder heads I recently tested that fit the parameters of this comparison (I am only including results of the larger, higher flowing cylinder heads I have had the opportunity to flowtest). Note that "F" and "P" were from the same vendor as you might have guessed reviewing the figures). Any changes in the averages were also updated based on the recent additions.
I think people were taking my words out of context. Midlift IS important, but moreso on slower rate cams. It also has nothing to do with the fact that they get hit twice. That was my point.
-Stu
Quote:
Originally Posted by Visceral
Before anyone starts letting their "knowledge" dick length become more important than their judgement, I want to share a few interesting numbers from a typical constant acceleration intake lobe profile, 236 deg. at .050, .603 peak lift with 1.7s.
Total duration spent between .01 and .10 valve lift: ~54 degrees
Total duration spent between .10 and .20 valve lift: ~32 degrees
Total duration spent between .20 and .30 valve lift: ~30 degrees
Total duration spent between .30 and .40 valve lift: ~32 degrees
Total duration spent between .40 and .50 valve lift: ~40 degrees
Total duration spent between .50 and .603 valve lift: ~97 degrees
Valve Lift during 90 degrees of peak piston velocity (downwards, obviously):.40 -> peak -> .582
Now... this does oversimplify (in some ways, grossly) the dynamics of valve timing, and very few lobes these days are exactly constant-acceleration.
But it certainly illustrated how important .40 and above flow numbers are in comparison to the .20 to .30 flow numbers. Obviously a head that goes turbulent at .55" of valve lift could really mess up cylinder filling during peak piston velocity. MANY after-market LS1 porting jobs go turbulant at .550 and above.
So... don't ignore the fellow that doesn't have 20 years of cylinder head porting experience... he was (IMHO) speaking in the right direction.
I think people were taking my words out of context. Midlift IS important, but moreso on slower rate cams. It also has nothing to do with the fact that they get hit twice. That was my point.
-Stu
i looked at the valve events of several cams and compared them to the flow # Tony posted and can definately understand your thinking on this now.
