66deuce

iTrader: (1)

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.

LSONE

iTrader: (1)

wow Tony, i'm sure alot of people are really going to appreciate this. once i save up some money I'll be giving you a call

Tony Mamo @ AFR

iTrader: (13)

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....

Damn....if I could only remember his name.

Ryne @ CMS

iTrader: (10)

Good comparo..........

gollum

iTrader: (1)

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

LS7 Cylinder Head, 2.200" Int./ 1.615" Exh, 4.125 plate

Int/Exh
0.100...71/60
0.200...145/120
0.300...222/159
0.400...271/192
0.500...315/207
0.550...332/214
0.600...348/219
0.625...350/220
0.700...359/222

disco192

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.

disco192

Would you be referring to Bret Bauer?

2c5s

iTrader: (11)

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?

disco192

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...

gollum

iTrader: (1)

Some are educated beyond their own intelligence.

2c5s

iTrader: (11)

Scoobie

iTrader: (8)

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.

Visceral

iTrader: (1)

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.

70 TA

I'm not an engineer but here is the way I see it.

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.

Visceral

iTrader: (1)

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.

SStrokerAce

iTrader: (2)

Might have been J-Rod too....

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

Bret

66deuce

iTrader: (1)

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.

Tony Mamo @ AFR

iTrader: (13)

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.

Thanks,
Tony

disco192

Good info...

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

66deuce

iTrader: (1)

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.