Importance of mid-lift flow numbers
On The Tree
Joined: May 2004
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Originally Posted by Greg Good
Tommy, the mid-lift and high-lift thing is much like a see-saw. If you favor one too much, you hurt the other. You can set up the valve job with a steeper bottom cut, open up the venturi, and lay the short side radius back for killer high-lift numbers, but the mid-lift flow will suffer. Mid-lift likes a fatter short side radius, a shallower bottom cut, AND and smaller venturi to flow well. So, basically, the valve job, short side radius, and venturi size is specific for either mid or high lift.
The trick that all head porters try to do is find a happy place where mid and high lifts perform well. These days, whre people are running so much lift, up to .650" on the street, finding a combination of all those things so that the head has good flow everywhere in the curve is tougher.
The trick that all head porters try to do is find a happy place where mid and high lifts perform well. These days, whre people are running so much lift, up to .650" on the street, finding a combination of all those things so that the head has good flow everywhere in the curve is tougher.
On The Tree
Joined: Sep 2004
Posts: 188
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From: Houston, TX
Flow curves act just like dyno curves.
Some are good down low with nothing up high.
some are bad down low and good up high (what we call peaky).
And then some are pretty damn good everywhere, with a lot of area under the curve. That's what we want.
Some are good down low with nothing up high.
some are bad down low and good up high (what we call peaky).
And then some are pretty damn good everywhere, with a lot of area under the curve. That's what we want.
Thread Starter
On The Tree
Joined: Aug 2004
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Very good comments so far, the thing I like to see is average flow numbers. Like FASTONE touched on, take all of the flow values and take the average. That my friends is what makes a great cylinder head, good averages. That is the reason LS1's run so damn good to begin with, a .500 cam and cylinder heads that flow like aftermarket street heads for SBC, all from the factory. Taking these engines apart is like taking apart a well planned street engine, good rockers, long rods, and so on.
6600 rpm clutch dump of death Administrator
Joined: Dec 2001
Posts: 4,983
Likes: 13
From: Texas
I was speaking with Erik (racer 7088) about this this today. We discussed head flow vs port volume, etc...
One thing to keep in mind is for instance how a port flows is important when the valve initally opens. That is when you have positive pressure, and the valve will fill the chamber. Now, once that equalizes, and the piston is on its way back up, velocity is what is going to continue to fill that cylinder. One of the issues with cylinders heads is you can get any flow you want if you make the port big enough. But, at the expense of velocity. You can also close up the port and increase velocity at the expense of flow. Then the problem is getting the air to get moving which means you can make good low end power, but after x rpm the head won't work.
Mid and low lift numbers tell alot about how a head is working. Also, the motor spend a lot more time in the mid and low lift numbers than it ever does a peak lift. So, that important not only in terms of the heads, but also in terms of the cam design, but folks only seem to look at .050 and call it a day... .200 .300 .400 those are all important.
BTW, y'all should consider yourselves fortunate that Greg is contributing to threads on here. Greg's skills in the Houston area are well know and much sought after. I myself am always interested in reading his comments.
Same for Larry Meaux. If you go over into Louisianna you'll see Meaux Racing Heads ground into the sides of a lot of cylinder heads. All the cars I have seen them on tended to be pretty darn quick...
These guys have more than a passing with how to make heads work. So, it would hurt to pay attention to what they have to say. You might end up going faster if you do...
One thing to keep in mind is for instance how a port flows is important when the valve initally opens. That is when you have positive pressure, and the valve will fill the chamber. Now, once that equalizes, and the piston is on its way back up, velocity is what is going to continue to fill that cylinder. One of the issues with cylinders heads is you can get any flow you want if you make the port big enough. But, at the expense of velocity. You can also close up the port and increase velocity at the expense of flow. Then the problem is getting the air to get moving which means you can make good low end power, but after x rpm the head won't work.
Mid and low lift numbers tell alot about how a head is working. Also, the motor spend a lot more time in the mid and low lift numbers than it ever does a peak lift. So, that important not only in terms of the heads, but also in terms of the cam design, but folks only seem to look at .050 and call it a day... .200 .300 .400 those are all important.
BTW, y'all should consider yourselves fortunate that Greg is contributing to threads on here. Greg's skills in the Houston area are well know and much sought after. I myself am always interested in reading his comments.
Same for Larry Meaux. If you go over into Louisianna you'll see Meaux Racing Heads ground into the sides of a lot of cylinder heads. All the cars I have seen them on tended to be pretty darn quick...
These guys have more than a passing with how to make heads work. So, it would hurt to pay attention to what they have to say. You might end up going faster if you do...
TECH Junkie
Joined: Aug 2002
Posts: 3,726
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From: Fort Collins, CO
Originally Posted by J-Rod
BTW, y'all should consider yourselves fortunate that Greg is contributing to threads on here. Greg's skills in the Houston area are well know and much sought after. I myself am always interested in reading his comments.
TECH Enthusiast
Joined: Feb 2004
Posts: 743
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From: Foley, Alabama-southern Alabama
I agree J-rod,Greg"s post are great and I too take what he says to the bank,so to speak.He sure knows what he"'s talking about.The Meaux info is very good too,but I haven't studied it like I need to yet.Pretty deep stuff!! 
Good to see you back on too J-rod!! 
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Brett Foote On The Tree
Joined: Sep 2004
Posts: 188
Likes: 1
From: Houston, TX
Originally Posted by J-Rod
I was speaking with Erik (racer 7088) about this this today. We discussed head flow vs port volume, etc...
Eric is way too nice to me. But while we're exchanging niceties, I see the makings of another Lingenfelter type in him. Pretty sharp dude.
TECH Junkie
Joined: Aug 2002
Posts: 3,726
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From: Fort Collins, CO
Originally Posted by Greg Good
Eric is way too nice to me. But while we're exchanging niceties, I see the makings of another Lingenfelter type in him. Pretty sharp dude.
I'm so hungry.
