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valve flow potential ??

General engine tech -- Drag Racing to Circle Track

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PRH

valve flow potential ??

Post by PRH »

im just wondering if Darin or Larry(or anyone else) might have a formula for determining the max flow for a particular valve based on the L/D and test pressure.

there is a chart in the Superflow operators manual that came with my bench when i bought it 12 years ago, but i have to believe that with the way the head technology has evolved in the last 12 years that that chart might be a little outdated.
or, is it more fundemental than that, and the available flow vs area is accurately represented in that chart?

what got me to wondering about it is the differences they show for wedge heads and hemi heads, and i figured the newer design canted valve and high port wedge designs must be getting closer to reaching the potential of the hemi design in this regard(flow vs L/D).
that, coupled with me getting results on some heads where i can slightly exceed the theoretical max flow for certain head and valve combinations has prompted me to ask the question.

when i was reading through one of the posts here where Larry was stating that the newer high port heads can benefit from running cams with higher L/D ratios than the older design, more traditional ports, it got me to thinking about how the new technology might impact the flow potential of the valves themselves.
PRH

Post by PRH »

i see after reading through some of the porting posts that the discharge coefficient method for determining valve efficiency is popular.

is this a better method for determining valve efficiency?

what kinds of discharge coefficiency numbers should i be shooting for at various lift points? whats realistic?

the 146cfm per sq/in of curtain area as opposed to the chart in the flow bench manual show quite different results for the same L/D.
Guest

Post by Guest »

well, i tried logging in about 6 times...and it didnt take.
i'm not sure what the deal is there.

i did some figuring to see how the Superflow valve flow potential chart works againt the discharge coeffient, and the numbers seem pretty low.

here is what the SF chart shows for valve flow at 28" based on the valve area(outside diameter minus stem diameter), and the L/D, for a wedge head.

L/D---flow per sq/in of area
.05--22.8
.10--45.6
.15--68.6
.20--78.5
.25--84.0
.30--87.4

plugging in those numbers for a 2.08 valve with an 11/32 stem, then calculating the D/C for those numbers gave these results:

lift-----flow-----D/C
.104--75.36--.759
.208-150.73--.759
.312-226.76--.761
.416-259.49--.653
.520-277.67--.559
.624-288.91--.485

the D/C was based on the 146cfm per sq/in that Darin posted in another thread.

so, how do those D/C numbers compare to what is possible with the newer designed heads on the market today??

Dwayne Porter
Porter Racing Heads
Darin Morgan
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Post by Darin Morgan »

How much should it flow? AAAH yes, the age old question that myself and just about every other head porter or cylinder head designer on the planet is asked on a daily bases. Its not an easy question to answer because of the underlying variables involved. Such as, Valve placement in the bore, valve cant or the lack there of,chamber design, shrouding, port layout and design, valve head shape, throat shape, port shape in general and couple of other subtleties that most people don't even know about. That is why the most dreaded question ever asked of a cylinder head porter is ,"HOW MUCH WILL IT FLOW."

If you have a great deal of experience whit given head port layout such as the 18 degree Chevy heads, the potential flow of any valve size is pretty easy to compute because you can take your prior experiences coupled with your CD equations and CFM/SQin potentials and get within one or two cfm. NOW ask me about some head I have never even seen or had on the flow bench and I will give you my best guess which is,

Wedge
.500 lift = 80 cfm/SQin
.800lift = 90 cfm/SQin

Really good Wedge head
.500 lift = 80-85 cfm/SQin
.800lift = 100-102 cfm/SQin

Average Canted
.500 lift = 85-87cfm/SQin
.800lift = 101-105 cfm/SQin

Low profile chamber 12 degree or less valve angle excellent head. ( Pro Stock )
.500 lift = 85-87 cfm/SQin
.800lift = 110-114 cfm/SQin

These are good numbers to shoot for. Will you go over by 5 or ten CFM/SQin? I don't think so. Unless its an SB2.2 head. The SB2.2 head has a valve placement that accents the mid range flow characteristics without sacrificing high end flow. They are very enshrouded and low profile heads with very efficient chambers at 35cc.

SB2.2
.500 lift = 96 cfm/SQin
.800lift = 113 cfm/SQin

Hope this helps.

AGAIN these are baselines to shoot for and are often very close but not written in stone. Nothing is in this game.
Darin Morgan
-Induction Research and Development
-EFI Calibration and Tuning
Reher Morrison Racing Engines
1120 Enterprise Place
Arlington Texas 76001
Phone 817-467-7171
Cell 682-559-0321
http://www.rehermorrison.com
Darin Morgan
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Post by Darin Morgan »

P.S

I have never seen ANY head exceed 114 CFM/SQin at .800 except a Hemi.
Darin Morgan
-Induction Research and Development
-EFI Calibration and Tuning
Reher Morrison Racing Engines
1120 Enterprise Place
Arlington Texas 76001
Phone 817-467-7171
Cell 682-559-0321
http://www.rehermorrison.com
Guest

The D/C numbers.

Post by Guest »

Darin, are the above numbers based on the actual valve size less the stem area, or are you referring to the exposed window area at the given lift in the chamber.

Thanks, VW Racer.
Darin Morgan
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Re: The D/C numbers.

Post by Darin Morgan »

Guest wrote:Darin, are the above numbers based on the actual valve size less the stem area, or are you referring to the exposed window area at the given lift in the chamber.

Thanks, VW Racer.
Valve head area period. I do not subtract the stem area.

2.515*2.515*.7854= 4.967 SQ/in

A Pro Stock head flows 558cfm @.800 28"

558/4.967= 112cfm/SQin

You can get them to 113 or even 113.5 but the low lift suffers to much and the power goes down the drain.
Darin Morgan
-Induction Research and Development
-EFI Calibration and Tuning
Reher Morrison Racing Engines
1120 Enterprise Place
Arlington Texas 76001
Phone 817-467-7171
Cell 682-559-0321
http://www.rehermorrison.com
Guest

Post by Guest »

so, using the 85cfm sq/in for a really good wedge head shows 320cfm for a 2.19 valve at .500 lift, with works out to a D/C of .632.
is that a fairly realistic number?

i've been playing with heads for 15 years, but have always been pretty "low tech".

the aftermarket head business is pretty competitive, and i guess its time to start taking advantage of the resources out there in an effort to put out a better product.
Guest

Post by Guest »

i thought i was logged in for that last post.

Dwayne Porter
Porter Racing Heads
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Post by Darin Morgan »

Anonymous wrote:so, using the 85cfm sq/in for a really good wedge head shows 320cfm for a 2.19 valve at .500 lift, with works out to a D/C of .632.
is that a fairly realistic number?

i've been playing with heads for 15 years, but have always been pretty "low tech".

the aftermarket head business is pretty competitive, and i guess its time to start taking advantage of the resources out there in an effort to put out a better product.
Yes that's correct. Not ALL wedge heads will correlate to that exactly but it will be close for standard valve placement. The flow will be higher of course if the valves are offset.
Darin Morgan
-Induction Research and Development
-EFI Calibration and Tuning
Reher Morrison Racing Engines
1120 Enterprise Place
Arlington Texas 76001
Phone 817-467-7171
Cell 682-559-0321
http://www.rehermorrison.com
Guest

Post by Guest »

Ok how about this set of heads that a customer of mine says he owns....

Here is a situation to throw into this.....

Do these numbers seem realisitic? Not knowing what the castings are, just that they are a production 23deg casting that's not a raised runner design....

2.00" Intake /1.56" Exhaust

int / exh
.100 70.5 61.4
.200 140.4 124.6
.300 206.6 180.0
.400 258.1 214.2
.500 291.7 231.1
.550 294.9 236.6
.600 298.8 247.5
.650 301.4 258.9

sf-600 bench 4.040" bore @ 28" with a clay inlet and pipe on the exhaust

Applying Darrin's rules

2.00 x 2.00 x.7854 = 3.14159 (obviously)
291.7cfm/3.14159= 92.85cfm/SQin @.500"

Seems a bit high. Maybe 270-275cfm, but I can't believe cfm/sq in flow numbers that are higher than a SB2.2 head. I could undstand maybe 86-87cfm/SQin at .500 if it was a highly researched out race head for Super Stock racing but this is too much for me to fathom.
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Post by airflowdevelop »

It appears from your post we are talking about some LTx heads.


REMINDER...don't forget the spark plug and rocker stud :P
Guest

Post by Guest »

airflowdevelop wrote:It appears from your post we are talking about some LTx heads.


REMINDER...don't forget the spark plug and rocker stud :P
Yep LT castings and that's the first thing I thought no spark plug and rocker stud.
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