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Originally Posted by DavidVizard-GFN
You obviously reading word for word what is being said here and throwing in liberal doses fo your own experience - great stuff. The subject material you are speaking of is going to be covered in the near future in this series so whatch this space - and see in detail what you are taliking of in terms of valve to port geometry, sizing, shrouding etc.
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I look forward to that.
Quote:
Originally Posted by DavidVizard-GFN
There is one point thought that I would dearly like some input from you on if you have it. You mention the supposed effect that low lift flow can have on hp. I have been trying to get other people to show their dyno tests indicating that too much low lift flow for a race engine costs power. Do you know of any good back to back tests conclusivly proving this?
DV
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No, I don't have any dyno tests to prove it. It would be a VERY difficult thing to PROVE. There are many different ways to change the flow characteristics of a port that could be used to reduce low lift flow. If you only made one change to affect low-lift flow, how could you know it was because the flow was less that caused the change in power? Anything that affects flow will also cause some other differences, such as wet flow, pressure recovery or the duration affect of low-lift flow. How many other things would need to be changed to find the ideal combo again after making one change. I think it would take a dedicated study to isolate the low-lift flow as the "cause" of any power difference, not just a single test.
There have been several engine builders and head porters who have made comments about this and their belief in it from their dyno tests. The post automotive breath made of Larry Meaux is but one. Meaux also has some dyno numbers he posted here is another. Not proof, but more evidence...
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Originally Posted by maxracesoftware from Speedtalk
Joe just within the last Month flow tested a pair of SBC Heads
that had a 2.225 OD Intake valve.
These Heads had the worst Low-Lift .200 to .300 Lift Flow
i've ever measured on my Bench !! in fact so terrible,
my SS #041x Heads with 1.940 intake valve have a bunch more
.200" flow , and the 1.940 ties the 2.225 valve at .300" lift.
by the time you reach .600" lift flow those 2.225 Heads
are about the same Flow CFM i get out of Track 1 or Dart Pro 1
Heads with a 2.100 or 2.125 valve,
then at .650 Lift..the FlowBench CFM numbers finally start to take off.
So basically those Heads have only .650 lift to .950 lift flow numbers
over a pair of Track 1's or Dart Pro 1's.
SF-901 Dyno test results=> the highest HP + TQ numbers so far
for that Class
DragStrip Run=> the very first Run was .02 hundredths ET
faster than the Record !!
the 1/8 mile was more than 2.5 MPH faster than Record Run !!
indicating pretty good mid-range TQ + HP
The above Engine Combo is one-way to get down the DragStrip,
its by no means for everyone....but pretty good realworld test Data
on the particular importance of high-lift flow numbers (.650 to .950) over
the terrible low to mid lift flow number were on this particular Combo !
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There is no question that most of the valve jobs used in high-end race heads today provide very poor low-lift flow compared to more conventional designs. Are these used because they hurt low-lift flow? I doubt if any of them are 100% sure that is why they help, but they know what works on the dyno. Maybe its a side-affect of designing the port/VJ to improve high-lift flow or improving pressure recovery that makes them work. It is my opinion that at least some of the benefit is less low-lift flow.
When some of the heads that make the MOST power have the WORST low-lift flow makes me think there is something there.
Rick