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1. Low pressure (10") is relatively numb to small changes which will show up as power on the track or dyno - not sensitive enough. Why do they use it? Because their bench is too small to pull a higher depression on a big port.


Winner! Winner! It's the old saying "If all you have is a hammer, everything looks like a nail." And I resemble that remark...

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2. High pressure (above 28") is very sensitive to small changes, to the point of being "nervous" and showing flow changes for mods too small to actually affect power.



I think the higher pressures today are being used to identify when issues exist that aren't apparent at 28" (or lower). I can't speak to the "nervous" tendency, having not been involved with it first hand (yet?).

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3. 28" showed the closest relationship between a change in flow to a change in power - as close to linear as he could get.



Right; he stated he found a direct correlation between flow improvements and dyno improvements for results taken at 28"... and that's been the rule of thumb for decades since.

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BTW: the "conversion tables" for comparing flows at different depressions? The math is correct, but the heads do not perform that way and the calculated result is not accurate compared to an actual test at the other depression.


Understood, which why (even for my amateur efforts) I'm looking into a higher-capacity bench.

FWIW, these are tests on the same two heads on the same bore adapter size w/ the first columns' results being from my SF-110 (w/ BIG correction factors applied) and the second from Dwayne Porter's Saenz S-600 bench tested at a true 28".

Victor test #3 cylinder on 4.375" bore
Lift --- 110 -- 600
.100 --- 73 --- 75
.200 -- 155 -- 169
.300 -- 224 -- 237
.400 -- 282 -- 280
.500 -- 317 -- 318
.550 -- 329 -- 329
.600 -- 343 -- 341
.650 -- 346 -- 347
.700 -- 350 -- 345

Stage VI test #1 intake on 4.375" bore
Lift --- 110 -- 600
.100 --- 68 --- 69
.200 -- 140 -- 143
.300 -- 200 -- 213
.400 -- 250 -- 262
.500 -- 288 -- 293
.550 -- 305 -- 305
.600 -- 305 -- 307
.650 -- 308 -- 307
.700 -- 310 -- 307

The high-lift trend I see is that the peak #s max at a slightly lower lift tested at the higher pressure, plus the Victor started showing signs of backing up slightly at a lift where my 110 still showed small gains.

The improvements in Dwayne's .200-300" #s may be from him having notched the top of his bore adapter... but I'm going from a fuzzy memory during one of our talks years ago.

I know from my own tests on my 110 over the years that even at lower test pressures some ports just sound "ragged" while others are much smoother. I'd like to know how that translates at higher test depressions, too.

The other thing I need to pay more attention to in the future is velocity profiling. / / /