by 200cfm » Sat May 03, 2008 10:48 pm
Ok, that one channel design makes sense now. The guide boss is rather thick and it would have to be "channeled" a good 1/4" down to equal the other one. I have a junk head and will study the quide boss thickness. If it will take say 1/8" inch depth second channel it might be what is needed.
I reflowed today with the wall insert repair and have moved up a tad. Odd part is I am getting my best low lift values now. Here's where it is at now.
.100 80.3
.200 105.3
.300 136.8
.400 164.7
.450 173
.500 179.4
.550 179.4
.600 180.6
.650 180.6
.670 181.3
Still seems maxed out after .500 lift. I started to grind some more and got curious/suspicious of the air speeds so I rechecked them and got 335 PRt (middle) around 362 on the turn itself and around 323 over the SSR apex. My pitot is DIY so I wondered if perhaps my static point was to far away from the air impact port on the J Bend. The gap is around 3/8"
So, spent the day making a version 2 pitot and put the static port pretty much on line with the other entry port near the tip of the J bend. This changed everything and the new numbers were shockingly high. So high I thought, this is wrong or something is strange. So I added a second hole to the static port and the readings came down better but still higher than version 1 design. So finally I decided to try a tube in a tube design and settle the mystery. Now this was tuff, especially the J bend and keeping both tubes with passages but finally got version 3 working late this afternoon. The new readings are closer to version 2 with the two holes static port and are higher than the version 1 design.
Anyway, the air readings with version 3 pitot are showing higer PRt and SSR apex. Getting 350 fps in the center of the PRT and 360's on the wall turn itself. The SSR is showing more than test pressure. Came in at 380 plus fps. I tested it both a 12" wc (with formula corrections) and at full 28" wc test depressions. SSR was going to 34" wc on the 28 test.
That's a big swing from the pitot version 1 design that has the static port gap.
So like the man with three watches, it's hard to know the real speed. I think version 3 pitot is more on target. Just hard to believe it could be moving that fast. Tubing is bigger on this version, could that be fooling the port CSA and falsing a fps reading?
Now if the air is indeed that fast, my strategy has to be what, slow it down or accept it? I am stuck with factory dual plane iron intakes so should that addition be factored in. The intake will kill a good 12-16 % of the cfm from earlier testings. That kills air speed too, right? Or do you forget about intakes and think head ports only?