After a few out of town delays and a bit of troubleshooting my turbo CB has finally got a taste of 8psi of boost!
I was having a problem with a lean out condition at the faint beginnings of where vacuum was transitioning to boost (WB A/F pegs at 18:1, more if the gauge would read it). After a sprint up the RPM band to about 5.5k-6k the bike would fall on its face stone cold dead. You had to let off the throttle and it would idle while you waited for the A/F to drop back down from the moon before you could produce power again and accelerate once more (throttling it did nothing). I increased the main jet sizes, then added a pitot tube, then a second pitot. Still there was not enough dynamic pressure being built in the bowls to overcome the pressure running through the carbs/venturis to force fuel through the main jets and into the air stream. I mentioning to a friend that after the lean out test runs I was noticing fuel weeping from the overflow tubes... he asked why I didn't have the tubes plumbed to the intake like his turbo RX1.. the light turned on.. I had not come across this point being stress before, or not paid attention to it... I had a window open (over flow tubes) to let the dynamic pressure escape.. I routed the tubes to the intake and took for a spin and the fuel lean out was history; and I saw boost.
How does the cheap $220 small T3 turbo spool? I'll have to admit defeat in this department and concede to what you others where noting about the T3 being too big. From the two small blasts of 8 psi I gave it (no wideband at the moment, broke, being warrantied, get a new one tomorrow), I was seeing boost being picked up at around 6.5k and a full 8psi at around 7.5k (wastegate limit). I don't know if this will improve at all with a proper A/F, as I don't know where its at during that boost, I'll pick back up when I have a WB, dial it in, and see what the end results are (barring no surprises/delays). I can say that when I did hit 8psi that CB was starting to move like it had never moved before... It was a very smooth and rapid pick up, it was grand, and I can't wait to play some more.
If this T3 is an ultimate flop and too laggy to be enjoyable I will replace it. I took the time and ran the numbers on the compressor flow maps (shouldn't I've done that before starting fab...) for three possible replacements, GT1548 (w/o water hooked up), GT2052 (if a rectangle opening T25 turbine can be used), and a GT2056 (winner so far?). There is a T3 to T25 flange 3/4" thick adapter plate on ebay that I hope might work if it gives enough clearance between the turbine (hopefully smaller in size) and the CB's oil filter housing to make it a painless swap... Otherwise I may have to fab up another header with a T25 flange and save the T3 header for a big bore kit down the road...
