Originally Posted by
billygraves
If you LEAN the calibration out @ WOT, just keep in mind that in SOME engine combos it is FAT because of Mal-distribution problems that lie within the intake/TBI. Some cyls run Lean at certain RPM and are on the opposite side of the O2 measuring. So a A/F Ratio meter (on the other side) would be a good check. (And not to miss this point, some fuel is FAT to actually COOL the top and ring pack IF pulling a load up a long hill ect ect ect......)
(I was coached on a 5.7L TBI and with the intake sometimes cyl 5 runs lean and 7 runs FAT. This is because of the fuel is being robbed from one and pulled into the other. This was the intake release person I had discussions with in the early 90's about intake gasket leaks and how to help seal them.)
The TBI steers the fuel toward the rear of the engine where it is a bit rich or Fat. TBI was used by the companies because PFI was 900 additional an engine. This was back in the early 90's.
For those of you who are considering TBI use in High RPM ranges, I would you look at some other approach and go PFI. If you look @ the Holley 4 BBL TBI you will see them use a small tab that rests against the injectors. It is for this reason.
As the fuel is blown into the air stream at hi rates the fuel stream is moved toward the center of the air stream and this ends up with the outer 4 cyl very lean and the inner 4 very rich. Another way to see this is hold a hose with a stream of water up in the air and as the wind picks up it moves the liquid or bends it. The same thing occurs at 5,500 to 6,000 RPM or at an air flow rate, inside the engine. Just be careful.
The reason I know this is I ran one of Holley's first 4bbl TBI on my 9 second Vega. With 2 fuel pumps and about 6 passes with a best time at 10.80 from 9.40 with a 1050 dominator, I pulled it and reinstalled the dominator. The engine headers were coated and had turned blue from being so lean.
Bookmarks