Re: Two barrel TBI must have a flaw, I give up.

["Bruce Plecan" <nacelp@bright.net>]

> >The reason I asked about the height above the manifold, is that
> >with a 2bbl, the air flow can slam into the bottom of the plenum.
> >(high velocity air stream).
> Yeah this is what I had hypothesized was theproblem in my first post.. but
> ive done some more tuning, and maybe not

Kinda mute, the real trick is how far the fuel discharge point is from the
intake valve on a wet manifold.   That depends on a host of factors also.
For a real good example of that look at some of the really well executed
Weber Manifolds.  On some weber stuff you'll see a long manifold runner,
with short stacks on the carbs, and on others short manifolds with longer
carb stacks.  This ain't just what looks good (well for those that really
dyno things out).
   Why do you think they fire the TBI injectors 2x as often as the port?.
   To better mechanically **chop** up the fuel before/as it hits the air
stream.
Take a timing light and look at the fuel cone in a TBI set-up (at say 4,000
rpm), and then use the timing light and look down a weber at about the same
rpm.  I say weber since you can actually see things so much better, but
anyway a Holley will work.  They look VERY simuliar.
   The worst is the TPI.  Why you say?.  Just to make it real easy to look
at.  A four stroke engine breaks it's time for each event equally, so at
best the intake is open 25% of the time, and alot of that is just clearing
the seat, and being lowered onto it (the intial accleration rates of valve
open and deccleration rate of close, are very different the when the valve
is 1/2 open). Anyway the injectors are on at LEAST 80% of the time at WOT so
that means the fuel is just puddling on the valve.

> >It can help to space the tbi up a bit.
> True, hood clearance is a problem though
> >The air director things are important on the tbi's. Bruce has
> >covered this in detail, so I'll just brief it. Notice that a stock
> >tbi air cleaner has a metal ring the diameter of the tbi top.
> >This ring extends toward the top of the cleaner, with a gap
> >at the top. This forms the air-flow into a column that flows
> >down past the injectors, drawing the fuel with it.

> Wow, ok now this might be a problem.. seems that early on in my TBI wars I
> saw that setup as a huge restriction, i thought that thing inside theair
> cleaner was a silencer (and the fact that there was like barely an inch
from
> thelid didnt look like ithelped) So I removed it
> later on I got an open element, then I saw that gold iridite spacer ring
as
> a restriction, since it seemed to shroud the tbi forcing air around the
> injector tops, so I tossed it, and got a non drop open element which fit
> wonderfully with a 3" element and exposed the tbi.. which to me seemed
like
> it would flow a whole hell of alot more.

Hmm, see what I mean about testing, and assuming.

> and ive seen some mention of what bruce went over with regards to the air
> cleaner in the archives. So I take it, if I went back to the drop base
> aircleaner with the spacer ring Id be better off then? I guess its the
same
> idea as a velocity stack.

Every little detail you can think of can be tuned for optimum perforance.
How the air reaches the mouth of the TB or carby is important.  It is my
personal beleif that the velocity (in a meaningful amount) must increase
thru out the useful rpm band or there will be a performance penalty.
Again, for street applications.
>
> Ill file this under well intentioned dumb moves of mine.. and all this
time
> I thought I had seriously improved my setup (it actually was .3 faster if
> that means anything, probably mostly cause ofjust being an open element as
> opposed to that really tiny single snorkle and pathetic filter)

One change atta time, and document what it did.
>

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