injector manifold design

[Tom Parker]

Gary Derian <gderian at oh.verio.com> wrote:

>Even with a short duty cycle, the injection event will stretch out at high
>rpm.  The intake valve for 2 opens just before intake valve one closes.
>This means some reversion from 2 goes directly into 1.  At least with a
>carb, the fuel goes where the air does, sort of.  With injection, any
>puddled fuel injected while both valves are closed will get atomized by the
>reversion and sucked into 1.  2 gets no benefit from this and will run much
>leaner.  Somehow fuel will have to be injected where it will remain near
>intake valve 2 while 1 is intaking but not get blown into 1 when intake 2
>opens.  I can't think of a good way to do this.

I'm not sure how huge this problem is. I run a Dellorto twin choke
sidedraft carb on a big long manifold and the main problem is the diverging
branches of the manifold. The ports are spaced wider than the chokes of the
carb so the manifold has to widen. This imparts an outwards component to the
intake velocity and so more of everything goes into the outer cyclinders.

At least, this is how David Vizard explained it in the 70's "How To Modify
Your Mini". A good read would be "Tuning BL's A-Series Engine", also by
Vizard. This book is out of print and somewhat out of date, but a new updated
edition is being published in April or May. Vizard is considared to be the
best A- Series engine tuner in the world, at least by the mini-list.

The A Series engine in the mini is very like the B series, but smaller.

I also know that for Mini's there are special "scatter" cams with different
patterns on the siamesed lobes to account for the charge stealing effect of
the other cyclinder.

>Has anyone else injected
>this engine.  Maybe the mixture distribution is not as bad as it seems.

Rover have done two fuel injection Mini's from the factory. The first had a
single injector in the throttle body and the second has two injectors. I don't
know where the TPI injectors are, but I assume they are near the ports. I've
never looked closely at either manifold. And never even see the TPI one.

The TPI system is cleaner than the TBI one which it should be since it was
developed to get the Mini through tougher emmisions standards that the TBI
couldn't do.

There is also a mythical "Weber Alpha" injection system for silly amounts of
money. Never contacted anyone who has one.

--
Tom Parker - tparker at nznet.gen.nz
           - http://www.geocities.com/MotorCity/Track/8381/