Ancient History

[Robert J. Harris]

Remember the Reichstag

----------
> From: Tony Bryant <bryantt at psc.fp.co.nz>
> To: diy_efi at coulomb.eng.ohio-state.edu
> Cc: 914 at giza.estinc.comPorscheFans-914@ioio.com
> Subject: Re: Ancient History
> Date: Monday, September 02, 1996 1:53 PM
> 
> <snip>
> > The Djet and Ljet EFI in the aircooled opposed VW and Porsche 914 
> > engines sprays directly at the intake valve from three inches away.
> > 
> > With the Djet, the fuel is squirted in at the beginning of the intake 
> > stroke two of the cyls, and at the beginning of the power stroke on the

> > other two cyls, so its operation is compromised.  
> > 
> > People on the 914fans lists have been debating the injector timing 
> > question, so your post is being forwarded there.  Hope you don't mind.
> > 
> > RD
> >
>  
> What I want to know, is what happens when you have radical
> cam timing? This nice puddle of fuel on the inlet valve
> gets blown back up the inlet duct when the valve opens?
> Makes nice flames, if you don't run an air cleaner :-) 
> But this surely can't make for repeatable fuel volume supplied
> to the cylinder?
> 
> comments?
> 
> ***********************************************************
> * There'll be no more misery      * I came, I saw, I left *
> * When the world's our rotisserie *  > bryantt at fp.co.nz < *
> ***********************************************************

Prior to cheap timing electronics, untimed fuel injection was 
the normal way.  Timing is merely the thinnest icing on the cake.
Alcohol fueled indy car engines screamed for hours at high RPM 
and dirt track sprint cars make 700+ horsepower from 400 ci engines
on alcohol using Hilborn type units. Modern AA fuel dragsters make
pushing 4000 horsepower with nitro fuel using Hilborn type units. 
World land speed records are routinely set at Bonneville Salt Flats
with these primitive systems. Weber carbed formula racing and even 
street engines made incredible horse power per cubic inch without the
benefit of timing.

In every case - the higher the quality the mixture - the higher 
the performance. Untimed fuel injection's have reliably repeatably
routinely 
made enormous amounts of power, with from mild to wild cam timing, with
fuels varying from gasoline to liquid dynamite.  Made it with the
consistency
needed to win races in virtually every category imaginable. 

This is not theory, this is proven fact that you can see every race day.
The
basic modification he made was move the location of the injector to what 
appears to be the optimum point.  

On every engine - a small portion of exhaust gas is pulsed into the 
intake manifold the amount depending on cam timing, load, and engine
RPM.  This is then sucked back into the cylinder diluting the charge. 
For you old timers, this is why you must richen a carb when putting 
headers on an engine - because the reversion pulse is damped - leaving
less flow thru the carb (the first pulse backwards - followed by the normal
forward pulse.)  Untimed fuel systems have a fuel air mixture that is 
pushed backwards up the manifold (reverted) before being sucked back
in.  As this is very hot gas with no oxygen present (e.g. no flame!!) and 
lots of CO2, and this hot gas is quenched by contact with relatively cold 
(far below ignition temperature) matter in the intake tract - cold mixture 
cold intake valve, cold head, all that happens thru almost all ranges of
performance is charge dilution and therefore less than theoretical power
is developed.  Aside - a very rich fuel mixture such as present when 
fuel is "puddled" on the valve is not combustible. A lean - i.e. 
minimally vaporized mixture such as from a mistuned carb or timed
injector is explosive!!

What timed fuel injection in conjunction with proper cam timing does is
allow this reversion pulse to go up and come back out the exhaust port
before adding fuel to the incoming air.  Properly done, no air pump is 
needed for the cat converter as the reverted air pulse shoves oxygen 
out the exhaust.  The chamber gets a full, dense properly mixed charge
and makes better power, fuel efficiency and lower emissions.  

In all endeavors we tend to forget what has worked and is working in our 
efforts to achieve the new.  We get enamored with new technology and 
scorn the old.  We should instead - understand the baseline from where
we want to go and use that to our advantage.  Use only from the new what
is needed to solve the unsolvable with the old - progress - not perfection.