[Diy_efi] Seqential or Batch??
Itsmejonyl at wmconnect.com
Itsmejonyl at wmconnect.com
Sun Jun 6 13:08:00 GMT 2004
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I need learn how to get the link to you, but maybe this will help..
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<HTML><FONT FACE=3Darial,helvetica><FONT SIZE=3D2 PTSIZE=3D10>I need learn=20=
how to get the link to you, but maybe this will help..
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Sequential Injection Realities
We receive many calls and enquiries about whether our system offers sequenti=
al injection. Many people asking this question don't even know what this is=20=
but they insist that they must have it.=20
Timed vs. Batch=20
Sequential is a bit of a misnomer. Technically, all EFI systems are sequenti=
al in that once all cylinders have been injected, the sequence starts from t=
he beginning again. A better term would be timed, implying that the starting=
and finishing of the injection pulse is timed with the intake valve opening=
. The idea behind this is to spray fuel only when airflow in the intake runn=
er is established. This is supposed to mix fuel and air better and reduce ma=
nifold wall wetting. The other injection strategy is batch fired where sever=
al injectors are triggered simultaneously and not timed to the intake valve=20=
open period. In effect, the fuel sits in the runner for a short period of ti=
me before the valve opens and the airflow carries the mixture into the cylin=
der. Some people are dismayed that anyone would use the batch fired method h=
owever, there were tens of millions of Bosch and Bosch derivative systems so=
ld in the '60s, '70s, and '80s which worked just fine using batch firing. It=
is a very well proven concept indeed. The SDS is also a batch fired system.=
The timed concept was developed mainly for tougher emission laws and EPA cy=
cle testing where much of the cycle is run at low rpm and part throttle, whe=
re the time available to inject is long and the injector pulse is short.
Performance applications are somewhat different from stock applications. Rpm=
s are generally much higher, fuel flow rates are much higher and emissions u=
sually take a back seat to power output. As rpm increases, the amount of tim=
e available to inject the fuel decreases. This is true whether the system is=
timed to valve opening or batch fired. The batch fired system has the advan=
tage of being able to inject fuel for the entire period of crankshaft rotati=
on whereas the timed system technically only has the time available that the=
air is flowing in the intake runner. This is determined mainly by the camsh=
aft characteristics. On an average performance cam having 220 degrees of int=
ake duration measured at .050 valve lift, the sequential system has only 61%=
of the time to inject the fuel as the batch fired system. As such, true, ti=
med, sequential systems must have larger injectors fitted for a given hp. It=
should be remembered that there is little airflow and velocity in the port=20=
and runner until the valve is open a fairly significant amount. Starting the=
injection sequence early and finishing late, partially negates the supposed=
advantages of timed injection. On a high revving engine, there are only a f=
ew milliseconds available to inject before the next cycle begins. On the oth=
er side of the coin, with batch fired injection, the amount of time that the=
fuel sits in the port shortens as rpm increases. In the end, there are no s=
ignificant differences in top end, wide open throttle, horsepower between ba=
tch fired and timed systems. We have also not seen any significant differenc=
es in fuel economy between the two strategies. Emissions at part throttle ar=
e likely to be better with timed injection as this is what it was developed=20=
for. On performance applications, emissions are often not an issue and most=20=
engines not equipped with a catalyst will not pass a modern emissions standa=
Complication and Expense
Batch fired EFI systems are far less complicated from a software and hardwar=
e standpoint so it stands to reason that they will be less expensive to purc=
hase and easier to program. Timed systems require camshaft timing informatio=
n for the ECU either derived from a camshaft sensor or a multiple input sign=
al from the crankshaft sensor. Timed systems also require a drive transistor=
for each injector, a separate trigger wire for each injector, cam timing sp=
ecs, injector response time specs, cylinder firing order and the software to=
process the information. The person programming also requires a lot more kn=
owledge on how all these aspects inter-relate to each other and the wiring f=
or the injectors becomes much more complicated. If any of these steps are om=
itted or misunderstood, the timed system is no longer timed. Additionally, t=
here are some aspects about intake port flow that very few people would have=
a clue about. You'd really be taking a bunch of guesses about when to start=
injecting and stop injecting the fuel. Is all this worth the trouble on the=
average performance/race application for little or no gain in hp? Would YOU=
understand how to hook up and program a sequential/timed system? I think th=
ose questions have already been answered. The batch fired system merely requ=
ires a tach frequency. Generally, for each ignition pulse, there is a fuel p=
ulse. There are less wires to run and no complicated timing software to figu=
re out. Very simple and it works very well.
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