Edelbrock TBI Conversion

[Fran and Bud]

Just one point of clarification - 
The SBC TBI intake is a dual plane manifold. As such, one runner feeds the
two outside cylinders on one bank and the two center cylinders of the
opposite bank.  Same thing for the other runner - only the opposite
combination. 

With the drivers side cylinders numbered 1-3-5-7 and the passenger side
cylinders numbered 2-4-6-8 
what you have with a TBI intake manifold is the drivers side
injector/runners are ported to supply 1-4-6-7 and the passenger side
injector/runners ported to supply 2-3-5-8. 

The TBI alternates firing the injectors, but one injector doesn't feed a
bank - it feeds 1-4-6-7. Same thing when the other injector fires - only
with 2-3-5-8. 

Then fit this over a firing order of 1-8-4-3-6-5-7-2.  

Disclaimer!
The early "Crossfire" injection did have single barrel TBI's that were
located over opposite banks with long runners, and therefore DID feed a
bank; 1-3-5-7 or 2-4-6-8. 

And then there is a single plane manifold fitted with a TBI - common open
plenum shared by both injectors. - at part throttle the atomization is good
enough that the fuel will follow the air and at open throttle both injectors
are open most of the time anyhow.

A single plane manifold fitted with 8 MPI injectors should also be connected
to fire injectors fed from both fuel logs at each pulse. If all of the
injectors on one side, or bank, were to fire at once the pressure drop in
the log can be excessive.  But, as with every question, there is no single
answer - bigger pumps, bigger lines, better regulators, etc can compensate
if you want to mess enough.

Just about anything will work well - you just have to pick which set of
problems you want to work with!
----------
>From: "Ward" <wspoonemore at excite.com>
>To: gmecm at efi332.eng.ohio-state.edu
>Subject: Re: Edelbrock TBI Conversion
>Date: Thu, Jun 10, 1999, 8:22 AM
>

>Its not just TBI Batch fire, all GM V8's run in batch fire up till the LT1,
>LS1 engines. that is right bank then left bank.
>
>The only demonstrated benifit of sequential fire is emmissions at idle are
>marginaly improved.
>
>Severel of the TBI systems fire every 12.5 msec in some power ranges.
>
>as to injector and cid size . it can be set at address $02B4 in the 1227747
>ECM, the value for 5.7l is 135 decimal. this is for a 7.71 grams/sec TBI
>injector or 15.42 total.
>
>for a sinble port injector 2.33 grams/sec the value at $02b4 would be 112
>decimal.
>
>Ward...
>
>
>On Thu, 10 Jun 1999 12:56:00 +0000, jweir at att.net wrote:
>
>> Ok, thats why I asked.  I was under the impression that 
>> with a batch fired system, it fired half the injectors 
>> and them fired the corresponding cylinders which on a 6 
>> cylinder would be 3 ignition events before it fired the 
>> other half of the injectors..
>> 
>> So are you saying that with every ignition pulse (at the 
>> coil) there is an injector event.. ? 
>> 
>> Maybe I need a basic course in how a TPI batch system 
>> works...
>> 
>> I understand that I need to keep the injector sizes/fuel 
>> pressure and such relative so I am still getting the same 
>> ammount of fuel vs. the TBI
>> 
>> Jason
>> 
>> --
>> 88 Wrangler - 155K miles and counting
>> 258 I6, 4.0 head, Cherokee header, 2 1/2 exhaust with 
>> high flow cat & Flowmaster
>> GM TBI, Crane 260H Cam
>> TJ Fender Flares
>> http://home.att.net/~jweir
>> CNC 4X4 Member - http://cnc.4x4.org/
>>    
>>    
>> > Jason Weir wrote:
>> > 
>> > > 
>> > > TBI
>> > > 
>> > > 1 injector fires for every cylinder firing.
>> > > 8 cylinders firing means 8 injector events, alternating 4 per
>injector
>> > > 
>> > > Edelbrock 7747 TPI Setup
>> > > 
>> > > 1 injector fires for every 4 cylinders firing
>> > 
>> > Huh???
>> > 
>> > > 8 cylinders firing means 2 injector events. 2 groups of 4 alternating
>> > 
>> > 4 injectors fire for every ignition pulse
>> > 
>> > > 
>> > > So my question did Edelbrock just put a divide by 2 after each
>original
>> > > TBI driver and use that to trigger a secondary driver that fed the
>> > > injector groups?  This is the only way that I can see how they might
>> > > have made it work?  Any other ideas..
>> > > 
>> > > This brings up my application question.  When we are dealing with a
>V8
>> > > things are easy its a divide by 2.. But what if I wanted to do the
>same
>> > > thing on a 6 cylinder?  Now I have 6 injector events that I need to
>turn
>> > > into 2.  Its not as easy to make a divide by 3.  Has anyone heard of
>a
>> > > chip that could do this.. Customizable to do a divide by x, with just
>> > > jumping pins or resistance to pins or whatever.
>> > 
>> > You're getting some strange numbers here.  Alternating batch systems
>> > fire 1/2 of the injectors per ignition event, when in synchronous
>> > mode.  The fuel pressure, injector size, and fuel map work together to
>> > prevent creating a rich condition.  To prevent large amounts of
>> > remappingin your case, the 3 port injectors together should flow as
>> > close to the same amount of fuel as one TBI injector as possible.   
>> > > 
>> > > Any ideas???
>> > Start looking up injector flow rates.
>> > Shannen
>> > > 
>> > > BTW I am running a TBI right now but I've got the Multi-Port manifold
>> > > just waiting till I can get the electronics figured out..  I know I
>> > > could just swap the ECM to a V6 TPI computer but thats the easy way
>and
>> > > them I have to learn a new ECM all over again, just when I almost
>have
>> > > my 7747 setup running great.
>> > > 
>> > > Jason
>> > 
>
>
>
>
>
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