Re: dual tbi on a big block

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

> I have a 468 ci (.060 over 454) with a large duration cam (comp 306/626
> lift) and so on. (The shop that did the machining predicted 540hp.)
> Currently, I have dual 600 cfm carbs on her. Runs good up to 7000rpm. Id
> like to replace the carbs with dual tbi. One thing that comes to mind is
> the motor has very little vacuum. If this is a problem, is it possible to
> overcome it via programming?

Probably,
using a open loop idle might be the ticket.

> Ive have seen the diagram explaining the different sized tbi injectors.
> I am not sure how to calculate which ones would be adequate for my
> combination.  4-90lbs/hr??

In theory that would take you to 700ish HP.
I ran 325 HP, on two 90s, quite well.

> Ive read that a single gm ecm, like the '747 will not support
> four injectors. Would the solution be to run dual ecms?

Use another output stage with like 4 Cherry injector drivers, or cut some
747s up for the injector drivers.
Dual ecms is alot more complex then you would imagine.  Gar has mentioned
this, but I don't know his scheme in how to share the sensors.  You just
can't wire them in parralel.

> Also, a while back,  I asked HalTech EFI about dual throttle bodies with
their ecm and they
> said it would not be enough fuel. Is this accurate?

If not using 2" butterflies not enough air.
Maybe they don't know about how big the BBC TBI is, afterall NoOne messes
with TBIs <g>...

> Also, would an ecm from one of the tpi motors power four tbi injectors?

No

> Is this a viable solution, or should I plan on mpi?

MPI is nice for a number of reasons,
TBI is nice and dumb.
Just depends on how you want to tackle it.
I just haven't worked with that big of cam yet, so I'm not dead sure of
which is best.
If you look at the 730 8D hac there might be some ansers about an open loop
idle.
If too radical, at worst, you'd have to go open loop full time, or come up
with some filtering.
Maybe some one could chime in with a low pass filter?....
Bruce
>
> All advise is appreciated.
>
> Thanks,
>
> Greg Gold
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