I'm trying to find out if it's possible to run twin 2bbl TBI units - the '7747 isn't an option, as Grumpy has proven that the injectors start to cut out at 3k RPM. I seem to remember someone using a TPI computer to run a TBI unit.. or do I have it backwards?

Anyway, is it possible to run a 4 injector setup off of a TPI computer?

Ken

 

Some guys claim to have run the dual TB TBIs by wiring the injectors in series parrarel. One vendor even sells a chip for doing that, I bought the *magic* chip, and it was just a stock 8D bin.

So in closing there are some P+H TPI 4 cyc applications, but no 4 P+H TBI ecms.

TPI P+Hs are 2.4 ohms
TBI P+Hs are 1.2 ohms

 

Grumpy, forgive my ignorance.. what is P+H? (Impedance?)

Ken

 

My setup is wired in series. Not series-parallel.

P+H is peak and hold.

------------------
1988 T/A,
9" Ford, 3.50 gears, Auburn posi, 700r4 -w- 2100 converter, 360ci, 9.8:1 cr,
AFR 195 Heads, Weiand #7525 intake, Lunati roller 219/227, .479/.480, 112 LSA
Holley 700cfm 4bbl on TBI truck 7747 computer and chip by Howell-EFI

 

Slipped a gear and was thinking 730 for a moment,

How well does yours run?

 

[QUOTE]Originally posted by Grumpy:
[B] Slipped a gear and was thinking 730 for a moment,

Arrgh, he was asking about a TPI computer, and to run a TPI ecm I was right about the wiring.

 

LOL, yep you're right, TPI ecm, didnt see that.

 

Well, Dan, have you experienced any problems with running the '7747 and four injectors? You're running them in series instead of parallel like TPI injectors; and it seems to hold over 3k RPM (where Grumpy was having trouble, I assume because he was wiring them in parallel?)

Ken

 

I dont think he did them in parallel... they wont fire at all with the TBI ecm that way. Maybe he did them in series-parallel. Grumpy?

This link might also be worth a look:
https://www.thirdgen.org/gmecm/file6235.txt
I can't say that I've seen any of those symptoms but havent specificly tried to test them. I can say this for certain, it works fine at low bat voltage.

It runs / drives at least as well as a carb but not as good as it could. I've done no eprom work on it yet... its running an ok but less than perfect howell custom chip.

 

I've tried series and series parallel on 730s, 749s, and 747s.
I've also smoked the 730s trying this.
None gave staisfactory results in my opinion.

What happens on a injecotr diver failure from this stuff is that the injectors get slower to react to rpm changes, and *sound* funny.

The overheating from over loading the injectors happens faster at higher rpm.
YMMV

 

I'm going to see about the 2-into-4 injector driver setup he talks about in that post. I can't imagine it being TOO difficult to create. The only thing I'd be worried about is programming; I wouldn't think you could do progressive linkage (or could you?) I would imagine you'd have to use 1:1 linkage so that everything is the same.

Ken

 

I think this would do the trick properly. The pic on the site doesn't show up, so here it is:



It's supposed to split off the four injector drivers from a Holley Commander 950 ECU to *eight* low impedance drivers. I wouldn't think there's much of a difference between GM injectors and Holley's injectors (impedance-wise) to where this couldn't be used on a '7747 to properly split the signals.

Any thoughts? (Grumpy? Dan?)

Ken

 

Also, how can the Edelbrock MPFI convrsion run 8 TPI-type injectors with the stock 7747 and a custom harness??? are the new injectors really low impedance, or something? how is that Eelbrock harness set-up, anyhow? Series or parallel? I would think if you can run 8 TPI injectors, you could run 4 TBI injectors, no??? guess we need the impedance numbers of the Edelbrock injectors to compare/contrast...

[This message has been edited by FastBroker (edited May 03, 2001).]

 

Fast,
The multi point conversions I've read about all wire the injectors in parallel so the current comes out very similar.

Ken,
Sorry, I dont know anything about the commander system.

 

Saturated Injectors 12-16 ohms
Peak and Hold TPI 2.4
Peak and hold TBI 1.2

You can get by with some honkin Power MOSFETS, thou, I'd be prepared for some failures.

Now,
Saturated suggested operatin times 2-10 msec
Peak and Hold 1-5 msec

Next info is injectors firing strategy, and then min tmes at idle.

The big P+H TBI injectors can get *erratic, and or none linear* at short PWs.

The 747 fires the injectors alternatively on each ignition pulse.
The others once per revolution.

A vacumm referenced FPR might help in this
HTH