260Z twin TB delco conversion

[Zedric]

I thought I'd better move the discussion. So I'm just wondering if what I want to do is possible. If not I'll just have to put up with the carbs until I can afford the ultimate setup (triple weber dcoe style TB's with aftermarket ecu).

[antus]

I'll get the back story in this thread:

With batch fired 808 delcos the ECU fires the injectors once or twice per cycle - in most (possibly all) factory calibrations its twice per cycle for all conditions. To get something that fires alternately use a VR auto PCM in banked mode, it has two injector drivers.

What are you tying to achieve?

I would like to EFI my 260z with the stock manifold, instead of twin carbs it'll be twin tb's with 2 injectors one for the front three cylinders and one for the back three. Because the firing order is 1,5,3,6,2,4. I would need the injectors to alternate between the front and rear bank. If I can do this the injectors will be firing only on the cylinders that need them.

I have done a 240z with an L20ET and now the same car has an L28ET in it. You will have better results and it will be simpler to run 6 injectors, and one 1 TB. We dont have a final tune yet, but will be willing to share once we've finished. We found that a VN commodore v6 tune, with adjusted injector rate and more advanced timing ran better than you'd think (especially fueling). The thread about that build is over here: https://pcmhacking.net/forums/view ... f=16&t=998 Will update when the L28 is running (probably after the VG30 is running another project in a 300zx heh).

That car is what brought me to this forum, I was on the Z car forum and someone posted "another delco Z" with a link to that post. I used to have an L28e manifold years ago but one thing I remember is that I would need to change my head because the L24e and L28e have notches at the top of the inlet ports for the injectors, because they are really close to the head and angle towards it. Anyway that might be good for a turbo setup but the stock twin carb manifold with twin z32 tb's would flow much better. I'm trying to get a hold of another manifold and see if I can get someone to put 6 injector bungs in and that would solve allot of problems, although I was hoping not to have to do that so I could offer fellow Z fanatics a low cost EFI solution. Since the VR v6 auto ecm's are common are there any issues with not using the pcm stuff? I think I should move this to another thread, I'm new to this forum and didn't want to start off by hijacking. I started a thread in Delco ecu conversions.

[antus]

I think you could try and run 2 injectors in TBI mode, which would need to be large high impedance ones (the delco can run 1 low impedance in TBI mode, but with 2 groups of 3, you'd need two, thus high impedance). They would need to be large enough to feed that many cylinders thus OEM items would generally be too small and not suit.

Better would be to install injector bungs on the intake runners, but not having a common plenum (for the MAP sensor) will be a pain too.

I know what you mean about the notches in the head. I wonder if it might be possible to create the notches yourself?

The path of least resistance would be to swap head and manifold to an EFI item, or to swap the whole engine to an L28E. It sounds like a big job, but from that point on things will be a lot simpler and you'll get a few extra CCs out of it too.

[festy]

I had a similar notch issue with my alfa, 15 minutes with a die grinder and I had an EFI spec head...

[Zedric]

I think you could try and run 2 injectors in TBI mode, which would need to be large high impedance ones (the delco can run 1 low impedance in TBI mode, but with 2 groups of 3, you'd need two, thus high impedance). They would need to be large enough to feed that many cylinders thus OEM items would generally be too small and not suit.

Better would be to install injector bungs on the intake runners, but not having a common plenum (for the MAP sensor) will be a pain too.

I know what you mean about the notches in the head. I wonder if it might be possible to create the notches yourself?

The path of least resistance would be to swap head and manifold to an EFI item, or to swap the whole engine to an L28E. It sounds like a big job, but from that point on things will be a lot simpler and you'll get a few extra CCs out of it too.

I would have to disagree on both accounts, for one, the injectors still only have to feed one cylinder at a time and two, the injectors on a VN V6 have all 6 wired in parallel, wouldn't that be low impedence? I'm sure that's why they have D15+D16 wired together so it can supply enough current for all 6. There is a balance tube between the two manifolds that is used as a common vac source so a map should work ok. But anyway someone has recently posted that the delco fires multiple times per cycle, so now I've got allot more to learn about Delco's than I thought.

[VL400]

Low impedance injectors operate differently to high impedance injectors. Yes, 6 or 8 high impedance injectors end up around the same load when wired in parallel but a low impedance injector is driven using a peak and hold driver - it is allowed to draw a large amount of current to open it quickly but then the ECU holds it open with a lower current. High impedance drivers do not do this. An 808 can drive low impedance injectors using peak an hold - how many I dont know, its used on some local Camiras but they only use 1 I think?

If you put an 808 delco in to TBI mode it will fire the injectors on every reference pulse - so 6 times per cycle on a 6 cyl. When running batch like a Commodore it fires all injectors twice per cycle, this can be changed to once per cycle though.

[Zedric]

I had a similar notch issue with my alfa, 15 minutes with a die grinder and I had an EFI spec head...

Yeah about 15 years ago my TAFE instructor bought an EFI manifold for his 302 Windsor and I quickly pointed out that problem. He was a little bit hesitant to let me die grind the notches in the heads for him, but when I showed him the templates I made up that you would normally do for port matching to show him where the notches should be he gave me the go ahead. When I was done he was wrapped. But anyway I don't like the L28e manifolds, they work ok on forced induction but for atmo there is no way you would get accurate A/F ratios on all cylinders across the entire rev range. And since when is 1 TB better than 2? That's like saying that a single carby for 6 cylinders is better than 2 or triple Webers (which in effect is 6 individual throats with each intake runner being identical length). The standard twin carby manifold is a much better design.

[Zedric]

Low impedance injectors operate differently to high impedance injectors. Yes, 6 or 8 high impedance injectors end up around the same load when wired in parallel but a low impedance injector is driven using a peak and hold driver - it is allowed to draw a large amount of current to open it quickly but then the ECU holds it open with a lower current. High impedance drivers do not do this. An 808 can drive low impedance injectors using peak an hold - how many I dont know, its used on some local Camiras but they only use 1 I think?

If you put an 808 delco in to TBI mode it will fire the injectors on every reference pulse - so 6 times per cycle on a 6 cyl. When running batch like a Commodore it fires all injectors twice per cycle, this can be changed to once per cycle though.

If I was running 2 injectors wired in parallel then I would leave it at 6 per cycle so OEM injectors should be able to cope with the fuel demand, I'm not trying to make huge kW's. This is the reason why I need help from you guys, I don't know anything about Delco's, all I know is that GM spent allot of $ on the development of these ecm's so the quality and reliability is undeniable.

[Jayme]

to be clear, by default in 6 cylinder mullti point injection mode, in double fire (default setting) it will fire one injector pulse every 3 ignition events. this isnt very good for TBI setups, as you get uneven fuelling. you can set the resistors on thememcal to put it into TBI injeciton mode, which will fire once every ignition event and so give you the accurate fuelling in tbi setups.

a while ago me and a mate tried to get 2 commodore injectors running like TBI in the plenum of a datto 1200. it didnt work well, as we figured out the injectors designed for mpi, sprayed a jet of fuel against the mainfold wall where it ran to the lowest cylinder by gravity and made that one rich, no matter what we did we couldnt get it right and gave up and put 4 individual injectors in it and it never missed a beat since. as long as they are tbi injectors and a manifold designed to have fuel running thru it it should be ok tho, but i am still very wary of custom TBI setups, try to aviod it where possible.

[festy]

And since when is 1 TB better than 2?

When the single TB is used with an MPFI setup, but the 2 are TBI