question

[Anonymous]

ok fi gurus,

when it comes to injector size it doesn't really matter if the injector is bigger than stock only that the fuel presure, flow rating and on time mesh with the programing correct?

so in theory 3 tbi's designed to fuel a 1.9l each would be fine to use on a 4.9l as long as all the math added up right.

any insight would be helpful

thanks

 

[SR_Crewchief]

Bill,

That's very similiar to what I was asking. Take a look at the topic below titled "throttle bodies and injectors". I think you'll find Strange Ranger's responses useful.

 

[Anonymous]

thanks cc

 

[Anonymous]

ok the i may be way of base here but....

the way i see it when you have a tbi with 2 injectors on it there is only one
tps reading for both of them so theroretically why couldn't you treat three
seperate 1bbl the same way as long as everything is balanced?

 

[StrangeRanger]

there's an input problem and an output problem

The input problem is that you would only have one TPS reading. You would be trusting that the other two corresponded exactly but they never will. This one is actually pretty minor, itmight give some drivability issues though.

The output problem is more important. The PCM is going to drive one injector or apair of injectors off a common signal depending on design. If you have 3 separate units you're going to have no way of driving 2 of them.

 

[fb71]

since I'm rather intimate with Ford EEC systems, I'll chime in here.

Throttle position is an important piece of information for the pcm (CFI strategy blends alpha-N with speed-density) but it is not exact, and doesn't need to be. Alpha-N fuel control is based on throttle position to determine approximate fuel deliver based on a best-guess of inlet air. Fine tuning is accomplished via closed-loop monitoring (HEGO feedback). Speed-density utilizes engine speed, ambient air temp and air pressure to guess at fuel delivery, also tweaked by closed-loop. Both of these system rely heavily on pre-programmed look-up tables, containing information about that particular engine's VE (volumetric efficiencey). Therefore, running 3 throttle bodies on one TPS is perfectly acceptable. However, driving multiple injectors from one driver transistor does present a problem. I know first hand the stock transistors in a CFI pcm can handle two injectors each (I've seen two CFI units on a 2x4 manifold on a SBF, run by one pcm). Now to run three, I suspect we may need to do some doctoring of the pcm. Its not as big a deal as it sounds. I've done it to run low impedance injectors with a stock pcm (added megasquirt flyback circuit to T-Bird SC pcm). I've not had reason (previously) to look at the drivers in a CFI pcm, but its basically the same surgery. The biggest challenge is finding the correct replacement transistors. After ID'ing the stock drivers, search the web for its data sheet. You will need to find a driver with the same base current and frequency, but capable of higher collector current. Then just desolder the old and solder in the new.

 

[Anonymous]

i am going to use a megasquirt
they have two seperate injector drivers
the guys over there seem to think that you could run all three tbi's
off of a single injector driver(batch fired),but know one has done it to there knowledge.

i could just use a single unit off of a 302 or 351 as there the same with different injectors.
but i thought it would be really cool to run three tbi's just like an old multi carb setup.
i can fab about anything i need as far as linkage and brackets go so thats
know problem.

i'm just looking for ideas here guys i can always put three carbs on if it doesn't work or go for the affore mentioned single unit with a different manifold.
i just don't think the carbs will react well to the 4wd as the vehicle will see
a lot of fire roads and such.

 

[fb71]

I can tell you right now that MegaSquirt will be able to handle the load. Its only three injectors per driver, and it can handle six per. In fact, I was lucky enough to have Mr Bowling (co-inventor of MegaSquirt) come to my school next week to deliver a presentation to my students on the logic and electronics internal to a pcm.

 

[Anonymous]

thanks fb71,
i guess i was posting the question on the wrong board at the megasquirt sight.

ok to the plan...

81 300
efi head with unshrouded intakes and port matched and cc'ed chambers
intake three stock center sections very similar to 52f-3's setup
block .030 over with efi pistons with .010 to .030 off the deck
cam isky mil-a-mor or stock cam grind with chebby rockers
megasquirt and 3 1bbl tbi's off a 1988 escort(1.9l)
efi exhast manifolds (port matched)
ds2 dizzy with jacobs electronics
possibly an msd might use the jacobs on something else
i'm going for the stump puller i might bump the compression numbers and
run it on e85 seems how its only $2.40 a gallon here in indiana and weve
got our own plant and all.

the info collecting is done this is what its going to be.

whats everyone think?

 

[StrangeRanger]

With that mild a build with a near stock cam, I don't see a need for multiple T/Bs. If you're doing it just to do it, that's fine but it's not going to give you much benefit.

 

[Anonymous]

when i'm starting with that cam selection for a baseline
i have 2 engines now and some after the shops closed dyno time
so i can really play around with and and find a good combo
without sacrificing reliability

and yes i am doing it just to do it
but i'm also doing it to compare the following
offy-c with 390 4bbl
offy-c with 302 and 351 tbi's and megasquirt
the 3 in 1 manifold with carbs
the 3 in 1 manifold with tbi's and mega squirt
and a offy dp if i can find one cheap

a friend of the shop owner that i work for has a speed shop and is
interested to find out what i can come up with.

after hours of course so his tech don't razz him about putting 6cyl's
on the dyno.

thats why i keep asking the same question over and over agian and posted all those combo's in the FIGURES thread.
i always like to have as much info as i can get before i make statements of any kind and now i'm going to back the "FIGURES" with some dyno numbers.

i will post everything for everyones benifit.

 

[Anonymous]

strangeranger,

what did you have the morning off as well?

 

[StrangeRanger]

Nah. Just a major case of not giving a damn about work.

Since you're playing with alternatives, take a look at dual T/Bs from something in the 2.5 litre range on a Cliffy 2 x 4v manifold. If you look at intake pulse timing and overlaps a dual induction system is much more optimal for an I6 than a triple. You get an intake pulse every 240° of crank rotation in each half manifold. With a stock cam that adds up to very little overlap and minimal inversion i the intake runners. The balance tube between the halves ends up doing very little if anything.

In a triple the intake pulses are 120°-240° in each manifold meaning lots of overlap and inversion on every other pulse.

 

[Anonymous]

if that cliffy didn't cost so much.

and i hear you

i am probably just going to use a single tbi unit with 2 injectors on the truck as it will be a daily driver and use the 3 in 1 setup for something fun.

what do you think about the e85 thing

 

[fordconvert]

The MS2 can direct control the ignition coil using the Duraspark pickup. I have not installed mine yet but as soon as I get the fuel part running I plan on trying the direct timing option. It will also control other OE modules that had variable timing. IIRC the jacobs systems dont change timing, they only do things like increase voltage and re spark if needed so if you can run the jacobs box with the MS2 you may have a sweet setup.

There is a FAQ about E85 and megasquirt. With the TB's and motors I was thinking about doing it with I cant get large enough injectors to get the extra fuel needed so for now I am just working on regular gas. My experience with E85 is IF you can deliver enough fuel it works but you loose a bit of power and obviously use more fuel (which in MN happens to be a wash cost wise because of the lower price) if you are using it in a motor designed to run 87-90 ish octane gas. Now since E85 is around 105 octane, you build a motor like its going to be an alky racer...... You get preimeum performance from a lower than regular priced fuel (depending on your state). You have to build your whole system for alky because the E85 is hard on some metals and rubber/plastic parts but its an interesting concept I would like to try sometime since E85 is not going anywhere soon and is pretty much everywhere in my area.

 

[Anonymous]

yeah got to use the neoprene or vitrex hoses, o-rings, and so on

the jacobs is a multistrike like the msd so i guess you would hook it up the same way at the neg on the coil or at the tach lead.