TBI to MPI

[V8GremlinX]

just curious what it takes to convert a TBI to a MPI. i did a search and links came up gone
let me know if u can help me
Rich

[Vigo]

you need the manifold, tb, tb sensors, injectors, fuel rail.. and maybe the bolts for the manifold if they are different.

you also need to wire the injectors together to make a suitable load for the tbi injector driver. i think the tbi injector is only a 1 ohm load.. other people have talked about stupid ways of wiring the injectors with added complexity but if you wire them in two pairs and then wire those two pairs together using both series and parallel it comes out to 2 ohm which imo would work.

[mike mckay]

I thought I had a copy of how they did this conversion; I'll have to see if I can find it. I was looking at doing this until I ran across a turbo car so I have never started on it other than info. Here is what I can remember.

You'll need what Vigo said but depending on your car you may have to also change your fuel pump. The car I saw on the Derek's site had a 36 psi pump.(late model Shadow).. If you have a pump with a 88 TBI like I have (14 psi) you'll have to change it to make it work.
It still uses the computer in the fire which is batch fire. The injectors were out of a Mustang and they were about 19#/hr. In this version the impedance of the injectors is important so you don't burn out the computer. Also note that the turbo TPS is wired reverse of a n/a throttle body. It won't fire if you don't get this right. He also had to do some juggling for an air filter which is not much compared to the rest. A cone filter would work or maybe one out of a 3.3 engine looked llike it has right location/orientation.

[sdac_guy]

If you tie all 4 injectors together in any manner to get the right impedance match, all 4 will fire every revolution or whenever any one is called for. This will provide way too much fuel and will also result in the fuel charge condensing and/or puddling on metal parts (manifold, valves) while it is waiting to be "inhaled" by the motor.

Since manifolds and other things like fuel pump need to be addressed anyhow, the easiest way to get a mpi motor is just use a turbo setup without the turbo (TBI exhaust manifold). This of course will require either switching the underhood wiring harness, or making extensive mods to it. But once done, just hook up the appropriate year ecu (or logic/power module pair) and it is plug and play.

All the fuel curves will be okay because the electronics are designed for mpi and also to run at non-boost levels. Probably less headaches doing it this way in the long run.

I do recall a long time ago, about folks that had a bad turbo and they switched the exhaust manifold to a NA manifold and drove the car as an mpi only setup for some time. Drivability was excellent and it got very good mileage.

Barry

[Vigo]

well, all of them firing is what you call batch fire, which is what every dodge v6 car prior to mid 92 had, and ive driven both pre and post smpi 3.0s and 3.3s and there is not one single difference in driveability.. the change was for emissions and maybe .5 mpg.

besides, on a tbi the injector sprays regardless of which or what valves are open or closed and it still works fine. so a tbi is pretty much the same as batch fire mpi, with less injectors, hah. also, carbs dont spray minute amounts of fuel intended to reach individual cylinders at the precise moment that the intake valve opens, and they still manage to do ok.

millions upon millions upon millions of tbis and batch fire mpi cars running around working just fine.

anyway, you could run the car on a turbo computer if somehow getting the turbo computer and wiring harness and intake manifold and putting that all in is somehow more sensible than just buying the manifold when you will still have a non turbo car when you are done.. imo if you're going to change the harness and computer and intake you might as well change the pistons and exhaust and have yourself a turbo car.

the beauty of the mpi switch is that its cheap and easy.. start changing computers and wiring harnesses and all that and it loses all its appeal imo.

in this case he has the later model tbi with the right fuel pressure, but you'll probly need a fuel pressure regulator anyway if you go with any injector size other than stock.. but stock injectors on the turbo 4s can support significantly more than you're going to make with a bolt on non turbo motor, so there's no point in going bigger imo.

good luck!

[mike mckay]

I forgot about fuel pressurre regulator; it was adjustable. The injectors were 19 #/hr; not the higher rate like in turbo. He also tried some Neon injectors but he mentioned they didn't work as well as Ford injectors.
Fuel pressure had to be adjusted some.
He didn't use turbo computer because there was some mention that it had been tried by Derek(Derek's Garage web site) and didn't work well. He mentioned it fell flat probably because there was no turbo there. I can run my turbo engine like is without boost by pulling a hose. But it doesn't run that great. The n/a engine is also higher compression
The mpi conversion is cheap particularly if you don't have turbo setup available and want to change over car quickly. New injectors were the highest cost items. Only wiring change is for injectors and around throttle body. He had even run it on track but I don't remember the times.

[V8GremlinX]

now im lost
lol
Rich

Check out this thread: Megasquirted Shelby Charger
If that guy can convert a carbureted car to mpfi, it's probably even easier on a TBI car.

[sdac_guy]

Quote:

well, all of them firing is what you call batch fire, which is what every dodge v6 car prior to mid 92 had, and ive driven both pre and post smpi 3.0s and 3.3s and there is not one single difference in driveability.. the change was for emissions and maybe .5 mpg.

I am sure that they did NOT have all 6 firing at the same time though. In the turbo cars, they had 2 pairs of 2 injectors batch firing. This resulted in either pair of injectors firing every other stroke on the 4 stroke motor.

Quote:

besides, on a tbi the injector sprays regardless of which or what valves are open or closed and it still works fine.

The tbi releases the air/fuel mix into the manifold plenum where there is constant motion of the a/f mix and it keeps the fuel from condensing.

Quote:

so a tbi is pretty much the same as batch fire mpi, with less injectors, hah.

Hah, not so at all. In the 2.2 mpi manifold, the injector releases the fuel directly to the intake port. So, if all 4 injectors fire at the same time then they are all firing at every stroke of the 4 stroke motor while the valve only opens during the intake stroke. So there WILL be fuel laying on the intake valve when it opens. Most of that extra fuel will not be burnt, but most likely will wash down the cylinder walls resulting in advanced ring wear.

Quote:

also, carbs dont spray minute amounts of fuel intended to reach individual cylinders at the precise moment that the intake valve opens, and they still manage to do ok.

Again, carbs release the a/f mix into the manifold plenum where there is constant motion of the charge.

Quote:

millions upon millions upon millions of tbis and batch fire mpi cars running around working just fine.

But none of those are running around with all of their injectors firing at every stroke event for every cylinder as you propose doing.

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anyway, you could run the car on a turbo computer if somehow getting the turbo computer and wiring harness and intake manifold and putting that all in is somehow more sensible than just buying the manifold when you will still have a non turbo car when you are done.. imo if you're going to change the harness and computer and intake you might as well change the pistons and exhaust and have yourself a turbo car.

Let's see, you're changing the intake manifold, throttle body, injectors, and making a bunch of splices to the existing wiring harness to get the injectors wired up. So instead of hacking up the wiring harness, why not UNPLUG it and PLUG IN another one and the matching ecu that goes with it? Yeah, you're right it is easier to splice, solder, tape, etc.

Quote:

the beauty of the mpi switch is that its cheap and easy.. start changing computers and wiring harnesses and all that and it loses all its appeal imo.

The issue of impedance to the ecu has been balanced by the series/parallel pairing of the injectors. But what has not been addressed at all is how well those injectors that are in series are going to operate at 6 volts each when they were designed to operate at 12 volts? Will there be cold weather starting problems because of sluggish injector operation? Could be....

My suggestion was for using parts that are already designed to work together as a system. Some folks may prefer to go the cheap & easy route, but when it is 10 below zero out, that is a tough time to find that cheap & easy won't start because the injectors aren't getting enough juice to them to make them fire.

Barry

[Vigo]

Quote:

The tbi releases the air/fuel mix into the manifold plenum where there is constant motion of the a/f mix and it keeps the fuel from condensing.

the batch fire 6s were firing 2 banks of 3 at a time, which would basically be the same as two 3 cylinder engines firing all 3 injectors at a time since not all 3 cylinders on either side are gonna be on their intake stroke at the same time anyway, and its the same concept as all 4 injectors firing on an mpi turbo dodge, i mean the fuel injectors are as close to the ports on the v6s as on the turbo 4s.

anyway, when you mix series and parallel, wouldnt you end up with the same voltage? two circuits of two injectors each, depending on which way you wired which ones, the voltage halves than doubles before you plug it into the injector driver.. so it should still be 12 volts, or whatever it is that drives the injectors.. for all i know the injectors could be on 5 volts.

anyway

Quote:

you're changing the intake manifold, throttle body, injectors, and making a bunch of splices to the existing wiring harness

the manifold has that stuff on it, no need to remove it, and the bunch of splices, seriously, you're cutting like 4 wires and adding two. and cutting the stock harness?? no need.. just cut the pigtail off your tbi injector and solder your new subharness to that, and plug into the stock plug.

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The tbi releases the air/fuel mix into the manifold plenum where there is constant motion of the a/f mix and it keeps the fuel from condensing.

i dont get that because air in all parts of the intake path behind the throttle body, the air is moving at around the same speed. i mean there are differences involved in equalization of pressure, but its minute in the grand scheme of things.

anyway im not trying to sell you on the mpi swap, if you think it doesnt work well, you can double the cost and significantly increase the complexity of the mod, up to you.

personally as far as im concerned at this point tbi cars are basically worthless ($$$ wise) toys that arent good for anything but experimentation and taking parts off of. other people may have different opinions, but thats the way i see it, and if my tbi has 20 more hp and only lasts half as long, sounds great.. its like a toothbrush.. if one worked a lot better but didnt last as long, would you use the crappy one? even here in san antonio where k-cars are really rare, tbis are still throwaways at this point.

so my .02, mod the crap out of your tbi and have fun with it while it lasts.. and if it breaks buy another one for a few hundred bucks and try to break even selling parts, or get one for free like me. on the trip to pick up my latest free car i saw about 7 k-cars that had been sitting obviously for a while. im sure i coulda picked up some more free crap if i had enough trailers to daisy chain..

[D-Cal]

The conversion isn't difficult, and while I had the page up several people emailed that they had done it successfully with no over-fueling issues.

Intake events even at idle happen frequently enough that fuel dropout doesn't seem to be much of a problem for those that have done it.

As has been pointed out, there are many applications where MPI injector banks are fired in a batch. This is nothing new.

Wiring four high impedance injectors in parallel will draw roughly the same current as a single low impedance injector. Ohms law. The voltage supplied is 12v and does not change to 6v or anything else.

Wiring in a turbo computer in place of a TBI is a much more complex operation and will not work well anyway. They are calibrated for an engine with completely different spark characteristics due to compression differences (9.5 vs 8.0) and the expectation of boost changes many things internally. Ironically my program D-Cal now may make that route more accessible since you can recurve the spark curves to anything you like.

When I locate a new provider to call home I will put the recipe pages up again.

Derek

[CRAZYMATT]

I used a T2 smec when i did my conversion worked great - ran even better till i blew it up a few times.

The 2.2/ 2.5 T1 smecs dont have enough timing or something to make it work right - my car always fell on its face at 4k and bogged

[Putter]

i converted a carb car to turbo fuel injected, its a big project but not impossiball, you need to know quite a bit about electronics and electrical, www.axode.net under the cars is the omni conversion to fuel/turbo..not tech conversion but an overall, and i still run the 9.5:1 compression and carb exhaust valves, 1500miles so far still going 10psi

[tmef]

Chrysler made a factory N/A, MPI. I saw one at the salvage yard today. I walked up to it, saw the blow through intake and was very surprised that there was no turbo. It was a 1993 Dodge Spirit. The SBEC and injectors were already taken off.

[OmniSRT4]

Quote:

Originally Posted by Putter i converted a carb car to turbo fuel injected, its a big project but not impossiball, you need to know quite a bit about electronics and electrical, www.axode.net under the cars is the omni conversion to fuel/turbo..not tech conversion but an overall, and i still run the 9.5:1 compression and carb exhaust valves, 1500miles so far still going 10psi

"It will be interesting to see how the non-turbo 2.2 with cast rods and crank, low tension rings and decently high compression for a forced induction setup will last."

I read this part on your site and figured I would answer it.

The cast crank will handle 400+whp.

The cast LW rods *suck* and will handle maybe 200whp.

The cast N/A pistons are fine until you get detonation, then they are toast.

THe high CR ratio will be fine at 10psi and below with an IC. Its borderline with a log intake and no IC.

I would be much more concerned about the valves if I were you, they are *not* designed for turbo use and are probably your weakest link.