Anyone have a dual TBI setup? Can you run them in parallel? What manifold are you using? Will they fit under your hood?

I have two throttle bodies for my 91 bird 305 and was interested in putting a dual carb manifold on and using two tbi carbs on it. Of course heads and exhaust, cam would be changed, plus computer tuning.

Are there any street legal manifolds that support two carbs?

Did a search but did not find much.

 

you can't run them in parrell, you need a second injector driver. there is a thread in the DIY PROM board about it, and the guys who did them was here in portand also if you dont' go the DIY route, holley had a piggy pack computer system for the command 950 that allows for use of dual 4bbl units.

 

Ok, what about in series, in parrallel you double the load amp wise and in serial you reduce the load by half. Anyway looking at the schematic it should be possible to use a solid state relay to up the amperage output ( solid state relays only cost about $15)

response time on your injector should be matched with the solid state relay. Here's a excert from
http://www.robietherobot.com/storm/f...ectorguide.htm

"Most domestic OE production EFI systems use an ECU with 12 volt Saturated Circuit drivers. These are very inexpensive, simple, and reliable. This type of driver works by supplying 12 volts to the injectors and the ECU turns it on and off to establish a fuel injector pulse. In general, if an injector has a high resistance specification (12-16 ohms) the ECU uses a 12 volt saturated circuit driver to control it. This means that the current flow in the driver and injector circuit stays low keeping the components nice and cool for long life. Conversely, a downfall of a Saturated Circuit driver is that it has a slower response time (and closing time) than a peak and hold type. This slower time can somewhat decrease the usable operating range of the injector energized by this driver. An injector operating on a saturated circuit driver typically has a reaction time of 2 milliseconds while a peak and hold driver typically responds in 1.5 ms."


Now these injectors have 10-16 ohm resistance 13v/10ohm=1.2 amps to 13v/16ohm=.8125 amps, as long as you have a fast solid state relay you can drive as many injectors as you like.

 

driver schematic

 

so in theory, then you can use 2 tbi wired in series and not have any adverse affects to the car or ecm? i would like to se this done. not only the dual tbi's but a 4bbl too.

 

In series each injector will only get half the amperage, so they may fire less or not at all. If you replace your injectors with ones rated at a lower amperage then is should be possible to hook them in series.

Two carbs give you shorter runners and better fuel and air mixtures, (I would think). Hmmm sounds like tpi. LOL But two carbs would look really cool. edelbrock makes a 3 carb manifold also, 3 tbi's, but dosn't look like the carbs would fit physically and you would have to tap and drill the carb mounting holes but cheaper than a adapter.

 

It looks like the injectors for tbi are 1.16-1.36 ohm called a peak and hold where it gets alot of current (about 3 amps) then goes down to a couple of amps. The driver board keeps it from drawing more than 3 amps.

Other injectors are called saturated injectors and the injector limits the current instead of the driver board. These injectors are typically 11-16 ohms and are used mainly on TPI systems. I believe they are smaller since each cylinder gets it's own injector.

The quad 4 uses injectors that are 1.95-2.15 ohm injectors, Still trying to find some app notes on these injectors. but you may be able to wire them in parallel. Don't quote me on that, if your engine runs to lean you can burn things up or your driver board.
Same goes for series, but since the circuit limits the current your injectors are only going to get half the current. If this works at all you may need to change the pulse width, running to lean can ruin your engine.

It looks like the tpi ones are only 18lbs/hr and the tbi units are about 40-60lbs/hr this makes sense, you have 2 injectors in the tbi and 8 injectors in a TPI.

Since I'm designing a diy ECM, will probally use an additional driver board for the other injectors. I should be able to control each injector seperatly.

Check this thread for extra injector boards.
https://www.thirdgen.org/techbb2/sho...injector+board

Research
http://www.pirate4x4.com/tech/billav...ector_info.pdf
http://members.shaw.ca/megasquirt/manual/minj.htm

 

IIRC one of the biggest problems people complained about was fueling at low rpms/idleing. Since both tbi's will open at once and both sets of injectors are always firing, youll have serious problems with the needed injector pulsewith being impossible to obtain on a small block thats intended for use on the street without having to sacrifice top end fueling with smaller injectors. With the holley 4bbl, they have progressive linkages as well as, i think, progressive injectors. Only two are active at idle so the unit can be used on lower output engines. Id definatly go with twin tbi's and an external injector driver with a big block but with a streetable small block id probably consider some other form of induction, like a diy-mpfi system. Now, if you could implement those features that holley has into your system, that would be great.

 

I've been reading a ton, and looking at a ecm dissassembly. You probally can run two injectors in parallel off of one driver. But you would need to keep PCM cycle below 50% duty cycle or you will blow the driver. But both injectors should fire up with just 1.5 amps each instead of 3. Or you could go with some after market injectors that have the higher resistance and don't need the high startup current. I been looking around but there does not seem to be much in diminsional specifications listed for different injectors.

I would'nt have a problem running 2 of the higher resistance 30lb units and 2 of the 60lb units in parallel. When you use up the 30lb start ramping up the 60lb units. You'll need to replace almost every table but would it be cool or what.

You can also just use a fast solid state relay to switch pwm the injector. I saw some for $9 on ebay with 400khz response time, some are optically isolated so no inductance problems

Check out this website for lots of good info.
http://www.bgsoflex.com/megasquirt.html


Just picked up this manifold on ebay, would have asked someone on this board if it was anygood, but could not get here this morning. Since knowbody else bought it for $70 I have to wonder.

Its a holley 300-65

, should be good to play with though
http://cgi.ebay.com/ebaymotors/ws/eB...ME:B:EOAB:US:6

 

that megasquirt ecu is ****... That along with an hei dist. or aftermarket ignition would be a real sweet setup. As for the injectors, why not just build a stand alone unit (or internal driver) to control the four injectors. youd be able to have more robust drivers as well as dedicated power and efficient heatsinking/cooling, which is something the ecm doesnt have.

 

That was what I was thinking if you look on the diy prom board I have a diy-ecm. I want the spark and timing control and be able to use the existing wiring harness for most everything. If I have to put it back to stock I just plug in the old computer and manifold. I certainly can run some extra wires for the injectors. I planning on cutting off the io chips and processor from my spare computer and wiring up a pic micro unit with fast basic built into the old board driver circuits. You can write subroutines in assembly if timing is that critical on anything. But it's 40mhz chip actually instructions execute at 10mhz each, thats 0.1 milliseconds or 100 nano seconds.