Thread: dual TBI ??

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all of this talk almost tempts me to try it. the biggest hangup right now is i would have to cough up big bucks for a dual quad intake for a 348 and not know if it would even work good. another thing is i know i wont have enough cam and exaust to handle the fuel. i'm going to be sitting at 300 hp with this motor so mabey one unit would be the smartest. ( still not the coolest though )

Originally posted by 53 Chevy5
all of this talk almost tempts me to try it. the biggest hangup right now is i would have to cough up big bucks for a dual quad intake for a 348 and not know if it would even work good. another thing is i know i wont have enough cam and exaust to handle the fuel. i'm going to be sitting at 300 hp with this motor so mabey one unit would be the smartest. ( still not the coolest though )

you need to get what youve got working first then worry about that.

I don't think it's possible to use the GM ECM to run the proposed dual throttle bodies, at least not without a substantial amount of work.

The GM injectors are low impedance (Lo-Z), usually around 1 ohm cold. Doubling the load would almost certainly overheat the drive FETs. You'd have to intercept the drive signals from the ECM, then buffer them individually for the four drives.

Use only the original O2 sensor, having two in the circuits is no better than having two watches - you're left with the question "which one is correct".

Plan on custom code for the ECM. It has a base fuel map which it follows in a rough manner, maybe within 10% of stoic. The O2 sensor just fine tunes the mess. With the dual throttle bodies and injectors the ECM will probably be off the map (pun intended).

You may be better off using a pair of aftermarket throttle bodies, then pick up 8 Bosch type injectors off eBay.

Typical throttle body :

http://www.auto-nomics.com/cgi-bin/s...rt=10850-002-D

You can also find a small EFI controller on ebay, the MS EFI units work well. You can put together a radical looking system for around $500-600. Just set it on top of a dual quad manifold.

FWIW, the Apple IIE has more horsepower in it's little 6502 processor than all but the most current automotive ECMs. The newest crop are DSP based, but still only in the 33MHz range. It's this bloated pig called windoze which has led us to believe anything less than 3.8GHZ is too slow to be useful.

A multiport would be a nice aproach, but I'm not aware of any single plane or tunnel ram manifolds available for the 348/409 engines. The fuel logs would be a pain to implement with a dual plane manifold. You'd really like the port runners at the same elevation to make life easy.

Regards, Mark

Originally posted by drg84
Wow, this has become one amazing thread. Nice to see this much input As for the %80 remark Lt1, your right. There is room for improvement. But based on current computations, its more than possible. Based on an outdated downdraft with 1984 technology, it wouldnt work. We have to remember that computers are constantly updating. In 1984 the top of the line was a AppleIIE with 740K of memory running at somewhere around 7 mhz. And even then, the automotive computers had not had the required sensors to evaluate differing running conditions. Anyone who has worked on a newer system knows that the computer can actually read misfires due to differences in voltage off the plugs. Basicly what im saying is that a dual TBI would be possible, but with a system that can read the engine, not guess at it. But if your taking that route, a Multiport would be much more effective. A cheap and easy way to accomplish this would be to locate a engine with the sensors already in place for a multiport setup and program the computer for dual TBI. Then it would run decently and still have the shock value. In fact, i wonder how much it would take to update a Cross-fire system?

i like the EFI idea but i miss the experimenting

Originally posted by lt1s10
you need to get what youve got working first then worry about that.

i got nothing else to think about while the motor is getting work. well, mabey i could finish putting the rearend in, sandblast the frame, paint it , set the body on do the rest of the body work to it and paint it , finish the interior and air conditioning, put the windows in and install an air freshener in the mean time .

Originally posted by 53 Chevy5
i got nothing else to think about while the motor is getting work. well, mabey i could finish putting the rearend in, sandblast the frame, paint it , set the body on do the rest of the body work to it and paint it , finish the interior and air conditioning, put the windows in and install an air freshener in the mean time .

that could tie you up for a few hrs.

I'm going to be doing a dual TBI setup on my shortbed chevy. Holley makes the throttle bodies up to 1000 CFM, and they make the Y adapter to connect the 2 to the computer.

I'm doing dual 670 CFM Throttle bodies with 85PPH injectors on a chipped up computer.

Originally posted by Colbycheesiest
I'm going to be doing a dual TBI setup on my shortbed chevy. Holley makes the throttle bodies up to 1000 CFM, and they make the Y adapter to connect the 2 to the computer.

I'm doing dual 670 CFM Throttle bodies with 85PPH injectors on a chipped up computer.

let me know that works.

I'm working on this project as we speak. I have a 1990 Camaro with a 302ci motor. I picked up the Offenhauser dual crossram intake along with two TBI to 4 bbl adapters. This is kinda my homage to Duntov. Working with Dual 850CFM TBI units. Problem right now is getting the linkage made. Olny going to use one of the throttle position sensors. Just hoping that I dont have to screw with the wiring to bad when I split the injector signals......

Also for better O2 readings I upgraded to a 4 wire......

The Crossfire injection can be made to work nicely. The biggest drawback is the very simple ecm that ran them. There's a cure for that though, although it's not cheap.
http://www.turbocity.com/product_inf...roducts_id=455
http://www.turbocity.com/product_inf...roducts_id=358
http://www.turbocity.com/product_inf...products_id=20

Guess you really, really have to want to be different.

Then there's this http://www.megasquirt.info/ which the magazine people say works very nicely for under $200.
And it's completely tunable.
http://www.carcraft.com/techarticles/116_0403_mega

GM's factory dual TBI set up was for two (2) single-bore TBI units atop a Crossram-style intake manifold. Each TBI had a single injector. The Crossfire was used as the L-83 350 in 1982 & 1984 Vettes and as the LU-5 305 in 1983-1984 Fcars as an optional engine.

I think what you are talking about is dual 2-bore TBIs, to get more airflow than just using either the Crossfire set up or the later GM 2-bore TBIs used on 305, 350 and 454s. That idea has been kicked around a lot on the Thirdgen.org forum, and on the Crossfire Vault website (forum), as well as on the DIY EFI email digests.

Here's two TGO (Thirdgen.org) starter links:

http://www.thirdgen.org/techbb2/show...ight=mefi+dual

http://www.thirdgen.org/techbb2/show...ight=mefi+dual

HTH.

Went with a MegaSquirt computer for the fuel system and ended up running twin 454 TBI's. Still working on the performance, but it started up on the first try. The offenhauser intake looks great on my third gen.....