Can carburetors be combined with TBI?

[StreetSleeper]

Could you put a 2 barrel TBI in the center of a six pack intake?

Or does EFI need a sealed intake manifold past the injectors?

Would it be minimal improvement if you tried it?

Just curious, thanks

 

[DionR]

I'm no expert, but seems possible. No need for a sealed intake or anything.

My first thought was, why go to the trouble and only do 1 TBI on a 6 pack. Why not all 3?

But, as I understand it, ultimate power seems to be better with a carb rather than TBI. So in some ways a center TBI carb would work well for drivability while 2 outboard carbs would keep the full throttle power up.

Seems like the fuel delivery would be a complex deal, high psi for the TBI but low for the carbs?

Interesting idea.

 

[RGAZ]

Anything is possible, I assume you are asking so you can have the efficiency of FI during normal driving and cruise with the WOT craziness of 6 barrels. Unfortunately I think you will be disappointed.

A good EFI system is closed loop. That means it adjusts based on feedback from other sensors to get close to an ideal run state. While this might work at part throttle and cruise, the system would be nearly impossible to tune during the secondaries opening. The transition would be bad, the EFI would likely go hard lean because it sees the other carbs dumping fuel and almost no vacuum. I wouldn’t even know where to start to tune this. I’m sure you could get this to work with hours on a dyno, but from a cost-benefit ratio it would be a loser.

Now, if you want to try it, go ahead! I would love to hear your story and challenges and you would have a one-of-a-kind setup which might get you some props.

Good luck
RGAZ

 

[TT5.9mag]

The o2 controlling the TBI would always be trying to compensate for the added fuel and air from the outboard carbs. So wot afr would always be off. You’d have to run it without the o2s and you’d better be a good tuner.

 

[TT5.9mag]

You’d also have a hard time getting any kind of idle control because of all the “leaks“ around the butterflies of the outboard carbs.

 

[RGAZ]

After some though this is how I would do it:

Setup the center TBI normal with O2s and a regular driving table.

Adjust the throttle position sensor to align with then the other two carbs just begin to move. In the table change the fueling mode from closed loop to open loop and set the center TBI to ramp based on MAP only. Adjust the outboard carb jets using your O2 at WOT in the range you want. This could work if you have a bit of time and patience.

I am assuming you are using the 2barrel carbs specifically designed for the 6 pack. You can’t use just any old carb there or it will be a mess.

 

[dano]

What would be the reason to consider doing this? Drivability? Economy?

 

[George Jets]

TBI to 4 Barrel, Now that's a Great Idea!

'90 Roller 318 TBI conversion to 4bbl/HEI.

Sweet Setup and simple, no onboard computers.

☆☆☆☆☆

 

[DionR]

TBI to 4 Barrel, Now that's a Great Idea!

View attachment 1716453788

View attachment 1716453791

View attachment 1716453792
'90 Roller 318 TBI conversion to 4bbl/HEI.

Sweet Setup and simple, no onboard computers.

☆☆☆☆☆

What's the point of using the TBI intake? Probably could have used a 2BBL on it and not notice a power difference while an actual 4BBL intake would make more. People have their reasons for doing things, so not knocking it. Just not seeing the point so wondering what is the reason behind it.

 

[George Jets]

What's the point of using the TBI intake? Probably could have used a 2BBL on it and not notice a power difference while an actual 4BBL intake would make more. People have their reasons for doing things, so not knocking it. Just not seeing the point so wondering what is the reason behind it.

318 intake runners match the 302 318 Closed Chamber Head ports. Not like putting a large port intake on 318 heads where there is definitely a step restriction.

318 TBI has a huge plenum and is Factory Mid Rise Dual Plane intake manifold.

 

[AJ/FormS]

Could you put a 2 barrel TBI in the center of a six pack intake?

Or does EFI need a sealed intake manifold past the injectors?

Would it be minimal improvement if you tried it?

Just curious, thanks

this is the original question.
How did we get to 318 heads and 2bbl intakes?

My opinion, for what it's worth;
Yes you could;
no it doesn't;
Yes it would be minimal at best.
Curiosity is good
More opinion;
If for a Street application, and for Fuel-Economy;
Before I would go that route,
I would just put a smaller 2bbl in the center with, if I could find one, a triple booster. I bet I could get over 30mpgs with one of those on a 223* cam, and overdrive; geared 75=1850. Oh wait, I already did that. This is NOT a brag! I'm just telling you that it's possible. you don't need no stinking Efi, and specifically Not a TBI.
But, you know, if you just want to be different and/or you have the skills, have at it.

By the way; @StreetSleeper
>the two biggest deals with fuel economy, are; Rpm and optimal ignition timing,
and additional snags are; a very late closing intake event, and a large overlap cycle combined with Headers.
If your Rpm gets to be too low you will run into TWO problems;
1) If the cam is too big, fuel-economy will start to run backwards, and
2) below 2200 rpm, it is darn near impossible for a factory style ignition system to provide adequate ignition advance, and the vehicle still be drivable, in other states of operation. Yes, you can set your total cruize-timing to say 56*@say 2000 rpm; this is perfectly fine for cruise-testing; but just try not to kill your pistons, when you stomp the go-pedal.
BTW:
I'm not saying yur engine will want 56 degrees. It could be less or it could be more; you cannot know except by testing.
A triple booster center-carb can easily provide accurate metering for best fuel-economy, and the smaller the better, until it fails to transition well with the bigger outboards.
But depending on the cam, I no longer see a point to cruising at very low rpm.
2200 in a tight-Q closed chamber is all you really need.
If yur still running the factory open chamber heads, with the factory 114* cam; just forget about fuel-economy; that combo, was never designed for more than a factory application; which included adhering to government-mandated, emission reductions. TBI will not make it more better.
Thems my opinions.

 

[MopaR&D]

318 intake runners match the 302 318 Closed Chamber Head ports. Not like putting a large port intake on 318 heads where there is definitely a step restriction.

318 TBI has a huge plenum and is Factory Mid Rise Dual Plane intake manifold.

View attachment 1716453797

View attachment 1716453800

I think the restriction going from 4-bbl to 2-bbl flange would be worse than the slight port mismatch with a 318 manifold on 360 heads.

 

[junkyardhero]

318 intake runners match the 302 318 Closed Chamber Head ports. Not like putting a large port intake on 318 heads where there is definitely a step restriction.

318 TBI has a huge plenum and is Factory Mid Rise Dual Plane intake manifold.

so you made this abortion with an adapter rather than just hunt down a factory 318 4bbl intake?

that step restriction must not have been that big of a deal in that ma mopar put that exact setup on TONS of engines. if it hampered anything to such a degree, i would think the engineers wouldn't have signed off on it. anyway, that's a moot point because a basic gasket match would clear that all up ez-pz.

 

[66Signeto]

What would be the reason to consider doing this? Drivability? Economy?

Both really. Probably 20 years ago now an older gentleman in my area was running around in a Slant using a cobbled together GM V6 TBI setup. I'm not sure if he had it rigged up to run in the closed loop map or just ran it in "limp home" or open loop mode. To be honest I remember driving those engines with TBI and never really could tell a difference in how they ran unless something was really wrong like the TPS voltage was out of whack.

 

[RustyRatRod]

318 intake runners match the 302 318 Closed Chamber Head ports. Not like putting a large port intake on 318 heads where there is definitely a step restriction.

318 TBI has a huge plenum and is Factory Mid Rise Dual Plane intake manifold.

View attachment 1716453797

View attachment 1716453800

You say this about the "step restriction" at the intake and head ports, but what about the step you created with the four barrel to two barrel adapter? Do you not see that as a restriction? I'm not being a smartass, I'm asking a legitimate question. If you know something I don't, lay it on me.