the primaries are going to favor the front bank to quite a strong degree, and the secondaries are going to favor the rear bank...
Okay, so let's say the carb is turned 90° (either way). Aren't the primaries and secondaries then simply going to "favor" the left (or right) ends of the two banks of cylinders instead?
I know what you're getting at, and I understand why you're saying it, but I wonder if a flow test would back up what you're suggesting.
If that carb is poorly positioned, then how about the TB on every 2.8? It would stand to reason with what you've stated that cylinders 5 & 6 get favored air flow, then 3 & 4... and then cylinders 1 & 2 get whatever little air flow remains way over on the passenger side of the intake manifold.
Okay, so let's say the carb is turned 90° (either way). Aren't the primaries and secondaries then simply going to "favor" the left (or right) ends of the two banks of cylinders instead?
I know what you're getting at, and I understand why you're saying it, but I wonder if a flow test would back up what you're suggesting.
If that carb is poorly positioned, then how about the TB on every 2.8? It would stand to reason with what you've stated that cylinders 5 & 6 get favored air flow, then 3 & 4... and then cylinders 1 & 2 get whatever little air flow remains way over on the passenger side of the intake manifold.
this is a actually true, and many obd2 cars have a table in the tune that allows you to scale the fuel for each individual cylinder unlike obd1. but on that note, a throttle body in a fuel injected car is only metering air, not air and fuel like a carb, so positioning is much more critical for a carb then for fuel injection.
honestly, as far as the carb setup in question is concerned, I think the whole setup is junk, I think it would be much better off using a high flow 2bbl, then a 4bbl, and if he's going to use a 4bbl, it should be a non-progressive linked mechanical secondary square bore carb.
honestly, as far as the carb setup in question is concerned, I think the whole setup is junk...
As much as you might be correct that this particular manifold/carb combination isn't ideal, I think you're perhaps being a little harsh on the fella who fabricated the manifold by referring to it as "junk".
I give trotterlg full credit for trying something different. I'd like to hear from him how well (or possibly not) the engine runs with this setup.
quote
Originally posted by trotterlg:
[This message has been edited by Patrick (edited 01-26-2014).]
However well (or not) it runs with a carb, it may have promise with a TBI unit. They flow plenty for a 2.8, and have plenty of injector options to feed it whatever you need.
However well (or not) it runs with a carb, it may have promise with a TBI unit. They flow plenty for a 2.8, and have plenty of injector options to feed it whatever you need.
WHY? for the same amount of work you could just do MPFI, and have a much more well engineered design.
BECAUSE! Besides, wet flow vs. dry flow wasn't the point of the post. It's the fact that it wouldn't have the fueling issues a carb would.
how do you figure? fuel distribution(what this argument has been about) would be unchanged carb vs TBI. TBI would be just as much of a wiring and tuning hassle as MPFI, so there would be no reason at all to do that. doing this with TBI seems as backasswards as it gets.
I've done a couple TBI swaps/builds. The problem is that when you have a high specific power output, you need big injectors.
Big enough injectors to make big horsepower at ~15psi are basically big on-off valves. They are extremely difficult to control at short enough pulsewidths to idle smoothly/consistently. Just try to get big injectors cycling reliably at pulsewidths under .9 ms. This, by the way, is the real reason that OEM TBI injectors are barely large enough for the engines they're on.
The magic bullet solution to this is to fit a manifold-vacuum referenced fuel pressure regulator, so the injectors act small at idle and large at WOT.
By the time you go to the effort to plumb this hardware in, you could've already had a MPFI setup with less plumbing, less complication, better fuel distribution, better fuel atomization, less crazy acceleration enrichment requirements and more commonly-available and modern injector options.
[This message has been edited by KurtAKX (edited 01-28-2014).]
Originally posted by KurtAKX:Big enough injectors to make big horsepower at ~15psi are basically big on-off valves. They are extremely difficult to control at short enough pulsewidths to idle smoothly/consistently. Just try to get big injectors cycling reliably at pulsewidths under .9 ms. This, by the way, is the real reason that OEM TBI injectors are barely large enough for the engines they're on.
The magic bullet solution to this is to fit a manifold-vacuum referenced fuel pressure regulator, so the injectors act small at idle and large at WOT.
Precisely. I'm running 80# injectors between 18-23psi on a ~380hp 383.
TBI doesn't have fuel bowls and other carb-related problems. You mount a carb 90º to what it's supposed to be, and you have it acting like it's been laid on its side every time you accelerate. You run it the 'proper' direction you would on a regular longitudinal engine, and fueling isn't spread evenly between cylinders (front bank gets primaries, rear bank gets secondaries). With TBI it's just like a 2bbl carb, no primaries/secondaries, and it can meter fuel more precisely. Any time you change altitudes with a carb, you would always have to tune it to get it to run at its optimum. TBI, other EFI systems measure barometric pressure when you turn on the ignition... so they instantly know how much fuel to use.
I never said anything about running TBI in place of MPFI, it was SOLELY related to that sideways carb setup.
[This message has been edited by Doober (edited 01-28-2014).]
Precisely. I'm running 80# injectors between 18-23psi on a ~380hp 383.
TBI doesn't have fuel bowls and other carb-related problems. You mount a carb 90º to what it's supposed to be, and you have it acting like it's been laid on its side every time you accelerate. You run it the 'proper' direction you would on a regular longitudinal engine, and fueling isn't spread evenly between cylinders (front bank gets primaries, rear bank gets secondaries). With TBI it's just like a 2bbl carb, no primaries/secondaries, and it can meter fuel more precisely. Any time you change altitudes with a carb, you would always have to tune it to get it to run at its optimum. TBI, other EFI systems measure barometric pressure when you turn on the ignition... so they instantly know how much fuel to use.
depending on the height of the butterflies in relation to the entrance to the plenum, there very well could still be a fueling issue. the plate will push the majority of the mixture down the lower side of the plate, if there isn't a long enough space behind the plate, the mixture will bias towards that side. either way, this would be wildly impractical when you could just run MPFI like the engine was designed to do instead of all of the fab work to do TBI, it would be completely and utterly pointless.
We're not arguing TBI vs carb, we're wondering why use TBI at all? It's outdated and quite inferior to SFI/MPFI despite needing the same amount of setup to get working. Do you have dyno sheets on your SBC?
We're not arguing TBI vs carb, we're wondering why use TBI at all? It's outdated and quite inferior to SFI/MPFI despite needing the same amount of setup to get working. Do you have dyno sheets on your SBC?
I wasn't even arguing that TBI was outdated, I like TBI, I just think the premise of trying to use TBI on a manifold for MPFI, when the parts for MPFI are SOOO cheap and EASY to begin with, just doesn't make a lick of sense.
What about a two barrel carb mounted in the correct direction?
I think it would work better than whats on there now, but like I said, I think the design is horrible, I see uneven distribution and poor fuel suspension problems all over the place with that design.
------------------ 1st class A**hole.
we're in desperate need of a little more religion to nurse your god-like point of view...
The Q Jet design intake would be prone to puddling in the bottom of the intake, Ever seen a Manifold explosion on a LS corvette? Youtube it, its not pretty. The plenum design is worlds better because the air fuel mixture isnt mixed in the plenum persay but in the lower runners just above the valves. Tin Boxes or sheetmetal intakes or as we call them "explosion chambers" offer no better benifit. Of course your going to be shoving alot more fuel and air to the motor and get that Loud Q Jet Secondaries sound but to the point your not burning all the fuel in the cylinder and pumping it out the exaust. (glowing Cat syndrome) washing the rings down and losing compression is another result. Not Bashing your design, just raced for a many of years and seen Thousands of new homemade designs come to the dragstrip with explosive results.
The Q Jet design intake would be prone to puddling in the bottom of the intake, Ever seen a Manifold explosion on a LS corvette? Youtube it, its not pretty. The plenum design is worlds better because the air fuel mixture isnt mixed in the plenum persay but in the lower runners just above the valves. Tin Boxes or sheetmetal intakes or as we call them "explosion chambers" offer no better benifit. Of course your going to be shoving alot more fuel and air to the motor and get that Loud Q Jet Secondaries sound but to the point your not burning all the fuel in the cylinder and pumping it out the exaust. (glowing Cat syndrome) washing the rings down and losing compression is another result. Not Bashing your design, just raced for a many of years and seen Thousands of new homemade designs come to the dragstrip with explosive results.
Fuel puddling doesn't cause a manifold to explode. In fact, when you have that much fuel and you're that far from stoich, the flame speed is slowed. Those manifold explosions on youtube are Nitrous Oxide related. In a sheetmetal box intake on an engine with a qjet and no nitrous or other oxidizer, you won't have that problem.
Jeez-Louise... I was only mentioning TBI because there was a carburetor on a manifold that would be better suited for TBI since the engine isn't longitudinal.
I didn't say TBI was better or worse.
I never even brought up port injection or how it relates to TBI, or the manifold it was on.
Would I run a carb (or TBI) on a manifold that was designed around port injection? No, I never said that, someone else got that idea somehow.
Hopefully this clears up whatever confusion there was when I originally brought it up... ridiculousness this has become
Jeez-Louise... I was only mentioning TBI because there was a carburetor on a manifold that would be better suited for TBI since the engine isn't longitudinal.
I didn't say TBI was better or worse.
I never even brought up port injection or how it relates to TBI, or the manifold it was on.
Would I run a carb (or TBI) on a manifold that was designed around port injection? No, I never said that, someone else got that idea somehow.
Hopefully this clears up whatever confusion there was when I originally brought it up... ridiculousness this has become
how is that design better suited to TBI? the LIM was designed clean sheet for MPFI...
------------------ 1st class A**hole.
we're in desperate need of a little more religion to nurse your god-like point of view...
I NEVER SAID THE INTAKE ITSELF WAS GOOD TO USE WITH TBI. I SAID THE TBI WOULD BE BETTER TO USE WITH THE INTAKE THAN THE CARBURETOR.
Are you seriously trying to troll here or something? I don't know how else I can say it.
once again, I'll ask how? how would tbi magically be better then a carb here, they both suck outright for this manifold design. both carb and tbi are wet flow systems, either way, you have a wet flow fuel system on a dry flow manifold. it's a bad idea no matter what way you cut it, tbi doesn't magically change the fact that the fuel has to stay in suspension throughout the runners.
------------------ 1st class A**hole.
we're in desperate need of a little more religion to nurse your god-like point of view...
It would be better because it's not feeding one half of the engine with the primaries and the other half with the secondaries... TBI doesn't care if it's mounted 90º to the direction the car travels, like a carb would.
I don't care how good it is or isn't for this intake, simply that TBI would be better off than a carb. Don't even let the thought of port injection enter your head.
Will a carb react differently being mounted the wrong way on and engine? Will an engine like one bank getting more of the primaries while the other bank gets the secondaries? TBI won't have to worry about any of that... again, don't even consider the original design of the intake runners.
That said, a 2bbl. carb would be more than adequate for the little 2.8, and no worries of primaries/secondaries like with a 4bbl. A 350ci engine at 6000rpm doesn't need more than 600-650cfm for the street. Are you spinning this little v6 to 10k?
Hopefully this clears the air a LITTLE more... and hopfully the OP comes back with new pictures and results of the new intake.
Seem to have gotten off topic. Thought the discussion was to improve airflow without loosing stock look. OP solution was to design a new intake with a style and look at least close to the factory intake. Card vs MPI should be a new thread.
[This message has been edited by Knight (edited 02-19-2014).]
