In regards to the "close hood clearance".....have you ruled out maybe dropping the engine lower with custom mounts?! That would solve the clearance issue once and for all........
6sally6

Daze wrote:

TKOPerformance wrote:

All kind of academic, but the point is that the runner length difference is typically less (shorter runners) and the flow runner to runner more balanced in a single plane.  With a TBI the closer you can get the TBI to the ports the closer it is to port EFI. 

While you are not wrong about runner length and atomization that is not why TBI "requires" an open plenum.  It has to do with the direction of the spray, batch firing, and the firing order.  If the problems associated with TBI and a dual plane intake were related to runner length a 1" open spacer would not fix the issue, but it does every time even though it lengthons the runner.  It's fuel distribution.  Obviously multiport injection is better and if this was a 302 I would be set but I can not find a multi port injection intake for a 351W that is not either extremely expensive or way to tall.
 

I didn't say runner length was the only advantage to a single plane.  I don't know that strictly speaking all TBIs requires an open plenum, a lot of it depends on design.  If you have two injectors and they fire bank to bank you could isolate each half of the engine and it should be fine, provided the fueling to both banks is essentially equal.    Practically, I think the open plenum serves a couple purposes.  If the injectors are not perfectly balanced, or the manifold doesn't flow balanced to both halves of the engine the open plenum allows one side to give and the other to take.  The plenum divider may also provide a hard surface too close to the injectors whereby the injectors are spraying fuel directly onto the divider and liquid fuel is dripping down the divider and pooling in the intake.  Then, depending on exactly how the elecronic side of the system works, you are going to likely need an MAP sensor and that vacuum source is best coming from an area common to the entire engine.  If you were running Alpha N it wouldn't matter, but the only guys I've ever seen run that are racers.  Every TBI system I've experience with is speed density and uses a MAP sensor. 

As for not being able to find a port EFI manifold for the 351, make one.  All you need to do is weld some injector bungs into an appropriate manifold.  Still can't find a single plane intake that fits under the hood?  Make one.  Come on Daze, I like watching you build stuff I don't have time to build. 

You probably know this already, but if you continue to use batch fire you can use most of the same electronics, etc. from the TBI setup with port EFI.  That's basically what the TPI was.  It fires one bank of injectors then the other.  Edelbrock used to make a system that did basically the same thing for TBI trucks.  I had one on my K5 at one point. 

With all of this mumbo jumbo we used to just bolt a carb on and go, thats what TBI did with some nice added features. Is it that important to worry about runner lengths unless you are trying to count ETs out on the track. 
I mean realy how many of us have burned up a engine due to the intake not performing. Just seams to me if this was such a concern all intakes would have already been made equal. 

Last edited by Cab4word67 (4/24/2023 3:37 PM)

First I would find out how tall your intake manifold is (don’t believe what Edelbrock tells you). Put a straight edge on the carb pad and measure down to the China rails in the front and back. Add the two numbers together and divide by 2 to get the average pad height. You can do this in the car but you have to take the carb off and the distributor out.
Make sure you have the air cleaner of your choice and any spacers and gaskets in place, then use Play Doh on top of the air cleaner to measure the distance to the hood. Do this in at least four places at 12, 3, 6, and 9 o’clock. My problem is that on my 69 Mach the hood scoop bolts/nuts get in the way (non shaker, stock fake hood scoop).
Now you’re ready to compare to the Edelbrock carb pad height specs. I found my Ford manifold was only 3.000” tall and there are nine Edelbrock manifolds available for my 351W. The shortest Edelbrock starts at 4.07” and the tallest is 7.08”. On three different occasions they told me different manifolds were the same height as the stock Ford, but theirs were ALL considerably taller. You can only trust the numbers for their pad height, not what they say about the Ford manifold.
You can see that if you subtract the Ford manifold height from the Edelbrock number, they will be taller from 1.07 to 4.08”. Now compare the distance from the air cleaner to the hood (2.016” in my case) to how much taller the Edelbrock manifold is. In my case I found that there is only one manifold that would actually fit under the hood with my air cleaner and spacer, and that was the shortest, which was the 2181 Performer.
FYI, carbs are typically 3.25” tall and the Sniper TBI is just a little taller at 3.28”.
 

Cab4word67 wrote:

With all of this mumbo jumbo we used to just bolt a carb on and go, thats what TBI did with some nice added features. Is it that important to worry about runner lengths unless you are trying to count ETs out on the track. 
I mean really how many of us have burned up an engine due to the intake not performing. Just seams to me if this was such a concern all intakes would have already been made equal. 

You are totally missing the point its not about runner length or track times.  TBI has issues on a dual plane intake.  Yes it self tunes but it is tuning to a bank of cylinders and a dual plane intake WILL create unbalanced cylinders unless you use a spacer or mill down the center wall.  Yes yours is running "well"  but that does not mean it is running correctly or balanced.  I asked this question because there is a big difference in low end torque between a dual plane intake and a single plane intake, I would prefer the dual plane BUT there are known issues running TBI on a dual plane that I am trying to avoid.
 

From what I’ve read, and seen on “Engine Masters”, is that the only way to avoid cylinder lean/rich differences is with the port injection system that the individual injectors are controlled by an O2 sensor on each cylinder exhaust pipe. 

I've "read"...where the "issues" of single plane intakes are slightly sluggish performance 'down low' RPM  butt....best performance in the upper RPM range  6/7-ish grand.
Welp..(tnx RPM)...
I've also "read" for some unknown reason...SBF do NOT have the low RPM issues Shivel-layz and others have. They actually perform equal to or BETTER than dual plane intakes...even in lower RPM's.
The reason no one hardly uses them on street engines is because "the proz" (who test everything on Shivel-layz only!) claim it.
My guy Joe Sherman (RIP) disputed their statements on a 289 build he made that kicked out 400 HP...streetable HP.
(His interpretation of streetable!) He used a single plane WITH a 2" open spacer ...(and said hood clearance is up to the builder)
Soooooo Daze...I would go with the single plane/360 intake and not look back....for a coupla reasons
You got BIG cubes
You got wayyy better flowing heads
You got FI that's "suppose" to make better power down low.
You got T-5 tranny to improve low RPM grunt
You got plenty of "nogg'in" to figger-it-out if it does run less than great.
End of discussion(s'all I got)
6sally6

You can use a dual plane intake. My Edelbrock Performer RPM was no problem.

But! … Cut a 1” relief into the divider beneath the carb. This allows the EFI charge to mix properly before heading down the runners to the cylinders. If you try to substitute a 1” open spacer, the engine is not as smooth. Can’t explain why, but I did it both ways and know what works.

Paul

Cab4word67 wrote:

You guys are all right on most everything, but I dont understand why the EFI would be any diferent than a carb with a dual plane intake? its fuel and air. What am I missing

 

The problem in this case and similar is the map sensor and how this type of setup functions.  Day was already on to the solution.

https://www.delphiautoparts.com/en-us/resource-center/article/making-sense-of-your-sensors-map-sensor

Higher pressure atomizes the fuel better.  Atomized fuel burns more completely, so in theory you are using less fuel and creating fewer hydrocarbon emissions.   Port EFI is just an electronic version of mechanical injection, which existed for decades before the electronics got good enough to allow EFI to be realistic and reliable.  I don't have an exact date, but my guess is that in the '20s or '30s some genius like Cord, Chrysler, etc. figured out that you got more power. better economy, and better running by being ale to tailor the mixture in each cylinder.  The only way to do that at the time was one barrel per cylinder.  It was race stuff then, but was on production cars at least by the '40s.  Mechanical injection evolved out of that idea, and EFI evolved from mechanical injection. 

I actually got to watch the Engine Masters show last night on sequential vs. batch fire.  Pretty interesting that batch fire initially made better power, but even once balanced they were making only a tiny amount more power with sequential, and this on a 700+ HP engine.  Then they went into individual cylinder trims and found they could correct the A/F ratio in lean or rich cylinders, but it made no difference in power.  Consensus was that those trims served to keep a nitrous or forced induction engine alive, rather than create more power by more precise fueling.  The only thing they didn't test, and I think its lack gave an incomplete picture, was efficiency, which would have been easy as all dynos can measure and record BSFC (Brake Specific Fuel Consumption), which measure efficiency.  They also didn't look at emissions. 

Obviously there is a benefit to sequential EFI or the OEMs wouldn't spend the money to run it.  If its not in power it must be in fuel economy and/or emissions. 

As far as idle goes there's a couple things going on with EFI vs. a carb.  First, yes, higher pressure and better atomized fuel would clean up the idle over fuel falling out of suspension, going liquid, and dripping off the runner walls into the cylinders.  Second, moving the point of fuel introduction to the port shortens the runner down which the fuel must travel also serving to keep it in suspension.  Third, and this is a big one, EFI engines tend to have much wider LSA cams.  This is necessary to create a more stable vacuum signal for the MAP, and allow the electronics to make sense of things.  That engine on Engine Masters had a cam with a 115 degree LSA, whereas a carb engine making the same power would likely be on a 110 or 108 LSA.  Less overalp all things being equal is going to clean up the idle by reducing reversion.  Lastly, an EFI engine has the ability to directly change idle speed at any time via the IAC.  Its ability to self learn and monitor the idle is going to naturally be better than whatever setting to which a carb is tuned, because that remains static in the face of temperature, air density, etc. 
 

Cab4word67 wrote:

You guys are all right on most everything, but I dont understand why the EFI would be any diferent than a carb with a dual plane intake? its fuel and air. What am I missing

If you look back at my post #4 in this thread, I linked an article that described the difference being associated with the 2 pair of sequentially firing cylinders.  With the dual plane manifold and a carburetor, the second cylinder has a reduced vacuum signal that affects the charge provided by the carb whereas the EFI does not rely on a vacuum signal to provide the charge.  The article says it better. (oh, and this is at low engine speed... at higher RPMs the issue goes away)

Last edited by Rufus68 (4/29/2023 2:42 PM)