Intake manifold design debate

[Aussie XAXB]

This one is open for discussion....


For as far back as I can remember (and I am 40) the quest for the perfect intake manifold design, besides correct volume for the application, was to achieve the straightest flow from the carburetor to the intake port of the cylinder head. This benefit is illustrated by full race intakes that are single plane and have a really tall rise and straight runners going to the intake port. Of course this is an extreme and not practical for the street, so the battle between manufacturers was to design an dual plane that had as straight as possible runners with a single carburetor.


Enter the Ford 5.0 generation of fuel injection. Now the air must flow through an intake manifold (upper) in almost a complete "S" shape and then through almost another complete "C" shape (lower manifold). This design carries through in some form to almost every Ford engine currently.

My question is how did the goal change?? How did the physics of airlfow change?? Why did the worst possible design suddenly become the best?

I can allow for the fact that fuel injection is a factor. With a carb the fuel needs to stay suspended in the intake charge as it travels to the intake port of the head. With fuel injection the fuel is squirted right at the intake valve and fuel suspension is no longer an issue.

That being said, why is all the friction that the air encounters traveling through the maze of modern intake design considered a plus now? As air flows through the 2 piece intake design it encounters friction from the long length of the runners, interrupted flow as it makes several very hard changes in direction, and all this adds up to less air reaching the intake port in the same amount of time that an old carbed intake would do it in. I just do not understand the engineering that went into this.

Discuss...........


steve

[quake101]

Hrmmm!!! I don't know.....I see what your talking about. I have seen some "box" upper intakes tho that really don't have any runners. I wonder what's up with that also.

[Aussie XAXB]

If they at least did away with that upper box that would be one less restriction for the air.


Steve

[W.O.T. Stang]

I do know that the long runner setup of the EFI 5.0 is what gives it such massive low-end torque.  The longer the runners, the more low-end you will end up having, but your top-end will start to suffer, although the E7's really hold that back quite a bit anyways.

Same deal with upper box intakes.  They are just that, a box.  Air enters, sits in a big box and gets sucked into the intake.  It kind of goes along with the same principle as exhaust.  When there is a big space, there is no "force" behind the intake charge.  When you force it thru a small spot, you get more torque from it.  But when it's just sucking in the as as it's need while it's sitting relatively still, its only going by what the engine is pulling it in by, no force behind it. (that's why you get more power under high rpms, and much much less low-end.. no driving force at low rpm's for more air.)  If you know anything about the '05's stang variable runner intake, or even the 96-98 cobra IMRC's, you should understand the whole theory behind this.

As far as why they changed it, i don't pretend to completely understand advanced engine theory, but if you think about it, not very many other engines use an upper intake design like the 5.0.  My only guess is that it had something to do with the beginning of a performance with modern day electronic fuel injection (which SEFI was rather new in those days) and the design was planned out and tried and worked well.  I don't think Ford has much experience with EFI being used as a performance application until then but they sure seemed to have got something right.

[Aussie XAXB]

I would love to see a comparison of an engine on a dyno with the stock set-up with the fancy dancy 2 piece manifold that the air has to do to go through to the cylinder head and then a dyno pull with a throttle body (carburetor looking kind) and intake manifold and fuel injectors in the intake manifold at each intake port. That way the fuel delivery would be the same in both instances but the airflow would be significantly different.

On the comparison I saw between a carbed intake set-up and the typical 5.0 fuel injection, on the SAME engine, there was no difference in horsepower or torque. Therefore the fandangled Ford intake set-up nets no power gain over conventional methods, in my opinioin.


Steve

[W.O.T. Stang]

I would love to see a comparison of an engine on a dyno with the stock set-up with the fancy dancy 2 piece manifold that the air has to do to go through to the cylinder head and then a dyno pull with a throttle body (carburetor looking kind) and intake manifold and fuel injectors in the intake manifold at each intake port. That way the fuel delivery would be the same in both instances but the airflow would be significantly different.

On the comparison I saw between a carbed intake set-up and the typical 5.0 fuel injection, on the SAME engine, there was no difference in horsepower or torque. Therefore the fandangled Ford intake set-up nets no power gain over conventional methods, in my opinioin.


Steve

You make an excellent point there.  I'm just going by "how it's supposed to work".  I have no hard proof, but like you, I'd love to see some examples of identical motors with different induction types.  I'm sure a magazine has done this test in the past, but i've never seen it.

A friend of mine has an '83GT with a complete '88 engine, but with the old '83 carb and intake still on it.  He claims to notice no major difference between EFI and carb performance wise.  You cant really use his timeslips to calculate that though, because he lives in Las Vegas where it's 120º at times, and at 2500 ft elevations.

I guess that brings us right back to the questions as to why they changed that type of setup.  My best guess would be for drivability.  But after re-reading your original post.. not only is the 5.0 efi intake long and twisted, it's also HOT.  As it's pulling in cool/warm air, it must increase air intake charge temperature quite a bit by the time it goes thru the throttle body until it hits the intake valve, or even the lower intake.  I guess that's the reason for air temp readings at both the MAF and the ACT.

Btw, the "throttle body carburetor" you refer to is called TBI.

[Aussie XAXB]

 

not only is the 5.0 efi intake long and twisted, it's also HOT.  As it's pulling in cool/warm air, it must increase air intake charge temperature quite a bit by the time it goes thru the throttle body until it hits the intake valve, or even the lower intake.  I guess that's the reason for air temp readings at both the MAF and the ACT

Excellent observation!!!


I didn't say TBI because I stipulated the injectors would be in the manifold instead of over the throttle body.

Would you believe I heard one old guy refer to that as "A carburetor with fuel injection assist". LMAO!!   


On some Ford  vehicles you will find tubes that branch off of the air duct to the intake that seem to lead nowhere and also just come to an end. There are also "Bladders" that will be branched off of the duct and then reconnect. Both of these are called "Air resevoirs" to supply extra air when the gas pedal is mashed because the duct otherwise cannot supply enough CFM to the throttle body. On top of that the ducts nowadays are rigid plastic and do not collapse, so the amount of extra air gained from these resevoirs is minimal.......kinda like sucking air out of a glass bottle. 


ANOTHER thing that bothers me is where the air duct is routed to on a lot of cars. In many cases to a "sheltered" location somewhere behind the headlight or next to the radiator but behind the radiator support!! And then they wonder why the engine can't breathe???


Man...........I gotta get off my soap box..............


Steve

[Freakingstang]

Ford had to do something for the Emissions and fuel economy and etc.  Times were changing, GM already had a fuel injection system successfully in place.

I believe they experimented quite a bit with this setup.  While the long runners of the EFI intake make a ton of torque, the regular manifold with injector bosses at the valve yeilds very little low end grunt.  They needed something that was very userfriendly and was easy to drive, provided great seat in the pants feel, and got 20+ mpg.  This was their result.  After years of use, it must have been an ok setup, because the same setup was used in the mustangs from 86-95 in the mustangs.  Was used in the F150's from 85(canada made emissions) to 96.

Now companies have made much shorter runner intakes.  These don't carry the air velocity needed for the low end torque, but still have the capability to flow large cfm at high RPM, where as the stock long runner intake quites making power at the 5000 +or- RPM.  Some of the "box" style intakes make power up to the 7000 rpm range.

Now, for curiousities sake, I would like to see a comparison of a 4bbl single plane intake with a throttle body and a short runner box upper.  These results would probably be very similar in all aspects (high and low RPM power).

[Aussie XAXB]

I agree that velocity is needed for low end torque, but I don't agree that the longer runners are needed to do this. The reason for this is that a big difference can be had just in porting cylinder heads. Modifications to just the runners in the heads can take an engine from being a low end grunt to a higher RPM horsepower brute, and this is accomplished in such a short distance of travel for the air flow. I don't believe that velocity is so much a product of runner length than I do the shape of the runner itself. That the runner is not too volumnous (that is a word, right? ) to begin with and then tapers in order to accelerate the speed of the air (moving the same amount of air through a smaller passage in the same amount of time, thereby accelerating the air).

One of the most notorious race engines of the early 60's was the Dodge Ramcharger with a Crossram intake. It was a 413 cubic inch engine with 2 4bbl carbs that were mounted on the looooonngest intake manifolds ever on a production car. One carb sat on a separate manifold over the valve cover on one side of the engine and its runners fed the opposite head. On the other side of the engine another 4 bbl carb sat above that valve cover but fed the head on the opposite side of the block. Very long intake manifold runners but the engine made upper RPM horsepower.

Cool, I found a pic!

 


This being too radical of a design it was modified down to different variations of what you see in this pic.




Since then it has been copied and applied to GM cars and possibly even some Fords.


Steve

[Freakingstang]

I remember that setup in the early 80's GM cars.  My buddy had an 84 Z28 that had a cross ram motor in it, it was a dawg compared to my stock 86!!!???

[Aussie XAXB]

Wasn't that "crossfire injection"??

[Freakingstang]

I think that was another setup.  I thought it had tow holley 600 carbs on it.  I know he bragged about it being rare.  I could be wrong, it has been a number of years.


Steve

[Aussie XAXB]

Yeah, the aftermarket made them for GM's and it is very possible he had put it on his car. Wasn't factory though. Cool you kicked his ass anyways!   


Steve

[tmoss]

Take a look at an old tunnel ram for racing - long straight runners and a plenum on the top with carb attached to the top of the plenum.  Made more torque than a single plane.  HP sells cars, torque wins races (know who said that?).  Ford took that same principal and had to bend things to make it fit under the hood - wella, the modern EFI intake.

[Aussie XAXB]

Tunnel rams provide volume and upper RPM flow for horsepower. Just ask Michelle.  That's one reason they went back to FI. The tunnelram is just not it for the street.

Tunnel ram - All the intake runners are straight and meet at a common plenum (the tunnel).  This type of manifold gives excellent fuel distribution and flow for top-end power.  The large plenum area  reduces signal strength and throttle response.

- http://www.eng.ed.ac.uk

A maximum torque intake would probably be a webber design that has a separate runner and carb or injector for each head port. No volume is shared with any other cylinder. The air flows at maximum velocity to each cylinder.

Steve

[tmoss]

A maximum torque intake would probably be a design that has a separate runner and injector for each head port. No volume is shared with any other cylinder. The air flows at maximum velocity to each cylinder.

Steve

Hilborn "porcupine" setup - used decasdes ago by gassers.

[Aussie XAXB]

Wow, never even heard of that one. Hiborne I know, porcupine I don't, but the name alone is image inspiring enough. exactly.


Steve

[Ray III]

Okay, FRICTION is never a good thing in any part of the engine. Friction is a waste of energy. You will usually hear of people polishing intakes when they have been ported, to make them more "slippery."

What is really being done with the long runners is imparting as much momentum as possible to the intake charge without too much of that airflow restriction.

First off, look at engine cylinder filling as filling a shallow tube with rough concrete. If you just use a shovel and dump it in nice and easy, it will kind of tumble in and then sit in there loosely, and less concrete will fit. But climb up a ladder with a shovelful of concrete and drop it over the tube, and it will accelerate and BAM its momentum rams it into the tube, and it can be filled to good density. Such is the theory of intake runners, only the acceleration is caused not by gravity but by forcing the air to flow through a small diameter which requires it to accelerate to high velocity to keep up with the demand for volume. The runners are a constant size because you want the entire length of the runner to store momentum, not just the mass of the air near the intake port. When the engine is in its optimal torque range, the intake valves are opening and a long column of air is accelerated by piston vaccuum, then has enough time to ram into the cylinder under force of its own momentum. At high RPM the length of time time the intake valve is open does not leave much room for fancy tricks, so the optimization is made for generally 1,000 to 3,000 RPM.

On top of that, there is a pressure spike created when each intake valve slams shut while that column of air is charging into it. This spike bounces back up the runner at the speed of sound if I remember correctly, and keeps going until it hits something it reflects off of. Now you see the reason for that large box from which each runner on a 302 originates after a U-turn from the inlet. Pressure spikes bounce off the wall of the box, re-enter the runner, bounce off the valve again, and back and forth a few times. The length of the intake runners are tuned such that at a certain RPM range, the pressure wave will eventually arrive back at the intake valve at the precise moment it opens.

Of course, this kind of trickery was not too popular with carbs since you didn't want the fuel to fall out of suspension in there somewhere. Carb intakes do have the advantage of less restriction in the intake, and easily meeting the airflow demands at high RPM. You can get the same effect with EFI simply by installing fuel injectors in a carb intake...

As a side note, this whole concept applies to the exhaust side as well. That is why long tube headers can generate free horsepower, because it too has pressure spikes caused by hot gas exploding from the cylinder when the exhaust valve cracks, and leaving a vaccuum behind it that draws out the rest of the spent gases. The longer the tube, the less interference from other cylinders. Those Top Fuel engines have a separate exhaust pipe for each cylinder, actually.

[tmoss]

The refelcted wave you speak of could be seen in carb setups and injector stacks when the harmonic rpm was just right by blowing the gasoline back out of the carb near the venturis or top of the tube for a brief period.  It looked like a fog right at the venturis of the carb and would come and go as the right harmonics of the reflected wave changed with rpm.  I observed it during dyno pulls.

[TireSmoke]

Actually....I have heard that slight imperfections in the intakes runners promote better flow and fuel mixture....

[Aussie XAXB]

Ray and tmoss, very interesting posts.


Tiresmoke, you are right. You don't want to polish the entire runners for a carbed engine. Some turbulence needs to be present to keep the gasoline molecules suspended in the air charge, or else it will just wet the sides of the runners.

[BadAndy]

Just like the skin of a shark is grainy like sand so it can glide through water better....

[MurPHy]

One of the most notorious race engines of the early 60's was the Dodge Ramcharger with a Crossram intake. It was a 413 cubic inch engine with 2 4bbl carbs that were mounted on the looooonngest intake manifolds ever on a production car. One carb sat on a separate manifold over the valve cover on one side of the engine and its runners fed the opposite head. On the other side of the engine another 4 bbl carb sat above that valve cover but fed the head on the opposite side of the block. Very long intake manifold runners but the engine made upper RPM horsepower.

Cool, I found a pic!

 

Steve

413 Max Wedge. The engineers discovered that by modifying the length of the intake runners, they could produce more torque, and this setup gave the engines a slight supercharging effect between 1000-3000 RPM. Very effective in it's day.

[Ray III]

I agree that velocity is needed for low end torque, but I don't agree that the longer runners are needed to do this. The reason for this is that a big difference can be had just in porting cylinder heads. Modifications to just the runners in the heads can take an engine from being a low end grunt to a higher RPM horsepower brute, and this is accomplished in such a short distance of travel for the air flow. I don't believe that velocity is so much a product of runner length than I do the shape of the runner itself.

Didn't notice your statement before, but anyways, yeah the velocity is affected by cross section not length. The smaller the diameter of an air passage, the higher the velocity must be to deliver the same volume in the same time. Like filling a funnel with sugar, it moves very slowly at the brim but falls rapidly throught the bottom. That is why carbs have venturis (small section of restricted diameter); to get high air velocity past the jets and atomize fuel better.

Long runners are for storing momentum. You can have air at high velocity, but unless you have a long column of it, it won't have any mass and won't pack itself well into cylinders.

[speedfreak87]

the only thing i can say is.. Ford is the best at what they do... that is all..

[tmoss]

the only thing i can say is.. Ford is the best at what they do... that is all..

Then they should have had Edelbrock designing their lower intakes (Cobra too).   They didn't hit a bullseye on that part.

[Aussie XAXB]

All the manufacturers are going to experiment (thank god for that) and make some good things and some not so good things. I also am glad for the radical things that they have attempted and gave a shot at, whether they worked well or not.

My reason for starting this topic is because I don't understand how the designs became so radically different in opposition to the goal based on the laws of physics and use of them that was previously trying to be achieved. Designs went from short runners in as straight a line as possible (more speed, less friction loss due to turns and runner length) to simply being any attempt at "routing" air to the intake port without regard to what the air is subjected to from a physics standpoint (increased friction due to distance the air travels through manifold, number of radical turns it must make, etc.).

I work with far too many engineers that merely want the prestige and desk that goes with the job, as well as the income, yet have no interest in the field they are in (mechanical engineers that design and build things around the house, electrical engineers that wire their homes with elaborate lighting or sound systems, weld engineers that......you guessed it......actually weld). I have to imagine these are the same type of people that are designing the new intake manifolds. Ever wonder who came up with the great idea of the opening to the intake air duct facing the back of the headlight? Hey, it fit that way. And then what about the "air reservoirs" because at WOT there isn't enough air flow through the duct to supply the engine. Just follow that "mysterious" tube that branches off the intake duct and seems to go nowhere and dead ends. That is what that is for. Heaven forbid an automotive engineer actually be a car nut. He might get his Dockers dirty that way. 

Ray, while reading your post I got to thinking about the carb venturi and using it as an example. I'm glad that you did. People in irrigation also understand increasing speed in order to get the same volume through a smaller hole. Most people misunderstand that as increasing pressure, but you can't make more pressure with opening diameter, only make the air or fluid pass through it faster or slower. Pressure remains the same, minus friction loss.


Ok, yeah, this is another pet peeve of mine. I'm done...for now.


Steve #7

[turbo54]

I'm seeing a bit of misinformation here...

The idea of the carb venturi is indeed to speed up the air...  In so doing, the pressure goes DOWN!!!  The pressure goes down, and there is a pressure gradient between the fuel in the nozzle and the airstream. 

THIS IS THE BASIC PREMISE ON WHICH CARBS WORK, AND ITS CALLED BERNOULLI'S PRINCIPLE!

That said, decreasing cross section of a port will increase velocity...  AND DECREASE PRESSURE!

Think about that for a while!

Aussie:  Couldn't agree more with you about engineers doing what they love...or just doing what makes some money.

[TireSmoke]

I was watching a tv show about engines, and the 302 HO came up.  It was talking about how Ford used the long runner design to "tune" the intake.  Apparently there are pressure pulses that are created based on valve timing.  These pulses travel up and down the intake runners as valves are opened and closed almost harmonically.  Apparently with long runners, if you get the length right, you can optimize the intake pulses for the 3rd of 4th order pulse which creates a mini supercharger effect.  As the pulse of pressure travels back down the intake runner towards the valve, the valve opens and higher pressure air enters the cylinder.  While the effects are most likely small, they seemed to work out well for engines with long runners such as the Ford HO 302, and the SHO 3.8L motor with that wild intake design.  The same can be said for exhaust, and exhaust scavenging.  A motor with headers can use scavenging to pull air out of the cylinder better which results in more power.  Same idea, turned around into the intake.

roll that around....I think its pretty interesting, and I would love to understand the physics behind it!

[Aussie XAXB]

I'm seeing a bit of misinformation here...

The idea of the carb venturi is indeed to speed up the air...  In so doing, the pressure goes DOWN!!!  The pressure goes down, and there is a pressure gradient between the fuel in the nozzle and the airstream. 

THIS IS THE BASIC PREMISE ON WHICH CARBS WORK, AND ITS CALLED BERNOULLI'S PRINCIPLE!

That said, decreasing cross section of a port will increase velocity...  AND DECREASE PRESSURE!

Think about that for a while!

Aussie:  Couldn't agree more with you about engineers doing what they love...or just doing what makes some money.

Ok, I read up on Bernoulli's Principle and thanks for correcting me. There is a drop in pressure, referred to as differential pressure, on the exit side of the venturi that I am still trying to decide whether or not it is attributed to friction? If that drop is due to friction then my statement would stand. If a force other than friction is the cause then my statement would be lacking. I guess I wil read more into it. Thanks for bringing this to my attention.  (We really need a nerd smiley )

I've heard about that tuning principle before. As much of a maze that the air has to pass through I cannot believe that tuning the length of the runner to take advantage of this mild supercharging effect actually overcomes all that friction enough to give an added benefit (additional weight of such a large manifold, violent path of travel of the air, etc.)

I have also seen many instances of engineers redesigning things merely in order to justify their job. It gives the company the illusion that it was a good thing that particular engineer was there to make an improvement. Sometimes that "breakthrough design" gets turned around back to the original after the flaws of the new one bite the company back.


Case in point: You've seen many Ford engines with a plastic type of valve cover. Notice how now they are going back to the aluminum ones. They "discovered" that the aluminum ones shield the engine noise much better (NVH) , no kidding, and that the plastic covers (a petroleum based product) breaks down and softens over time, while exsisting in an oil saturated environment. Well, no kidding. I knew that stuff. I thought it was obvious.

Steve #7