Pablo

iTrader: (1)

there was some talk on the other thread about how the rear plugs are CLEARLY richer than the front ones. Try doing some plug cuts from WOT runs. The reason your plugs at the rear cyls look rich is because the angle of the throttle plates on your tbi setup. This is old news this is the reason we space the injector pod such that the fuel cone hits just above the edges of the throttle plates. At idle the air rushing past the edges of the plates is primarily responsible for atomizing it. Otherwise the fuel hits the plate and rolls off the rear of the plate and drips to the manifold floor (on the rear side) this isnt because of g forces.. slap a new set of plugs in and just let your car idle for awhile and youll see the same thing. Its even worse with a big cam and low manifold vacuum... which is compounded furthermore by an overactive IAC which is typically the case without serious tuning.

The effect of g forces on our cars and even really fast cars on the distribution of fuel has to be so minute as to be nearly immesureable especially what with so many other MUCH stronger forces at work and the fact that the manifold is at less than atmospheric and there is so little mass to the fuel hell its lighter than water!... ever do that cloud in a bottle trick for your jr high science class when you were studying bernoullis principle?.. try it again and shake the bottle in any direction you want and see how much you can get the cloud inside to "move". Hell, fill a jar up with some hot gaseous fuel and put it in a centerfuge and get back to me im willing to bet its not gonna do a whole hell of alot of changing right away and thats giving that its at atmospheric pressure and its not moving along at all

tbi distribution problems are caused by mainly two things and that is the throttle blades at low throttle angles (theres an SAE paper on this if you care to read it) and the fluid dynamics of cyls pulling air from non identical flow paths from the same plenum

Slade1

Pablo, you and I and a small few TBI owners actually understand the TBI setup...

The greatest force acting on the fuel is the manifold vacuum though. Just as in a carb that dictates fuel atomization more than anything.

You don't have to be a rocket scientist to understand that.
What happens when any liquid is depressurized AND heated??? It vaporizes a whole lot quicker.

Just how much acceleration force do you need to make it a factor?

Hmmm here comes the rocket science just to show you how silly it is to say acceleration and gravity is a factor. Acceleration let alone gravity can'y be a fuel flow factor...

It takes 43 MJ/kg of typical 87 octane fuel to vaporize. It takes more energy to vaporize higher octane fuel, but since higher octane fuel does vaporize quite easily we'll use the lower case just for kicks since acceleration forces can't even touch that. Since fuel IS being vaporized we know there's a lot more energy available to vaporize the fuel.

Now to compare let's see just how much acceleration is needed to match, let alone beat that 43MJ/kg over the entire 1/4 mile. I'm gonna do some metric engineering conversions so follow if you can. 1/4 mile = 402 m, just 400 for simplicity's sake...

43000 J per kg
1 J = 1 N * m
1 N = 1 kg * (m / s^2)
(43000 m^2 / s^2) / 400 m
= 107.5 m/s^2

That's 0 to 240 mph in 1 sec for the whole 1/4 mile...

Where's this miracle car that can do the 1/4 mile in 1 sec with a trap speed of 240 mph??? If you're car can do this, then acceleration is a factor...

Gravity is only 9.81 m /s^2 just for comparison...

Gravity and acceleration forces ARE not a factor...

What holley was taking about was the fact that hey someple daily drive their cars and some people's injector / fuel flow gets deflected by the throttle plates at part throttle (although it shouldn't be the spray should hit the walls of the tb above the throttle plates.) They angled the manifold plane because of this occurence.

Kevin Johnson

Slade1 writes in part:
“Just how much acceleration force do you need to make it a factor?

”Hmmm here comes the rocket science just to show you how silly it is to say acceleration and gravity is a factor. Acceleration let alone gravity can'y be a fuel flow factor...

”It takes 43 MJ/kg of typical 87 octane fuel to vaporize. It takes more energy to vaporize higher octane fuel, but since higher octane fuel does vaporize quite easily we'll use the lower case just for kicks since acceleration forces can't even touch that. Since fuel IS being vaporized we know there's a lot more energy available to vaporize the fuel.

”Now to compare let's see just how much acceleration is needed to match, let alone beat that 43MJ/kg over the entire 1/4 mile. I'm gonna do some metric engineering conversions so follow if you can. 1/4 mile = 402 m, just 400 for simplicity's sake...”


Kevin:
There is a flaw in your reasoning here. You have not demonstrated that the ‘energy’ in your calculations is diametrically (say) opposed to the effects of gravity and/or some other linear acceleration so your subsequent calculations are moot.

One of the first things I learned about shooting as a kid is that if you drop a bullet at the same instant you fire a level gun, both bullets will hit the ground at the same time. Gravity does have an effect despite the fact that the cartridge powder imparts a much greater force. Now, this is the case with an expanding gas that is essentially imparting its energy linearly (down the barrel). You, again, have not shown that same linear quality with the forces involved, but even if you did, gravity and acceleration would still be a factor.


Slade1:
”…Gravity and acceleration forces ARE not a factor...

”What holley was taking about was the fact that hey someple daily drive their cars and some people's injector / fuel flow gets deflected by the throttle plates at part throttle (although it shouldn't be the spray should hit the walls of the tb above the throttle plates.) They angled the manifold plane because of this occurence.”

Kevin:
I am guessing that “holley” refers to my quote from Mike Urich and Bill Fisher who wrote a book *about* Holley carburetors and manifolds. They were pretty clear that gravity was a consideration in keeping the plane of the manifold level.

But, just in case, here is another opinion (Aside: Pablo, it’s even from the SAE):

Engineering Index 1970-1989

Author(s):
Gardiner, D. P.
Bardon, M. F.

Title:
MIXTURE MALDISTRIBUTION DUE TO MANIFOLD FILMS IN A METHANOL FUELLED S. I. ENGINE.

FOUND IN:
SAE Technical Paper Series 1986. SAE, Warrendale, PA, USA. 13p 860234

Conference:
International Congress and Exposition - Society of Automotive Engineers. Detroit, MI, Engl

Conference sponsor(s):
SAE, Warrendale, PA, USA

Publication year:
1986

Abstract:
Geometric maldistribution is recognized as a major impediment to obtaining maximum efficiency from carbureted or single point injected methanol fuelled engines. In this program engine tests have been conducted with the inlet manifold inclined to provide a gravitational influence on the flow of fuel in order to study maldistribution effects due to manifold fuel films. It was found that substantial distribution errors were caused by this slight gravitational influence, which was only a fraction of that which could occur periodically in a maneuvering passenger car.

1st author affiliation:
(Royal Military Coll of Canada, Can)

Document type:
DTCA (Conference Article)

Major descriptors:
AUTOMOBILE ENGINES--Manifolds

Minor descriptors:
METHANOL--Combustion
FUEL ECONOMY

Subject terms:
GEOMETRIC MALDISTRIBUTION
METHANOL FUELLED MULTICYLINDER ENGINES
INLET MANIFOLD RUNNER
FUEL VAPORIZATION
TEMPERATURE DATA

Subject codes:
661 804 521

Coden:
STPSDN

Conference code:
07834

Language:
English

Slade1

You're reasoning on the bullets has a flaw as well...

you're comparing a y dimensional force with an x dimensional force.

When you fire a bullet perpendicular to the ground the energy for the most part is passed along the x dimension. We can go frther on recoil and barrel deflection energies, but there is very little y force applied. So yes both bullets will still hit the ground at the same time as gravity is acting on them in the y direction equally, the bullet's x directional force will be lessened by frictional force with air, but none of the force was directed in the y dimension.

All forces have an effect, but we have to see which forces are the determining factors for what we are looking at. We are comparing though which would have more of an effect.

I could probably do a research paper on this and have it published as well...

Objective: To determine if fuel vaporization and fuel distribution is affected more by acceleration forces or heat and pressure decrease.

Factors that cause fuel vaporization:

-kinetic energy transfer (heat)
-pressure decrease

Factors that are related to air/fuel distribution:

Acceleration forces:
-Gravity
-Acceleration (flow opposed to direction of acceleration)

-Pressure decrease

Let me ask you this. What would a drop of fuel in the intake manifold be more inclined to do?

Will it drop to the bottom of the manifold, roll to the back due to the acceleration then when it reaches the back of the manifold then vaporize?

Will it instantly vaporize when it touches a source of energy enough to force a state change to a gas?
Or will it form into a gas because the drop in manifold pressure is large enough that the kinetic energy of the molecules of fuel is enough to force a state change to a gas?

Are they opposed... that's a perspective really...

Can you please find the part of the paper you are referring to which lists the forces during this gravitational test? Was that test done at idle? Was it done at wot? What was the drop in pressure? Engine temperatures? Throttle body temperatures?

You have to state what scenario this gravitational test was done at. I don't have access to scientific papers, but when you read them you have to be aware of what were the factors tested at. If they were just trying to determine does gravity have an effect yes or no, then the answer is yes sure it has an effect.

Now is that effect larger than the other factors in the engine... which affects fuel vaporization and flow the most...

The fuel due largely in part to heat transfer and manifold pressure drop will vaporize at the entrance of the manifold. Once there we're dealing with two parts. Fuel vapor and air.

Will those gases flow with the drop in pressure or will they flow in the opposed direction of acceleration?

As rpm increases, vacuum increases... vacuum is a measurable force and is directly opposed to mass of the air/fuel * acceleration.

Kevin Johnson

Slade1 wrote in addition to a great many other things:

"You're reasoning on the bullets has a flaw as well...

you're comparing a y dimensional force with an x dimensional force."

Kevin:
You forgot the curvature of the Earth. But I remember wondering about that as a kid.

And, no, I didn't neglect the move from two dimensions to one (or vice-versa). Read more carefully: "diametrically *(say)*"

There are scientific papers on your proposed topic: They came up in my search. However, I don't think you can afford my hourly rates to do your homework for you.

Ciao

Slade1

Those scientific papers will back up the fact that once in vapor form, the air fuel flow will be more directed by vacuum than acceleration forces. So yes I'm saying they are opposed,

front cylinder vacuum force vs acceleration force
front cylinder flow vs rear cylinder flow

Do you agree that the fuel will vaporize when it hits the hot throttle body?

Do you agree that when subjected to a vacuum the fuel will vaporize?

Unfortunately for me today, I'm not planning on visiting the university library to research a physics paper today. I on the other hand would contribute my knowledge and research for the sake of helping people understand that at low acceleration (thirdgen cars to top fuel dragsters on track) it doesn't really make a difference. This is the whole point we're trying to say.

The fact remains. A TBI will not direct all its fuel flow to the back at WOT. At WOT, air/fuel distribution among the 8 cylinders is within 5% of each other in a properly setup TBI.

hectorsn

Well I never went to a university but you keep saying vacuum and referring it at WOT. Now, am I nuts or aren't you not supposed to have vacuum at WOT? And since no vacuum, no vacuum force like you refer to. AFAIK, when you mash the pedal and you get the blades vertical, the fuel is going to hit the floor of the manifold and will not be in an atomized state yet which I think would cause some of it to go backwards in the manifold under acceleration, no matter how slow the car, since there is no vacuum to act on it. I didn't go to school for this, but I do work on cars for a living and one of the things I do is a lot of throttle body blade and PFI manifold cleanings. Since the manifold is dry it has a tendency to coke up with EGR and PCV fumes which require periodic cleanings. What we use is a pressurized can filled with a cleaning agent and aim it at the TB blade(s) and let it suck it in. We blip the throttle occasionally to get more into the manifold and I've noticed that the fluid that was getting sucked by the blades gets pushed forward by the rapid opening and the exposure of the plenum to atmosphere. Now, that may not prove anything but it tells me that fluids aren't acted upon much when there is no vacuum. That this isn't a major problem for TBI and carb cars driven on the street, I totally agree. So I would think you're both kinda right. But like I said, I didn't go to school for this.

Guest

"Hmmm here comes the rocket science just to show you how silly it is to say acceleration and gravity is a factor. Acceleration let alone gravity can'y be a fuel flow factor..."

If you really think that gravity (and atmospheric air pressure for that matter) have zero effect on a running engine (and this pertains more to the whole mixture, not just fuel), take a look at most race cars and you'll find tall manifolds and stacks on top of carburetors. Theres a reason for this. I'm not going to bother explaining or arguing about it, you'll just have to figure it out on your own and accept the fact that people who constantly race cars for a living know it makes a difference. It doesnt apply much to 15 second cars, but it does to cars that are alot faster that are looking for a slight edge and better consistency. The only silly person saying it "can'y" be a factor is you. I think a more appropriate statement would be that it IS a factor, but for your 14 and 15 second cars it doesn't matter.

"You're reasoning on the bullets has a flaw as well..."

Ummm, no. Gravitational force always exists. You fire a bullet at 2200 ft/sec (I wont even bother to explain how much faster that is than air moving through an engine) and the path the bullet travels is affected by gravity. Graph it out on a piece of paper if you have to, one with gravity one without. Fuel, even vaporized, has mass. Mass is affected by gravity. Hence, fuel is affected by gravity, no matter what other forces are applied unless the force is opposite of the direction of the gravitational force, and even in that case you have to subtract the gravitational force from the other force. Diametrically opposed. Sound familiar? Didn't Kevin say that?

Slade, THINK for a minute next time. Your argument is that some things dont exist, when in fact they do. What the problem is, is significance. I think Pablo understands that pretty well. You attack the significant problems, and forget about insignificant ones like gravity. It does, however, have an effect. On a slow car, who cares? On a fast car looking for another measly .01 in speed, it does matter.

soulbounder

Slade, the thing I don't understand in your explanation is your use of 43 MJ/kg. I am an engineering major, and to me the prefix 'M' means Mega and stands for 10^6. So in your calculations it would be 43 000 000 J/kg. 43 000 J/kg would be 43 KJ/kg.

dimented24x7

iTrader: (2)

i dont understand what the enthalpy of vaporization of fuel has to do with acceleration either. Bit vague... They also seem to be a bit unrelated. The thing that drives the fuel vaporization is heat tranfer.

92RS shearn

Man, I could probly do a research paper for my ME senior design on this thread alone

Anyway I am going to have to agree with madmax on this one. I thhink that gravity does have an effect on the fuel. But for our cars it is so negligable you could forget it.

Now after reading the thread, I agree the the throttle blades at partial throttle would cause uneven fuel distribution. Now to correct this I would design it so that one blade would turn clockwise on its axis and the other blade would turn counter clockwise. Through the use of some light gearing, in between the blades. Now thats not a perfect fix, but it would even things out a bit.

Maybe I should do that as my senior design.

dimented24x7

iTrader: (2)

i solved it just by raising up the injector pod with a few washers. Totally free and all the plugs are nice and even. The spray cone hits right above the throttle blades, now. Of coarse i have an engine that makes more vacuum than a hoover so that porbably helps, too.

dimented24x7

iTrader: (2)

Nother thing to consider is that most tbi's are being run on dual plane intakes so they cant counter act eachother because each bore feeds each side of the engine. I remembered something on the spray cone coming up a while back so when i put my tbi on my new engine i added in the washers too to move the spray cone off the tb blades.

AJ_92RS

You are right that the stock TBI is a dual plane, however it does not feed "each side of the engine". If you look at the runners on a dual plane you'll see there are an uppper and lower plenum. The upper/right side feeds cylinders 2-3-5-8. The lower feeds 1-4-6-7.

The idea is to equalize runner length and the flow to each cylinder. The other idea is to lengthen the runners to produce more low/midrange torque. Kind of like TPI.

Due to the divider between the plenums, I doubt alternating the direction the throttle blades open will have much effect. If any gain would be seen, it would be from only 2 cylinders. If you used a single plane it would be more of an advantage.

Hopefully you meant parellel to the ground? 'Cause I ain't not rocket scientist, but I can gaurantee that if you fire a gun perpendicular to the ground and drop another bullet at the same time, from the same height, that the bullet comin' outta the gun will win. If you feel I'm wrong, stick yer hands under them bullets. You'll understand after that.

I'll even bet the farm that you grab that other hand before the bullet that was dropped, even hits the ground. Hell, you might even have dialed 9-1-1 before then.

AJ

dimented24x7

iTrader: (2)

good point aj, never bothered to look which runners go to which cyls.

snflupigus

cant believe so many people think there isnt liquid fuel within the manifold. if you think there is NOT fuel still in liquid form on the plenum floor or runner walls then you would be right saying that vacuum has more of an effect on fuel dist than gravity or acceleration.

however, there is liquid fuel within the manifold. even though its hot, and even though a vacuum exists. sorry, but there is liquid fuel in there. which fuel do you think is going to make your cylinders run rich? atomized or liquid? hmmm TOUGH ONE.

quick question. if you mounted a small block chevy engine backwards in a car and ran the driveshaft forward, etc.. which cylinders would be rich? hmm, again, TOUGH ONE. but gravity and acceleration have no effect? LOL

so, seems nearly everbody here is a little bit correct.

the blades do direct liquid fuel and vaporized fuel into the plenum.

vacuum from the individual cylinders also effects the movement of the vaporized fuel and air.

gravity and acceleration effect the remaining fuel that fails to atomize.

heat and vacuum help fuel to become vaporized.

liquid fuel is more dense than vaporized. gravity and acceleration pulling the liquid fuel to the rear cylinders is what makes them run rich.

even with all that said, i still will revert to what madmax stated. there are many effects, most of them none of you need worry about for getting more power from the engine in your 15 second car.

many people were able, and still are, to make power with carbs for before anybody cared think much about all these factors and/or tried and fix these slight effects on fuel distribution.

why do people need to make this stuff so technical. working with 500hp and want 10 more? ok, think about this, working with a mere 230-350. forget about it guys!


the really sad thing about all you guys talking about this, is the guys who are just now deciding they have read my article on how to install an open element air cleaner enough times to finally feel confident enough to put one on. no offense to any of you guys who just did the open el, but its a newbie thing, completely normal to start there... congrats on your first mod. are worrying their asses off thinking, o ***, i need to fix this horrible problem of fuel dist before i can make any real power. so please, newbies and low techies please do not worry about fuel dist problems, leave that to the over technical ME's LOL!!! engineers. gotta love em :lala:

Kevin Johnson

"the really sad thing about all you guys talking about this, is the guys who are just now deciding they have read my article on how to install an open element air cleaner enough times to finally feel confident enough to put one on. no offense to any of you guys who just did the open el, but its a newbie thing, completely normal to start there... congrats on your first mod. are worrying their asses off thinking, o ***, i need to fix this horrible problem of fuel dist before i can make any real power."

Hmmm...

This is about car #60 or 61 for me. First Chevy, though. Having fun with it. Most of the sidedraft carbureted cars I've had used open elements. Not ram air though.

91Bird305

Tbi sucks....figure that out.

Good thread going guys, keep it up and I can write a paper on it. :lala:

rsc350

:lala: see what you started Pablo? :lala:

Kevin Johnson

I know that some of the thread readers are seriously interested in intake system design theory. I just scanned through my copy of the following text again and while it doesn't appear to mention gravity per se, it does have a good deal of general considerations for manifold (and exhaust) design.

Philip H. Smith & John C. Morrison, _Scientific Design of Exhaust & Intake Systems, Third Edition_, Cambridge: Robert Bentley, Inc., 1971.

Bibliofind lists paperback copies of this text at about $18 new. Good investment for the serious student.

Rather than quote the text extensively, I think there is a lot to be said for knowledge that is actively rather than passively acquired. Make the effort to go to the primary source: It's worth it. Smokey Yunick's texts would be another excellent source of info on the sbc.

Kevin

snflupigus

usually acedemic sources are not used after that many years for good reason, especially scientific theory. i dont know for sure about this one in particular, but i will look into it.

might be a good idea for people to find more recent scholarly journals etc...

Kevin Johnson

Most of the serious guys I have talked to knew who Sir Harry Ricardo was and what he did and he has been dead now for almost 30 years.

A firm he founded still exists.

It's good to have a foundation in the basics/history of the field.

Kevin Johnson

particularly since the design of the sbc dates back almost 50 years.

kdrolt

I suppose I should see what C.F. Taylor says in Vols I & II. I don't think I'll be too surprised.

Kevin Johnson

Dang, Ken!

Making me max out my library card here (I perpetually live on the edge of financial ruin should I ever forget to renew them all ), but they have both volumes in the stacks.

Kevin Johnson

This section seems most relevant to the question of whether liquid fuel is present in the manifold during acceleration to be acted upon by gravity or other forces, such as in drag or road racing. If anyone reading is a student at MIT, many of the citations in this text should be readily available and interesting reading. If a student at another institution, you should be able to get copies of them and Taylor’s texts as well through a system like Illiad (Inter Library Loan). Takes a little time usually, however. Taylor’s texts are definitely worth perusing.

Charles Fayette Taylor, _The Internal-Combustion Engine in Theory and Practice, Volume II: Combustion, Fuels, Materials, Design_, Cambridge: MIT Press, 1968, pp. 188-189:

“Mixture Requirements for Acceleration.
The term “acceleration,” with regard to engines, is generally used to refer to an increase in engine speed resulting from opening the throttle. The immediate purpose of opening the throttle, however, is to secure an increase in torque, and whether or not an increase in speed follows depends on the nature of the load. With governed engines, the throttle is opened in response to a demand for increased torque, and little change in speed occurs. On the other hand, engines driving fixed-pitch propellers or driving vehicles on a level road will respond to opening the throttle with a speed increase.

“In carburetor engines using liquid fuel the process of acceleration is complicated by the presence of unevaporated fuel in the inlet manifold. Investigation (5.77*) shows that during normal steady operation with gasoline the inlet manifold contains a large amount of liquid fuel which clings to the manifold walls and runs along them to the cylinders at a speed which is very low compared to that of the rest of the mixture, which consists of air, fuel vapor, and entrained fuel droplets. Under steady running conditions at a given speed, the quantity of liquid contained in the manifold at any given moment becomes greater as the manifold pressure increases. The principal reason that high manifold pressures result in large quantities of liquid is to be found in the fact that fuel flow must increase with increasing air density, and evaporation is slower as total pressure increases.

“When the throttle is opened for acceleration, thus increasing the manifold pressure, fuel must be supplied to increase the liquid content of the manifold. If the carburetor provides a constant fuel-air ratio, the fuel-air ratio reaching the cylinders will be lowered during the time the liquid content of the manifold is being built up to the larger value. With a sudden opening of the throttle, the resulting reduction in the fuel-air ration received by the cylinders may be such as to cause misfiring, backfiring, or even complete stopping of the engine.

“To avoid an abnormally lean mixture in the cylinders as a result of sudden throttle openings, it is usually necessary to increase the supply ratio by injecting into the manifold a quantity of fuel known as the accelerating charge. Injection of this charge must take place simultaneously with the opening of the throttle. The optimum amount of accelerating charge is that which will result in the best-power fuel-air ratio in the cylinders. In general, this amount varies with engine speed and with throttle position at the start of acceleration, as well as with fuel volatility, mixture temperature, and the rate of throttle opening. Thus, carburetors are designed to furnish the amount required under the most difficult conditions, and when this amount is too large, the error will be on the rich side of best-power mixture, where the sacrifice in output is small, as indicated by Fig. 5-1. Since partial or slow opening of the throttle requires less than the full accelerating charge, the amount of charge delivered is usually made roughly proportional to the rate of throttle opening and the angle through which the throttle moves. Mechanisms that are used to provide the accelerating charge will be described in Chapter 6.”


*5.77 Turner et al., “Investigation of the Liquid Layer in a Transparent Manifold,” Report for Course 2.802, 1942, Sloan Automotive Laboratories, MIT.


On page 681, Taylor gives an interesting series of bibliographic references with respect to distribution research (5.70-5.82) dating from the early 1920s through the late 1950s.

92RS shearn

Hmmm, thats good reading. I'll have to find that here, I'm sure we have it. Thanks Kevin.

snflupigus

ive seen a show on tv a while ago where there was a quick glimpse at holley's design process on manifolds. they had plexi windows in the runners on a carb/wetflow manifold. Even to this day they are designing manifolds to better ensure the liquid fuel (that is present in a large enough qty to worry about) does not flow down the runners into the cylinders.

the acceleration that Turner is speaking of is not the acceleration force that i beleive the rest of us are. He is talking about the engine rpm, whereas we are talking about speed of the vehicle.

i would have been researching this today because i dont have a life. but i need my new student id before they will let me into the library's computers.

i will get to the bottom of it, im sure people have written more recently.

kevin are you implying that you are an MIT student? If so, please let me know, i want talk to you bout some other stuff you might know about there.

Kevin Johnson

Smokey Yunick's _Power Secrets_ (S-A Design Books, 1983) has a nice picture of a manifold with a plastic top on page 65. Seems like you could use an adjustable strobe light to help get a better idea of the flow pattern variations as well.


the acceleration that Turner is speaking of is not the acceleration force that i beleive the rest of us are. He is talking about the engine rpm, whereas we are talking about speed of the vehicle.

I have not looked at Turner's cited article. You are correct that Taylor is talking about the engine itself with respect to "acceleration" in this quotation. I think he is being careful to define it just so that no misunderstandings arise. Elsewhere in the volumes (I have since returned them else I would give page references) Taylor mentions that proper manifold design needs to be used so that equal distribution would result during engine operation. I think reading his bibliographic references (Turner, for example) might shed some light on distribution research for moving vehicles. But again, that is exactly the topic of the much more recent SAE paper I cited earlier (Gardiner & Bardon 1986).

i would have been researching this today because i dont have a life. but i need my new student id before they will let me into the library's computers.

i will get to the bottom of it, im sure people have written more recently.

kevin are you implying that you are an MIT student? If so, please let me know, i want talk to you bout some other stuff you might know about there.

No, sadly I am not at MIT but one of the leading figures in one of my majors, theoretical linguistics, is there, Noam Chomsky. Excellent school--met a grad student of his at a conference a couple years back.

Taylor was a professor emeritus at MIT when he updated the volumes I read. Presumably it would be easier to locate the references he used if one was a student there as well. Illiad (Inter Library Loan service) has made that less of an issue (As an aside, many students don't take advantage of that -- usually it is provided free of charge to students).

Keep looking into it!

dimented24x7

iTrader: (2)

I agree with that but i beleive that the fuel being in liquid form (still atomized form the injectors and not yet vaporized) is only a problem at higher engine loads where there is a low amount of vacuum and the fuel just doesnt have time to vaporize because of the high velocities the runners. My experience with my engine at partial throttle is that the fuel flashes over to a vapor almost instantly when it encounters the high vacuum of the manifold. So much so that ive had ice formation on my tbi on a humid day. Neat, huh.

Kevin Johnson

Yes, but Taylor points out that the liquid film is already present in these conditions. Part of the fuel that you observe going into the manifold condenses--or never even evaporates in the first place--to maintain that film at an equilibrium. [This is also pointed out by Turner et al. 1942 and Gardiner & Bardon 1986.]

To actually find out what is happening inside the manifold itself appears to require a plastic covered manifold. Or perhaps radioactive tracers in the fuel -- but that move would require another order of complexity in the measuring instrumentation, I should think.

dimented24x7

iTrader: (2)

interesting. Even though im probably wrong, i find it hard to beleive that the fuel can form a film or condense and form a film on a manifold thats around 200 degrees or so in a partial vacuum.

Kevin Johnson

Seems like my reply got lost in the internet ether...

On page 121 of Yunick's _Power Secrets_ he states that the optimum running temperature of a racing engine should be in the 200-210* F range measured at the point where the coolant is returned to the radiator. That in combination with his investigation of wet-flow patterns leads me to believe that this phenomenon does occur with the sbc in that temperature range (and many people have modified their cars to run substantially cooler).

You are correct that the higher the manifold temperature the less film and pooling, in general. Here is a citation in support of that (but they don't state at what temperature the fuel film and pooling end in the truncated abstract -- maybe they do state that in the article itself):

Engineering Index 1970-1989

Author(s):
Kay, I. W.

Title:
MANIFOLD FUEL FILM EFFECTS IN AN SI ENGINE.

FOUND IN:
SAE Prepr n 780944 for Meet Nov 13-16 1978 25 p

Publication year:
1978

Abstract:
A test program was conducted with a carbureted 2. 3-liter engine in which a map of engine operating conditions over which intake manifold wall films of appreciable magnitude exist was defined on the basis of visual observations. It was found that the largest maldistributions of fuel/air ratio among the four cylinders of the engine occurred during operation at conditions characterized by the presence of extensive fuel puddles on the intake manifold floor. However, it was also found that while the intake manifold fuel films and puddles could essentially be eliminated by heating the manifold floor, the fuel/air ratio distributions among cylinders under such conditions were virtually identical to those measured under conventional operating conditions. On the basis of these data, it was concluded that the steady-state distribution of fuel among the cylinders was not affected by the presence of liquid films or puddles within the intake manifold but rather
that the resulting maldistributions .

1st author affiliation:
(United Technol Corp, East Hartford, Conn)

Major descriptors:
AUTOMOBILE ENGINES

Minor descriptors:
FLOW OF FLUIDS--Pipes
VAPORS--Condensation

Subject terms:
AIR-FUEL RATIO
SPARK-IGNITION ENGINES
CHARGE STRATIFICATION

Subject codes:
661 631 641 802

Coden:
SEPPA8

dimented24x7

iTrader: (2)

To be honest, i dont beleive flilms can form appreaciably in he manifold unless its an air gap maniflold running on a nice cool engine running at WOT. Off the top of my head octane itself boils at around 125 deg. C but the boiling point of fuel can range anywhere from 70 - 150 deg C. When films do form at WOT, when the pressure is close to atmosphiric, They will probably consist of only the heavier parts of gasoline. One thing i would like to know is how these tests where performed. Where they under normal operating conditions or at WOT. Under normal operating conditions with vacuum, films will probably be non-exsistant. At WOT, however, i do concede that films of fuel consisting of the longer chain HC components of gasoline can form.

A bit off topic, but anyone know what components are present in gasoline? Cracking and catalysts have raised the ammount of availible octane in gasoline but i dont know how much other stuff is present. I know theres benzene, hexane, and heptane, among other things present but not in what ratios.

Kevin Johnson

dimented24x7:
“One thing i would like to know is how these tests where performed. Where they under normal operating conditions or at WOT. Under normal operating conditions with vacuum, films will probably be non-exsistant.”


Kevin:
While not every citation states the test conditions, they can be inferred with Kay 1978 to include a range (from the term “map” and the phrasing “operating conditions over which”). Taylor 1968 is fairly specific, i.e., “during normal steady operation,” in which Taylor cites the technique of Turner et al. 1942. See below:

Kay 1978
“A test program was conducted with a carbureted 2. 3-liter engine in which a map of engine operating conditions over which intake manifold wall films of appreciable magnitude exist was defined on the basis of visual observations.”

Taylor 1968
“In carburetor engines using liquid fuel the process of acceleration is complicated by the presence of unevaporated fuel in the inlet manifold. Investigation (5.77: Turner et al. 1942) shows that during normal steady operation with gasoline the inlet manifold contains a large amount of liquid fuel which clings to the manifold walls and runs along them to the cylinders at a speed which is very low compared to that of the rest of the mixture, which consists of air, fuel vapor, and entrained fuel droplets. Under steady running conditions at a given speed, the quantity of liquid contained in the manifold at any given moment becomes greater as the manifold pressure increases. The principal reason that high manifold pressures result in large quantities of liquid is to be found in the fact that fuel flow must increase with increasing air density, and evaporation is slower as total pressure increases. “…Since partial or slow opening of the throttle requires less than the full accelerating charge,…” ”

dimented24x7:
“A bit off topic, but anyone know what components are present in gasoline?”

Kevin:
Normally that is proprietary information. But here is an MSDS for typical gasoline formulations:

http://www.brownoil.com/msdsgasoline.htm

Guest

I see someone else is getting off subject...

Taking formulas and analyzing an engine using static explanations and straight math conversions doesnt work. The articles posted above are based on observations of running engines, and I see people trying to explain away results these people saw and published, and better yet they are trying to do it from their computer chair over a day or two of reading with no testing at all. Scary.

You guys are forgetting some things:
An engine is dynamic, not static.
Airflow path through an engine is not necessarily in the middle of the port. Quite often in fact, its not.
Air pressure isnt consistent in a manifold.

Thats the best way I can try to explain why you are seeing something you think cant/shouldnt/wouldnt happen. There are, I'm sure, many other factors that I didnt mention and dont know about. There are no hard and fast rules, and nothing is 100% infallible. Thats why even today there are improvements, and why there are still analysis' being done.

Kevin Johnson

Per Madmax's comments,

"Hear, hear!"








Just in case:

http://www.straightdope.com/mailbag/mhear.html

The correct term is, "hear, hear!" It is an abbreviation for "hear, all ye good people, hear what this brilliant and eloquent speaker has to say!"

:hail:

dimented24x7

iTrader: (2)

hehehe.... i have an old trash postage stamped sized camara w/ led illumination floating around in my junk trunk. I was thinking what a neat experement it would be to mount it underneath my tbi adapter in my carb intake and see what actually goes on in there. Hmmm... maybe if my work load is light next weekend ill shove it in there and go out and do some WOT runs.

dimented24x7

iTrader: (2)

well... found it... After around 4 years of having tools and junk sitting on top of it it still works. Nice minature camara, it can focus in to objects just a centimeter or two away but the field of view is far too narrow, just 30 degrees. Far too narrow to see any thing but a small portion of the bottom of the intake, which makes it pretty useless for this. Lol, plus i forgot how nice it is so i dont want to sacrifice it yet. So, if anyone has a wide angle minature camara or a fiber optic one...

Kevin Johnson

Sounds like your camera would have gone on "Mr. Toad's Wild Ride" (Aside, sad news: http://www.pansophist.com/fanttoad.htm)


I requested a photocopy of this article to find out more about what manifolds and injector types (multi- or single-point, etc.) were studied. Despite the lack of direct visual observation (seeing is believing, in other words), the model appears sound (The assumption is made that fuel that is injected that is not promptly combusted has deposited in a film on the interior of the manifold):

Engineering Index 1990-1997
Author(s):
Monden, H.
Kataoka, R.

Title:
Practical measuring method of deposited fuel and evaporated fuel in the induction system.

FOUND IN:
Proceedings - Society of Automotive Engineers. Publ by SAE, Warrendale, PA, USA. p 295-302

Conference:
Eighteenth Fisita Congress - The Promise of New Technology in the Automotive Industry Torino, Italy 19900507-
19900511

Conference sponsor(s):
Regione Piemonte
Provincia di Torino
Citta di Torino
Alitalia
Allmag
et al

Publication year:
1990

Abstract:
The fuel film flow on the inner surface of the intake manifold which causes a delay in the supply of fuel to the combustion chamber is described by the deposition rate X and the time constant of evaporation tau in the mathematical model of fuel supply. These parameters X and tau were calculated using the exhaust air-fuel ratio hysteresis. As a result, it became clear that the deposition rate X is a function of the throttle valve opening angle and also depends on the temperature of the coolant. It also became clear that the time constant of evaporation tau is a function of the aspirated air quantity and the engine speed and that it, too, depends on the temperature of the coolant. The engine operating conditions during which the injected fuel was conducted into the cylinder as fuel film flow also became clear. (Author abstract) 5 Refs.

1st author affiliation:
(Fuji Heavy Industries, Fuji, Jpn)

Document type:
DTCA (Conference Article)

Treatment:
TREX (Experimental)
TRTH (Theoretical)

Major descriptors:
AUTOMOBILE ENGINES--Manifolds

Minor descriptors:
INTERNAL COMBUSTION ENGINES--Flow Problems
MATHEMATICAL MODELS
HYSTERESIS

Subject terms:
FUEL FILM FLOW
AIR FUEL RATIO HYSTERESIS
SINGLE POINT INJECTION SYSTEM

Subject codes:
661 631

Coden:
PSOED4

Conference code:
13957

ISSN:
8756-8470

Language:
English

dimented24x7

iTrader: (2)

lol...
i was going to drill and tap some small holes in the carb 2 tbi adapter and mount it up top but the angle of view was just too narrow to see anything. Oh well... probably wouldnve been pretty neat to see an induction system at work in real time.

Silverado5.7L

I'm probably going to get a Carb manifold soon.
I work at KU and we have a CNC machine going into operation soon. Would I be able to get a better distribution by making one myself? Or would the summit one work as good?

I may not CNC it, but I can get it machined up for nothing.

snflupigus

just move it forward about a half inch. i beleive the majority of the ones out there now have done that but i might be wrong. this is the consensus ive heard here on the tbi boards for the last 3 years.

Slade1

All articles presented indicate extensive studies of carbs where engine vacuum plays a major part in fuel draw of the engine. Have there been any recent studies on TBI systems where the fuel delivery is under pressure and not dictated by manifold vacuum?

I imagine there would be a significant difference in air fuel delivery under this situation as proven on track by the significant difference stock LO3 showed compared to the stock LG4.

Under ideal situation, air has to flow through the fine spray of the TBI injectors. TBI setups and EFI in general use significantly less fuel than carb based setups.

Not to make you max out your funds, but think you can find something actually designed to study TBI distribution?

Kevin Johnson

Slade1:
"All articles presented indicate extensive studies of carbs where engine vacuum plays a major part in fuel draw of the engine. Have there been any recent studies on TBI systems where the fuel delivery is under pressure and not dictated by manifold vacuum?"


Kevin:
One cited article, Monden & Kataoka 1990, has under "Subject terms:" the descriptor "SINGLE POINT INJECTION SYSTEM," which appears to indicate that the study was carried out using a TBI system rather than a carburetor.

Another cited article, Gardiner & Bardon 1986, states in the first line of the abstract: "Geometric maldistribution is recognized as a major impediment to obtaining maximum efficiency from carbureted or single point injected methanol fuelled engines." (My emphasis)

Slade1

It doesn't necessarily mean they tested on a TBI...

Injection is a term that was loosly used in carb setups... the first article done in 1990 may have been done on a TBI, not certain though. You can't use a pressurized injection system and say this is the same in carbs simply because a carb and a TBI have a dual plane manifold. I have to stress that these two setups despite initial glaces function very differently.

The other article done in 1986 pre-dates GM's improvement to the TBI arrangement which first appeared in 1988.

The differences in fuel efficiency and power is already a call for concern that the TBI and the carb are vastly different in fuel distribution efficiency. This particular study can't be used on both systems in my opinion. The end results of the performance of both engines, despite identical parts, heads, block, headers, cam show that the key difference in the two distribution methods is the efficiency and ability for the air fuel to mix in the intake. This points to there being a radically different arrangement in how the fuel flows/pools/condesnses/vaporizes between the two methods.

The ECM meters fuel delivery according to the O2 sensor readings, trying to keep the air fuel mixture as clost to the ideal ratio as possible. If the pooling/film issue was as great in a TBI as a carb setup, then the TBI would always run rich.

Kevin Johnson

Slade1:
"It doesn't necessarily mean they tested on a TBI..."

Kevin:
I am in the process of trying to contact the authors of the later papers as well as requesting copies of those papers via our library. If someone else has access to them in the mean-time, perhaps they will post some remarks.

Pablo

iTrader: (1)

move the TBI forward and youve robbed peter to pay paul (the saying goes something like that anyways)

leave it in the middle, reduce iac counts to the absolute minimum, raise the injector pod, and fuel pressure

then go man go

Ken73

Uhm.. just a thought...

but why not run hotter plugs on the richer sides, and colder ones on the leaner sides?

Old trick from some hardcore racers I've talked to..

This may also explain why the CrossFire has the "swirl plates" underneath the TBI's, too.

Kevin Johnson

So far, none of the authors have responded.

I learned from the library that the SAE will not provide article copies free of charge. I called them yesterday and found that a student membership costs $10 and includes an online subscription to their mag. With the membership you also get a 20% discount on reprints which normally run $10 each. I'll probably spring for it.

I did find an article in Automotive Engineering (which should be available to ILL services) which is a rehash of I.W. Kay's 1979 SAE paper "Manifold film effects in an SI Engine." It is in the Feb 1979 issue, Volume 87, Number 2, pp. 35-40, and entitled, "Fuel distribution unaffected by manifold films."

Lest some of you jump to conclusions based on the title, I should append the prefix, 'steady state': "Steady state fuel distribution unaffected by manifold films." Great article.

Some bits from the paper...

Coolant temps (manifold floor temp) in the 2.3 liter engine were run at 50, 70, 90, and 115 degrees C +/- 2 deg C (last temp attained by steam heating the manifold floor). Fuel films were reduced with increasing temp but not eliminated.

87 octane lead-free pump gas was used, as were two others:

(Page 38)
"... Studies with research grade Indolene HO-III fuel, whose volatility characteristics closely match summer-blend [Kevin: circa 1979] pump gasoline, indicated essentially the same results as those of [Lead-free 87 octane pump gasoline]. A strong effect of fuel volatility was found using pure iso-octane as fuel. It is significantly more volatile than either pump gasoline or Indolene, having a normal boiling point of 99 deg C. With 90 deg C coolant temperatures, the only wall films of appreciable magnitude occurred under WOT conditions at 1200 rpm or less."*

*Kevin: but wall films still occurred with iso-octane.