Vintage Ford Intake Manifold CFM flow numbers

[JohnSlack]

The perceived advantage of the IR intake manifold is that you can adjust the mixture in each port with all of the variables that your carburetor allows you to adjust.

In a plenum style intake either 1x4 or 2x4 you can have extreme mixture variation between cylinders.

Particularly on a 1x4 intake manifold you have really long ports that go to (in the case of the SBF) cylinders #1,4,5 & 8. Where in order to get the same amount of volume to those ports velocity must be higher than in the shorter/tighter cylinders #2,3,6 & 7. Depending on how the intake manifold is configured cylinder variation costs you horsepower because you have to run the lean cylinders richer than the ideal mixture. A well designed 2x4 intake manifold that is balanced in port length and volume reduces some of this.

An IR intake allows you to adjust the mixture per cylinder (per se nothing is perfect) however you loose the beneficial effects of a balanced plenum. It is all compromise all of it.

Electronic engine management is better, however I prefer the dark arts.

There you go Scott, now you get better insight on exactly what I do not understand.


John

[shelbydoug]

The perceived advantage of the IR intake manifold is that you can adjust the mixture in each port with all of the variables that your carburetor allows you to adjust.

In a plenum style intake either 1x4 or 2x4 you can have extreme mixture variation between cylinders.

Particularly on a 1x4 intake manifold you have really long ports that go to (in the case of the SBF) cylinders #1,4,5 & 8. Where in order to get the same amount of volume to those ports velocity must be higher than in the shorter/tighter cylinders #2,3,6 & 7. Depending on how the intake manifold is configured cylinder variation costs you horsepower because you have to run the lean cylinders richer than the ideal mixture. A well designed 2x4 intake manifold that is balanced in port length and volume reduces some of this.

An IR intake allows you to adjust the mixture per cylinder (per se nothing is perfect) however you loose the beneficial effects of a balanced plenum. It is all compromise all of it.

Electronic engine management is better, however I prefer the dark arts.

There you go Scott, now you get better insight on exactly what I do not understand.


John

Yes but it is also that you have a better runner configuration. Somewhere, someone determined that the optimum distance from intake valve to throttle plate opening was 4.5".

The Weber intakes on the 289's are right there as is the 351 Cleveland set up.


The question in my mind is, does the dual Dominator set up permit that intake runner length also?


In theory, you cannot have a more equal flow then equal length runners, with equal flow throttle "devices". The only variation you can have would be with the pumping capacity of each cylinder, and the intent is those to be equal as well.

With cylinder head ports CNC'd, the flow is equal as well.

Then it comes down to flow under the intake valve. Ford in fact understood that big valves got shrouded by the cylinder walls and realized that you could reduce the shrouding with a big valve by angling it away from the cylinder wall, enter the "Boss Cleveland" heads.

Now interesting to me, the current aftermarket Windsor heads largely are not taking advantage of reangling particularly the intake valve except for one. I think that is the Brodix, but I may be wrong on that.

The interesting thing that I am seeing though is that these aftermarket heads like the AFR's are making equal or better power then the canted valve Cleveland heads are. So maybe they already realized that angling the intake valve for unshrouding the intake flow was/is over rated?

You can't make the engine more equally distributed then that.


As far as not giving manufacturers certain credits, I noticed that the Edelbrock Performer RPM intakes have the carb plenums more centered then something like the C60A and more closely resemble the Unicorn's centering? I'm thinking I should give them credit for that thinking but also realize that they make the AFB/Carter/Edelbrock configuration carbs that are smaller then the Holleys are and make that possible without an offset distributor.

So I give them a credit for centering but take it away because they want you to buy their carbs for the manifold. I try to be fair but sometimes I admit that I do play favorites.

The Ford intakes we are discussing originated out of the Ford Racing Program so granted they likely just skipped over some steps and went directly to what they thought would be the top.

Why can't we use the Unicorn without an offset distributor by turning the regular Holleys sideways like the Dominator intake does? Ah, questions, questions? Randy baited you because you like to fish. I don't like fish. "Give me the facts". "Hit me with your best shot".

Henny Youngman used to talk about going to the doctor. "Doc, when I do this (he raises his hand) it hurts. "What should I do about it?" The doc replies, "don't do that". When I say that "I want a second opinion on something", the Doctor says, "ok, and you're ugly too". We all have unique lives.

[pbf777]

The perceived advantage of the IR intake manifold is that you can adjust the mixture in each port with all of the variables that your carburetor allows you to adjust.

    True, but........... as stated previously, generally the practice for engines seeking peak performance is to strive for equality in actions among each the cylinders, therefore although individual tuning is a possible benefit, it is one that should not be necessary to capitalize upon in any major fashion.

    Rather, probably the initial intent of an I.R. manifold was more attuned to the ideology of the possible benefits of the resonance effect, or as popularly coined here "ram-tuning"; this providing for greater efficiency in cylinder filling utilizing the kinetic energy of the gas column created and retained.   

Yes but it is also that you have a better runner configuration. Somewhere, someone determined that the optimum distance from intake valve to throttle plate opening was 4.5".

The Weber intakes on the 289's are right there as is the 351 Cleveland set up.

The question in my mind is, does the dual Dominator set up permit that intake runner length also?

    The "optimum" inlet tract length for the purpose of ram-tuning is dependent on a calculation involving engine R.P.M. as a major factor, as this is mostly a prospect based on a timing element, but of course also including a multitude of other considerations of lesser influential factors.  So, I believe with research, one would probably conclude that 4.5" is 'not' the "optimum" distance for any and all applications. 

    As for the examples mentioned, I think this similarity is due more to packaging/fitment concerns, hence the repetitious similarities, this rather than anything ideal for gas-flow function.

    And in my opinion, it is this fitment issue that is probably where the T.A. Dual Dominator induction was compromised to the point of crippling it, as in order to get the whole "shebang" under that flat hood, the carburetors ended up just to close to the inlet valve; this creating just to much "signal" fluctuation for the carburetors to cope with.       

    Oh, and generally the distance of consideration is more often that from the engines' inlet valve, but not to the "throttle plate" or butterfly, but rather to the top of the bell opening to atmosphere. 

     Scott.

[JohnSlack]

The perceived advantage of the IR intake manifold is that you can adjust the mixture in each port with all of the variables that your carburetor allows you to adjust.

    True, but........... as stated previously, generally the practice for engines seeking peak performance is to strive for equality in actions among each the cylinders, therefore although individual tuning is a possible benefit, it is one that should not be necessary to capitalize upon in any major fashion.

    Rather, probably the initial intent of an I.R. manifold was more attuned to the ideology of the possible benefits of the resonance effect, or as popularly coined here "ram-tuning"; this providing for greater efficiency in cylinder filling utilizing the kinetic energy of the gas column created and retained.   

Yes but it is also that you have a better runner configuration. Somewhere, someone determined that the optimum distance from intake valve to throttle plate opening was 4.5".

The Weber intakes on the 289's are right there as is the 351 Cleveland set up.

The question in my mind is, does the dual Dominator set up permit that intake runner length also?

    The "optimum" inlet tract length for the purpose of ram-tuning is dependent on a calculation involving engine R.P.M. as a major factor, as this is mostly a prospect based on a timing element, but of course also including a multitude of other considerations of lesser influential factors.  So, I believe with research, one would probably conclude that 4.5" is 'not' the "optimum" distance for any and all applications. 

    As for the examples mentioned, I think this similarity is due more to packaging/fitment concerns, hence the repetitious similarities, this rather than anything ideal for gas-flow function.

    And in my opinion, it is this fitment issue that is probably where the T.A. Dual Dominator induction was compromised to the point of crippling it, as in order to get the whole "shebang" under that flat hood, the carburetors ended up just to close to the inlet valve; this creating just to much "signal" fluctuation for the carburetors to cope with.       

    Oh, and generally the distance of consideration is more often that from the engines' inlet valve, but not to the "throttle plate" or butterfly, but rather to the top of the bell opening to atmosphere. 

    Scott.

Tuned length, which is compromised/changed in the 2x4 intakes by the "tube" that extends from the bottom of the carburetor throttle plate to the lower intake plenum.


John

[pbf777]

Tuned length, which is compromised/changed in the 2x4 intakes by the "tube" that extends from the bottom of the carburetor throttle plate to the lower intake plenum.

     To each his own in preferred definition; but,............in the endeavor for any significant "ram-effect" from the I.R. effort, this reversionary effect takes place when the higher than atmospheric air pressure column created when the inlet valve closes and the inertia retained in the in-motion gas column compresses and then rebounds, retained within the "tube" but in motion now headed upward (vertical stack) and exits into the atmosphere above the 'stacks', trailing with it out of the tube length is an excess volume that then creates a lesser than atmospheric pressure within the tube, that now "mother nature" (free atmosphere) races down the tube to normalize.

     The trick, and the reason there are different "ideal" lengths for this "tube", is in an effort to effectively time this reversion pressure pulse coming back down the stack on a following intake valve opening event.

     But none of this involves the actual throttle(s), as their function is exactly that, to "throttle" (disrupt) the air column which precludes this ram-tuning effect.  And the presents of an intake manifold consisting of a plenum promoting communication between port runners also disrupts and negates much of this value.   

     Scott. 

[shelbydoug]

Well what I know about reversion in IR intake manifolds is that it is essentially caused by a late closing of the intake valve.

That being intentional in the design of the camshaft to push or pressurize atomized fuel in the center plenum of a 180´ intake manifold to aid loading of fuel into the next opening cylinder.

When you eliminate the common plenum, there is no where for that power pulse to go but up and out of the carb.
You can fix that to a degree with a camshaft timing change but not completely eliminate it by closing the intake valve sooner.

For me that was easier to understand by stating it as "valve overlap" although not completely accurate since the solution on the "Weber cam" was to reduce valve overlap to about 28°.

My experience with that is that solution reduced the fuel plume being pushed out of the carbs but the engine lost significant power of about 80 hp.

In the case of my Pantera, I discovered by accident that changing the velocity stacks from the stock length of about 2-1/2" to 5", kept the vapor plume within the stack and eliminated the spreading of the fuel issue.
That enabled me to keep the non-Weber cam so as John said, everything is a compromise and we are just trying to find the least power losses and lessen the tangential problems.

There is no room in a 69 B2 T/A car under the hood to find that kind of resolution. It just happens to work in the Pantera because of the size of the engine compartment.

I think that is somewhat to your thinking on the Dominators being just too close to the intake valves on the B2? Although lengthening that intake runner if possible to reduce reversion is sending me back on the long road to Grandma's house again AND exactly how long would that runner need to be to eliminate the reversion? 3 feet?

I stand by the 4.5". That isn't my number and may have come from Holman-Moody on the subject of the design of the Detomaso script Weber intake manifold? You may want to suggest that it is just co-incidental in the case of the 289 and 427 Weber intakes but I have come to not really believe in co-incidence.  Co-incidence to me is just the result of undiscovered intentions of someone or something else.

[pbf777]

Well what I know about reversion in IR intake manifolds is that it is essentially caused by a late closing of the intake valve.

You can fix that to a degree with a camshaft timing change but not completely eliminate it by closing the intake valve sooner.

For me that was easier to understand by stating it as "valve overlap" although not completely accurate since the solution on the "Weber cam" was to reduce valve overlap to about 28°.

    This could all be perhaps accurate when analyzing the situation at engine speeds below optimal, but also opening the valve too early compounds this issue too. But if this subject proves to be the capital concern it's more a statement that one chose the wrong camshaft. 

That being intentional in the design of the camshaft to push or pressurize atomized fuel in the center plenum of a 180´ intake manifold to aid loading of fuel into the next opening cylinder.

    I don't think it was ever intentional (in engines relevant here) by design for one cylinder to be pushing fuel into another, that would incur greater complexity into the design elements than engineers would have wanted to approach, but it does take place to a degree regardless, but I would have to say only unintentionally. Rather the purpose for the 180° plenum design with it's alternating acquisition, in this case L-R-L-R-L-R.......,  was to separate cylinder draw from each volume for period to equalize and allow a sum of normalization in the atmospheres' pressure and turbulence this so as to encourage more equivalent charging of both air and fuel to each cylinder, also providing better signaling for carburetor function, etc..  Consider the plenum somewhat like the muffler in the exhaust system, it dampens the atmospheric pulsations and hence noise. 

I discovered by accident that changing the velocity stacks from the stock length of about 2-1/2" to 5", kept the vapor plume within the stack and eliminated the spreading of the fuel issue.

    This brings us back to the possible effects length has on the timing and placement of the air column in motion.

I stand by the 4.5". You may want to suggest that it is just co-incidental................

     We need to differentiate what your stating as being positioned at 4.5" (from the inlet valve). 
     
     Again, the throttles are not part of the plan in I.R. reversionary tactics, they just mess it all up;  the only thing that counts is the end of the tube!  The throttles can be (nearly) anywhere, the major effect in placement, beyond fitment concerns, and some directional air motion effects they create which need to be considered, is that generally the closer to cylinder head inlet valve they are, the quicker the engines' response to their movement will be; but still no effect on the other subject.   

     Scott. 

[shelbydoug]

https://www.youtube.com/watch?v=7nEGFfDH9e4

These are the iron GT40 heads and a Cobra single 4 high rise.

The C60A intake numbers have to be out there somewhere.

The head flow numbers are right around where Randy said they would be.

[shelbydoug]

To those of you who are secretly following this thread, here is a link to an article about single four v. dual four inductions.

It explains in part how I arrived at this point, but not entirely.

It probably may also answer your question of how the Trans Am cars are involved in this discussion and comparisons...maybe? I find the description of the intake manifolds especially helpful to the novices amongst us.

It does not address at all the involvement of the Boss 302 or how it evolved into the Boss 302 in the discussion, but what do you want from a magazine article anyway, "everything, everywhere, all at once"?


I should also comment that I think it is significant that I am seeing different results in what my engine likes with the C60A T/A intake and carb sizes.
It may simply be that my combination varies enough from the mule engine that was tested in camshaft profile, engine displacement and induction ability of the cylinder heads I am using?

Where the article discusses a little difficulty in getting the jetting right on the 465 carbs which even after rejeting are running lean, is an indication that they are too small for that test engine, to me. The engine isn't getting the quantity of fuel it needs, and that is caused by the design of the T/A intake manifolds race capability.

There is a bit of an educated guess here since I am not artificially limiting the RPM range of the test due to concerns over breaking the engine? A 6,000 rpm limit is not really illustrating the true advantage of the T/A intake manifold, just showing that it has very decent "street type" manors.

As opposed to the much smaller capacity carburetors tested, I am showing good results with 2-600 1850 cfm vacuum secondary carbs and 2-715cfm  list 3300/3301BC/BD  carbs. Why? I don't know, just speculate on why they work well also.
It may be a much simpler answer in that the C60A may just run well on any combination? A bigger engine usually likes a bigger carburetor with some degree of predictability.


Anyway, check this out. To me it is a good read. I predict that it likely will create as many new questions as it does answering old ones? That really is the nature of the development process anyway. It is necessary to chase down ideas about how you thought things worked, then find you were completely wrong. But at least that saves time in ending theories created on false beliefs...to an extent.

https://www.motortrend.com/how-to/mdmp-1207-dual-quads-twin-win-or-double-trouble-part-2/


I'd LOVE to see a 351w build with the Price 2x4 intake. I haven't come across that anywhere but for me I'm fine with all this induction stuffed into a little 8.2 Ford Windsor'd head engine. Kind of like the "Hulk" busting out of too small of a shirt. Even if they are shiny aluminum AFR heads too. The open mouthed unblinking staring at car shows alone is worth it especially with the cold air induction built into the '68 Shelby hood.

It must be similar to what "Super Models" experience when they walk by in their micro-bikinis and guys start tripping and spilling their beers and coffee even in front of their own wives and girlfriends? Do you think that is cruel? 


Who says that this Forum is 98% just about Concourse cars? Not me.

[Clara]

Good luck.

[pbf777]

Where the article discusses a little difficulty in getting the jetting right on the 465 carbs which even after rejeting are running lean, is an indication that they are too small............. The engine isn't getting the quantity of fuel it needs...........

    This suject of the "carburetor being to small and not delivering enough fuel", is often the thought, but stop and think about it; with the exception of the accelerator pump system the carburetor does not pump fuel into the engine, it's pushed in by the differential between the lower pressure venturi area vs. atmospheric pressure; and the smaller, more restrictive (C.F.M.) the carburetor might be, the lower the pressure (greater vacuum) value is presented and the stronger the siphoning effect is going to be.   

    Aka, larger carburetors don't just have larger fuel jets because they potentially flow more air and yes would potentially need to flow more fuel commensurately, but also because often this differential pressure (signal) is less prominent and therefore the fuel delivery is less effective, so larger (less restrictive) fueling jetting offsets some of this also.    

    As far as for the 465's not providing the better performance, well in my experience, that has generally been the result, this to the point that I just don't prefer, nor recommend them. 

    Scott.

[JohnSlack]

Where the article discusses a little difficulty in getting the jetting right on the 465 carbs which even after rejeting are running lean, is an indication that they are too small............. The engine isn't getting the quantity of fuel it needs...........

    This suject of the "carburetor being to small and not delivering enough fuel", is often the thought, but stop and think about it; with the exception of the accelerator pump system the carburetor does not pump fuel into the engine, it's pushed in by the differential between the lower pressure venturi area vs. atmospheric pressure; and the smaller, more restrictive (C.F.M.) the carburetor might be, the lower the pressure (greater vacuum) value is presented and the stronger the siphoning effect is going to be.   

    Aka, larger carburetors don't just have larger fuel jets because they potentially flow more air and yes would potentially need to flow more fuel commensurately, but also because often this differential pressure (signal) is less prominent and therefore the fuel delivery is less effective, so larger (less restrictive) fueling jetting offsets some of this also.    

    As far as for the 465's not providing the better performance, well in my experience, that has generally been the result, this to the point that I just don't prefer, nor recommend them. 

    Scott.

As far as for the 465's not providing the better performance, well in my experience, that has generally been the result, this to the point that I just don't prefer, nor recommend them. 

Scott,
I think that if someone wanted to run 465 Holley carburetors that was knowledgeable about circuits they could get the carburetor to function just fine.


John

[pbf777]

I think that if someone wanted to run 465 Holley carburetors that was knowledgeable about circuits they could get the carburetor to function just fine.

    No disagreement here, but if not a required for some reason, why start with a carburetor that one already knows is going to require greater effort than perhaps something else? 

    Scott.

[shelbydoug]

I view some things, like these induction combinations, like playing with Legos.

We just take various shapes and assemble them in all possible combinations until we arrive at one with the best results. Sometimes the more outrageous, the better the solution?

Some would call that the empirical method? That is being very diplomatic. 


The way some of you speak of this suggests that there is no carburetor that is too big or none too small? That just makes no logical sense to me whatsoever but this has just turned into a food fight with little or no point anyway?


I would go with copying the actual results as best I can to those who were the most successful in racing. Not to the extent so much as when "Grumpy Jenkins" would pull out his dipstick and hold it up to the sunlight to look for something, and seemingly almost everyone else would also, but looking for the failures that seemed so obvious that I didn't want to go down that road as well?

So then why not have a disagreement? It does seem entertaining to a point? Maybe it is just Quantum Physics and it is the creation of an equal but opposite electron instantaneously created at the opposite end of the Universe, then extinguishes itself instantaneously? Makes as much sense to me?


Some of these combinations are just going to work better then others and one of the keys is this C60A intake. It does seem to have this zenomorph capability and considering the unpredictability of the various carburation combinations, that's as good of an explanation as anything at this point?


I can't help but think though that there is an actual correlation between engine size and carburetor size? Someone could probably even write a simple equation there with a pretty much direct proportion predicting outcome? An outrageously abstract thought isn't it? I probably need shock therapy or some serious medications...but that's another subject all together for another day.

[JohnSlack]

Where the article discusses a little difficulty in getting the jetting right on the 465 carbs which even after rejeting are running lean, is an indication that they are too small............. The engine isn't getting the quantity of fuel it needs...........

    This suject of the "carburetor being to small and not delivering enough fuel", is often the thought, but stop and think about it; with the exception of the accelerator pump system the carburetor does not pump fuel into the engine, it's pushed in by the differential between the lower pressure venturi area vs. atmospheric pressure; and the smaller, more restrictive (C.F.M.) the carburetor might be, the lower the pressure (greater vacuum) value is presented and the stronger the siphoning effect is going to be. 

    Aka, larger carburetors don't just have larger fuel jets because they potentially flow more air and yes would potentially need to flow more fuel commensurately, but also because often this differential pressure (signal) is less prominent and therefore the fuel delivery is less effective, so larger (less restrictive) fueling jetting offsets some of this also.   

    As far as for the 465's not providing the better performance, well in my experience, that has generally been the result, this to the point that I just don't prefer, nor recommend them. 

    Scott.

As far as for the 465's not providing the better performance, well in my experience, that has generally been the result, this to the point that I just don't prefer, nor recommend them. 

Scott,
I think that if someone wanted to run 465 Holley carburetors that was knowledgeable about circuits they could get the carburetor to function just fine.


John

I view some things, like these induction combinations, like playing with Legos.

We just take various shapes and assemble them in all possible combinations until we arrive at one with the best results. Sometimes the more outrageous, the better the solution?

Some would call that the empirical method? That is being very diplomatic. 


The way some of you speak of this suggests that there is no carburetor that is too big or none too small? That just makes no logical sense to me whatsoever but this has just turned into a food fight with little or no point anyway?


I would go with copying the actual results as best I can to those who were the most successful in racing. Not to the extent so much as when "Grumpy Jenkins" would pull out his dipstick and hold it up to the sunlight to look for something, and seemingly almost everyone else would also, but looking for the failures that seemed so obvious that I didn't want to go down that road as well?

So then why not have a disagreement? It does seem entertaining to a point? Maybe it is just Quantum Physics and it is the creation of an equal but opposite electron instantaneously created at the opposite end of the Universe, then extinguishes itself instantaneously? Makes as much sense to me?


Some of these combinations are just going to work better then others and one of the keys is this C60A intake. It does seem to have this zenomorph capability and considering the unpredictability of the various carburation combinations, that's as good of an explanation as anything at this point?


I can't help but think though that there is an actual correlation between engine size and carburetor size? Someone could probably even write a simple equation there with a pretty much direct proportion predicting outcome? An outrageously abstract thought isn't it? I probably need shock therapy or some serious medications...but that's another subject all together for another day.

Well I for one don't have anything else to add to this particular discussion.