Crossover pipe

[DoomsdayMelody]

I’ve seen all the data that suggests that as far as intake mods go, the crossover pipe is generally the only thing that is worth spending money on. I’ve also seen the photos of the stock crossover pipe with all the weird lumps/fins inside the tube, but part of me has to be wondering if there is any sort of benefit to it? I mean I have to imagine it would’ve been cheaper for Ford to find a normal piece of tubing without all the extra material inside of it, so unless turbulent airflow going into the turbo helps with lower rpm range torque delivery or if it helps with fuel economy somehow I don’t see how or why Ford would go with a, relatively speaking, restricted pipe instead of just something that would maximize airflow.

Wondering if there are any fluid dynamics experts, engineers, or engine builders on here that would be willing to hazard an educated guess.


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[M-Sport fan]

I'd also like to know about this as well.

It could also be they did this for intake noise reduction reasons.

 

[Hypergram]

Just a guess from a person almost completely ignorant on the topic, but maybe restricting airflow helps with the economy of the car? Less air requires less fuel, and since it obviously works for the "relatively low" power set up on the stock tune it helps?

 

[zumakid70cc]

Just a guess from a person almost completely ignorant on the topic, but maybe restricting airflow helps with the economy of the car? Less air requires less fuel, and since it obviously works for the "relatively low" power set up on the stock tune it helps?

I can't 100% agree with you on the tourqe. I just put on the whoosh pipe and at 2.75in the responsiveness of the car is almost as instant as when I put my catless downpipe on. Now maybe it helps the feul econ. I know that with the sound I get makes it really hard to keep the right foot from putting the pettle down. That's gonna eat majority of my econ up.

 

[DoomsdayMelody]

Well based on what my engineering textbook has to say about it, it sounds like turbulent flow has two distinct advantages compared to laminar flow: heat conduction and thermal mixing. It is possible that ford engineers wanted the air going into the turbo to pull as much heat as possible away from the turbo, in my head I see it as a decision to heat soak the intake tract, thereby limiting power and fuel consumption during hard use? Otherwise turbulent flow is noisier and has a lesser efficacy in that laminar flow would enable a greater amount of airflow. I dunno, that’s what my new textbook says.


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[gtx3076]

Does the crossover benefit from additional tuning? Or will gains be found without it? I feel like there's a lot of lag in my Dizzy tunes, but it could be because I'm completely stock otherwise.

The airbox has never been cited as a restriction on the stock turbo, but maybe the crossover pipe is, since it seems to show decent gains in torque.

 

[Dpro]

I think a lot of the reasons for the way the crossover pipe was designed as well as the J pipe hot side was to quite the system down. I know in changing those two pieces on my car you immediately started hearing more turbo noise and even the factory diverter valve letting off like a almost having a aftermarket blowoff valve. Therefor I am guessing that engine builders looked the positve and negatives along with the fact that corporate was concerned about not making the car too noisy after all it was being mass marketed.
Look at the soft rubber in our engine mounts and in our exhuast hangers. In suspension joints. Car makers are really hung up on making sure there is no NVH no external noise that wil bother some people. Toyota went as far as putting in out of phase speakers in their cars to make them quiter in the cabin . Its turned almost fanatical lol.

It is true that air turbulence in a flow tract can have both positive and negative effects depending on design. Though that could be a whole other topic of discussion as it pertains to a lot more areas of the flow track of our engines than just the intake or the hotside pipe.

 

[D-resonant]

The factory crossover has interesting engineered/designed elements despite its tube size. It's polymer so it insulates the intake air from the heat inside the engine bay. It has additional exterior aluminum heat shielding to reflect radiant heat. Overall, it has sweeping compound bends with gradual ID reduction from beginning to end (instead of a sudden reduction that most of the aftermarket have to the stock turbo elbow). The constrictions near the PCV hose connection help draw air (oily mist) through the PCV hose. The tube opening inlet of has a slight bell-mouth taper...

But, there's no substitute for larger inlet tube size when there is a "lengthy" tube run...and the FiST does have a bit of piping before the turbo.

 

[DoomsdayMelody]

I think a lot of the reasons for the way the crossover pipe was designed as well as the J pipe hot side was to quite the system down. I know in changing those two pieces on my car you immediately started hearing more turbo noise and even the factory diverter valve letting off like a almost having a aftermarket blowoff valve. Therefor I am guessing that engine builders looked the positve and negatives along with the fact that corporate was concerned about not making the car too noisy after all it was being mass marketed.
Look at the soft rubber in our engine mounts and in our exhuast hangers. In suspension joints. Car makers are really hung up on making sure there is no NVH no external noise that wil bother some people. Toyota went as far as putting in out of phase speakers in their cars to make them quiter in the cabin . Its turned almost fanatical lol.

It is true that air turbulence in a flow tract can have both positive and negative effects depending on design. Though that could be a whole other topic of discussion as it pertains to a lot more areas of the flow track of our engines than just the intake or the hotside pipe.

The whole noise argument seems like a weird thing to me, but only because Ford included the symposer. Why attempt to quite something down just to artificially amplify it after 4 and a half feet of pipe?


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[DoomsdayMelody]

The factory crossover has interesting engineered/designed elements despite its tube size. It's polymer so it insulates the intake air from the heat inside the engine bay. It has additional exterior aluminum heat shielding to reflect radiant heat. Overall, it has sweeping compound bends with gradual ID reduction from beginning to end (instead of a sudden reduction that most of the aftermarket have to the stock turbo elbow). The constrictions near the PCV hose connection help draw air (oily mist) through the PCV hose. The tube opening inlet of has a slight bell-mouth taper...

But, there's no substitute for larger inlet tube size when there is a "lengthy" tube run...and the FiST does have a bit of piping before the turbo.

I’m not gonna lie, I’m a bit confused about the larger inlet tube size because IIRC, most crossover pipes neck down with a silicone adapter just in front of the turbo, since air can only flow as fast as the most restricted portion of the entire system would allow I’d assume that SHOULD make for a negligible difference in total airflow... especially since they’re relying on the turbo to suck the air in anyways.


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[D-resonant]

I’m not gonna lie, I’m a bit confused about the larger inlet tube size because IIRC, most crossover pipes neck down with a silicone adapter just in front of the turbo, since air can only flow as fast as the most restricted portion of the entire system would allow I’d assume that SHOULD make for a negligible difference in total airflow... especially since they’re relying on the turbo to suck the air in anyways.


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Generally, pre-turbo compressor, a larger ID "long" tube with sudden constriction at end would still be less restrictive than a smaller same length tube. A short silicone reducing adaptor is not optimal. A longer, more gradually tapered, silicone adaptor would be better. I suspect, it's not done in current intakes now due to additional cost it would add.

 

[D-resonant]

The whole noise argument seems like a weird thing to me, but only because Ford included the symposer. Why attempt to quite something down just to artificially amplify it after 4 and a half feet of pipe?


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(The factory J-pipe is another interesting engineered nugget. It has a smaller inlet ID before the baffles than out.)

Ford suppressed exterior noise for regulatory compliance. Added interior noise gazoo for "driving pleasure". (LOL. symposer delete was my first mod!)

 

[Dpro]

(The factory J-pipe is another interesting engineered nugget. It has a smaller inlet ID before the baffles than out.)

Ford suppressed exterior noise for regulatory compliance. Added interior noise gazoo for "driving pleasure". (LOL. symposer delete was my first mod!)

Could Ford have been going for Venturi effects in both the factory crossover pipe and the J pipe. After thinking about it does make sense.
As far as noise suppression goes indeed what I alluded to in my original response as to why they did it is regulatory. Generally large scale automotive manufactories are really keen to the idea that their are noise laws now and people react to noise. Unlike a speciality manufacturer or low production number speciality vehicle were the noise issues might not be as concerning one has to remember that in general the FiST is a high performance version of a mass market economy car manufactured by a large scale automotive company that strives to agree with regulations not float them.
So the Noise Gazoo would indeed be deemed as a must for the drivers pleasure.
BMW does this as well I might add as do a few other manufacturers now.
Noise pollution has become a legitimate concern in many countries. Now if someone could get Harley owners to comply lol.

 

[DoomsdayMelody]

Could Ford have been going for Venturi effects in both the factory crossover pipe and the J pipe. After thinking about it does make sense.
As far as noise suppression goes indeed what I alluded to in my original response as to why they did it is regulatory. Generally large scale automotive manufactories are really keen to the idea that their are noise laws now and people react to noise. Unlike a speciality manufacturer or low production number speciality vehicle were the noise issues might not be as concerning one has to remember that in general the FiST is a high performance version of a mass market economy car manufactured by a large scale automotive company that strives to agree with regulations not float them.
So the Noise Gazoo would indeed be deemed as a must for the drivers pleasure.
BMW does this as well I might add as do a few other manufacturers now.
Noise pollution has become a legitimate concern in many countries. Now if someone could get Harley owners to comply lol.

I may be mistaken here, but I was under the impression that for a Venturi effect to take place it has to be an incompressible liquid. Gases, as demonstrated by turbochargers, are very compressible, while liquids already occupy a given shape at maximum density and are generally considered incompressible. Not that I believe that gases are compressing prior to the turbine on the turbo, but part of me also doubts that once a KP39 spools there’s any piping that is larger than the size of the turbo inlet that can limit the amount of flow. That said, I’m merely a student at this point, so there may be something I’m missing.


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[Dpro]

I may be mistaken here, but I was under the impression that for a Venturi effect to take place it has to be an incompressible liquid. Gases, as demonstrated by turbochargers, are very compressible, while liquids already occupy a given shape at maximum density and are generally considered incompressible. Not that I believe that gases are compressing prior to the turbine on the turbo, but part of me also doubts that once a KP39 spools there’s any piping that is larger than the size of the turbo inlet that can limit the amount of flow. That said, I’m merely a student at this point, so there may be something I’m missing.


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Well Venturi‘s were used on carbs back in the day and the air fuel mixture is definitely compressible.

 

[DoomsdayMelody]

Well Venturi‘s were used on carbs back in the day and the air fuel mixture is definitely compressible.

Wonder if that had anything to do with the Fuel component of the air/fuel mixture.


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[SteveS]

Wonder if that had anything to do with the Fuel component of the air/fuel mixture.


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No. Venturis work with all fluids, compressible or not. As mentioned, carburetors are a prime example. Look at the pictures in the Wikipedia article of venturis for air on small planes. https://en.wikipedia.org/wiki/Venturi_effect

 

[Ecmdrw5]

I use a Venturi valve vacuum system on a CNC machine. They definitely work for air.


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[DoomsdayMelody]

I use a Venturi valve vacuum system on a CNC machine. They definitely work for air.


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Yeah I posed a similar question at one of my instructors, and he essentially said that it wouldn’t work for fast moving air because after a certain speed compression of the air becomes an issue. When I asked him what velocity the air would have to be moving he said that there was a really nasty differential equation involving the volume of moving gas, plus the change in area through which the gas is being forced through, plus the change in velocity of the gas between two established points, plus ambient stuff like pressure temperature and humidity. Generally speaking though, you can count on the Venturi effect to work for air in most applications on our planets surface, that is unless your trying to shove, in his words, a metric fuck ton of air through a very small area.


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[gtx3076]

Yeah I posed a similar question at one of my instructors, and he essentially said that it wouldn’t work for fast moving air because after a certain speed compression of the air becomes an issue. When I asked him what velocity the air would have to be moving he said that there was a really nasty differential equation involving the volume of moving gas, plus the change in area through which the gas is being forced through, plus the change in velocity of the gas between two established points, plus ambient stuff like pressure temperature and humidity. Generally speaking though, you can count on the Venturi effect to work for air in most applications on our planets surface, that is unless your trying to shove, in his words, a metric fuck ton of air through a very small area.


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Or, we could just run a larger ID pipe and forgetaboutit.