Throttle body diameter and air cleaner piping

[Adrien]

Hi !

I have some theorical questions about airflow. I'll be glad to hear for enlightened opinions !

The question : Noise attenuation apart, does the piping going to the airbox play a role on power/torque/efficiency ?

Context : Engine is 1.6L vvti from a 2003 Toyota Corolla (3zz-fe engine). It is already fitted with 1.8L (1zz-fe engine) Intake manifold, throttle body, and injectors (see my presentation)
I like to have an economical car, but I really appreciate small smiple power mods. The last one being taking out the snorkel/piping going to the airbox.


Taking out this snorkel made me think about why it should make the car more powerful and more importantly, why it shouldn't change fuel economy.

Correctly if I'm wrong :

1) Less restriction equals more air equals more power, especially at high revs.
Piping connecting to the airbox is narrowing down to 40mm (see picture), which seems the same diameter than the stock throttle body (3zz throttle body plate is ~42mm). I guess it shouldn't be a restriction in that case.
In comparison, the 1zz throttle body I have installed is ~55mm at the plate. Cross sectionnal area is almost twice at 13,5cm² vs 23,5cm². In this case, the 40mm pipe seems to be a huge restriction, right ?

2) I was concerned about fuel economy, as keeping it low and reliable is my main goal, the rest is just for fun !
I know that air velocity is important in an engine, and I read that longer piping may give an advantage in terms of low end torque, but as we are talking about fuel enonomy, we are definitely talking about very low to moderate throttle input. In this condition, the main restriction would by far be the throttle plate angle ?

-> So let's imagine an hypothetical situation where we are cruising on the highway at constant speed. Our car needs 20hp to overcome friction losses and air resistance. Throttle is open at an arbitrary 20° angle to give the engine sufficient airflow for this power.
I If this piping was really doing an amazing job for airflow, whitout it I now wouldn't have enough air to produce 20HP. No problem, I press more on the throttle to give the engine a little more air.
On the other hand, if the piping was restrictive, even at partial throttle. I now have too much air, too much power, so I let off the pedal to keep a steady speed.
Am I forgetting something that would make this situation unrealistic ?


3) Finally, this problem is more or less the same than "stock airbox vs CAI/SRI" . I read a lot on the topic, but often people doing this kind of mod don't care about their mileage. But I don't see why a CAI/SRI would alter fuel use at partial throttle ? (assuming that temperature variation between stock and CAI/SRI is negligible).


What are your thoughts on this matter ?

[Adrien]

Nobody has any thougts about how fuel economy and performance at partial throttle could be affected by this kind of modifications ?

[Piotrsko]

Well look at it another way: your throttle plate is causing a huge restriction and flow in the system is limited by restrictions. Matters not part throttle because it can only flow what the throttle allows. If you used a variable system like the old strombergs it still wouldn't matter because the carb is still the choke point. It matters a lot when your throttle is wide open because then the restrictions determine maximum airflow. If you do diesel, it might matter but once again only at full demand.

[Adrien]

Thanks, so to be clear I reformulate my question :
During partial throttle operations, as the throttle plate is the main restriction in the system, is it correct to assume that every modification before the throttle wouldn't affect engine's performance or efficiency ?

[freebeard]

is it correct to assume that every modification before the throttle wouldn't affect engine's performance or efficiency ?

No, but I can't prove it.

My Dasher's snorkel has a bellmouth to prevent vena contracta.

[Piotrsko]

Not every modification. If you straighten the flow before the throttle plate you might see an efficiency gain because it isn't turbulent at the map/maf sensor and so could signal leaner operation. You can also get a pressure boost. I suspect the throttle plate causes swirls and eddies even full open

[Adrien]

Originally Posted by freebeard

No, but I can't prove it.

I would really love to see some proofs

Originally Posted by Piotrsko

If you straighten the flow before the throttle plate you might see an efficiency gain because it isn't turbulent at the map/maf sensor and so could signal leaner operation.

I haven't thought about this, it is an interesting point. More consistent readings of maf sensor would indeed mean more consistent afr and combustion characteristics.

Originally Posted by Piotrsko

You can also get a pressure boost

In this case, pressure boost = more power = driver should adjust by decreasing throttle input. It is what I tried to explain with my "hypothetical highway situation" in the first post.

I'm suprised about how difficult it is to find information about partial throttle performance of an engine when it represents 99% of our driving situation.

[freebeard]

I would really love to see some proofs

Here's a thought experiment. Strap a face mask over the end. That's a[ny] modification.

[Adrien]

Originally Posted by freebeard

Here's a thought experiment. Strap a face mask over the end. That's a[ny] modification.

Actually that's a great idea !

Do you know about a consistent fuel economy test with/without a CAI/SRI/snorkel/resonator that would have been done on this forum ?

[Adrien]

Ok, so the face mask thing really made me think about clogged air filters, and actually if I didn't find conclusive threads about snorkel modification and mileage, I did find two interesting threads about clogged air filters and mileage (can't post links yet):

Thread "New study shows 0 impact of a clogged air filter on fuel injected cars"
-> Very interesting reading from the EPA website, concluding to absolutely no difference in fuel economy between new and clogged air filters.

Thread "The Great Filter Debate"
-> post 17 is an interesting testimony in this direction


This confirms what I was thinking, and I can't see why these findings couldn't be extrapolated to any kind of modifications of the air intake system before the throttle body.