Designed induction restriction

[dicer]

I would like to see if anyone can make some sense of this.

A 1996 Ford F250 with a 460 Engine.
Running from the airfilter is 2 large rubber hoses, they come to a plastic junction, that has a very small hole maybe an inch or so diameter that connect from each hose, that restrict the airflow, then 2 large hoses come off the other side that then feed the air to the throttle body.
This is so counter to any logic as far as getting airflow into the engine. Does anyone know why this was done? This is stock factory on all these, and I think many more models as well. I would think this would help to decrease fuel economy as well. Any ideas? Thanks.

 

[IceStationZebra]

Could you post a picture or drawing? Is it the same as this 1992?

http://www.alpinemotorswyoming.com/car/1992_Ford_F250_4x4_HD.html

Generally when you see odd things in the intake it was put there for sound/noise reasons. I'm unclear from your description if the 1" hole is connecting the two hoses together or if both hoses are being restricted down to 1"? Since the hoses are different lengths connecting them together probably helps to dampen each other's natural resonance, making it quieter. I checked on a couple of web sites, included Gale Banks, and they don't remove that plastic piece with the power kits - which makes me believe it isn't hurting your power. (but a picture would convince me!)

ISZ

 

[dicer]

You are correct one smaller hole for each side. It seems alot of restriction for trying to quiet it down. I suppose at normal low speed and no huge power demand they would work fine. But they look like huge CFM destroyers. I could take a photo but there is no way to put it on here that I know of.

 

[ivymike]

there's filesharing via engineering.com - use the link at the bottom of the post window where it says "...or upload your file to engineering.com"

 

[Lou Scannon]

Could be deliberately shaping the torque curve of the engine?

 

[franzh]

I have one of those exact Fords and Dicer is right, there are two perfect Bernoulli 1-2-3 profile venturi "restrictors" inline, one for each throttle bore.

They are mounted midway between the air filter box and the engine throttles but are tucked inside the outlet hoses of the ISC supply tee. On the photo from IceStationZebra, it is visible directly over the AC compressor.

On a whim, I sawed them off (I have a spare) and can detect no difference in performance or noise, although I suspect it has to do with intake pressure wave tuning.

Franz

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[GregLocock]

At a guess it is a friction damper for one axial mode of the intake duct, but that is a pure guess. If that's right then it should be at the antinode of the wave.


Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[IceStationZebra]

Franzh - can you post a pic of the venturi?

 

[franzh]

Well, I'm sure to screw this one up. How to imbed a photo? I've forgotten how and cant find the FAQ on it. Oh, wait, it's at the bottom. Lets see how this works.

Here are the two venturi's I sectioned off. They are in the inlet of the tee, between the air filter box and the tee. I cant find the replacement tee, they are frequently removed when converting one of these monsters to propane. Oh well, its running just fine, right now, its on the road.

Franz

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[GregLocock]

Let me guess, shallow taper towards the air filter?

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[franzh]

Yes, classic venturi. They sort of remind me of old WW 1 binoculars. I cant find the one I had reserved as a spare, it may have been tossed.

Franz

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[GregLocock]

I wonder if it started life as an antireversion feature?

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[franzh]

I sort of dont think so. This venturi is a LONG way from the fuel. My guess is close to 1.3 meters. I have heard it called an airflow straightener(?), a pulse dampner, Heimholz resonance dampner (my best guess as well) and so on. The ID of the venturi is almost half of the OD, the convergent distance is the venturi ID, the divergent distance is three times the venturi ID. All of the venturi dimensions are what I call the classic profile.

Franz

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Thecardoc]

The venturi's in the intake tube are a pulse dampner. They are both for noise reduction, or resonance in the air inlet, as much to help promote steady airflow through the MAF (Mass Air Sensor). Under specific driving conditions, the reflected pulse wave from air entering the cylinder and then being stopped against the closed intake valve will transmit all the way back through the mass air sensor and cause it to undershoot the air flow measurement. Taking them out, without measuring the reported VE (volumetric efficiency of the engine) from the MAF does not necessarily cause the driver to feel anything different because the on-board engine controls will simply end up compensating for the error in the air flow measurement. However, this airflow measurement is also responsible for the spark timing map, and that could result in an error for the spark advance calculation, and short of doing a lot of testing, I cannot predict what the results of that would be.

BTW, measure the intake valve opening, and figure out air speeds, and flow from that and you will see it's a much greater restriction than those two venturi's were. They will have an effect on airflow at very high engine speeds, but you will destroy the engine from an over-rev long before you max out the drlivery through those tubes. That of course is why there was no obvious improvemnent in performance when they were removed.

 

[Burnit]

To me it looks like they have found that the low end tourque has suffered & as a quick fix they have devised a method to increase the air velocity to the throttle body. Being the vehicle it is it would require low end torque & the venturies would certainly aid that.

More than likely it would have been advertised as some wiz bang idea that covered up the inadequate breathing design.

Even though i haven't viewed the port sizes on this particular engine one would imagine they would be like typical Ford design ports & big enough to stick your head in & destroying good Torque curves.

Remember it is just a factory engine & nothing special.

Anti reversion could be ruled out---anti reversion needs to start at the valve seats, valves & intake runners etc.
If there is a reversion problem that far up the intake tract then Ford had better go back to the drawing board.

 

[patprimmer]

How does a very localised restriction increase torque as it will only increase velocity at that one point. The air will be accelerated and decelerated significantly as it passes through the restriction.

Waves can exist in any part of the duct and therefore reversion can exist anywhere.

This seems to me to be a device that will limit power and reduce noise emissions from the inlet tract.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[franzh]

This isnt the only engine Ford uses the venturi on. A Ford Aerostar (minivan) with the 3.0L engine has the filter mounted up front with molded hoses connecting to the throttlebody. The molded hose is one piece with cast in place venturi's, but this time, there are 4 of them. The hose has two venturi's in parallel, with an additional pair in series immediately after the first two. They are still the same profile and the same size.

Patprimmer is right on about increasing air velocity, it just aint happening in this case. The hose diameter immediately after the venturi body is the same size as the hose size immediately before it.

Franz

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[SomptingGuy]

There are definitely frod engineers lurking around here. Surely one of them could put the feelers out for an answer?

- Steve

 

[dicer]

Thanks for the replys, yes I wish a Ford engineer would chime in. I did not run the engine before removing them, so don't know how it would run with them. I wonder if they are used to cancle or change a standing wave?
Though it could be other factors, but it seems to idle a bit rough and has a slight what I call a mid range flutter. Could be the China autolites, or the old cap/rotor, other wise this is a fresh engine. So now I'm on the hunt for another part. When I get a chance I'll take some measurements and post them.

 

[Burnit]

Can you give me the specs on the particular engine.

Bore 4.440" ?
Stroke 4.5" ?

Intake valve size?
Intake valve lift?

Thanks