[ace.cafe]

Anytime you can radius the air entry path, either at the outer entry, or at any "shelf" that might exist on the way into the engine, this is a flow improver.

A sharp edge on the perimeter of the air path causes an aerodynamic impediment which causes a dead flow layer around that edge that extends a little bit into the duct, and the incoming air needs to flow around that dead zone, so the actual air entry area is restricted to a smaller actual area than the measurement of the physical part. So, your cross-sectional area is invisibly reduced by that sharp edge. This is why we try to match all the manifolds and other inlet tract parts to reduce the occurrences of this kind of thing. We matched the manifold to the port on the Fireballs when porting the head. We have sized the inlet port on the Ace Billet GT head to be as close to the size of the manifold as we could make it, but there may be a little ridge, possibly.

The general rule here is that if the flow transition goes from smaller diameter to larger diameter, there is not much of an issue. But if the transition goes from larger to smaller, then that will be very likely to cause the problem, so matching the ducts, or using a  radius or bevel will almost always help with that.

[Farmer_John]

So then there's a good probability that the Hitchcock big gulp is a good start along with smoothing the entry to the throttle body.

4hp +- is a pretty good gain for a rather non intrusive mod!

[Otto_Ing]

I personally find the hitchcock big gulb too edgy. What Aus.GT did looks way better. Gives the bellmouth a little length as well so that the inflow would be more stabilized.

[ace.cafe]

The big gulp could be used as a basis to be modded. When we flow test a head on the flow bench, we build up a clay ring around the port entry, and shape the clay with a nice radius, so that the entry is not a problem. I see no reason why the big gulp couldn't get the same treatment by using some epoxy dough/putty  to make a radius entry into it.

Just for the record, when the opening to the airbox already well exceeds the throttle body entry size, then improvements by radius airbox entry are approaching superfluous,  so it is the open area that counts most, and the radius just will smooth the flow more. If the stock air box entry is too small, that needs correction by some means. If you plan to tune the air box, then the diameter of the entry needs to be the appropriate size for the tuning.

Also, be aware that the presence of the filter element in the middle of the air box can/will break up wave activity, and could/will affect the tuning because of that. When we tune air boxes for performance,  we normally have no filter in the box, and it is located elsewhere,  or not present. With untuned airboxes, the presence of the filter element is not an issue, except that the critical airbox volume is measured by the volume that is on the engine side of the filter barrier.

[Otto_Ing]

Why not printing it instead directly? Much more design freedom and a printout is almost as good as plastic mould and won't cost more than the alu plate big gulp.

Do I understand correctly? Non tuned Airbox has to have as big hole in it as possible. Tuned Airbox has to have a entry which is matched for the tuning? What about a bottle neck entry? That should work too and can be seen on many airboxes, I thought of doing something like that, should I find a place for the duct. That should in theory add to the airbox volume.

It does not look too good for the tuned airbox however because of the packaging and very little room available.

[ace.cafe]

Why not printing it instead directly? Much more design freedom and a printout is almost as good as plastic mould and won't cost more than the alu plate big gulp.

Do I understand correctly? Non tuned Airbox has to have as big hole in it as possible. Tuned Airbox has to have a entry which is matched for the tuning? What about a bottle neck entry? That should work too and can be seen on many airboxes, I thought of doing something like that, should I find a place for the duct. That should in theory add to the airbox volume.

Otto,
I was adding some more info to my previous post when you posted, so check out the edits that I added.

Printing it would be fine, if you have the equipment.

Yes, untuned boxes can have any large entry, but the internal volume on the engine side of the filter must be sufficient  ( more than 1.25 x displacement ).

A "bottleneck" duct that expands as it approaches the box is for pressure recovery purposes.  This allows a more graceful transition of air flow from velocity to static pressure (Bernoulli's Principle  and conservation of energy ), and both ends could benefit from bellmouth radius ends. If pressure recovery is done well, it can drastically reduce turbulence and energy robbing vortices. However, getting really good pressure recovery typically requires more room for ductwork than is available in most situations, so compromise is the usual result.

[Otto_Ing]

Thank you for the clarification Tom.

SLA/SLS printing services are plenty available even online.

One question i had regarding the epoxy. Is there something which can be recommended for smothing the edges inside the tube which goes in the throttle body? Idealy something which would not damage the engine should it come loose...

[ace.cafe]

Thank you for the clarification Tom.

SLA/SLS printing services are plenty available even online.

One question i had regarding the epoxy. Is there something which can be recommended for smothing the edges inside the tube which goes in the throttle body? Idealy something which would not damage the engine should it come loose...

Regarding flow matching, I recommend grinding the transitions to match each other whenever possible, bearing in mind that the cross sectional area should never get larger in any section outside the throttle plate, as it progresses from the airbox toward the throttle plate. It can decrease gently like a venturi, or it can remain a constant diameter. The blending and matching in this area should follow that guideline. If there is an enlarged area that intervenes, it can be filled with a good grade of epoxy such as Belzona 1111 or Splash Zone,  and ground to the proper shape with a die grinder or Dremel,  or sandpaper. If ethanol laced fuel will be used, spray a coat of protective paint over the epoxy to help reduce the effects of the alcohol on the epoxy. The epoxies that I mentioned have good reputations for use in intake ports, and should not fall out.

For matching or blending on the intake tract inside the throttle plate location, we must address the issue individually, with the particular location and dimensions involved, so as to preserve or enhance the integrity of the flow path design.

In EFI engines, the walls of the inlet tract can be polished finish, up until the location of the injector,  and then the port should have textured finish between the injector and the valve.  In carburetor engines, the  entire intake tract should have texture finish between the carb and the valve.

[Otto_Ing]

Just as info, the problem with the stock inlet is not the size of the area, but the 90 degree flow turn without radiuses, all very edgy. Although i think that most likely the radius on the inside of the airbox contributed more to the 4hp's than the "big gulp".

[ace.cafe]

From what I can see of that item, there is not 4hp to be found there. Something else was a contributing factor.

[Otto_Ing]

Anyways...I ordererd my proto. "Big Gulp" as 3d print. 

If anybody wants the STL file just PM.

[Aus.GT]

4 HP is a good increase. Where did you source the bellmouth?

I got one of the guys at work to make it on the CNC to my specs.
I would have made it myself but turning the radius would have been
difficult. I did however cut the entry off and turned the outside flat to
mount the bell mouth on and used Sikaflex to stick it on. Cheers

Just as info, the problem with the stock inlet is not the size of the area, but the 90 degree flow turn without radiuses, all very edgy. Although i think that most likely the radius on the inside of the airbox contributed more to the 4hp's than the "big gulp".

I agree but I do think the bell mouth helps smooth out the airflow entry into the box.

From what I can see of that item, there is not 4hp to be found there. Something else was a contributing factor.

Ace I don't know for sure but freeing up the intake side of things may have allowed the free flowing muffler to work better.

[ace.cafe]

.Ace I don't know for sure but freeing up the intake side of things may have allowed the free flowing muffler to work better.

I'm sure that was part of it.

[Otto_Ing]

...on the printer.  , not given up entirely on the tuned abx yet.

[pearcey2]

All this manufacturing looks a little over the top to me! I dropped down to the local hardware store (Bunnings for those in Australia) and picked up a zinc coated 75mm down pipe fitting and rubber gasket for a total of $15.

Its a little rough but I'm a little bit impatient. Might get some washers for the screws but at the moment it's all locked on pretty well and not exactly a high stress area. The 75mm fitting fits snugly on the filter but goes in a little deeper than it needs to so might shorten it a bit. Will give it a test out tomorrow!
https://www.dropbox.com/s/w141qtguzv52kxp/IMG_20151204_163939960.jpg?dl=0

Also while I was there I noticed fuel pooling at the bottom of the air box. Is this an indicator of some issue (too rich?) or normal?
https://www.dropbox.com/s/t6giwez36xwagpw/IMG_20151204_124056785.jpg?dl=0

And finally...on the interior edge leading to the engine how much thickness is there to smooth out the edge? I'm worried I might break through and create a hole