Ok so I have a new intake tube from filter to TB. I thought all was well and awesome. Someone here posted that the stock tube has a larger internal volume than a straight 3" pipe. Silly me for not paying attention.

I used the "tape off one end, fill with water" to gauge the (approx) volume of the stock piece.

Stock came in around 2100ml

My fancy-dancy intake is 3" diamter, 15.5 inches long. That gives us an internal volume of dun dun dun!! 1800ml.

Like I said, not 100% accurate but 300ml is a fair amount to be off. Oh well, time to upgrade to 4" piping and 3180ml!!!

 

What is the stock plastic octopus diameter intake tube vs the caldoofy or Qwiketz? Not asking you to go out and measure just wondering if anyone knows?

 

You can make the pipe 10.000ml, but that doesn't give you more horses. Imho a 3.5" would be large enough from air filter to TB, and easier to fit as well.

 

What exactly does the volume of the intake tube have to do with the price of fish? The total volume of intake air is important, but this is a factor of flow rate rather than volume of the tube. The only things that affect the flowrate are the diameter of the pipe and the air resistance from the filter and any resonance chambers on the pipe.

 

I am by no means an engineer of any type so I will throw that out there.

Know that a vacuum in the intake tract means a restriction, I was thinking that the smaller volume available in the new pipe would create more resistance to the flow. Please correct me if I am wrong.

 

Vehlin is correct.

 

If you go purely by volume the standard 'octopuss' has the greater due to the chambers however as rightly stated by Vehlin it is more important to get the flow as smooth as possible to reduce the vacuum and therefore resistance in the intake system.

The intake tubes that i do are 80mm internal diameter stainless as when i measured the maf tube on the airbox this was the diameter i got meaning no bottle neck and no restriction due to diameter.

When i started on the 'stage 2' i thought no problem just carry on the tube to the throttle body but what is developing is a larger version of the cast unit already in use but changing the 'cobra head' shape to a more tubular shape, issues are (as seen on Michael Stars) having to cut a section out of the plastic section at the bottom of the front windscreen and also modifying the heat insulator to allow the new one to fit. Still work in progress.

 

Put on the 3 ". You wont notice a difference unless on full throttle. The performance issue is flow and any internal restrictions cause a range of significant eddies etc that effectively reduce the access for air. I custom made an inlet for my car and one part had an unintended 6 mm intrusion that seriously took away performance. Paul

 

Ok, based on some calculations, 3.5" should be the size of the intake for a 78mm bored out tb. General rule of thumb seems to dictate that you want your intake 25% larger than your throttle body

Area of TB = 4778.36 (all units are in mm)

4788.36 * 1.33 = 6368.52 (area of the intake)

6368.52 will give us a radius of 45.024

90mm = 3.54 inches


So let's see what this will do!