intake ducting question

[Belgian1979]

Considering a V8 where each bank has it's own airbox/intake tubes (3.5"). Would it be better to route the tubes into one tube going to the airfilter or have 2 seperate tubes feeding the boxes.

On the one hand I would think that less restriction would equal more air to the cylinder, but on the other hand I could see an effect were intake pulse would create a more continious airflow in the common tube and thus more pressure above the throttles.

Any ideas ?

[BOOT]

Is boost being used?

[Belgian1979]

No, NA.

[mag2555]

Where are you grabbing the air from, the front of the car?

[Belgian1979]

front of the car, behind the spoiler. (no holes in spoiler btw and this was the only possible way to do it)

[cardo0]

With 2 air inlets and separate banks you have what I call a split plane intake (don't really know what anyone else calls it). Split plane single planes showed up for a short while (Holley had at least one) but faded away. They don't behave like a dual plane intake since the firing order and intake valve timing are different so the reversion is different with the reflected shock wave (Hemholtz). I guess what I'm saying is I have never read any advantage to a split plane intake. Though my imagination tells me that if each of the plenum volumes are large enough it could behave like a tunnel ram intake on each bank - but only if the runners are spect'd correctly like a tunnel ram.

As far as using one or two inlets (which might be you actual question) my guess is the dual inlets would have less restriction and be the winner of the 2. But if your inlet is behind the spoiler it might be a negative pressure region where in front of the spoiler it would be a positive pressure area to aid intake air flow.

Good luck.

[Belgian1979]

That's the problem : I need to go over the radiator and its support and the space is too thight to get any tube over it.
If I understand you correctly connecting the 2 boxes to one common tube wouldn't help any.

[MadBill]

How about a wide, low profile duct like this? Some production cars (Corvettes?) use a similar design.
https://www.google.ca/search?q=aftermar ... zW22s4vVzM:
BTW, as long as the area is adequate, one tube or two makes no difference unless you're going for an elaborate Helmholtz resonator-like system, so feeding a tube from each bank into the back of such a duct should work fine..

[cjperformance]

Similar to Bill's example, this https://goo.gl/images/J3BXbt cold air intake/tray was used on some Aussie Brock Commodores, very effective setup for a setup with not much room.

[Belgian1979]

How about a wide, low profile duct like this? Some production cars (Corvettes?) use a similar design.
https://www.google.ca/search?q=aftermar ... zW22s4vVzM:
BTW, as long as the area is adequate, one tube or two makes no difference unless you're going for an elaborate Helmholtz resonator-like system, so feeding a tube from each bank into the back of such a duct should work fine..

I have looked into this quite some time ago. Have to add I use an L88 type hood with the bulge and depression right behind the radiator to resolve hood clearance issues. The problem is that the depression reduces space even further just behind the rad support requiring me to create some sort of S right before going over the support. The space between the support is 40 mm if I remember correctly, so really, really small.

[MadBill]

A pair of 3.5" round ducts (~20"²) would be more than sufficient, so a 4 cm x 30 cm rectangular one would too.

[cardo0]

That's the problem : I need to go over the radiator and its support and the space is too thight to get any tube over it.
If I understand you correctly connecting the 2 boxes to one common tube wouldn't help any.

I'm not sure of your design there w/o pix. So the best advice I can think of is to use a vacuum gauge to look for restrictions. Any vacuum reading of more than zero in front of the throttle blades will indicate restriction. Upstream of the carb throttle blades should be atmospheric pressure or zero vacuum. If you measure any vacuum upstream of the throttle blades you are losing volumemetric efficiency by a ratio amount. Pretty simple test and you can also connect to the valve cover to measure PCV effectiveness.

Vacuum gauges are fairly cheap and I can find large 4" dial gauges under $30. And when connected on the intake side you can mount them inside the passenger compartment - but I wouldn't put a crankcase connected gauge in there.

[MadBill]

Per David Vizard, the pressure drop through a filter and air cleaner should ideally be no more than 1.5" H20.
The easiest way to measure such low pressures is with a home-made U tube manometer. Tape a length of clear tubing in a u shape to a yardstick, fill it with colored water to the 18" mark and connect the ends to the duct work at the inlet and just upstream from the throttle body.

More $$ but easier to use are gauges like this: https://www.staples.ca/en/dwyer-magnehe ... lsrc=aw.ds

[turdwilly]

Does the car have 4 headlights? Just sayin...

[Belgian1979]

With regards to the filters I can add this : I checked while driving without the filters. I didn't give any difference in VE with regards to the fueling my ecu had to use, so my guess is that the filter(s) are not a restriction. Since they are behind the spoiler, there could be an effect of low pressure. I just don't know about that.

Car has 4 headlights, but they are retractable. (Corvette)