ITB's and airbox questions

[Yves]

I have recently built 2 airboxes on my Chevy V8 with ITB's. Due to the type of manifold (crossram) and placement of the stacks this has become a dual plenum (meaning each bank has it's own airbox). Each box is fed by it's own 90mm tube and K&N conical filter. I calculated the filter area of the K&N's based on info on the website of K&N and they should be more than sufficient for the job.

However, I made a couple of first runs, where I had autotune on to rough in the tables and it seems that compared to the fines mesh filters that I previously used, I'm losing some VE's in the higher kPa areas. In the lower kPa areas the loss is almost nothing. It looks like a pretty large hit I'm taking (like 10%). Engine did not run bad and my impression was that it was smoother, power enough and when looking at the tables in 3D it has smoothed out a lot of the peaks and valleys I was seeing in the same areas before...

I've since been looking at what could have caused this drop in VE and making comparisons to the V8's with this type of box on the market. When looking at Ferrari 360 and 458's with V8's and dual plenums it seems that these have one or several crossovers between the plenums. However these are intakes with the throttle body on the inlet side of the plenum and not after the stacks.

I'm also using a innovate system with only 1 exhaust gas sensor (right bank) so different aspects might play a role as well. Vacuum levels (which are measured at a point where all cyls are connected is common for all cyls.

Someone already suggested that it might be necessary to attach a crossover between the 2 boxes.

Any input is appreciated.

[dontz125]

You say you've lost VE at the top end, but I don't really see your description of what you had before. It takes a REALLY well-design airbox to out-perform bare filters at WFO. It also makes sense that you're seeing little to no loss at the bottom, because the pressure loss due to resistance is much smaller at smaller flows; dP is a function of the square of the flow rate.

Cross-overs work because they double the effective size of the intake - you're breathing through 2 filters instead of just one. Also, they alter the Heimholz frequency, so that the airbox assembly resonates at a different rpm - many of these cross-over designs have butterflys in them that open and close at different speeds.

It does also make sense that you're seeing smoother operation at low end, even with an indifferently-designed box - ITBs like large volumes of (relatively) still air.

[Yves]

You say you've lost VE at the top end, but I don't really see your description of what you had before. It takes a REALLY well-design airbox to out-perform bare filters at WFO. It also makes sense that you're seeing little to no loss at the bottom, because the pressure loss due to resistance is much smaller at smaller flows; dP is a function of the square of the flow rate.

Cross-overs work because they double the effective size of the intake - you're breathing through 2 filters instead of just one. Also, they alter the Heimholz frequency, so that the airbox assembly resonates at a different rpm - many of these cross-over designs have butterflys in them that open and close at different speeds.

It does also make sense that you're seeing smoother operation at low end, even with an indifferently-designed box - ITBs like large volumes of (relatively) still air.

Before I had fine mesh type screens with a silicone edge that were pulled over the stacks to provide some filtration.

http://stackinjection.com.au/main-group ... it-v8.html

I thought those were more of a resistance than an airbox, tube and cone filters.

Meanwhile I ran the VE analyzer in megalogviewer and it seems to suggest values which are closer to what I had before putting on the boxes. Not sure what to believe now. Anyway losses occor in the + 90 kPa and more pronounced in the 2300-2500 rpm column.

[kaeman]

ANYTHING you do to change the air flow is going to change the ve numbers... whether its air boxes or airbox, change is change.. the key to it is whether it is so much of a change that you cant live with it. I went from unfiltered stacks to a coarse screen to stop bolts from possibly falling in, it was .015 wire on .250 centers. That changed the ve tables on my engine, then when I made my single air box with a large square filter... I had to change the ve tables again. with stack injection anything you do the the stacks changes the air flow. shortening the stacks or lengthening them by as little as 1 inch will change the torque curve and the ve table. If your engine runs well with the dual airboxes tune it that way and go with it. a crossover will effectively in crease the surface area of the filter per cylinder....GOOD luck.

[Yves]

Yes, I'll have to live with it.

Got some comments saying this is because of the helmholtz resonance. So that could mean that in higher rpm's it would have a positive effect.