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Old 02-11-2011, 10:19 PM   #1
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Modify stock VX air box

So I'm looking for advice on this intake mod. The car originally came with an air box that someone drilled a bunch of large holes in. I put the stock box back in after testing tank to tank and having my numbers lower.
Now that I have a guino I decided to re-test this ABA style.

Here's what the thing looks like modified:


Note that the snorkel below the air box has been absent since I've owned the car. It didn't come with it, and I can't seem to find a reason to go to the scrap yard and get one. This is up for debate. Can anyone tell my why I should use it?


Okay, so ABA.
Two types of driving. I feel like this mod could effect town or highway driving in different ways.
In town: 2 stop lights, so little room for error as possible. 3.1 miles.
Highway: 18 mile loop, there and back- No choice really, it's the closest exit that doesn't involve a toll and is more than 2 miles of interstate driving.
I pulled the ECU fuse between all tests.
The temperature dropped from 2df to -5df during testing. (approximately 3 hours at night)
The car was unloaded with the drum gear I carry about 1/2 of the time.

Test A, with STOCK intake.
Town: 50.95 mpg
Highway: 64.44mpg

Test B, DRILLED intake.
Town: 54.08mpg
Highway:64.32mpg

Test A second time, STOCK.
Town: 54.20mpg
Highway: 63.65mpg

I equate the first low in town number to the fact that the car was warm but had cooled more than the other tests after it. There was maybe 20 more minutes between my trip to the grocery store and the beginning of testing. The needle was almost at warm.
Either way, it seems in town is well within my margin of error.

Highway, shows different results.
It looks like perhaps the temperature drop was effecting my testing. The numbers went down over the night.


What I noticed with the drilled intake:
The car gets on the highway MUCH easier. I can climb hills that used to require second gear now 4TH GEAR. It growls, but it will do it. In theory, this should be better. This extra oomph would be great with the added weight of my equipment in the back. However, I did notice that it CURRENT FE went down more quickly when getting on the interstate than before. It was easier to lose FE more quickly. OTOH, I noticed that FE numbers went up faster when cruising at highways speed.

These tests were done during a very cold evening. It's possible that numbers for the drilled intake might be better on a warmer day.


So, what do i do? It looks like things are pretty flat either way. I'm thinking I might as well put the drilled intake back on since the extra get up and go might help FE in the long term if I learn how to use it. (relearn shift points for my given routes)

What does everyone think?
B
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Old 02-12-2011, 03:40 AM   #2
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Re: Modify stock VX air box

You'll need to do long-term A-B-A testing to get useful data. The effect is too small to measure in 3 runs.

The data you gathered shows zero effect on highway driving (one 63rd is nothing) and inconclusive effect on city driving (less than 10% is well within the margin of error for this type of testing IMO).

I wonder how the snorkel would affect things. I'd be surprised if Honda's engineers failed at something so simple, cheap, and problem-free as providing sufficient intake air flow...especially on the VX. Where does it get its air currently? Does it get warmer air with the drilled box?
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Old 02-12-2011, 10:58 AM   #3
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Re: Modify stock VX air box

HC-
In theory, the air temp should be about the same. I have a dryer duct run over to the bottom of the air box from the exhaust mani. It is not a snug fit at all, so when I had my thermometer on it I was getting readings of 50-75 degrees Fahrenheit in the box. I'll have to get out my thermometer again and drop it in the box. These holes point directly at the front of the motor/radiator so I suspect it is about the same. I'll gather some more data on that.

Yes, I totally agree with your sentiment about air flow from the factory. That's why this is perplexing. Perhaps there was a trade off between Intake noise (this is slightly louder) and where the normal person would drive the car (in terms of throttle position). I use hypermiling techniques which means I rarely see revs higher than 2.5k. That being said, I can tell that if I was at full throttle all the time I'd be using more gas. The gauge indicates that.
OTOH, I can climb hills in at least one and sometimes two lower gears than before. In second gear on one particular hill (that is .5 mile long) I used to get 18-22mpg. Now, in fourth, I get 24-28mpg climbing the same hill. At least that part of things seems to be better.

So, I'll snag my thermometer from the house and put it in the air box. I'll leave this intake on for a while and see how the numbers treat me.

B
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Old 02-12-2011, 11:42 AM   #4
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Re: Modify stock VX air box

Good thoughts and reasoning.

One gripe: It's unclear what you're saying about gears, but I think you meant "higher" instead of "lower"...4th is a higher gear than 2nd.
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Old 02-12-2011, 11:56 AM   #5
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Re: Modify stock VX air box

Yes, that is what I meant. I was thinking lower revs.
We'll see what time brings.
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