Intake air flow problem?

[johned]

I put a filter box from a 4.0l on my 3.0l and modified the tubing from the MAF to the throttle body to reduce restrictions. Kept original MAF. One thing I noticed, was that the 4.0l filter box had a plastic tube on the inlet to the box (between box and radiator support) that seemed restrictive. I removed that so now I have a larger opening into the filter box. I have no performance measurements. So I won't make any claims to power gains. I just measured stuff and tried to make sure nothing replaceable had an opening smaller than the id of my throttle body.

Great post. I will look for that plumbing and make any corrections I can. I will delete the paper filter ause I can measure the flow through the paper and it is very restrictive. I wish there is an alternative to the K&N as that filter actually has small holes in the fabric that can pass dust particles.

 

[johned]

Looked into this a bit more. All tubing and every filter will create some amount of flow restriction, and therefore some pressure drop from atmospheric when and engine tries to pull air through it. This device is simply measuring the pressure drop from atmospheric to a point downstream of the filter. Any further restrictions downstream of wherever the device is connected will be invisible to it. Where was the device connected to the intake?

It appears it is calibrated to somewhere around 20" H2O. Keep in mind however that when you measure intake vacuum you are looking at inches of Hg. 20" H2O is less than 1.5" Hg, so this is a pretty sensitive measurement.

When does the filter restriction affect hp? Well that depends - anything that reduces the volume of air drawn in will reduce max hp, so in theory any restriction limits max hp. However with some carbs it will be much worse. If the carb has a bowl vent direct to atmosphere any filter restriction causes the mixture to get richer. If the bowl vents to downstream of the filter (like in any car from later years of carbs), then the mixture is more constant - but still not as constant as a modern EFI system. Not sure about dirt bike carbs, but any all-position carb is especially sensitive to intake restriction as they don't provide a mixture that is constant with airflow anyway.

That said it must be seeing some pressure drop greater than usual, but I'm not convinced how important that is, or how unusual it is on a vehicle. Especially at other than max hp. The ECU could probably detect this based on air flow, throttle position and rpm, but I don't think any bother with it.

Located right after the MAF.

I think it is very sensitive but only as much as needed to generate the info it does.

My delima is would there be a "fix" that is cost effective and justified. The MAF restriction bothers me.