Hey there, I purchased a 3.5" AF1 CAI a couple months ago for my 2008 Ford F-150 5.4L and I am running custom tuning on a Xcal3 from VMPtuning. Despite having the tunes, I've noticed some annoying drive idling sounds and rough throttle response when coming stop. I live in South Texas where the temp is routinely over 90F so I'm going to assume with the excessive heat in the surrounding area and the large 3.5" Inlet Diameter, my truck is failing to compensate, despite having custom tuning.

Now I've heard that some people have made the switch to a 3.0" and all rough idling issues and hesitation have more or less been corrected. I noticed that some of the AF1 models for my truck come with an isert to narrow it down to 3.0". Is there any way I can exchange or fix this issue by placing an insert inside my tube and having my truck retuned? Almost 90% of my driving is stop and go traffic inside the city, and it only has 3000 miles, so I would imagine that the smaller tube might be better for it in the long run.

I've contacted Justin, but have yet to hear back from him yet, so I'll try calling tomorrow, but is running the 3.5" a plausible reason for my driving issues and do you think switching the a 3.0" might actually resolve the issues?

Thanks in advance! hopefully you guys can give me a bit more advice on this topic

 

To my knowledge, 3.5" is what you will want to run if you have more performance modifications to justify for the large amount of air induction ( LT headers, hi-flow converters for example ).

3" would be suitable for just a simple exhaust cat-back, and a custom tuning.

 

I sent my 3.5" tube back to AF1 to have the 3.0" insert put in. I contacted them directly, shipped it to them and 53.00 later, including return shipping I have my tube back. I haven't gotten it re-installed yet as I'm going to be talking to Justin at VMP about new tunes. (previously tuned by TP prior to my transmission taking a dump....not connected to the tuning of course. I just don't want to wait 3 months for a new tune)