Originally Posted By: URG8RB8
The K&N is OK, but not what I am looking for here. I would like to find one of the top 4 100% synthetics. I found an almost match. The Fram XG-3985 will fit, but the bypass valve spring is set to 12 psi versus the normal 32-36 psi. Is running a light bypass spring highly detrimental? Also this is an XG part number, but not an Ultra. What is the difference? I can’t find much literature. XG seems to be rated for 7000 miles versus the 10,000 on the Ultra.
The XG is the old Extended Guard and they are out of production now, but they were rated for 10K miles to the best of my knowledge. The XG numbers now apply to the Ultra, but you will still find old stock Extended Guard on some shelves. All the numbers translate to the same applications so al you need to do is find an Ultra of that number and you are set. They haven't changed all the pics over from old to new yet, I guess. We were warned of that some time ago but I guess the transition is not yet complete.
That XG number is a very small filter compared to what was on there so I don't think it's worth considering.
As to the difference in bypass pressure, that's a lot. Bypass pressure is most often based on the filter media and the application. A high bypass number with a cellulose filter is often seen on filters that have either a dense, efficient cellulose media that is built for high DPs and/or in high-revving performance cars spec'ed for thick oils. The bypass is high so that the filter will bypass less with thick oil or sudden, high revs. The media has to be robust to handle a 32-36 psi DP. That much difference is a bit troubling to me but generally speaking, with a syn media you could get by with a lower bypass number (because they flow better) but I wouldn't make a big change without a LOT more research. FOr me, that would mean hooking up a DP gauge setup any trying it (I built one for my truck and am experimenting now).
