So about 10 years ago, i installed a 6637 filter with a 4" no cat exhaust.
I also installed DP Tuner with a 60 and 80 HP Tune.

Stock injectors. stock Hpop.
I just wanted a little more something for towing at that time.


Well, i just had the transmission rebuilt because it started giving my issues when towing.
it would tow fine until you put it in park and put in to drive again.
It would not go in to drive. it would just spin like there was no transmission fluid in it
then run fine again. never slipped when not towing anything.

when I had the transmission rebuilt, i had a billet converter and a shift kit installed,
so now , i had to send the Tuner out to be re programed for the shift kit and De-cell program.

Back then at first the truck ran great with all the new goodies on it and never really noticed that i had a flat spot in acceleration.
just thought that being a diesel, that's how it was.
it would pull until about 3K RPM and feel like it hit a wall but the truck ran so much better than it did stock.

I had read threads over the years about the 6637 filter. Most good, some Bad.
most say that the down fall of this filter set up is it's not a cold air intake anymore because your using the hot air form around the motor.
I was good with that believing that it's a bigger filter with a bigger surface so it must be getting more air.

I was told by other over the years that this was not true, but i still kept it in.
So now after talking to Jody and a couple of other Diesel mechanics, about the stock air filter letting more air in than the 6637.

They say YES it dose. Jody did a air flow test on the same truck with both the 6637 and the stock air filter.
the flow test did not lie. the stock filter passed more air than the 6637.

Now Getting back to that flat spot. Today i did a small test of my own. i ran my truck full throttle about 6 times on each filter.
by Feel of seat and watching the RPM's with and without the Tuner installed.

All 6x2 times with the 6637, my truck hit that flat spot at the 3k+ RPM range with and without Tuner
All 6x2 times with the stock box and filter installed, the truck pulled up to about 4K and the flat spot was completely gone with and without the Tuner.

I know the AIS and other filter set up's flow more air, but i don't want to drop $300+
everyone has their opinion on air intakes and i was a believer in the wix 6637

The 6637 may work ok for other trucks with a different set up's
It just didn't work well with mine and i never knew until today. my truck was being choked out at higher RPM's. Lack of air flow or maybe from the hot motor air.

These are my opinion of the two.





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I don't think you're reving to 4k. The limit is at 3200.

 

Other than the specific parts you mentioned, any other modified, swapped out or upgraded parts on/in the truck during testing?

Examples: bellowed up-pipes, billet turbo wheel, CAC boots, etc...

I can tell you that with the Donaldson blue 6637, pre-filter cover, 4" intake tube, Borg Warner SXE turbo, 4" exhaust, 1023/PHP tuning and stock 250,000 mile injectors there are zero dead spots in the acceleration.

Interesting thread though which has great potential to be educational.

 

for me i want my air filter to fo exactly that so the most important considerations are it’s ability to filter dirt and how much dirt it can hold between changing it, $300 is inexpensive compared to the cost of the parts it is protecting.
Donaldson Ford AIS wins hands down for how i judge a air filter.

if i wanted more HP i would buy a diffrent Turbo that was designed to move more air through the filter that filters out and holds the most dirt. again the AIS or its equivalent.

the whole marketing of air filters to “add more HP” is retarded..... i want “ filter and hold more dirt”. that is their purpose. it just doesnt have the same appeal to the young ( ignorant ) kids who buy that crap.

 

I don't think the draw of the 6637 is necessarily how much it flows, but its capacity. Its quite large and by simple logic, if a larger filter flows less, it must filter more. Although, I am no science-matician.
I personally had the 6637 and the AIS. If you want the best of the best, go with the AIS. I don't think you will find many people who dispute that it's pretty great, although I doubt its been bench tested against other aftermarkets.

This is the cheapest AIS I was able to find, buried in Amazon. https://amzn.to/2H4Xa9J

 

IIRC the AIS flows less than the 6637. If you want a setup that has one of the highest flow test results, go with the AFE 2.

I feel like something must be off either your truck or the test. I cannot see how the stock can flow more than the 6637 unless your 6637 was dirty or wet.

 

My guess is that your 6637 was clogged up. I've never seen anyone else have this issue with stock or modified trucks and the 6637.

As for the hot vs. cold air; cold is better and every degree helps, but I'm not sure it makes a huge difference after going through the turbo where it's being superheated.

 

Which is why we have intercoolers... But it still matters. Maybe not noticeably, but still important.

 

There is differences in "6637" filters..
I recommend using donaldson,fleetguard,etc.
Those are big oem manufacturers..

 

Wow... there is so much speculation here without taking variables into account. A proper-breathing truck can have a "flat spot" at high RPMs, but every time I've seen it - it was fueling-related, not air related. Choking the air down can remove the flat spot on acceleration, fooling the seatofpantsometer. I'm not saying straight up this is what happened here, but I'm saying It is not only possible - but likely.

Using the sensors in the truck and having an S&B cold air intake, I did some testing with the lid on and off on a very hot day. One thing I learned was the temperature in the box was hotter with the lid off in town than it was with the lid on. Once the RPMs came up on the open road, the temperature differences were marginal - I saw no reason to put the lid on other than to reduce the noise under the hood. So much for cold air intake.

The 6637, stock, and AIS filters HAVE been flow tested, with plenty of documentation. I remember reading the information and seeing the graphs, but my curiosity has been satisfied and I'm not inclined to repeat that search. I'm sure the readers would appreciate somebody either Googling and linking, or sharing what they may have in there library.

If the engine is reaching 4000 RPM, bent pushrods (or worse) will ensue.

 

AIS is $243 + shipping at Rock Auto

 

to tuglys point, valid test have been done comparing all the big names, back when the AIS came out the engineer for the AIS was active on another forum and shared much technical date and helped direct some user done dyno test comparing filters. s seatch should turn up the discussion but filtering out ( pun intended ) the subjective opinions is a chore.

bottom line i threw away my expensive Brand X setup and have been AIS ever since.

 

Tugly,
If you are running an open s&b now, is there much or any difference in noise compared to 6637? Would you recommend the 6637 over s&b?
Rob

 

I've been in rigs with the 6637, and it was just too loud under the hood for my taste. I much prefer the AIS, it is the quietest semi-big breather out there, it has superior filtering, and it lasted a very long time between filter swaps (cheaper to maintain). I was forced to go from the AIS to the less-quiet S&B because of all the mods to my truck - it needed a LOT of air, but the AIS is for stock injectors and turbo. I have to change my filter more frequently now and listen to the subdued siren under the hood - but at least the whine is not obnoxious like I've heard with the 6637.

A fellow member bought my used AIS to eliminate his 6637. His comments were along the line of how relieved he was to be rid of the racket under the hood.

 

Here is the rub...

I had a modified stock turbo with a RiffRaff wheel and the AIS.

Since I installed the SXE turbo, I sold the AIS and installed a Donaldson 6637 with a pre-filter cover.

The SXE turbo at full boost paired with the 6637 is no louder than the modified stock turbo at full boost with the AIS. I can imagine that the 38R is a nightmare to drive with the 6637.

So, clearly not only does the filter play a big part in the noise, but the turbo is the star of the scream fest show. I have zero complaints concerning noise or air flow with my Donaldson 6637 and SXE turbo.

AIS looked better, but the 6637 looks pretty good too with a black pre-filter.