Flapper off...........
 

Finally got around to cutting out the exhaust flapper and how I wish I'd of gotten to this sooner, really don't like the spring tension. But now it's off and over all the truck runs smoother...………..

https://cimg7.ibsrv.net/gimg/www.per...3834992b59.jpg

Here it is open, really don't like the tension needed to open that up...………….

https://cimg1.ibsrv.net/gimg/www.per...03a7fd465d.jpg

could it have been tie wired open?

I have heard of folks doing that as well as welding them open; I've also gathered that there is a round outer knob as opposed to the square one that I have...……..

https://cimg9.ibsrv.net/gimg/www.per...5e54e91ee7.jpg

so is exhaust pressure supposed to push that open? Its passive, rather than active?

Right- passive and that you need pressure to 'punch' it open. It feels less labored now and a touch more growl.....

hey, off topic but if your location is accurate we should meet up!

Otherwise, glad you cut that thing out. Im interested to hear if MPG changes with the more flow. Does she feel any different up top?

Cool- yeah, where ya at, man? Keep ya posted on mileage as time goes on...………..:thumb:

Rio Rancho. Travel up your way every weekend May-Oct for mountain biking, and I have family up in Eldorado.

Son of a gun- I live in Eldorado, and starting on a mountain bike project myself. Did the Century back in 2017...…………...

well, I dont do that hahahaha

Imma a downhill/Enduro guy. I ride Angel Fire, Crested Butte, Keystone, Winter Park, etc. I ride the foothills in Abq, but only with the gf because the foothills are lame.

What is your normal steed? I am a Commencal and Intense guy myself. As a welder, I have a thing for hand welded bikes and I dont like the harshness of carbon frames so I am still rocking aluminum frames

I think it's a GIANT Sedona SE. Don't know what year- I had a flair to build a cruiser once got a putrid green frame off eBay stripped it with aircraft remover hunted down forks and everything else went overkill painting it after priming I wet sanded with 5 then 7000 grit paper, paint/ wet sanded, paint/ wet sanded, decals clear coat wet sand, clear coat wet sand. juggled chainrings and cassettes etc and took a stab at the century for kicks...….

Sorry to derail the conversation gentlemen but shit I had no clue it blocked THAT much airflow. I guess I have to do something now especially since the Whip. Really appreciate the pics! OK back to visiting :)

I cut mine out months back (edit did a magnaflow straight through muffler at the same time). Probably the single most impactful thing I've done to my truck so far.

I noticed a very considerable amount of power pick up and MPG. Honestly, it was a big change. I now go around telling everyone to cut theirs out, and do it yesterday.

Locking the flap open alone doesn't make as much of a change as some may think, I locked mine open for a while and didn't notice much, had it removed and the biggest thing I noticed was MPG was up a lot. But I did a magnaflow straight through muffler at the same time that I had the flap removed. The stock muffler by the flap isn't a straight through.

With all the rest of the exhaust stock, and just the magnaflow and the flapper. The sound was perfect. You could hear it fire up inside the house when you remote start it and hear a low low rumble. But driving it you hear damn near nothing. At very light throttle you hear a really deep tone, roll into the throttle and it kinda goes away. I super recommend that setup for guys staying closer to stock especially if you want just a little bit of sound but zero drone and not gonna annoy the neighbors.

Right, Pooter- that's what prompted me to altogether remove the flapper; I had seen pics of a flapper both closed and open and just wouldn't sleep well with it propped open leaving so much on the table...…………..

Anyone documented mileage gains? I see lots but don't have anything solid. I'll be removing it when I do the headers but if it's worth enough I may chop it out early if I get a minute. Mine is welded open right now just because it whistled like crazy.

Whistle, haven't hear that; I've heard of squeaking from the spring rusting up and stuff. Haven't been about enough to see mileage benefits or any advantage when wringing it out, yet...…………...

When I got my truck it was stock except it had the K&N intake on it.
It got 11 MPG on e85 mixed city and highway. And 14 on gas.

Then I got it tuned and also had the 4 cyl mode deactivated. The gas mileage stayed about the same for the most part since it picked up a little mileage in v8 mode but no longer had 4 cyl mode it kinda equaled out

The day I got the flap cut out and the flap removed was the first time I ever got 16 mpg mixed city and highway on E 85
Put gas in it and got 19

I'd like to say it gave me 5 mpg but my testing wasn't scientifically exact. And all of this was just basing the MPG off of what the dash display said, not actually hand calculating mileage and staying on the same exact roads.

On the same exact roads I saw an increase of around 3 mpg. Some tanks I average around 16 and some around 18 where before best was 14.x. That's on gas and going my everyday route to work.


Yours may end up a little different since you have the aftermarket exhaust with the flapper and flapper bypass

When I cut out the flapper and got the muffler I called my tuner and said "you're not gonna believe this but I got a good 2-3 mpg from cutting the flap out and changing the muffler" he said "yeah I will you're not the first person to tell me that". He said he put a cat back on one of these trucks and the customer called him a couple of weeks later and said he got a couple of mpg additional from it.

As hard as they are to twist open, you can bet they are always closed. Mine was not stuck, it rotated, but that spring is strong and I don't see the exhaust gasses alone pushing it open, they may. But I can't see it.

I'd be skeptical of what I wrote above too. Sounds like crazy bull shit. But I saw it, and it happened.

If you're getting that high of mileage you probably wont see a lot of gain. But who knows, my buddies wife's 17 denali 6.2 still has the flap and gets 20 mpg on the regular.

You also have the bypass pipe which I don't understand having a flap and a bypass.

But hey man, it's probably $50 at most to have it cut out and it'll increase flow. To me that alone is worth it.

lol I hear that

At your earliest opportunity take it off. My flapper wasn't stuck, but that spring pressure sure requires a helluva lot of exhaust pressure to shove it open...…….

It's welded open currently.

Ill be looking at mine this weekend. Didn't realize these trucks had something like that. Just picked my new one up at then end of November.

Are you already pretty familiar with the MPG the truck gets say on a normal route? I'm curious to see what you'll see MPG wise. Again I also recommend replacing the muffler right next to the flapper because the pipe necks down there and because that muffler is chambered. The straight through magnaflow add's the slightest amount of sound where it's actually really hard to tell any change was made. But it's nice and far from annoying.

Your color truck and those wheels look damn good together btw

Both of mine are long gone or I would man.


Sounds like a good time to come down with the flu lol. Everyone has it right now

You can have it, man. Say- I can drop it off sometime as I'm planning a trip to the boneyard in Albuquerque...………..

Well I said I was not going to modify my 18 but I can definitely tell a difference when that flapper opens. Looks like I'm going to do something after all haha

I just went and messed with mine, it's super easy to rotate with the spring so not sure how much I would benefit really. Does the valve rotate forward or back to open?

Yes- it rotates back...…………….

It can go either way really. It hangs straight-ish down when at rest and I could rotate mine both directions.

Here's a vid showing it if you haven't seen this yet

I've noticed some of the flaps are different with a small hole in them. Mine looked exactly like the one in the vid

Mine was stiff enough to rotate that I have a hard time seeing the exhaust open it up. Would like to have been able to go pro it at WOT but I don't have a go pro..

Never.

Such changes will not require a tune. If you want other stuff done or to disable the AFM/DoD with a muffler change, that will require a tune or a OBD2 disable device they sell on ebay/amazon.

Technically you shouldn't need a tune from it. Never a bad idea to look at the tune though when you make changes. And deleting the flapper and going to a straight through increases flow a considerable amount.

Do you have to? No. Should you? IMO yes. Will it hurt anything if you don't? Very unlikely.

All that being said, I'd get it tuned ASAP because there's a decent amount of power and MPG left on the table on the stock tune.