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High Flow Exhaust Overhaul

FirstExplorer

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City, State
Flower Mound, Texas
Year, Model & Trim Level
1991 XLT 4WD
Hey group, new to the modified forum...mostly lurking in the stock forum. Today, I had a Magnaflow high flow catalytic converter and Magnaflow exhaust system installed on my 1991 XLT 4WD. What an amazing difference!! So far, I have only done some city driving and the computer may need about 50-100 miles to adjust, but wow! At city speeds of 45mph, I barely have to press the gas pedal...it just practically glides on idle power. Nice low growl at idle to about 2000 rpm, after that very quiet. Instant start up...one crank and it lights off...this is new. Very, and I mean very smooth idle.

Question for the group: I keep real clean Wix filters in the stock box, but am interested in the KKN or KN cold air intakes. I have read some mixed reviews and there are many who believe this set up fouls the MAF. Also, has anyone used the KN filters available for the stock filter box?

BTW, I had an ignition system flush done and bye bye to the valve pinging.
 



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It won't foul your MAF, you won't get any extra power, and whatever you are feeling from your exhaust swap is likely due to cleaning your injectors unless there was something wrong with your stock exhaust.

You have picked up a few horsepower if you are lucky, but I guarantee you cannot feel that through the specially calibrated butt dyno. I have 3.27 gears on a totally stock engine, and it cruises along at 45 without much weight on the pedal either.

Now, if you were to go all out with breathing mods, you might get more of a cumulative difference, but honestly, you aren't gonna see much with these modifications. I mean, if you went all the way with headers, larger MAF, TB optimization, port matching, intake and exhaust..... Of course, it would be helpful at that point if you could adjust your timing slightly. Really, for all of that to come alive, what you really need is a different cam.

That being said, a KKM intake looks real nice. But this kind of improvement in your intake will only really cause changes at WOT or fuel mileage for normal cruising.

I am not trying to put you down, but unless an engine needs more airflow, improvements in airflow will do nothing. The stock exhaust isn't much more restrictive than the stock intake system, therefore, you can't improve much on an unmodified explorer. Plus, the stock exhaust flows nearly equally to the stock exhaust manifolds.
 






I understand what you say about the "feel" of extra mojo, butt, the throttle response is much more sensative. I have been driving this truck for 18 years and I know every little subtle noise and habit. You telling me that replacing an old technology 18 y.o. cat with newer and improved hi-flow cat does nothing for power response is absurd. There is a difference. I think you are incorrect. I know you are.
 






I understand what you say about the "feel" of extra mojo, butt, the throttle response is much more sensative. I have been driving this truck for 18 years and I know every little subtle noise and habit. You telling me that replacing an old technology 18 y.o. cat with newer and improved hi-flow cat does nothing for power response is absurd. There is a difference. I think you are incorrect. I know you are.

I didn't say it does nothing. I said it does very little. I used to do quite a bit of tuning and modification work in the past, believe me, I know what modifications do. Feeling placebo effects are nothing to be ashamed of, and I am not telling you the exhaust will do nothing for your truck, I am just saying it will do very little. If I still had access to a flow bench, I could work it all out for you, it is actually fairly straight forward, since there isn't a HUGE change in air density between the ports and the cat.....

I wasn't trying to put you down. I was just saying, sit back and think about it for a minute. I am sure you have seen it before, excitement always makes something feel better. Besides, it is not like you were wasting money on that exhaust. You were replacing 20 year old parts that will probably soon be bad anyways. For relatively little money, not much more than you would on an OEM replacement, you just bought that part of your truck another 20 years of life AND you got a much nicer sound I am sure. I'd say that is money well spent. You were right there at the normal age threshold for those parts to have rotted away into nothingness anyways.
 






The dyno charts from both Magnaflow and K&N show a range of torque and HP increases for various vehicles, and that's only with a cat-back system and not with a new high flow cat. If both of these mods were installed, the HP increase would be an average of
+15 and same for torque. It is modest but would be noticable.

I believe that the Ford Explorer stock engine is literally suffocated in California/EPA driven equipment. What would happen if you just removed the intake gear and from the catalytic converter aft? Would you see power and torque increases? I would say yes.

Aside from this debate on whether "performance" mods actually work or are simply in your head, I really would like some feedback on the MAF fouling issue with cold-intake filters.
 






The dyno charts from both Magnaflow and K&N show a range of torque and HP increases for various vehicles, and that's only with a cat-back system and not with a new high flow cat. If both of these mods were installed, the HP increase would be an average of
+15 and same for torque. It is modest but would be noticable.

I believe that the Ford Explorer stock engine is literally suffocated in California/EPA driven equipment. What would happen if you just removed the intake gear and from the catalytic converter aft? Would you see power and torque increases? I would say yes.

Aside from this debate on whether "performance" mods actually work or are simply in your head, I really would like some feedback on the MAF fouling issue with cold-intake filters.

See, this is why you "feel a change". It is because you have convinced yourself there is one. An explorer is fitted with a high flow cat from the factory, these are not the catalytic converters of the late 70s early 80s.... The exhaust is actually fairly well suited to a stock engine as well. I will bet you $100 that if you put your truck on a dyno, you would not see more than 3-7 HP improvement. You cannot feel ~5 horsepower. I can give you two identical cars that differ in horsepower by that much so you can see that fact. Plus, any improvement will not be in the part of your RPM range where you need it anyways, low to mid range, it will be at the high RPMs for WOT situations.

Never trust a dyno chart from someone trying to sell you something. It is amazingly easy to manipulate dyno results..... Trust me. Also, K&N shows improvements on their charts even for their panel filters that replace OEM panel filters.... A stock air box is a bigger restriction than a filter, and in most cases, a stock air box isn't even a restriction on vehicles.... I have had stock air boxes on a flow bench with OEM paper filters, K&N filters, and without any filter at all. The stock air box almost always flows exactly the same volume of air.

Now, moving on. No, a cold air intake filter will not foul your MAF. I have heard some stories of people doing it by over-oiling their filter, but, you would have to have them soaked pretty well to do that even. As long as you apply common sense when cleaning them, you never have cause to worry. There are thousands and thousands of cars on the road running aftermarket intakes, K&N filters and the like. If any of those things were detrimental to engine life or the life of the parts, they would have to state those things or be subject to lawsuit. There have been lawsuits regarding those types of things and warranty disputes from the adding of a K&N filter or such, and in all cases, it has been agreed upon by the courts that these products will not negatively impact engine life or the life of the components.

If you decide to run an aftermarket filter (of reputable brand and quality such as K&N and not an ebay no-name special), it will never have any effect that would degrade the life of the components of your engine. There is some possibility that it could allow more contaminants by, but most people change their oil before it is necessary anyways, especially if you follow the 3000 mile rule, so you don't have to worry about it.

I will tell you this right now. If you buy a K&N intake, I am so certain that it will not foul your MAF, that I would tell you right now that if it ever did (assuming you maintain it properly), I would send you a new MAF.

Still, none of it is necessary, the engine is not suffocated. Unless you are planning on making more changes to your engine, there is really no sense in doing it. Your stock air box flows as much air as your engine can handle in stock form. You seem to be getting angry about me telling you this stuff though and have it set in your head that these things are going to make your Explorer faster, stronger and better, so why are you even asking these questions in the first place. You are asking if a filter is going to make your truck better and are probably going to put it on regardless of the answer. Your exhaust swap was a good swap, but only because it is replacing worn out components that are nearing the end of their usable life and are giving you a nifty sound.

If anyone disagrees with anything I have said, I defy them to put their explorer on a dyno and prove otherwise.
 






I'm more interested in this "ignition system flush". Need to get rid of my pinging.
 






Some thoughts

I myself have also upgraded from the stock air box to a K&N FIPKII and did my own Magnaflow "cat-back" exhaust on my 99. Granted, it's different from the 94 with the OHV. But I do have to point out Aldive's mileage monster, from the minor changes that he did with his he gained many MPG and even HP and torque. Granted the biggest gain he had was with the underdrive pulleys and the computer tuning. But he also made adjustments using the CAI and throttle body and MAF size increases, and he only went with a Flowmaster exhaust which doesn't even flow as well as Magnaflow. The gains can be considered minimal but the synergistic effect is the goal. In the end an engine is a big air pump, more air in more air out. Now I've never dyno'ed my truck and probably won't any time soon. And I can't make any guarantees about what parts do what.

But someone like Al who took that much time to research his parts and put them in and manage to gain so many MPG is pretty amazing. Yes switching out aging parts is going to make a huge difference and if you've really owned the rig for 18 yrs you've felt it lose any power slowly over time, and opening it back up to how it was will be a big change. I'm not saying you didn't gain some power, and I'm not saying you should've just gone with stock replacements. But I'd say you would gain something at least from allowing more air in and out. Search for the mileage monster and read his posts, he dyno tested after every change. He got gains from almost every part he added.

Another thing I would like to add too, I used to have an 88 Caprice Classic and I opened up the air filter to expose more air and I noticed right away that my K&N round filter allowed the engine to rev higher than it did with the stock air cleaner assembly. I don't know what exactly that meant, but it was nice to see it use more of its power band before shifting. Best I can say is research, research, research. You'll find lots of info online, finding legit data can be a struggle, but when you find enough data that matches, you're probably on the right track.
 






An exhaust does make a difference, BUT the difference really depends on what was on there before. It will be less of a difference going from a well designed stock system or other aftermarket replacement to a straight-through magnaflow, than going from a rusty old stock system that's too small, to a straight through that's slightly larger.

I'm sure there's a good difference, going with the magnaflow cat and the muffler, especially if you stuck with the 2.25" piping all the way back. Even more so if you used a mandrel-bent rear pipe.

I went from a stockish 2" exhaust to a 2.25" Dynomax Super Turbo, with the Dynomax rear pipe, and it made a very obvious difference. The stock cat is fine and didn't need replacing.

As for the intakes, you can do ok with just using a drop-in K&N air filter for a budget setup, but the KKM is definitely worth it, especially with a straight-through Magnaflow.

I've had a KKM for years, and it doesn't foul the MAF or anything. The oil that gets in the intake tube comes from the hose that connects the oil filler neck to the intake tube, so the vapors are burned. You can save a little and get a generic MAF adapter and use a K&N filter instead, but I see no reason not to get the KKM, as the aluminum MAF adapter is top quality, and the S&B filter it comes with seems to be better than a K&N.
 






Thanks to everyone for the good posts. As for the throttle body flush, so far I have had no pinging afterwards. However, I did refill with premium and am running a whole bottle of Lucas cleaner through the system. After I run that through, I will try regular gas and report back.
 






I've had a KKM for years, and it doesn't foul the MAF or anything. The oil that gets in the intake tube comes from the hose that connects the oil filler neck to the intake tube, so the vapors are burned. You can save a little and get a generic MAF adapter and use a K&N filter instead, but I see no reason not to get the KKM, as the aluminum MAF adapter is top quality, and the S&B filter it comes with seems to be better than a K&N.

Is there an increase in the interior noise level with the KKM mod? I have not been able to find sound files or vids for the X, but there are plenty for V8s and it seems fairly loud. I want to do this mod but also want a quiet interior.
Thanks
 






The KKM, like all cold air intakes, removes the plastic air box, and so it makes more apparent noise under the hood, but really only under load, either when accelerating, climbing hills, etc. It's a bit like exhaust drone, and is at such a deep level that it's not really annoying to me, and if anything, just makes for a really mean sounding X with the combo intake/exhaust. Between the intake and exhaust, blipping the throttle or really getting on it gives a roar rather than just the sound of engine noise. There is probably a slight increase in noise under regular acceleration, but I'm probably used to it. At highway cruising speed, there is little noise difference, unless the engine is in the RPM range that makes for some exhaust drone. The road/wind noise is louder at speed, until you accelerate or are going up a hill.

I also had the KKM before I had the catback exhaust, and even with a stock-like exhaust system, it made a noticeable difference. I also had a K&N stock-type replacement air filter before that. Now with a KKM and a Dynomax exhaust, I would find it hard to go back. I don't mind the intake noise under throttle or exhaust drone since the tone is so deep and the growl really fits the 4.0L and the sporty nature of my ride.

If you're looking for quiet, luxury-car type noise levels, you're best off with a stock replacement exhaust (Walker makes a great one with the Quiet-Flow muffler for the 91-92) and either the stock air filter or a drop-in K&N. You can also find the FRAM Airhog K&N knockoff filters around the web for cheap. Rockauto and a few other places have them, $6-8 or so.
 






I installed the KKM cold air intake kit yesterday and there is a very noticable increase in throttle response. Cabin noise is about the same, except on acceleration there is a hollow sucking sound. In road test before and after, on the same stretch of road at 45 mph in O/D, before the cruise rpms were right at 2000, after 1600.
 






I installed the KKM cold air intake kit yesterday and there is a very noticable increase in throttle response. Cabin noise is about the same, except on acceleration there is a hollow sucking sound. In road test before and after, on the same stretch of road at 45 mph in O/D, before the cruise rpms were right at 2000, after 1600.

did you change gearing in your rear end or something? An air filter won't change your cruising RPMs, that is all gearing. If it is geared to run at 1600 rpms at 45, and isn't, then there is something wrong with your truck.... I'm not looking to get on your case, but this is how bad information gets spread if you keep making these claims and attributing them to snake-oil parts or giving the parts too much credit.
 






making these claims and attributing them to snake-oil parts or giving the parts too much credit.


It sounds like you have plenty good expertise in auto engineering, and I admit that I am a dabbler. My professional expertise lies elsewhere. I probably did not express my opinion in the most correct terms, but I don't believe that these performance upgrades are snake oil by any means. You can comb these forums and find dozens of posts claiming performance improvements.

I have driven every mile on this Explorer, and I notice a significant improvement in the performance and drivability. If this type of upgrade doesn't work, maybe you should instruct all those NASCAR and Formula drivers to place a stock exhaust system on their cars and hum around the track as quiet as a Lexus LS460 because it is otherwise all in their heads.

I have found your posts to be quite informative, but also bordering on rude.
It takes all types to make a good forum. Amateurs and experts can work out a lot of issues together in a friendly, community-minded way.
 






It sounds like you have plenty good expertise in auto engineering, and I admit that I am a dabbler. My professional expertise lies elsewhere. I probably did not express my opinion in the most correct terms, but I don't believe that these performance upgrades are snake oil by any means. You can comb these forums and find dozens of posts claiming performance improvements.

I have driven every mile on this Explorer, and I notice a significant improvement in the performance and drivability. If this type of upgrade doesn't work, maybe you should instruct all those NASCAR and Formula drivers to place a stock exhaust system on their cars and hum around the track as quiet as a Lexus LS460 because it is otherwise all in their heads.

I have found your posts to be quite informative, but also bordering on rude.
It takes all types to make a good forum. Amateurs and experts can work out a lot of issues together in a friendly, community-minded way.

The people at nascar and formula drivers put tuned exhaust systems on their vehicles. The diameter of pipe (and hopefully the length between bends as well as radius of bends) is dictated by the characteristics of the engine. Then further tuning is done on the engine to match the characteristics of the exhaust flow. They don't just put big free-flowing exhaust on and claim 15whp on the butt dyno.

If my posts are bordering on rude, it is because I have tried to explain things to you and you keep arguing with me about them and putting up information that is misleading. I am aware you have been driving your vehicle since new, however I am certain the performance has degraded over the years of many components and you are demonstrating a tendency to compare the performance of the new components to what I can only judge as being the performance of worn out components.

Furthermore, I never said that an increase in performance is all in your head, I am saying your perception of an increase of performance is all in your head. Each of the changes you have made will only make minuscule changes to the performance of your vehicle that should be unnoticeable when compared to stock. They should have a cumulative effect that may be borderline noticeable, but not in the ways you are stating. For all intents and purposes, your mods should have returned to you the feeling of driving the truck when it was new (though in actuality, you may experience improved fuel economy and slightly more horsepower especially at WOT at higher RPMs).

Now, as to whether I can search this site and find other people attesting to an increase in performance and feel. Well, I can link you to people stating for certain they have an increase in horsepower using an intake tornado.

Now, lemme ask you some stuff to think about on your own. How many vehicles have you test driven in your day? Have you ever test driven 2 identical vehicles at a dealership? Did you know that completely stock cars brand new can differ by as much as 5-10 horsepower? Some of this due to the different adaptation by the ECUs, some of it temperature differences, yadda yadda. Can you take your Explorer out on a winter day and feel how much more power it has than it does on a normal day in the fall? Can you feel the difference in horsepower when you put ethanol and non-ethanol fuel in your Explorer?

Now, sorry if I have sounded rude, but I must retort in kind. I have tried to explain to you that these things don't make MUCH difference. You keep trying to claim I am saying they make no difference and that you know better because you have owned your explorer for 20 years and a nascar does not have an explorers muffler and 2.25" diameter crush bent pipe. What I have been trying to tell you all along is that these parts aren't making a HUGE difference over stock, the difference is slight. There is certainly a difference, but, you are making these huge claims that don't match the difference between two products. People need to understand that these are small differences, minor changes that all work together and end up with an overall gain however slight. Someone mentioned aldive's mileage monster, and while I am of the opinion that his HHO generator violates the second law of thermodynamics, the rest of his thread provides a great reference. He is listing TONS of modifications and noting the VERY small changes that accompanied each. Of course, his biggest change came from tuning, which is unfortunately VERY hard to do on a pre-obdII vehicle, but still, it illustrates a good point. This is a vehicle where he was careful about measuring and documenting and found very slight incremental improvements. If I were to take your threads at face value, I would expect an air filter, exhaust and an oil change to have transformed my truck from the well cared for 20 year old brick that it is into something with performance that exceeds anything ford dreamed of when they produced this. My truck has 3.27 gearing and cruises down fairly level sections of highway at 1600 rpms. If I put on a KKM intake, will that go down to 1200 rpms? no.....
 






Interesting reading here.... I will just stick with the drop in aftermarket filter, and my own magnaflow cat and "cat back" exhaust, which is a dumped magnaflow in front of the axle.

My question, will 2.5 in exhaust pipe be too much for the v6? I mean it is feeding everything through a 2.25 already, so would the extra quarter inch make that much of a difference?

I have a 5 speed in mine, so I cruise @ 60 @ about 1300 rpm w/ 3.27 rear.
 






No, I believe 2.5 inch is not oversized for this engine.... 2.25 and 2.5 are probably both ends of what is optimal for the engine if you have are primarily stock....
 






No, I believe 2.5 inch is not oversized for this engine.... 2.25 and 2.5 are probably both ends of what is optimal for the engine if you have are primarily stock....

Yes the engine is stock, and will probably stay that way. I've read that headers are pretty useless on a stock engine. However the set for 265 from summit it's almost hard to pass up. Peoples thoughts on the summit set of headers?

My only expirience with headers was on my vortec 350 from my 97 z71 that had a programmer, CAI, and aftermarket exhaust....there was a "seat of the pants" thrill. It also got better MPG's but I'm sure it was a combination of all the above mentioned items.
 



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Yes the engine is stock, and will probably stay that way. I've read that headers are pretty useless on a stock engine. However the set for 265 from summit it's almost hard to pass up. Peoples thoughts on the summit set of headers?

My only expirience with headers was on my vortec 350 from my 97 z71 that had a programmer, CAI, and aftermarket exhaust....there was a "seat of the pants" thrill. It also got better MPG's but I'm sure it was a combination of all the above mentioned items.


I wouldn't say useless, just not a lot of ROI. Depending on how you drive, you can see an improvement on mileage on a first gen. The biggest factor here would be a cumulative effect if you paired it with a decent flowing exhaust system and a reasonable induction system (like optimizing the throttle body and whatever other minor flow improvements you feel like doing, portmatching, smooth good flowing intake. Doing any of them by themselves will barely make a difference, all together and it will actually do quite a bit... though, the cost of it all is hard to justify for the small gains.
 






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