K&N Airfilters

[ni7irs]

On to a more important topic. I have a 7.4 MPI. It makes what I charecterize as a squeeling. After several posts here regarding the belt, pulleys, alternator, etc. and after all of them checked out, I spoke to a local shop that said the engine sucks a lot of air and whistles while it works. Some other people have said the same thing.

However, in my regular engine checks, I keep seeing the flame arrestor covered in gunk. This cannot add to performance. In reading one of the admiral's posts, he mentions the rubber from the belts. This is clearly a large part of the gunk. After remvong the flame arrestor, I see that the inside of the intake is covered in the gunk as well.

I know about the debate with K&N vs stock flame arrestors, but how can this crap going into the engine intake be any good? Doesnt it make sense to install the K&N which increases surface area and keeps out more of this stuff?
Can anyone see why it would hurt?

The only thing I saw that would cause me concern is the assertion that 7.4L MPI engines are calibrated as to how much air comes into the engine. If this is true, then its possible that the engine would run leaner with more air which is not a good thing. Does anyone know if this is true?

 

[v8power]

Re: K&N Airfilters

I wouldnt think it would run lean, It should self adjust, Does it have a mass air flow sensor, MAP sensor or o2 sensors? If it does, it will adjust itself for the change in air flow.. Switching to a K&N filter is a good idea for performance and cleaner intake air but I dont think they are coast guard approved. But how often does a MPI backfire?

IMO

 

[Philster]

Re: K&N Airfilters

The best thing is to get a good supply of cleaners and change them often. Nothing fancy needed.

Also: Are your belt pulleys rough/rusty and beating the belts to death? They need to be smooth.

 

[littlebookworm]

Re: K&N Airfilters

I would strongly urge you not to use any "flame arrestor" (note: NOT "air filter") which is not Coast Guard approved. If something does happen, you will be liable and your insurance will not protect you. Your problem seems to be that pullies are eating you belts. That's why you're getting all that gook coming into your air intake. Therefore, you need to find out which pulley or pullies are bad and replace them and the belts. Once a belt starts to shred, it will keep on shredding even if you change the pulley. Find the cause and repair it rather than treating the symptom and putting yourself at risk. Just my thoughts. Hy

 

[Fishermark]

Re: K&N Airfilters

K&N does make marine air filters / flame arrestors... but I agree with the above. You need to fix the source of the problem causing the debris - not simply filter it out.

 

[bigdaddypt]

Re: K&N Airfilters

Out of curiosity...are you using marine belts or did you put auto belts on it? If you used auto belts, that's probably why they're getting eaten. My mechanic explained that the pulleys on marine engines are at a different angle than cars, so if you use an auto belt, the pulleys will eat them up.

 

[Sunking22]

Re: K&N Airfilters

I think this is my issue as well, I've been getting a buncha fine black "powder" (which I now know to be rubber) clogging up my flame arrestor. After reading this thread I went and inspected my pulleys and sure enough the crank pulley has some mild pitting due to rust - thanks for the answer!

 

[skipdow]

Re: K&N Airfilters

Just to confirm K&N does make a coast guard approved flame arrestor. I bought one recently.

 

[John_S]

Re: K&N Airfilters

Yes they do make flame arrestors, and the CG number is stamped on the cover edge.

I have been running one on a carb for about 4 years. I can't say if it improved anything, because too much other things were changed at the same time. I'd rather doubt you would feel any change.

Only the very latest engines have O2 sensors. I don't know if the computer can adjust or not. I think not, but not sure. There wouldn't be much of a market if it did cause a lean condition. Before I purchased, I saw many a comment that its best feature is filtering, not any perf gain.

I have never had an issue with belt dust. I just changed my belt for the first time this year, and that was only because of a service bulletin (plastic power steering pulley). I clean the K&N every year, and it is only slightly dirty with oil near the vent lines.

 

[LAC_STS]

Re: K&N Airfilters

I dont know if there is a difference between marine and auto K&N filters but I have always been a fan of K&N until I bought a new Cadillac about a year and a half ago.

I did what I usually do and put one in shortly after. But then I started reading about other problems with them on the cadillac forums.

This is not an issue with a marine engine with no MAF but on my cadillac (others reported this as well on the forum) the oil in the filter combined with the crap it lets in throws the MAF off and makes the check engine light come on. In my case the MAF had to be replaced.

On the cadillac forum a couple techs and others who are very into it all have said that the K&N lets in a lot of dirt and other crap.

I havent saw any kind of advertising for an auto K&N that said it is a cleaner filter, just that you can get better performance.


So maybe marine ones are better at filtering but a K&N for a car lets in more air supposedly for better perf but at the cost of letting in dirt.

 

[John_S]

Re: K&N Airfilters

I dont know if there is a difference between marine and auto K&N filters but I have always been a fan of K&N until I bought a new Cadillac about a year and a half ago.

I did what I usually do and put one in shortly after. But then I started reading about other problems with them on the cadillac forums.

This is not an issue with a marine engine with no MAF but on my cadillac (others reported this as well on the forum) the oil in the filter combined with the crap it lets in throws the MAF off and makes the check engine light come on. In my case the MAF had to be replaced.

On the cadillac forum a couple techs and others who are very into it all have said that the K&N lets in a lot of dirt and other crap.

I havent saw any kind of advertising for an auto K&N that said it is a cleaner filter, just that you can get better performance.


So maybe marine ones are better at filtering but a K&N for a car lets in more air supposedly for better perf but at the cost of letting in dirt.

Standard mercruiser flame arresters look like strips of stainless steel, riveted together, with gaps between. Sand can get through those cracks. They are flame arrester only, and not designed to filter dirt/dust. ie you are on the water not the country seasonal road. Sand will not pass through a K&N flame arrester. While I do not have any data, I suspect a K&N flame arrester does not filter as well as a car filter.

While they are marketed for "performance" with the theory being free-er flowing and the base providing a curved entry vs a sharp one, have not seen any dyno data that would verify that for a boat engine. Theory without data is hype or marketing. I suspect there is some improvement, but would need to be over 10hp to have a chance of noticing.

 

[ni7irs]

Re: K&N Airfilters

Sorry for the long delay in responding. Yes, I replaced it with a genuine mercruiser part. The pulleys seem to all be in alignment, I cannot see any that are out of alignment. I replaced the tensioner pulley along with its bearing assembly. I pulled the alternator and that checked out fine too with no play.

Short of tightening the tensioner more, I am not sure what to do. All of the pulleys seem to be rust/pitting free. Also, I took it to a marina in Michigan City and he said that the 7.4 MPI is known to eat belts and to just wipe down the flame arrester. Some people have said that the 7.4 MPi sounds like a whistling gopher, but who knows if they dont clean their flame arrestor.

Believe me I would rather treat the symptom and not the problem, the problem being finding the problem or if there is a problem at all.

This is my first 7.4 MPI.