I had a flowmaster 40 series installed yesterday on my 86 F-150 302 FI along with new pipes(not duals though). I basically just replaced the stock exhaust from the cat back with the same thing with the exception of the new muffler (stock size pipe with single entry & exit flowmaster 40 series muffler).

My problem is that it is VERY quite (honestly) and it "puffs" when I let off the gas (I am assuming it is a back pressure problem). I did not want an obnoxious loud but the deep throaty sound of a 40 series flowmaster. Does anyone now what could be wrong or should I expect a quite sounding system since I did not run true duals? Could it be my CAT's are bad? Would removing the cat's make it sound more like a true 40 series or would it still "puff"?

Basically when it idles you can tell I have a new muffler but when I give it any gas at all, it sounds very quite just like stock! You can't even tell it's an aftermarket muffler????

Please help if you can!!

Thanks for the help!!!!!

 

do you happen to have 2 cats? cause that reduces sound alot right there. if so go buy one high flow cat and u will love whaqt u get!

 

Yes, I do have 2 cats. The large one in the front near the exhaust manifold is the original (I think) and has a metal shield around it. The second one is about a foot past that one going towards the muffler. It is an aftermarket cat that looks almost new from the outside and it is a very SMALL cat (the brand name I think is catalytic converters unlimited).

Do you think if I cut the first one off and keep the second small and newer one it would be a lot louder?

Thanks again for the help!

 

I have Magnaflow, but from all the posts I've read about the Flows, the 40 Series is fairly loud and throaty. Are you sure they installed the 40 series? My dad had the 70 series installed on his Dodge and it was just like stock, he had it removed and replaced with the 40 series and it was loud. Maybe the shop made a mistake? Are the Flow mufflers marked somehow where you can check?

Just my guess.......

 

I measured the muffler and it has the exact dimensions that the flowmaster 40 series has. I think I have decided it is one of the catalytic converters. I was wondering if I removed the one closest to the engine and keep the other one, would it make a difference?

Also, how difficult would it be to cut off the converters myself and replace them with a straight pipe from an auto parts place? What would be the cost and time required?

Thanks

 

Farm,

I had a 91 F150 with the 2 cat setup. I learned the device closest to the engine is just a pre heater and the device closest to the muffler is your cat. Your truck being FI that it is, most likely has a puter on it. A preheater has very little if any effect on backpressure on the engine. what you could do without messing up the computer is have a shop take the preheater and stock cat out, have them install 1 high flow cat. Flowtech and Magnaflow make a good one. Taking off the preheater won't have any effect on the engine, a high flow cat with that Flow 40 on there should really wake up the exhaust note. Good luck,,,,,91

 

Thanks for the advice! That's probably the route I'll go but I am still considering trashing the entire set up and going with a straight pipe.

Thanks

 

When you say 'puff', are you talking about smoke, or a sound the exhaust is making.

If smoke, all exhaust systems are coated with a rust inhibitor to keep them from rusting in storage. It will take day or two to wear off.

If sound, was this sound present before - or were you able to tell before the exhaust system change?

 

The "puff" is the sound the exhaust makes when the gas pedal is released. Basically a lot of back pressure. Also, the sound comes from underneath the cab of the truck as well as the exhaust pipe end at the rear of the truck. The sound did occur before but it wasn't as noticable as it is now. I have check the welded points and it looks like they are all in good shape with no leaks. I had planned on cutting off both converters with a saw and then purchasing a "flared" straight to put in it's place and just clamp the flared ends down.

If I did this, I would of course keep my cat's, just in case I have to install them for inspection purposes in the future. Currently the county I live in doen NOT test for air quality from the exhaust, so this is a plus.

Let me know what you think.

Thanks for the help!

 

I looked under the truck last night and the "puffing" sound is coming from the pre-heater, which is located right before the cat. This looks to be the original pre-heater for the cat, so I'm sure it's got to be bad after almost 17 yrs.... I might go ahead and cut the cat of to, since it will help my performance and sound. I am going to keep it though, just in case it won't pass inspection next July.

Thanks everyone