John in Selma, IN

As far as resonance is concerned both my truck and the T bird have a low speed resonance that I find annoying.  I think that it is a function of the mufflers because I have Dynomax mufflers on both vehicles. Otherwise they sound about the same which is to say pretty good.

I remember reading in some motor test in YBM that the flow of the rammies is about the same as the late model pass car manifolds.  This is probably better than some of the really cheap headers but long tube ones may be better than the rammies.  In order to get the max benifit for the headers the cam should be selected to match.

I like the rammies on my truck much better than the stock setup with that incredably stupid cross over or the somewhat better solution of two right side pass car ex manifolds.  The rammies look right a home and were a big improvement over the stock setup.  But for a cruise-in the long tube headers might impress a little more with the know nothing Scrub crowd.     

In regards to the reasonance, are you running a H-Pipe or a crossover between the exhausts?  If not, then installing an interconnecting pipe has been known to reduce if not eliminate the reasonance depending upon the placement or location of the H-Pipe.  General rule of thumb is to install the interconnecting pipe as close as possible to the engine.  Adding an H or X pipe also invariably increases the torque value so it’s good to do it for that reason if no other.  If your duals are already interconnected, then never mind as there's obviously other factors at play here.

I have wondered if the exhaust crossover in the intake works like a small H pipe.  Many guys are blocking that passage to prevent burned paint on the intake manifold.  I know that blocking the crossover causes more noise out the tailpipes.  I have a friend that years ago heard my flathead powered car run down the street, and he said, "you have the crossover blocked, don't you?".  It had steelpacked mufflers and did have a distinctive "rap" to it.

John

Well to add to the confusion on the Bird I do run a cross over between the collectors on the headers and usually block the under carb crossover at both heads with a thin piece of steel.  The resanance is worse or at least more noticable on the Bird.  The truck's exhaust system is a set of a rammies and no crossover but the under carb crossover was open.  The exhaust outlets on the truck discharge under the bed behind the cab.  The engine in the truck was a pretty tired out 292 and the T birds engine was pretty much as shown in my profile.  The mufflers are 2 1/2"Dia x 22" long Dynomax (they fit in the X member) on the Bird,  and 24" long 2 1/4"Dia on the truck.  I got the truck with stock type '56 ex manifolds and a Gabriel's horn pipe on the left side to 2" glass packs then necked down to 1 3/4" tail pipes somewhat rusted away. What was left of them went to the back bumper.  It had a distinct glass pack sound but no resanance. 

Even with the tired engine the truck picked up noticably with the new setup and I really like the Dynomax for very low pressure drop at flow.  As you may know they have a bent deflector to turn the flow around which in theory reduces turbulance and therefore pressure drop. They advertise no more pressure drop than a straight pipe which isn't true but I did flow the 2 1/2 inch Dynomax once and they were much lower than a set of 2 1/2" glass packs.

Doug, I was afraid you were going to say you already had crossovers.  Don’t have an answer for your reasonance.

But for everyone else, here’s my take on what happens with an H-Pipe in place.  The crossover in the exhaust smoothes out consecutive firing exhaust pulses within an exhaust pipe.  A V8 by design inherently has two cylinders on each bank that fire consecutively which in turn makes for an increase or surge in exhaust pressure.  The crossover relieves the excess pressure that’s created by the second firing and allows this pressure to bleed off in the other pipe that’s suddenly devoid of an exhaust pulse.  The crossover in the intake would have a similar effect but not near as pronouced due to being much smaller in size than the exhaust system itself and basically only working off of one cylinder on each bank rather than all four.

As has already been mentioned, spark plug placement would be the main issue with trying to retrofit a set of scrub block hugger headers on the Y.  For the trucks, there are already a good number of long tube headers available which would be the better choice in that instance.  On the cars, the Y motor mounts are simply in the way due to their central location.  The scrub engines have the motor mounts more to the front thereby permitting a more centralized outlet for the exhaust when using the block hugger design.

     I think (careful now) that the tailpipe size and diameter affects the resonance thing also. When I converted the Ranger from Tail pipes to 3' in Front of the rear wheels I picked up some that wasn't evident before. Same mufflers, and headers.

       I have no way to directly compare mufflers except the Magazine tests, I can't afford to buy them all and run tests, but the Flowmasters on the Red car do not resonate badly. I do run an X pipe and MANIFOLDS. It has been my experience that the cast iron manifolds absorb some of the frequencies that cause the problem. I think that muffler or total exhaust volume has a major effect on this by evening out the pressure spikes Ted was talking about. In talking with a friend who was in engineering at MareMount the muffler and Cat volume is part of the deal. Also note that when we used to replace factory exhaust systems on motorcycles, the smaller volume "Shorties" developed a much harsher sound, indicitive of higher sound wave amplitude, Sounded good to us but I'm not convinced we went any faster. Might help to explain my lousy hearing now though.

Automotive exhaust systems will ring if you have them isolated and hung from rubber mounts like we often do. Take a hammer under there and give it a lick. My buddy made his Flowmasters sound a good bit different by welding pair of 1/4 thick x 2 inch ID washers on the flat sides of them.