demon 3" exhaust routing?

[northeastmopar]

I have my X pipe hooked to my headers. 3" pipes. They seem to fit fine in the two indents in the transmission crossmember. I am now trying to figure out where I need to locate and what size and shape mufflers? Do the mufflers just go up against the floor of the passenger area or further back? I was thinking about a 4" thick muffler. I am thinking I want something with no drone and I understand there are a few which do well, but don't know which ones? Chip Foose always talks about the magnaflow? Should I put a pipe off the xpipe to move the mufflers further back? Any pictures of how your setup is. I have Dougs headers with the dougs 3" x pipe on my 340 motor. Where do I go from here?

 

[dragondan64]

First question is what type engine are you running to need 3 inch exhaust? Street engines that aren't full race built don't need 3 inch exhaust. The back pressure needed for street engines can be exhausted through 3 inch pipes and it might kill performance. I have 10 second big block cars running 2.5 inch pipes out the back of the car and tried 3 inch and lost et and low end power so switched back to 2.5 inch. Just curios what your engine is?
Proper exhaust-pipe size is a function of both engine output and displacement. The higher the engine’s output, the larger the pipes should be. Likewise, larger engine displacements call for bigger pipes. But you don’t want to become a victim of “More’s Law,” either: While up to a point reducing exhaust restriction generally helps both power and gas mileage, going too large can over-scavenge an engine and actually decrease engine output as well as fuel efficiency. The accompanying exhaust system size guidelines are compiled from Flowmaster Mufflers and RoadkillCustoms.com data. To avoid becoming a restriction, all muffler and catalytic converter inlet and outlet sizes should correspond to the exhaust pipe sizes, and design your exhaust system to use the minimum number of bends.

 

[1Fast340]

First of: fourstroke engines dont want any restriction,thats BS and if they for some weird reason make more power with a exhaust restriction something is way wrong elsewhere.


Back on topic. have a good look under the car and you will find that you have some space under the backseat that is made to hide mufflers in. magnaflowmuffllers are usualy fairly good. how long of a mufflerbody you want is depending on your skills in building tailpipes ;) you want mufflers with an offset inlet and preferably a center outlet. feel free to ask more if you need any more information.

 

[northeastmopar]

First question is what type engine are you running to need 3 inch exhaust? Street engines that aren't full race built don't need 3 inch exhaust. The back pressure needed for street engines can be exhausted through 3 inch pipes and it might kill performance. I have 10 second big block cars running 2.5 inch pipes out the back of the car and tried 3 inch and lost et and low end power so switched back to 2.5 inch. Just curios what your engine is?
Proper exhaust-pipe size is a function of both engine output and displacement. The higher the engine’s output, the larger the pipes should be. Likewise, larger engine displacements call for bigger pipes. But you don’t want to become a victim of “More’s Law,” either: While up to a point reducing exhaust restriction generally helps both power and gas mileage, going too large can over-scavenge an engine and actually decrease engine output as well as fuel efficiency. The accompanying exhaust system size guidelines are compiled from Flowmaster Mufflers and RoadkillCustoms.com data. To avoid becoming a restriction, all muffler and catalytic converter inlet and outlet sizes should correspond to the exhaust pipe sizes, and design your exhaust system to use the minimum number of bends.

My motor is a built 416 stroker motor. I suspect once on the dyno it will be looking at about 500HP. And yes, it is just going to be a cool cruising street car. My headers are Dougs and the collector on the headers is 3"? So why would I want to right off the header collector reduce things down? Seems that would defeat the header purchase. Secondly, I was thinking about using the 3" up to the mufflers and then go with a 2 1/2" tailpipe section. That should give me back some of that backpressure? Do you still think I am making a mistake?

 

[northeastmopar]

First of: fourstroke engines dont want any restriction,thats BS and if they for some weird reason make more power with a exhaust restriction something is way wrong elsewhere.


Back on topic. have a good look under the car and you will find that you have some space under the backseat that is made to hide mufflers in. magnaflowmuffllers are usualy fairly good. how long of a mufflerbody you want is depending on your skills in building tailpipes ;) you want mufflers with an offset inlet and preferably a center outlet. feel free to ask more if you need any more information.

I was actually looking at the recess in the floor out back. I was thinking of just ordering a pair of stock 2 1/2" tailpipe sections and locating them on the stock hangers that are there and then working backwards to my X pipe through a pair of 3" mufflers?

 

[Bad Sport]

Should I put a pipe off the xpipe to move the mufflers further back?

Yes, the mufflers hang in the opening where the floor rises up to meet the trunk pan, one on each side.

Any pictures of how your setup is. I have Dougs headers with the dougs 3" x pipe on my 340 motor. Where do I go from here?

This is a Dart Sport, but same platform. This will give you an idea.

 

[northeastmopar]

This is a Dart Sport, but same platform. This will give you an idea.

Yes, Thank You. That makes sense. As stated earlier. I wanted to install 2 1/2" tail pipe sections over the rear end and install stock chrome tips. I think I should locate them first along with the mufflers and then fill in between to the x pipe for best fitment? Does that make sense?

 

[AJ/FormS]

Totally. They make pre-bent stuff too. I put the full length TTI 3 inch on my Formula S 366cid clone, with dynomax muffs. My motor dont want no stinking back-pressure. Ran it on my 318-4v too.After a slight retune that 318 did pretty good.Granted the 3inchers are overkill on a 318/so what? The headers cant scavenge into back-pressure.The pipe size to cid ratio, is a minimum, not max.Race motors run open headers; so.....wheres the back-pressure in that? If the pistons have to push the exhaust out, would that be "negative energy"? Anyway thats power lost to the wheels.Sure theres such a thing as "overscavenging". But since headers generally can only be tuned over a fairly narrow rpm band,I wouldnt be overly concerned with it. When the exhaust is hot it occupies a larger space than when it has cooled. That translates to big headpipes.And somewhat reduced tailpipes are possible,if you have fitment issues.For me I solved my fitment issues.So yeah,3inch might be more than a small block needs,85%(pick a number) of the time, but when my engine is pulling hard and money is on the line, I dont want to be thinking about negative energy. I want to be concentrating on banging the next shift, and getting on down the track.
-And BTW, my 366 has over 125000miles on it with those pipes.It has gone 93 in the 1/8th with a [email protected] cam. Lack of backpressure hasnt seemed to hurt it.And just so you know,That system,at full song,is fairly loud.Not annoying type loud, just voluminous. I put turn-downs on it.
-Put backpressure on a vacuum cleaner. See how much that sucks.
End of rant.

 

[1Fast340]

I was actually looking at the recess in the floor out back. I was thinking of just ordering a pair of stock 2 1/2" tailpipe sections and locating them on the stock hangers that are there and then working backwards to my X pipe through a pair of 3" mufflers?

That would probably work! but not sure you want the stock type tailpipes considering that they are probably pressbent, i would want them to be mandrelbent

 

[Dartn440]

Same exhaust under a 72 Dart. I went with Flowmaster which requires them to mod prior to ship.