New Dual Exhaust

[73Coupe]

So I made an appointment for the 18th this month. It'll take a couple days.

I was able to print out a few photos plus the diagram from TTI and show my shop, so he'll install as I wish. I will have him run the tail pipes below the rear frame rails like original and as pictured under Alan's car above, except they will go straight back, turning down just before the back of the bumper. I might also have him tuck them back a bit more so there's room for a future hitch, as Will did with Jazebelle.

@75LandYacht thanks for the photos as well; I see there's enough room to tuck the exhaust pipe above and to the left of the shift linkage shaft. Do you ever notice any heating of the floor board in this area?

I also found an original style hanger for the left side above the axle - Accurate exhaust had them in stock still, so I ordered one. The shop can make a bracket to attach it. I'll also just use a walker hanger for the tail pipe.

 

[75LandYacht]

So I made an appointment for the 18th this month. It'll take a couple days.

I was able to print out a few photos plus the diagram from TTI and show my shop, so he'll install as I wish. I will have him run the tail pipes below the rear frame rails like original and as pictured under Alan's car above, except they will go straight back, turning down just before the back of the bumper. I might also have him tuck them back a bit more so there's room for a future hitch, as Will did with Jazebelle.

@75LandYacht thanks for the photos as well; I see there's enough room to tuck the exhaust pipe above and to the left of the shift linkage shaft. Do you ever notice any heating of the floor board in this area?

I also found an original style hanger for the left side above the axle - Accurate exhaust had them in stock still, so I ordered one. The shop can make a bracket to attach it. I'll also just use a walker hanger for the tail pipe.

View attachment 160670

No issue that I’ve noticed.. glad I could help ya.

 

[75LandYacht]

So I made an appointment for the 18th this month. It'll take a couple days.

I was able to print out a few photos plus the diagram from TTI and show my shop, so he'll install as I wish. I will have him run the tail pipes below the rear frame rails like original and as pictured under Alan's car above, except they will go straight back, turning down just before the back of the bumper. I might also have him tuck them back a bit more so there's room for a future hitch, as Will did with Jazebelle.

@75LandYacht thanks for the photos as well; I see there's enough room to tuck the exhaust pipe above and to the left of the shift linkage shaft. Do you ever notice any heating of the floor board in this area?

I also found an original style hanger for the left side above the axle - Accurate exhaust had them in stock still, so I ordered one. The shop can make a bracket to attach it. I'll also just use a walker hanger for the tail pipe.

View attachment 160670

Take some pictures of the install if you can.. would love to see it..

 

[73Coupe]

Definitely will do!

 

[saylor]

id hand him the stock pics from mr mopar, dont tell him 1 word about how to install it, tell the guys you are gonna go get enough pizza to feed the guys, leave and go get enough pizza to feed the guys, and when you come back you will have the immaculate exhaust.

try not to die -

- saylor

 

[78Brougham]

My exhaust guy did it right in front me. Had it up on the lift, took me under the car, we talked about it, asked me "how's this look"? Took his advice on most of it and let him do his thing. The good guys know what they are doing and don't need any chiming in. Done in about an hour, paid him a buck and a half cash and out the door I went.
It's not rocket science. The more you over think the plumbing the easier it is to stop up the drain. Just sayin'.

 

[70bigblockdodge]

Nothing less than 2.25", don't let them B.S. you into 2" to provide back pressure and torque. That is laziness and untrue, if it were true then putting a slant 6 exhaust on a 70 Hemi Cuda would make a torque monster. Obviously that does not work or Hot Rod magazine would be putting it in their cheap go fast tricks.

 

[73Coupe]

Right, zero back pressure is the preferred. I don't understand where back pressure (i.e. restriction) could be seen as a benefit. Pure B.S.!

2.5" pipes will be used. I'm confident in Todd, the owner. He'll do an amazing job just like he's done before.

Update: Accurate Exhaust said those hangers are out of stock and they can't get 'em anymore. So I think I'll just let Todd hang it as he pleases.

 

[CBODY67]

2" pipe is what most shops have in stock. Easier to bend and place than the larger sizes. Might work on a '57 Chevy 283 PowerGlide, but not as well on a large engine OR one with some performance credentials.

Years ago, somebody put a pressure/vacuum meter on their single factory exhaust. Very little backpressure at lower rpm and at cruise. Open the carb to WOT and backpressure happened then Seems like this was on a '66 Coronet 318 or similar?

CBODY67

 

[cantflip]

F-it... I haven't done this for a while...

I dislike speaking to "back pressure", the benefit most who are talking about is better discussed as "volume and velocity"... a too big pipe lowers the speed of the exhaust gases, a smaller pipe helps speed up the exhaust gases (velocity)... that is a real factor at low engine speeds and explains why your 1.6L does not work right with a 3" exhaust... Period!

The other term "volume"... when you restrict the volume of exhaust, you will begin to build pressure in the pipe... Zero benefit... this causes the cylinders to scavenge poorly and can lead to reversion... the intake pulses get pushed backwards at valve opening... the result is like an EGR valve opening at WOT... maybe worse.

A generic back pressure spec. of 3 PSI means... at full power and full load and maximum RPMs, you should never make more than that number. If your engine never was capable of making any back pressure, your exhaust is too big and the low speed power is reduced. If your engine makes back pressure too easily, your high speed, and more importantly, high load power is reduced.

Simpler terms... a 4" exhaust will hurt the idle and probably the off idle power (smoothness) of your 440. An 1.5" exhaust will cause you run out of power around 3000 RPM +/-

Because your exhaust is being fitted to the car, not tuned for the engine's ability to breathe, Going with what you can fit (maybe 2.5" from the manifolds, 2.25" more easily) isn't going to cause a dramatic change in low end, but may very well help with higher end power.

If you're building a beast that is superturbodupercharged... you might want to look into 3" cut outs... but then, turbos need a properly sized exhaust (waste gate) to work well.

 

[70bigblockdodge]

dislike speaking to "back pressure", the benefit most who are talking about is better discussed as "volume and velocity"... a too big pipe lowers the speed of the exhaust gases, a smaller pipe helps speed up the exhaust gases (velocity)... that is a real factor at low engine speeds and explains why your 1.6L does not work right with a 3" exhaust... Period

This is only true at super low rpm, <3000 at WOT, basically standing on the throttle at a red light/stop sign. Anything above 20-25 mph even with 2.76 rear this becomes a non factor. Factory exhaust manifolds would still be restrictive enough and absorb enough heat to make it past this brief period.
Even the cheapskate factories put larger pipes after the cats than they ever did in the past because the need for fuel mileage against the competition outweighs the $2 they could save on each smaller exhaust.

A wastegate on any turbo system is a crutch to make a non variable turbo work over a large RPM range. They are not a mandatory item on a turbo engine. Most big truck and stationary or equipment engines since they work in a narrow RPM range have the turbo optimized for that specific rpm and do not have a wastegate.

One other point that follows Jeff's logic is sound wave pulses. Dumping the exhaust pulses of a small displacement into a 4", essentially a chamber, will not help flow because the noise vibrations are allowed to run haywire and stall the pulse, not helping flow. Think of the long ram intake manifold you have seen on big blocks, the tubes increase the speed of the air to increase flow into cylinders. Taking this and watching it in reverse the velocity coming out of the cylinder slows the speed gradually, dumping into a open chamber (the 4" pipe on a 1.6 litre) will stall the air resulting in a loss of flow. Basically what Jeff was talking about.
This is the reason headers work better over exhaust manifolds, longer sized tube to slow the high temp and speed of the gasses at the port. Rather than a short passage dumped into the log area of exhaust manifold.

Not disagreeing with Jeff just detailing it a bit more, I hope. Stan can get out his red pen and fix anything he sees fit.

 

[cantflip]

Not disagreeing with Jeff just detailing it a bit more, I hope. Stan can get out his red pen and fix anything he sees fit.

 

[commando1]

F-it... I haven't done this for a while...

 

[Duncan]

OK, now I'm confused - I am thinking of putting dual exhaust on my 68 Fury III with a 318 engine. Would I actually be better off with the 2" exhaust with the smaller engine or would it still be better to go to 2.5"?

 

[70bigblockdodge]

OK, now I'm confused - I am thinking of putting dual exhaust on my 68 Fury III with a 318 engine. Would I actually be better off with the 2" exhaust with the smaller engine or would it still be better to go to 2.5"?

You could probably get away with 2" on a stock 318. I would prefer 2.25 all the way back on it, I think it looks better FWIW. 2.5 is probably overkill on a 318 unless highly modified.
I don't think the 2" would net much over a stock 2"& 2" into 2.5 Y pipe single exhaust except having 2 mufflers to blow through instead of one. I would be interested in cost difference, not including that the 2" is easier to bend and fit.

 

[PontiacJim]

Often, it is the size of the factory cast iron exhaust manifolds which dictate the front pipe size. If the outlet and flanges are for a 2" pipe, then 2 1/2" may not work. Using Pontiac as my example, factory outlets are 2", but the bigger factory Ram Air exhaust manifold/header were 2 1/4" and used a different pipe flange to bolt up the pipes while an aftermarket manifold is sized up to 2 1/2"

Typically, you use what ever size pipe that matches the exhaust manifold outlet, and then decide where you might want to size up from there. I have on a number of occasions built my own exhaust system only because I can weld and have the equipment to do the fabrication. It can take a lot of time to fit, tack weld, adjust, weld, and keep on going with it. I have come right off a factory 2" factory exhaust manifold outlet and using pipe reducers that size up/down go right up to a 3" pipe and continue with a 3" dia system all the way back.

The thing most concerning is clearances. Bigger pipes are going to hang lower (you may bottom out on them) and trying to fit some of them under/over transmission crossmembers or up and over axles can become problematic. Muffler size also has to be considered as these come in different shapes and configurations - long, short, fat, narrow, oval, square, etc..

You want mandrel bent pipes versus crush bending pipes. Crush bending will do as it is called, crush the tubing causing greater restrictions and poor flow. It is cheaper and quicker than mandrel bent pipes, so it is often used by many muffler shops. What good is a 2 1/2" dia pipe if it gets crushed down to an 1 3/4" dia in forming a bend?

In my opinion, back pressure concerns are more about the factory cast iron exhaust manifolds than pipe size -unless you use too small a pipe. If you are talking headers, it is more about over scavenging and this is where cam selection & head flow need to be taken into consideration. With a cast exhaust manifold, their design builds in back pressure because most are restrictive - even the HP versions, so bigger pipes are the way to go in an effort to minimize the back pressure. Most heads/exhaust manifolds will have port matching issues and these mismatches can kill exhaust flow even if you go with larger pipes.

Bigger is better. I run a minimum of a 2 1/2 pipe on any car I run and will go 3" in most applications if fit/clearance is not a problem. I also don't use tail pipes and end my system at the rear axle and use turn downs. Going with a larger pipe/muffler (or not using a tail pipe - if local laws allow) will also increase exterior/interior noise, which some people really don't care to hear. I like loud, but that is me.

If you have 2" or 2 1/4" exhaust outlets, you can size the pipes up with a reducer that will fit the smaller pipe and go up to a larger pipe as soon as they make the turn coming off the manifold and straighten out going back. Some will go into the muffler with let's say a 2 1/4" pipe and then go out with a tail pipe of 2 1/2". It would actually be better the other way around because hot gasses expand and you want a larger diameter pipe coming off the manifold and as the gasses cool, the gases contract and a smaller dia pipe will work just fine. However, again using the Pontiac example, the front pipes were 2" and the tailpipes were 2 1/4." (probably used to give a little more sound - just like the rice burner cars with their exhaust cans at the bumper).

Another worthwhile addition is a crossover pipe, whether an "H-pipe" or an "X-pipe." This helps exhaust flow as on most dual exhaust systems you have one pipe/muffler/tailpipe on each side independent of each other. With the addition of a crossover pipe, you are connecting both side and actually providing more flow through the use of both sides. The benefits can be a balancing of the exhaust flow, a deeper tone, and a few extra HP.

Just my 2 cents worth on it all.

 

[Duncan]

Thanks for the advice. I will now be going into this knowing much more about what to look for and what to ask for than I would have otherwise, that is for sure.

 

[Fratzog]

How do you reconcile this...

In my opinion, back pressure concerns are more about the factory cast iron exhaust manifolds than pipe size -unless you use too small a pipe.

With this ...

Bigger is better. I run a minimum of a 2 1/2 pipe on any car I run and will go 3" in most applications if fit/clearance is not a problem.

Intuitively once past the exhaust manifolds larger size pipes shouldn't matter. Shouldn't it only matter of you go smaller? What am I missing?

 

[PontiacJim]

How do you reconcile this...

With this ...

Intuitively once past the exhaust manifolds larger size pipes shouldn't matter. Shouldn't it only matter of you go smaller? What am I missing?

Not sure what you are asking? Are you thinking that a 2" exhaust manifold outlet only needs a 2" dia pipe owing to the restriction already incorporated in the manifold outlet?

 

[Fratzog]

Not sure what you are asking? Are you thinking that a 2" exhaust manifold outlet only needs a 2" dia pipe owing to the restriction already incorporated in the manifold outlet?

Yes.