Slant six dual exhaust proposal

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MarcD

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Mostly completed the mechanical stuff on my '63 Dart: rebuilt '74 block 225, block decked 0.40, polished ports/hardened valve seats, Offenhauser intake with Holley 390, Dutra front manifold/cut rear manifold, 10" clutch, A833 trans, 8 1/4 Sure-trac 3.21 axle and all rebuilt front end with '74 disc brakes/dual master.

The current exhaust is just cobbled together with a pair of 2" tubes leading from the exhaust manifolds to individual Thrush glasspacks and 2" outlets exiting in front of the left rear tire; no crossover or h-pipe...all this stuff is off the shelf pre-bent exhaust clamped together. Ridiculously loud, and it just lights up over 3200 rpm...

I'm considing "doing it right" with the exhaust, and here's the suggestion:

Two 1 3/4" head pipes from the Dutra/rear manifolds to a single dual inlet/dual outlet muffler (Jones Full-Boar with the inlets bushed down to 1 3/4") with two 2" tailpipes exiting in front of the left rear tire.

The rationale for the smaller head pipes is that the stock exhaust is a single 1 7/8" or 2" all the way from the manifold to the rear bumper...restrictive for any performance boosts, but I feel that doubling that capacity is overkill and may actually hurt performance by reducing exhaust velocity and scavenging effect. Also, space is at a premium until after the clutch Z-bar, and finally smaller pipes will radiate less heat into the engine compartment.

The dual-in/dual-out muffler should provide some smoothing of the sound and reducing resonance.

Any thoughts?
 
We went with true dual exhaust on our Dart wagon. 2" all the way to the back. Runs nice.
 
I don't see any issues with your plan. I ran 1 3/4 head pipes off of spilt headers into a 2 inch x pipe to 40 series flowmasters then 2 inch out the back through 340 tips on my 74 dart slant six. I really like the sound but the drone was bad from those flowmasters.
 
i have dual hooker headers , 2 1/2 inch stainless steel pipes out the rear with flowmasters on it. everyone thinks its a 340. i get called a liar all the time. looks and sounds great

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Pete Hagenbush (sp?) was one of the engineers who helped develop the 2 barrel Super6. In an article in Allpar talking about the /6 he said splitting the exhaust in two, 1-2-3 and 4-5-6, running 2 pipes back about 6-8 feet, then re-joining them into a single exhaust out the back made a lot of power. He wanted dual exhaust on the Super6 but it was not done because of the cost.
 
I went with Dutra front manifold and cut one in rear with 2" pipes and 40 series flow masters and everyone thinks it is a V-8 car as well, it has a really nice tone and no rapping when you accelerate like glass packs give you...
 
KosmicKuda said:
Pete Hagenbush (sp?) was one of the engineers who helped develop the 2 barrel Super6. In an article in Allpar talking about the /6 he said splitting the exhaust in two, 1-2-3 and 4-5-6, running 2 pipes back about 6-8 feet, then re-joining them into a single exhaust out the back made a lot of power. He wanted dual exhaust on the Super6 but it was not done because of the cost.
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You get a 2nd, lower RPM resonance doing this; has been pretty common with 4 bangers using 1-4 and 3-2 into their own pipes and then recombined into one large pipe later. The 2nd lower resonance point is to help the low and mid range torque. I would do the combining into 2.5" pipe well before a single muffler to acheive this.
 
I don't like duals on a slant. I think better torque can be made with a well thought out high performance single exhaust. For instance, going from the collectors into something like a Flowmaster Y and then into a nice 3" single exhaust. Those Ys really scavenge like a big dog. You won't get that with duals.
 
Dual outlets are probably more for looks. Many current cars jump thru hoops to realize that. Worst look of all IMHO is the single centered "a-hole" exhaust.

The 64-65 HiPo 4 bbl 273 has a complicated custom single exhaust. Why not dual many ask? The factory tested both and got more HP w/ a single pipe. In the 1970's I had a Honda 350-4 motorcycle w/ 4 exhausts. There was a big after-market for 4-into-1 exhausts, claiming 30% more HP. Finally, Honda and others designed a 4-into-1 exhaust. The sellers seamlessly changed to selling separate exhausts, claiming 30% more HP.
 
On the 64-66 273 Hi Po had a single exhaust because the TB X-member was notched only on the driver's side. The passenger side pipe would run under the X-member making it the lowest point of the underbody. Results are predictable.

If there is concern about maintaining good exhaust gas velocity and scavenging, going from a small to a larger pipe is bass akwards. IMO, better scavenging would result by starting with a 2¼" head pipe (like the super six) and muffler. Step the tail pipes down to 2 or 1 7/8 to the atmosphere.
 
I will be running these headers ( Pacemaker ) with a single 2 & 1/2" exhaust with a Mercury Super-Turbo muffler.
They have 1 & 1/2" primary pipes, 2" secondary pipes....with a 2 & 1/4" outlet....but that will be swelled out to 2 & 1/2".

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If it were mine I would go with 2 1/2 pipe all the way back and bolt a fart can muffler to it , just to piss the jap cars off
 
2 Darts said:
... On the 64-66 273 Hi Po had a single exhaust because the TB X-member was notched only on the driver's side. ..
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More likely, the other way around. I expect they put one notch in the tranny cross-member because they decided on a single pipe. I forgot where I read the info "single pipe = more HP", probably on the AllPar site. Many mod's are silly. I have yet to see a Jap fart-canned car fly by me on the freeway. Usually, you see them in the slow lane, jarring their teeth at 55 mph because they f'ed up the suspension in lowering it and adding rubber-band tires, while making useless noise. To me a quiet, smooth dependable engine is ideal, not an over-cammed, over-carbbed blubbering pollution-maker that keeps stalling, w/ noisy exhaust bothering the neighbors, but then I wouldn't ride a messed up Harley either (endemic around here).
 
A large single is almost always better than duals for a small displacement N/A engine. Resistance due to the gasses dragging against the inner walls of the pipe is a very big deal. It would take a pair of 2.5 inch duals to equal the flow of a single 2...and even though the flow would be equal, there would be zero scavenging effect because of the lack of velocity.
A Slant through a large single sounds better too. Throatier.
 
2 Darts said:
On the 64-66 273 Hi Po had a single exhaust because the TB X-member was notched only on the driver's side. The passenger side pipe would run under the X-member making it the lowest point of the underbody. Results are predictable.

If there is concern about maintaining good exhaust gas velocity and scavenging, going from a small to a larger pipe is bass akwards. IMO, better scavenging would result by starting with a 2¼" head pipe (like the super six) and muffler. Step the tail pipes down to 2 or 1 7/8 to the atmosphere.
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That's easy enough to fix. I just dropped the mount, trimmed, welded and repainted. Easy peezy.

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