Custom duals to y pipe

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Slantsix64

Slantsix64

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Made some custom duals going into a flow master y pipe my question is what diameter should I have the head pipes that are going into the y pipe, 2inch or 2.25 inch the rest of the exhaust is 2.25 already flowmaster has 2inch to 2.5 scavenger y pipe and a 2.25 to 3 inch y pipe. What you guys think I know this thing needs back pressure ,
9 to 1 500 Avs 4 speed 473 lift Howard's camshaft 3.55 gears
 
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Heres some pictures. Also going to block off that heat riser with a block off plate from eBay tired of that heat soak bullshit.

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I bet 2 will be plenty to take 3 cylinders. They ran them back 10 feet to the merge per an old ramchargers conversation. That was a stock cam profile so your mileage may vary.
 
Nothing naturally aspirated needs back pressure. That's a common misconception. I have planned a very similar exhaust for mine. I plan on 2" primaries going into a Flowmaster wye and then into a single 3" pipe.
 
pishta said:
I bet 2 will be plenty to take 3 cylinders. They ran them back 10 feet to the merge per an old ramchargers conversation. That was a stock cam profile so your mileage may vary.
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RustyRatRod said:
Nothing naturally aspirated needs back pressure. That's a common misconception. I have planned a very similar exhaust for mine. I plan on 2" primaries going into a Flowmaster wye and then into a single 3" pipe.
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Yeah after looking at some picture of the dutra s split looks like a lot of people are running 2.25, I'll probably run 2.25 to flowmaster y that exits to 3 inch then reduce it back to 2.25 I'll keep you guys posted.
 
My notes for setting up Dutra Duals says 2" pipes from the engine into a wye, 2-1/4" from the wye to the muffler (a Walker quietflow), then 2" to the tail of the car.
 
halfafish said:
My notes for setting up Dutra Duals says 2" pipes from the engine into a wye, 2-1/4" from the wye to the muffler (a Walker quietflow), then 2" to the tail of the car.
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there you go, they dont mention the length of the head pipes? Strange....

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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..."
KosmicKuda Slant six dual exhaust proposal
 
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No way in hell would I ever reduce it back down at the tail pipe. That's nonsense. Don't even know where that came from. The only reason the factory ever did that was to back off on noise and drone just a little. Remember this. Anything that quiets exhaust also restricts it. That's where muffling action comes from.
 
Looks like on a early a body four speed it's too tight to put the flowmaster y pipe 2.25 to 3inch, looks like I'm gong to just have them do a custom y pipe 2.25 to 2.25 spliced in a custom y done by the muffler shop.
 
RustyRatRod said:
No way in hell would I ever reduce it back down at the tail pipe. That's nonsense. Don't even know where that came from. The only reason the factory ever did that was to back off on noise and drone just a little. Remember this. Anything that quiets exhaust also restricts it. That's where muffling action comes from.
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The idea comes from David Vizard.
 
kesteb said:
The idea comes from David Vizard.
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No it doesn't. Auto manufacturers were downsizing tailpipes before he was born. He's no end all be all. The reason it was done is because of gaining more space for moving rear suspension parts. It doesn't unlock any "secret" power. I don't care who says it.
 
"The idea comes from David Vizard."
Hey Kesteb,, please provide chapter and verse where DV said anything like that.
 
It's a common theory based on the premise(factual) that the gasses cool and shrink as they progress thru the system, the longer and more convoluted, the more the "heat exchanger" contracts the gasses. Go to Burns' exhaust site, They stated that any exhaust past 5' long costs power regardless of size design etc. The fact, from a performance standpoint, is that a longer system has a higher frictional factor that gets worse with higher velocities. Bigger is better. The "backpressure" myth has validity in some cases when the torque was boosted by the velocity in the system, or the A/F ratio changed in an unfavorable direction w/a big reduction.
 
Several years ago there was a discussion on fordsix.com on how to run your exhaust system. A system was described that involved running intermediate pipes all the way back to axle into a resonator box. This was attributed to David Vizard. A gent built such a system for his '64 Falcon, using a flow master muffler as the resonator box. Claims were made of improved low end torque. There is video on YouTube of the car and exhaust system. Were the claims true? I don't know. No before or after dyno slips, so maybe the butt-o-meter was wrong.

I do know that when I extended my intermediate pipes about 6", it messed up the jetting in the carb. Which means it was flowing more air thru the engine. Just my observation.
 
Still debating on where to connect the Y pipe at, Before or after my torque shaft Z bar, Pishta i found that article from Pete Hagenbush recommending to run the two pipes from the split manifolds 6 to 8 feet before connecting them to a Y pipe. Probably will try that out so how it works out for me keep you guys posted
pishta said:
there you go, they dont mention the length of the head pipes? Strange....

<edit>

"...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..."
KosmicKuda Slant six dual exhaust proposal
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i wonder if it would flow better if you bought a second manifold and cut the front of that one aswell, and installed it on the back 3 cylinders?

(would look better for sure)

but with it exiting in the center, it might flow better?
 
No carb heat....But the Dutra duals are like that, they just run 2 fronts (with a universal flange), or the cheaper system is a Dutra front and a DIY chopped rear.
Diymirage: "...i wonder if it would flow better if you bought a second manifold and cut the front of that one aswell, and installed it on the back 3 cylinders?..."
Wouldn't fit. The mount bosses are opposite on each side of carb.
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I guess I'm not sure what the problem is, as far as the interference goes
 
Exhaust manifold has \ bolt mounts and intake has / bolt mounts (front 3, opposite on back 3) so they make a nesting \o/o\o/o\o/o*o\o/o\o/o\o/ pattern . (bolt centerlines are through ports) so you could not use a front triple on the back. Newest castings of Dutras rear has a mounting pad across the entire top and bottom so they can get clamped on either side so they are adaptable to both front and rear mounting.
 
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ok, now that makes perfect sense
(i dont know why i was thinking you were talking about the carb mounts)
 
What I have noticed right off the bat, car revs up higher faster, car is running lean and pops, need to enriched the mixture with better metering rods,Too soon to tell about mileage and power. Cost 120 to have the pipes made, 60 for y pipe 200 for the manifolds less than 400.00 for the whole set up. Sure beats paying almost 400 shipped for the front casting only.
 
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