Dual Exhaust Q

[Shake N Bake]

Holy Cow! Posting up a storm today!

Just wanted to ask, I'm planning on doing a dual exhaust on my wagoneer (w/ 360) running the exhaust and the mufflers down the outsides of the frame rails.

Just curious, how important is a cross over pipe in the system? I was taught years ago on duals that you really need it. But I've heard many people argue otherwise... Would I be loosing performance if I left the crossover off?



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Andy
79 Wagoneer LTD "Shake N Bake"
Calgary Alberta Canada (Eh!)

[porkchop]

I have dual exhuast on my Wag. It was there when I bought it with the 327 in it so I frankensteined it to work with the transplanted 360. I do not have crossover, YET! I will be putting one one as soon as I can afford it. I don't really know what difference it will make but I heard you need it so I am going to do it.

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'67/'79 Wagoneer mix
“Old Timer”
Check it out! (http://members.fortunecity.com/porkchopsfsj)

"I have a dream that one day FSJ's will be equal at every parts store."

[JeepFreak]

The cross over is supposed to help with scavenging.

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JeepFreak

[Shake N Bake]

Yeah, scavenging is what I was told origionally (origional project was a 93 vette drivetrain into a Triumph Spitfire) heh

But I figure with dual 3" exhausts, scavenging shouldn't be a big deal? Am I missing something?




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Andy
79 Wagoneer LTD "Shake N Bake"
Calgary Alberta Canada (Eh!)

[jod man]

Well....Take off to the Great White North Eh!..... This forum is filling up with us d@mn Canadians.

Where ore you originally from Shake n Bake? No one in Calgary is originally from there right? http://www.ifsja.org/ubb/wink.gif I am jealous of your close proxemity to changes in altitude. Not that much here. When I was a kid I watched my dog run away for three days. Mail me off forum if you like and welcome to the best bunch of guys (and girls!) the FSJ community has ever seen.

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'74 J-20
'83 J-10
Sportside Honcho
258 I6, T-176, NP208 all totally rebuilt Dec. 2000
Totally restored to stock except for K&N and Nutter Bypass now
Juicebox ignition upgrade, Dyno Flow muffler & 2.5 inch exhaust next week
lonely for other FSJers near me!!

[nograin]

Someone better explain "scavenging" in more technical terms.

A single crossover tube can do two things - both based on the fact that the exhaust comes out in pulses. As the exhaust from one port shoots down the exhaust system, there is a slight negative pressure area behind it, helping pull the next cylinders exhaust with it. A cross over tube can help share the pulses, and also share the load on the mufflers when the engine is putting out alot of exhaust (high rpm).

Now, on a truly tuned header, at a given rpm, an harmonic frequency is set up and does help pull the exhaust gases along. An set of x cross over tubes might help this. Yes, it really works. Chrysler used tuned intake and exhaust manifolds on their 426 Wedge. They had short runner, high rpm version, and a wild looking long runner, low rpm version.

My guess is a cross over tube is not going to make a lot of difference if you are putting on 3" tubes and mufflers, especially if the cam and manifold are stock.

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360 auto select
body by beer (PO)
carries wood inside
no "wood" outside

[mhoffor]

You can have too free exhost, I have a little hesitation at low speeds from it. Im in the process of building an engine to match my exhost, becuse those pipes shure sound GOOD!

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Mike Hoff
74 J10
360 Edelbrock Carb
TH400 w/shift kit
Headman Headers 3" pipes w/flomasters
Spring over front 8" net lift
Shackel flip w/2 1/2 steel blocks rear 7" net lift