I'm currently installing Dutra dual exhaust on the race car. I'm planning to have the two pipes run into a collector, but I'm curious about what pipe diameters and collector length would be best. This motor lives between 3000-4500 RPM.

I also plan to upgrade again to "dual duals" at some point in the future if we ever actually follow through on our plans for supercharged MPFI. So designing to that application might be advisable so I don't have to do redo everything again.

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Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing

I used 2" diameter from the manifolds and into a collector that goes to 2 1/2" diameter. I did SS and then ended up ceramic coating it. The manifold flanges are 3/8" thick I believe. If you're doing race engine maybe use 2 1/4" from the manifolds? Anyway, with 2" going into a single 2 1/2" I have very little back pressure (decent flowing muffler, but not a high level of flow, I think's its a "turbo" muffler with some packing). The only time I see back pressure is under full acceleration and then it's only 1-4 psi. I have O2 sensor bungs in each down pipe to measure AFR and back pressure. I didn't do any calculations or anything for flow or where the collector should be, but I did use all shallow mandrel bends most all of them are 45 degree.

http://s785.photobucket.com/user/67dart ... html?o=175

http://s785.photobucket.com/user/67dart ... html?o=182

You can see there is plenty of room for it, here's a top view (prior to ceramic coating): http://s785.photobucket.com/user/67dart ... html?o=240

http://s785.photobucket.com/user/67dart ... html?o=241

The collector is vibrant performance, I think. I can look it up if you pm me. As you can see from the pics above, the collector is near the bottom and tilted about 30 degrees (hmmm) from the horizontal. I tacked together the front pipe (as you can see it has cleaner lines) and then did the rear pipe and fitted the collector last so it would be at the bottom spaced well between the T-bar and tranny.

http://s785.photobucket.com/user/67dart ... html?o=308

Brian

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https://tinyurl.com/yynpj4v2

I would use 2" primaries 31" to 35" long into a 2 1/2" or 3" single pipe.

I like the Magnaflow 2 into 1 collectors

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Yeah....Im the one who destroyed this rare, vintage automobile.....

Thanks for the pictures, Brian. I might print those out and bring them to the exhaust shop with me. That routing looks like it would pretty easily accommodate converting to a new rear pipe if/when we go to dual-duals. Hopefully the shop can pull it off in my narrow-body '64.

I think I'll stick with 2" primaries going into a single 2.5" as this isn't a very high-revving motor.

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Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing

Hi SpaceFrank,

Yes, and DD says that dual 2" into 2.5" single has plenty of flow and power vs doing dual exhaust all the way back. I've done both on mine and the split into single setup is as least as good as the duals were and way simpler to install.

Let me know if you need more pics or any measurements.

Brian

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https://tinyurl.com/yynpj4v2