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I have bought one of blue hands 4 cylinder L series down pipe flanges and I intend to purchase one of Columbia River Mandrel Bending Companies 2-1 merge collectors but don't know which one to order. I am running an L18 exhaust manifold on an L20b in a 1974 620. I intend to run a 2" exhaust system. CRMB website offers many different options and I want to get the right one the first time. I know that I want a 2" outlet but I am not sure of the inlet sizes (1.5"?) And is the spacing correct? Does anybody know either the proper part number or the right sizes to accomplish my goal?

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Seems to me the twp pipes merge right away and then curve under the cab. A nightmare. Can you run two down pipes of 1.5" from the manifold with proper bends to get it past the torsion bar under the cab and then join them?


I put an L16 exhaust on my L20B 710. Used one of Mike's flanges. I cut the flange off a set of 240sx down pipes and mated it to Mike's flange. The 240sx twin pipes travel down and under the car before joining. This got me under the car where the two pipes joined. All I had to do (sounds simple, but was not) was join into my system.


I would imagine a truck Z24 or maybe Hardbody (I think they are 2") down pipe would have the bends for the torsion bars. You would just need to get Mike's flange on the end. (by 'just' I mean with a lot of work and test fitting)

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Well, I have read on here that people have used Mr. Klotz's down pipe flanges and the Columbia River merge collectors together. I was just trying to come up with something to make my exhaust installers work go quicker as he charges by the hour. I think buying one premade (approx.$45) would be cheaper than having him make one. I intend to have a new 2" system to the back. I would be doing it myself but the recent installation of a defibrillator in my chest ended my welding abilities. Firing up a welder could end up in getting kicked in the chest like a mule. Columbia River has a merge collector that is twin 1.5" inlets and a 1.75" outlet. I think that is the one I need, I was just concerned about the spacing of the twin inlets.

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Thinking about it, it may be better like you said to run 2 pipes down under the truck and then join them under the cab with a merge collector. That would solve the problem of whether or not the Columbia River collectors would fit. Does a 1.5" pipe fit inside Klotz's flange?

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