518 Swap For 727

Tech Question


Matt Storch, Moorpark, CA, 1970 Dodge Swinger 360

Hi Rick,
First a few words of thanks. It is in large part because of your answersto my past questions and your excellent tech articles over the years, that Iwas able to build a car I love.

My Mopar is a 1970 Swinger 340 look-alike with a fairly healthy 360,backed by a 727 and 8 3/4 with 3.55 diff. What is fairly healthy? A coupleof weeks back I strapped it to a SuperFlo 840 chassis dyno and pulled a bestof 316 rwhp @ 5600 and 335 lb-ft @ 3800 with an almost flat torque curve.Not bad for a car that idles at 900 rpm and has factory A/C.

Anyway, here’s the question: I love to drive the car everywhere, butkeeping up with So. Cal. traffic, even in the slow lane, means spinning themotor at 3300 rpm, or more. I would love to have an overdrive gear and alsothink a couple of more forward gears would help the e.t. on those occasionaltrips to the drag strip.

I’m weighing the pros and cons of the Gear Vendors overdrive vs. theKeisler 5-speed conversion.

I’ve got an awesome 727 stuffed full of good parts so I’m reluctant topart with it, and I’m sure the GV setup would be less costly.

On the other hand, I guess the 5-spd would free up some more horsepowerand probably wins hands down on the Fun Factor.

I’m looking to you to give me your wisdom on the technical/mechanicalconsiderations of the two systems.




There’s a third possibility than you haven’t mentioned: An A-518 swap. Mostof your 727 parts could be carried over to a built 518. The only realdownside is the floor pan and crossmemeber hacking required. Once installed,you have a factory-reliable setup. I like that!

The GV unit has been proven over many thousnads of installations. However,I’m not a GV convert, I just don’t like the fact that the unit iscantilevered off the back of the rear mount, and that the very shortpropshaft required in an A-body forces some pretty wierd U-joint angles.

The Keisler is also proven over a zillion installations. And the newestversions have much improved ratios and torque capacity over the originals.And they fit like a glove, not to mention being butter-smooth and quiet.I’ve driven one of these at least 50-60,000 miles and would do it again in aheartbeat. It definitely wins in that fun factor you mentioned.

Also, Passon’s new 4-speed overdrive must be considered. This is probablythe easiest installation of all (basically a 100% factory stock swap), andyou will have an overdrive fifth. But the wide ratio spread isn’t gonna helpat the drags.

You could also simply jam in a pair of large-diameter rear tires for streetuse.


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