Exhaust Restriction On Built 273

Tech Question


Jim Johnson, Lawton, OK, 1965 Dodge Dart 273

Rick, once more I need your sage wisdom on a problem. I have a ’65 two door Dart, 273, 904 column shift automatic that I have been building up to mimic your Green Brick (handling, brakes, rear end etc.). My question is: How much motor can I build with the restriction being the tight exhaust space? I want to build up a 360 to put in the car but TTI says their really cool headers won’t fit with a column shift auto. Anyway I don’t want to build any more motor then the exhaust can handle. So what are your suggestions?



Very good question. On the Green Brick (’69 Valiant, 3.79″ stroke, 0.040″O/S 340, W-2 heads) we had a very expensive set of custom Tri-Y headersbuilt. They suck. Looking at the engine’s dyno curve, it “noses over”(passes the peak HP RPM) way too early. We estimate that a set of big TTIs,w/3” pipes, would probably net us over a 75 HP increase! The car “works”because it is low mass, but it would work way better with either a mildercam or the aforementioned exhaust upgrades.

From reading between the lines, it sounds like you’ll be using ironmanifolds. If that’s the case, by all means, tune for torque and mid-range.Keep the cam mild, especially re: overlap (wide lobe sep. angle). I did havesome reasonable results years ago with a 340 in a narrow A-body, using 273manifolds that were painstakingly port-matched and hogged out. The otheroption are the re-issued “Spitfire” headers from Layson’s, which are surelyway better than even ’68-’70 340 manifolds (which will not fit an earlyA-body, incidentally). At that point, you can be a bit more radical.


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