343 build ideas 350+hp

If you the want stock look then you can only really play with the cam, head porting and compression, you could slip a 360 crank in there though.

Edited by WesternRed - Feb/24/2013 at 5:57am

Having just been down that route with a 390, and knowing someone who took a 343 and brought it up to 408 hp at the crank, you'll have to make substantial changes.  You WILL have to ditch your current, stock carb, intake, and cam.  You can paint the new intake to match the engine, thus reducing the "non-stockness" of the intake.  You WILL have to either run free flow exhaust, Rebel machine exhaust manifolds, or headers, as the factory exhaust manifolds are too restrictive.  You don't have to run Eddy heads; just get your stock iron heads ported to a great extent.  And, of course, most engine internals will change. Those more well-versed on the internals will comment, I'm sure.  Have fun!

Not all that hard to do.  Some head work, a performance cam and intake and a bigger carb and then better flowing exhaust as suggested by others.  You will not hit 350 with stock exhaust manifolds on stock 343 heads.  You can get there with 291C heads and AMC freeflows or possibly even with 090 or 993 heads and freeflows.  Of course headers will resolve the issue by replacing the poor flowing factory log manifolds on the stock heads. 

All we really did to the stock 68 heads on my old AMX was to cc them and do a 5 angle valve job (and of course better springs and retainers for the much bigger cam).  The headers took care of the stock exhaust restrictions.  Freeflows adapted to the stock rectangle port heads require that you use the rectangle port gaskets and defeat most of the benefit.  In the early 70s, a car mag added freeflows to an early rectangle port 390 and only picked up a measured 6-8 HP.  There is nothing wrong with 68/69 343/390 heads for a mild build and headers are a lot easier to install than swapping out the heads and having to modify the intake to bolt to the higher center manifold bolts.  I am not usually a big fan of headers but they are the best option for big power increases on the early heads due to the factory log manifolds being so restrictive.  Machine manifolds on the early heads won't provide much benefit due to also being log style and only have a scant 1/4" increase in outlet pipe ID but are still the much poorer log style when compared to  much better designed and flowing later model AMC freeflows.

Edited by amx39068 - Feb/25/2013 at 8:55am

skynless wrote: Hello, I plan to do one of two things to my '69 Ambassador: 1. Rebuild 343 2. Find 360 and create a 383 stroker using the generic recipe i've seen posted around the web. Should I use the 343? I don't have much engine experience so I'm wondering if you have the actual recipe you used for the 343 to 383 stroker? I'd like the cheaper route for just a street car that can smoke the tires and sound good. Here is the general recipe I am interested in for the 360: http://www.ifsja.org/forums/vb/showthread.php?t=110924 Thanks!