340 Build Spec's

headsbikesmopars said
9.0 to 1, Factory heads, bowl ported and matched, Air Gap, 3310, headers 1 3/4, Comp 268, file to fit rings, stock lower end. You can substitute TQ and factory TQ manifold if you want stock look, and they will work good. I believe 1 5/8 headers are too small for 340/360. this would be solid street performer, run on middle grade fuel and be turn key. If you need more, you can add more camshaft and head work. Good luck. Terry.

FWIW, I have been following a lot of these tech articles in the Engine Masters series by Popular Hot Rodding and in the past month they did an article on headers. This was a big block engine but they tested in succession 8 different sets of headers from 1.75" tube to 2.25" with different length tubes and collector configurations.

The conclusion: All the different headers made with in 1 HP and 1 FT-LB average over the 2500-6500 rpm test range. They could suffle around the torque peak and change the shape of the torque curve but the averages stayed the same.

General design guide lines tell you the larger the tube diameter of a header the higher in the rpm range the torque peak occurs. So if you are building a daily driver motor stay with the 1 5/8" headers you will keep the power down in an rpm range you can use it.

A 3310 is also to much carb for a daily driven car, you would be much happier with something in the 650cfm range. Again another article where a 383 stroker small block in a Camaro was bing tuned on a chassis dyno. They were limited in what they could do to this engine because the goal was to keep it 100% California Smog legal. I believe they were testing up to about 6000 rpm maybe 6500. The engine had a 600cfm 4160 Holley vacuum secondary carb. At the peak test rpm they only had 0.8"Hg manifold vacuum which indicated that the carb was not resricting air flow into the engine.

The bigger carb may give you a slight edge in the upper rpm ranges (above 6000 rpm) but it will be at the expense of throttle response in the lower rpm ranges you will be driving the car. You will also likely see a mileage advantage with the smaller carb too.