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I have a set of headers to bolt on a 302. The size of each tube is 1 1/2 " to a collector of 3". If i replace the plate who bolt on the head they will fit on the 400. My question is did those headers will be better than the stock exhaust manifold ? What size i need if those one are to small ?
depends upon your intent for the engine, how much rpm do you plan to turn?
if you're planning on a low-end application, your flange swap headers will be better than any you can buy, the small tubes will provide great low-end torque but will probably not do as well as big tube headers in a wide open throttle situation.
you may even be able to create a 'step down' header by using some of the stub/tube from the 400 flanges and fit the smaller tube into the larger tube.
I plan to use it mostly street and maybe strip but i'm not very serious about the strip. This 400 (.030 over with tim piston, aussie head, roller rocker, xe-256 cam, 1405 carb) will never see more than 5000-5500 rpm.
It's a light weight car, 1980 mustang and want to play with that 400 torque. Yesterday i send the aussie heads for a complete rebuilt, can't wait to have them back and finish that long long term project on a tight budget.
i forgot about the difference in deck heights of the different engines, in the slice and dice operation you'd need to address that the finished set of headers will need to have more downward tube length than the original 302 headers did because the 400 X ports are up higher in the chassis, but i still don't see why you can't pull the project off
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