Thread: 1 7/8" primaries to 2 1/2" exhaust

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Originally Posted by tcodi

Does running headers with 1 7/8" primaries going into a 2 1/2" exhaust sound like it would adversly affect performance?
I know I shouldn't have primaries that big on a low rpm 402, but it's a long story as to why I ended up with them. I went with a 2 1/2" exhaust because I figured 3" was too much for the engine use.
Does this combo sound stupid or should I leave it alone?

this size is ok have used bigger on small blocks 1 7/8 is not that big for this engine .2.1/8 to 2.3/8would be over kill and you would not want to go smaller the ex port would be plug up by smaller tube 1 7/8 is ok for low rpm and mid. but if it s a hi rpm big block then go bigger on the primaries and 3 inch ex with a x cross tube